JP7597802B2 - Multi-Channel Optical Coupler - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. Provisional Application No. 16/670,224, entitled “MULTICHANNEL OPTICAL COUPLER,” filed on October 31, 2019 (Attorney Docket No. CHIRA.020P4), which claims the benefit of U.S. Provisional Application No. 62/923,383, entitled “MULTICHANNEL OPTICAL COUPLER ARRAY,” filed on October 18, 2019 (Attorney Docket No. CHIRA.020PR4).

The present disclosure generally relates to optical coupler arrays, e.g., multi-channel optical coupler arrays, for coupling, e.g., multiple optical fibers to at least one optical device. Some embodiments may relate to coupling light to and from multiple fibers, such as one or more single mode fibers, few mode fibers, multimode fibers, multicore single mode fibers, multicore few mode fibers, and/or multicore multimode fibers. Some embodiments may relate to coupling light to and from photonic integrated circuits (PICs) and multicore fibers (MCFs). Some embodiments may have fiber arrays used in coherent or incoherent beam combining illumination. Some embodiments may generally relate to high power single mode laser sources and apparatus for coherently combining multiple optical fiber lasers to generate a multi-kilowatt single mode laser source. Some embodiments may relate to monolithically designed phase-locked optical fiber components. This can be manufactured with a very high degree of control over the precise positioning (e.g. lateral or cross-sectional positioning) of the many waveguides, and can potentially be configured to increase or optimize the fill factor of the component (which can be related to the ratio of the mode field diameter of each waveguide at the "output" end to the distance between adjacent waveguides).

The present disclosure also generally relates to couplers for providing optical coupling between multiple optical fibers (or other optical devices) and optical devices having multiple waveguide interfaces, and more particularly to a configurable optical fiber coupler device. The configurable optical fiber coupler device comprises an array of multiple optical fiber waveguides configured to provide a set of high optical coupling coefficient interfaces at each of its ends having a configurable numerical aperture (which may be the same or may vary between the coupler ends), with the channel spacing at the second end of the coupler being smaller than the channel spacing at the first end of the coupler, thus enabling beneficial coupling between multiple optical devices (including optical fibers) at the first end of the coupler and at least one optical waveguide device having at least a corresponding number of proximate waveguide interfaces at the second end of the coupler.

Optical waveguide devices are useful in a variety of high technology industrial applications, especially in telecommunications. In recent years, these devices, having planar waveguides, two-dimensional or three-dimensional photonic crystals, multimode fibers, multicore single mode fibers, multicore few mode fibers, and multicore multimode fibers, have been increasingly employed in conjunction with conventional optical fibers. In particular, optical waveguide devices based on refractive index contrast or numerical aperture (NA) waveguides different from conventional optical fibers and multichannel devices are advantageous and desirable in applications where conventional optical fibers are also utilized. However, interfacing dissimilar NA waveguide devices and multichannel devices with channel spacing smaller than the diameter of conventional fibers with conventional optical fibers presents significant challenges. For example, in some instances, at least some of the following obstacles may be encountered: (1) size differences between optical waveguide devices and conventional fibers (especially with respect to core size differences), (2) NA differences between optical waveguide devices and conventional fibers, and (3) channel spacing smaller than the diameter of conventional fibers. Failure to adequately address these obstacles can result in increased insertion loss and reduced coupling coefficients at the respective interfaces.

For example, a conventional optical fiber-based optical coupler, such as that shown in FIG. 6 (PRIOR ART), can be constructed by inserting a standard optical fiber (used as the input fiber) into a capillary tube made of a material with a lower refractive index than the cladding of the input fiber. However, this approach has many drawbacks. For example, the fiber cladding-capillary tube interface is a lower quality light-guiding interface than the interface inside a standard optical fiber, and thus introduction of optical losses can be expected. Furthermore, the capillary tube must be manufactured using expensive fluorine-doped materials, significantly increasing the cost of the coupler.

No. 7,308,173, entitled "OPTICAL FIBER COUPLER WITH LOW LOSS AND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF," incorporated herein, beneficially addressed some of the above problems by providing various embodiments of optical fiber couplers that can provide a low-loss, high coupling coefficient interface between conventional optical fibers and optical waveguide devices.

Nonetheless, many challenges remain. With the proliferation of multi-channel optical devices (e.g., waveguide arrays), establishing low-loss, high-precision connections to arrays of low or high NA waveguides has often been problematic. This is especially true because the spacing between the waveguides is so small that coupling to all becomes more difficult. U.S. Patent No. 8,326,099, issued Dec. 4, 2012 and entitled "OPTICAL FIBER COUPLER ARRAY," incorporated herein, attempts to address the above challenges in at least some of its embodiments by providing an optical fiber coupler array. The optical fiber coupler array provides a high-coupling coefficient interface with high precision and easy alignment between an optical waveguide device having multiple closely spaced waveguides and multiple optical fibers separated by at least one fiber diameter.

U.S. Patent Application Serial No. 8,712,199, entitled "CONFIGURABLE PITCH REDUCING OPTICAL FIBER ARRAY," expressly incorporated herein, discusses the importance of cross-sectional or lateral positioning accuracy (and in some instances, precise cross-sectional positioning) of individual waveguides. Improvements in the cross-sectional positioning accuracy of waveguides remain desirable.

It may also be desirable to improve and/or optimize the optical coupling between a pair of separated fibers (e.g., single mode fibers) at one end and the individual modes (e.g., few mode or multimode fibers) and/or cores (e.g., multicore fibers) at the other end. Further fiber array improvements may be desirable.

Furthermore, in many practical applications of coupler arrays, back reflection (or reflection loss) of light traveling through the coupler array at one or both of the first and second ends of the coupler array can be very significant. For example, improvements (e.g., optimization) to reduce back reflection can be important for some telecommunications and some sensing applications (e.g., when the light inserted into the coupler array is used for sensing) because back reflection can undesirably distort the characteristics of the sensed light and thus adversely affect sensor performance. Therefore, it can be advantageous in various implementations if the refractive index and size of both the inner and outer cores and/or other characteristics of the missing core waveguide in the optical coupler array can be improved (e.g., optimized) to reduce back reflection for light propagating from the multiple optical fibers at the first end of the coupler to the optical device at the second end of the coupler, and/or vice versa.

The exemplary embodiments described herein have innovative features, no single one of which is essential or solely responsible for their desirable attributes. Without limiting the scope of the claims, some of the advantageous features are summarized below.
Example Set I
1. A multi-channel optical coupler array for optically coupling a plurality of optical fibers to an optical device, the multi-channel optical coupler array comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure;
A plurality of longitudinal waveguides;
an outer cladding;
the plurality of longitudinal waveguides each being spaced apart from one another, each having capacity for at least one optical mode, each embedded in the common unitary housing structure proximate the second end, at least one configured to be coupled to one of the plurality of optical fibers at the first end, and configured to be coupled to the optical device at the second end; has an effective refractive index Neff1 for the at least one optical mode at the first end and an effective refractive index Neff2 at the second end, the at least one missing core waveguide comprises an inner missing core and an outer core, the inner missing core having a first refractive index (N-1), a first inner core size (ICS-1) at the first end and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounding the inner core and having a second refractive index (N-2), a first outer core size (OCS-1) at the first end and a second outer core size (OCS-2) at the second end;
the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3), a first cladding size at the first end, and a second cladding size at the second end;
the common unitary coupler housing structure has a fourth refractive index (N-4) and comprises a laterally continuous medium surrounding the plurality of longitudinal waveguides, the relative magnitude relationship between the first, second, and third refractive indices (N-1, N-2, and N-3) having the following magnitude relationship (N-1>N-2>N-3), a total volume of the medium in the common unitary coupler housing structure is greater than a total volume of all of the lost core waveguide inner cores and the outer cores confined within the common unitary coupler housing structure, the first inner lost core size (ICS-1), the first an outer core size (OCS-1) and the spacing between the plurality of longitudinal waveguides are simultaneously and gradually reduced according to a reducing profile along the elongated optical element between the first end and the second end until the second inner missing core size (ICS-2) and the second outer core size (OCS-2) are reached, the second inner missing core size (ICS-2) being selected to be insufficient to guide light therethrough and the second outer core size (OCS-2) being selected to be sufficient to guide at least one optical mode, such that
light traveling in a first direction from the first end to the second end escapes from the inner lost core into the corresponding outer core proximate the second end;
light traveling in a second direction from the second end to the first end travels from the outer core into the corresponding inner lost core proximate the first end;
the common single coupler housing structure proximate the first end has a cross-sectional shape comprising a laterally continuous structure having at least one hole, the at least one hole containing at least one of the plurality of longitudinal waveguides and creating a gap between the coupler housing structure and at least one of the plurality of longitudinal waveguides;
The relationship between Neff1, Neff2, NeffFiber, and NeffDevice is:
(1) Neff2 is approximately equal to NeffDevice, and Neff1 is not equal to NeffFiber;
(2) Neff1 is approximately equal to NeffFiber, and Neff2 is not equal to NeffDevice;
(3) A multi-channel optical coupler array, where Neff1 is greater than NeffFiber and Neff2 is less than NeffDevice.
2. At least one of the lost core waveguides comprises a refractive index profile;
In the refractive index profile,
the first refractive index (N-1);
the first inner core size (ICS-1);
the second inner core size (ICS-2);
the second refractive index (N-2),
the first outer core size (OCS-1);
the second outer core size (OCS-2), and the third refractive index (N-3),
2. The multi-channel optical coupler array of example 1, configured to reduce back reflections of light traveling in at least one of the first direction from the plurality of optical fibers to the optical device or the second direction from the optical device to the plurality of optical fibers at an optical fiber interface and/or an optical device interface.
3. The multi-channel optical coupler array of example 1, wherein Neff1 is greater than NeffFiber and Neff2 is approximately equal to NeffDevice.
4. The multi-channel optical coupler array of example 3, wherein the one of the plurality of optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, the optical device has a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice, and wherein N-3 is approximately equal to NcladdingFiber, N-2 is approximately equal to NcoreDevice, and N-1 is approximately equal to (N-2) + (NcoreFiber - NcladdingFiber).
5. The multi-channel optical coupler array of example 1, wherein Neff1 is approximately equal to NeffFiber and Neff2 is less than NeffDevice.
6. The multi-channel optical coupler array of example 5, wherein the one of the plurality of optical fibers has a cladding refractive index NcladdingFiber, and the third refractive index (N-3) of at least one of the missing core waveguides is less than NcladdingFiber.
7. The one of the plurality of optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, and the optical device has a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice;
6. The multi-channel optical coupler array of example 5, wherein N-1 is approximately equal to NcoreFiber, N-2 is approximately equal to NcladdingFiber, and N-3 is approximately equal to (N-2)-(NcoreDevice-NcladdingDevice).
8. The multi-channel optical coupler array of example 1, wherein Neff1 is greater than NeffFiber and Neff2 is less than NeffDevice.
9. The multi-channel optical coupler array of example 8, wherein the one of the plurality of optical fibers has a cladding refractive index NcladdingFiber, and the third refractive index (N-3) of at least one of the missing core waveguides is less than NcladdingFiber.
10. The one of the plurality of optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, and the optical device has a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice;
9. The optical coupler array of example 8, wherein N-3 is less than NcladdingFiber, N-2 is approximately equal to (N3)+(NcoreDevice-NcladdingDevice), and N-1 is approximately equal to (N2)+(NcoreFiber-NcladdingFiber).
11. At least one of the lost core waveguides comprises a refractive index profile;
In the refractive index profile,
the first refractive index (N-1);
the first inner core size (ICS-1);
the second inner core size (ICS-2);
the second refractive index (N-2),
the first outer core size (OCS-1);
9. The multi-channel optical coupler array of Example 8, wherein the second outer core size (OCS-2) and the third refractive index (N-3) are configured to reduce a sum of back reflections of light traveling in at least one of the first direction from the plurality of optical fibers to the optical device or the second direction from the optical device to the plurality of optical fibers at an optical fiber interface and an optical device interface.
12. The optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device comprising:
Free-space based optical devices,
2. The multi-channel optical coupler array of Example 1, comprising one of: an optical circuit having at least one input/output end coupling port; or an optical circuit having at least one optical port comprising a vertical coupling element.
13. The optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device comprising:
Multimode optical fiber,
Double clad optical fiber,
Multi-core optical fiber,
Large mode area fiber,
Double-clad multi-core optical fiber,
2. The multi-channel optical coupler array of Example 1 comprising one of: a standard/conventional optical fiber; or a custom optical fiber.
14. The multi-channel optical coupler array of example 1, wherein the optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device comprising an additional optical coupler array.
15. A multi-channel optical coupler array as described in Example 1, wherein N-3≦N-4.
16. The multi-channel optical coupler array of example 1, wherein proximate the second end, the coupler array has substantially no gaps between the coupler housing structure and the plurality of longitudinal waveguides.
17. The multi-channel optical coupler array of example 1, wherein the cross-sectional shape comprises a ring surrounding the plurality of longitudinal waveguides.
18. The multi-channel optical coupler array of example 17, wherein the plurality of longitudinal waveguides are in a hexagonal arrangement.
19. The multi-channel optical coupler array of example 17, wherein the ring has a circular inner cross-section.
20. The multi-channel optical coupler array of example 17, wherein the ring has a non-circular inner cross-section.
21. The multi-channel optical coupler array of example 17, wherein the ring has a circular outer cross-section.
22. The multi-channel optical coupler array of example 17, wherein the ring has a non-circular outer cross-section.
23. The multi-channel optical coupler array of example 1, wherein the cross-sectional shape comprises a structure having a plurality of holes.
24. The multi-channel optical coupler array of example 23, wherein the holes are in a hexagonal arrangement.
25. The multi-channel optical coupler array of example 23, wherein the holes are in a rectangular arrangement.
26. The multi-channel optical coupler array of example 23, wherein the plurality of holes are defined in an XY array.
27. The multi-channel optical coupler array of example 23, wherein at least one hole has a circular cross-section.
28. The multi-channel optical coupler array of example 23, wherein at least one hole has a non-circular cross-section.
29. The multi-channel optical coupler array of example 23, wherein at least one of the holes has a different dimension than another one of the holes.
30. The multi-channel optical coupler array of example 23, wherein at least one of the holes has a different shape than another one of the holes.
Example Set II
1. A multi-channel optical coupler, comprising:
an output optical coupler array; and
a plurality of optical fibers, at least two of the plurality of optical fibers being connected to each other at ends opposite the output optical coupler array.
2. The multi-channel optical combiner of example 1, wherein the output optical coupling array comprises a reflector to form a Talbot cavity.
3. The multi-channel optical coupler of example 1, wherein the output optical coupler array comprises a reduced-pitch optical fiber array.
4. The output optical coupler array comprises:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are spaced apart from one another, each having capacity for at least one optical mode of a predetermined mode field profile, each embedded in the common unitary housing structure proximate the second end, at least one of the plurality of longitudinal waveguides being an lost core optical guide, each of the at least one lost core waveguide comprising:
The optical fiber comprises an inner lost core, an outer core, and an outer cladding, the inner lost core having a first refractive index (N-1), a first inner core size (ICS-1) at the first end and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounding the inner core and having a second refractive index (N-2), a first outer core size (OCS-1) at the first end and a second outer core size (OCS-2) at the second end, and the outer cladding is disposed on the outer a common single coupler housing structure having a third refractive index (N-3), a first cladding size at said first end and a second cladding size at said second end, said common single coupler housing structure having a fourth refractive index (N-4) and comprising a laterally continuous medium surrounding said plurality of longitudinal waveguides, wherein the relative magnitude relationship between said first, second, third and fourth refractive indices (N-1, N-2, N-3 and N-4) has the following magnitude relationship (N-1>N-2>N-3);
a total volume of the medium or common single coupler housing structure is greater than a total volume of all of the lost core waveguide inner cores and outer cores enclosed within the common single coupler housing structure, the first inner lost core size (ICS-1), the first outer core size (OCS-1) and the predetermined spacing between the plurality of longitudinal waveguides simultaneously and gradually decrease according to a predetermined decreasing profile along the optical element between the first end and the second end until the second inner lost core size (ICS-2) and the second outer core size (OCS-2) are reached, the second inner lost core size (ICS-2) being selected to be insufficient to guide light therethrough and the second outer core size (OCS-2) being selected to be sufficient to guide at least one optical mode, such that
4. The multi-channel optical coupler of example 3, wherein light traveling in a first direction from the first end to the second end escapes from the inner lost core into the corresponding outer core proximate the second end, and light traveling in a second direction from the second end to the first end moves from the outer core into the corresponding inner lost core proximate the first end.
5. The output optical coupler array comprises an elongated optical element having a first end operable to optically couple with the plurality of optical fibers and a second end operable to optically couple with the optical device;
The elongated optical element comprises:
a common single coupler housing structure;
a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are each spaced apart from one another, each having capacity for an optical mode of a predetermined mode field profile, each embedded in the common unitary housing structure proximate the second end, at least one of the plurality of longitudinal waveguides being a missing core optical waveguide, each of the at least one missing core waveguide comprising an inner missing core, an outer core, and an outer cladding, the inner missing core having a first refractive index (N-1), a first inner core size (ICS-1) at the first end, and an intermediate inner core size (ICS-2) at the intermediate cross section; the outer core longitudinally surrounds the inner core and has a second refractive index (N-2), a first outer core size (OCS-1) at the first end, an intermediate outer core size (OCS-IN) at the intermediate cross section, and a second outer core size (OCS-2) at the second end; the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3), a first cladding size at the first end, and a second cladding size at the second end; and the common single coupler housing structure is
a laterally continuous medium having a fourth refractive index (N-4) surrounding said plurality of longitudinal waveguides, a predetermined relative magnitude relationship between said first, second, third and fourth refractive indices (N-1, N-2, N-3 and N-4) having the following magnitude relationship (N-1>N-2>N-3), a total volume of said medium in said common single coupler housing structure is greater than a total volume of all of said inner cores and said outer cores of said lost core waveguides confined within said common single coupler housing structure, a first inner lost core size (ICS-1), a first outer core size (OCS-1) and a front space between said plurality of longitudinal waveguides, the spacing simultaneously and gradually decreases along the optical element between the first end and the second end according to a decreasing profile until the second inner missing core size (ICS-2) and the second outer core size (OCS-2) are reached, the intermediate inner missing core size (ICS-IN) being selected to be insufficient to guide light therethrough, the intermediate outer core size (OCS-IN) being selected to be sufficient to guide at least one optical mode therethrough, and the second outer core size (OCS-2) being selected to be insufficient to guide at least one optical mode therethrough, such that
light traveling in a first direction from the first end to the second end escapes from the inner missing core into the corresponding outer core proximate the intermediate cross section and from the outer core into a coupling waveguide formed by at least two adjacent outer cores proximate the second end;
4. The multi-channel optical coupler of example 3, wherein at least one waveguide mode of light traveling from the second end to the first end travels from the coupled waveguide formed by at least two adjacent outer cores into the outer core proximate the intermediate cross section and from the outer core into the corresponding inner lost core proximate the first end.
6. The multi-channel optical coupler of Example 1, wherein the plurality of optical fibers include one or more gain blocks configured to enable optical amplification.
7. The multi-channel optical coupler of Example 1, wherein the plurality of optical fibers comprises at least one optical fiber that is not connected to other optical fibers at an end opposite the output optical coupler array.
8. The multi-channel optical coupler of example 7, wherein the at least one optical fiber that is not connected to another optical fiber is configured to form a laser cavity suitable for passive or active phase locking.
9. The multi-channel optical coupler of example 7, wherein the at least one optical fiber that is not connected to other optical fibers comprises at least one reflector, fiber Bragg grating, or modulating element.
10. A device configured to generate a single polarization mode, said device comprising the multi-channel optical coupler of example 1, and said at least two fibers connected together comprising one or more polarizing beam splitters.
11. A device configured to generate a single polarization mode, said device comprising the multi-channel optical coupler of example 1, and said at least two fibers connected together comprising one or more isolators.
12. A device configured to generate a single polarization mode, the device comprising the multi-channel optical combiner of example 1 and one or more polarization converters.
13. The device of example 12, wherein the one or more polarization converters comprise one or more circular-to-linear or linear-to-circular converters.
14. The multi-channel optical coupler of Example 1, wherein the plurality of optical fibers comprises at least four optical fibers.
15. The multi-channel optical coupler of example 14, wherein the plurality of optical fibers comprises at least six optical fibers.
16. The multi-channel optical coupler of example 15, wherein the plurality of optical fibers comprises at least eight optical fibers.
17. The multi-channel optical coupler of example 16, wherein the plurality of optical fibers comprises at least 10 optical fibers.
18. The multi-channel optical coupler of Example 1, wherein the output optical coupler array comprises a plurality of waveguides.
19. The multi-channel optical coupler of Example 1, wherein the output optical coupler array comprises a plurality of cores configured to support at least one propagation mode.
20. The multi-channel optical combiner of Example 2, wherein the reflector comprises a Talbot mirror.
21. The multi-channel optical coupler of Example 1, wherein the output optical coupler array comprises at least one reflector at an end opposite the plurality of optical fibers.
22. The multi-channel optical coupler of Example 1, wherein the output optical coupler array comprises a common reflector at an opposite end to the plurality of optical fibers.
Example Set III
1. A multi-channel optical coupler for optically coupling a plurality of optical fibers to an optical device, said multi-channel optical coupler comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are each spaced apart from one another, each having capacity for at least one optical mode of a predetermined mode field profile, each embedded in the common unitary housing structure proximate the second end, at least one of the plurality of longitudinal waveguides being a lost core optical waveguide, each of the at least one lost core waveguide comprising an inner lost core, an outer core, and an outer cladding, the inner lost core having a first refractive index (N-1), a first inner core size (ICS-I) at the first end, and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounding the inner core, the common single coupler housing structure has a fourth refractive index (N-4) and comprises a laterally continuous medium surrounding the plurality of longitudinal waveguides, the first, second, third, and fourth refractive indices (N-1, N-2, N-3, and N-4) having the following magnitude relationship: N-1>N-2>N-3;
a total volume of the medium or common single coupler housing structure is greater than all of the lost core waveguide inner cores and the outer cores enclosed within the total volume or common single coupler housing structure, the first inner lost core size (ICS-I), the first outer core size (OCS-I), and the predetermined spacing between the plurality of longitudinal waveguides simultaneously and gradually decrease according to a predetermined decreasing profile along the optical element between the first end and the second end until the second inner lost core size (ICS-2) and the second outer core size (OCS-2) are reached, the second inner lost core size (ICS-2) being selected to be insufficient to guide light therethrough and the second outer core size (OCS-2) being selected to be sufficient to guide at least one optical mode, such that
light traveling from the first end to the second end escapes from the inner lost core into the corresponding outer core proximate the second end, and light traveling from the second end to the first end travels from the outer core into the corresponding inner lost core proximate the first end;
a common single coupler housing structure proximate the first end having one of the following cross-sectional shapes: a ring surrounding the plurality of longitudinal waveguides; a laterally continuous structure having a plurality of holes, at least one of the holes containing at least one of the plurality of longitudinal waveguides.
2. A multi-channel optical combiner array, comprising:
an elongated optical element, the elongated optical element having a first end and a second end, the first end and the second end operable to optically couple to a plurality of optical fibers, optical devices, or a combination thereof;
The elongated optical element comprises:
a coupler housing structure;
a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are disposed relative to one another, each having a capacity for at least one optical mode, the plurality of longitudinal waveguides are embedded in the housing structure, and at least one of the plurality of longitudinal waveguides has a lost core optical path, the at least one lost core optical path;
the at least one lost core waveguide comprises an inner lost core, an outer core, and an outer cladding;
the inner vanishing core has a first refractive index (N-1) and an inner core size;
the outer core longitudinally surrounds the inner core and has a second refractive index (N-2) and an outer core size;
the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3) and a cladding size;
the coupler housing structure comprises a medium having a fourth refractive index (N-4) surrounding the plurality of longitudinal waveguides, where N-1>N-2>N-3;
the inner core size, the outer core size, and spacing between the plurality of longitudinal waveguides decrease along the optical element from the first end to the second end such that at the second end, the inner core size is insufficient to guide light therethrough, and the outer core size is sufficient to guide at least one optical mode;
A multi-channel optical coupler array, wherein the coupler housing structure proximate the first end has the following cross-sectional configuration: a ring surrounding the plurality of vertical waveguides, with gaps between the ring and the plurality of waveguides, or a structure having a plurality of holes, at least one hole containing at least one of the plurality of vertical waveguides.
3. The optical coupler array of Example 2, wherein the coupler housing structure comprises a common single coupler housing structure.
4. An optical coupler array as described in any of the preceding examples, wherein adjacent the first end, one of the plurality of longitudinal waveguides extends outside the coupler housing structure.
5. The optical coupler array of any of the preceding examples, wherein adjacent the first end, one of the plurality of longitudinal waveguides is disposed within the coupler housing structure and does not extend beyond the coupler housing structure.
6. An optical coupler array as described in any of the preceding examples, wherein adjacent the first end, one of the plurality of longitudinal waveguides is disposed in an outer cross-sectional boundary region of the coupler housing structure and does not extend beyond the coupler housing structure.
7. The optical coupler array of any one of Examples 2 to 6, wherein the medium is a laterally continuous medium.
8. An optical coupler array as described in any one of Examples 2 to 7, wherein the total volume of the medium of the coupler housing structure is greater than the total volume of all the inner cores and outer cores of the at least one lost core waveguide confined within the coupler housing structure.
9. The optical coupler array of any of Examples 2-8, wherein the inner core size, the outer core size, and the spacing between the plurality of longitudinal waveguides decrease simultaneously and gradually from the first end to the second end.
10. An optical coupler array as described in any of the preceding examples, wherein proximate the second end, the coupler array has substantially no gaps between the coupler housing structure and the plurality of longitudinal waveguides.
11. An optical coupler array according to any of the preceding examples, wherein one of the cross-sectional structures is a ring surrounding the plurality of vertical waveguides.
12. The optical coupler array of example 11, wherein the plurality of longitudinal waveguides are arranged in a hexagonal pattern.
13. The optical coupler array of any one of Examples 11-12, wherein the ring has a circular inner cross section.
14. The optical coupler array of any of Examples 11-12, wherein the ring has a non-circular inner cross-section.
15. The optical coupler array of example 14, wherein the inner cross section is hexagonal.
16. The optical coupler array of example 14, wherein the inner cross section is D-shaped.
17. The optical coupler array of any one of Examples 11 to 16, wherein the ring has a circular outer cross section.
18. The optical coupler array of any of Examples 11-16, wherein the ring has a non-circular outer cross-section.
19. The optical coupler array of example 18, wherein the outer cross section is hexagonal.
20. The optical coupler array of example 18, wherein the outer cross section is D-shaped.
21. The optical coupler array of any one of Examples 1 to 10, wherein one of the cross-sectional shapes is a structure having the plurality of holes.
22. The optical coupler array of example 21, wherein the holes are in a hexagonal arrangement.
23. The optical coupler array of example 21, wherein the holes are in a rectangular arrangement.
24. The optical coupler array of example 21, wherein the plurality of holes are defined in an XY array.
25. The optical coupler array of any of Examples 21-24, wherein at least one hole comprises a non-waveguide material.
26. The optical coupler array of any one of examples 21-25, wherein at least one hole has a circular cross-section.
27. The optical coupler array of any one of examples 21-26, wherein at least one hole has a non-circular cross-section.
28. The optical coupler array of example 27, wherein the non-circular cross section is D-shaped.
29. The optical coupler array of any of Examples 21-28, wherein at least one of the holes has a different dimension than another one of the holes.
30. The optical coupler array of any of Examples 21-29, wherein at least one of the holes has a different shape than another one of the holes.
31. The optical coupler array of any one of examples 21 to 30, wherein the holes are insulated.
32. The optical coupler array of any one of examples 21 to 30, wherein some of the holes are connected.
33. The optical coupler array of any of the previous examples, wherein the at least one missing core waveguide comprises a single mode fiber.
34. The optical coupler array of any of the previous examples, wherein the at least one missing core waveguide comprises a multimode fiber.
35. The optical coupler array of any of the previous examples, wherein the at least one lost core waveguide comprises polarization maintaining fiber.
36. A multi-channel optical combiner array, comprising:
an elongated optical element having a first end and a second end, the first end and the second end operable to optically couple to a plurality of optical fibers, optical devices, or a combination thereof;
The optical element comprises:
a coupler housing structure;
a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are disposed relative to one another, each having a capacity for at least one optical mode, the plurality of longitudinal waveguides are embedded in the housing structure, the plurality of longitudinal waveguides each having at least one lost core waveguide, the at least one lost core waveguide;
the at least one lost core waveguide comprises an inner lost core, an outer core, and an outer cladding;
the inner disappearing core has a first refractive index (N-1) and an inner core size;
the outer core longitudinally surrounds the inner core and has a second refractive index (N-2) and an outer core size;
the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3) and a cladding size;
the coupler housing structure comprises a medium having a fourth refractive index (N-4) surrounding the plurality of longitudinal waveguides, where N-1>N-2>N-3;
the inner missing core size, the outer core size, and the spacing between the plurality of longitudinal waveguides decrease along the elongated optical element from the first end to the second end such that at the second end, the size of the inner core is insufficient to guide light therethrough, and the outer core size is sufficient to guide at least one optical mode;
a coupler housing structure proximate the first end having a cross-sectional shape with at least one hole, the at least one hole containing at least one of the plurality of longitudinal waveguides, the hole being larger than at least one of the plurality of longitudinal waveguides such that at least one of the plurality of waveguides is laterally movable relative to the coupler housing structure.
37. The optical coupler array of example 36, wherein the coupler housing structure comprises a common single coupler housing structure.
38. An optical coupler array according to any one of Examples 36-37, wherein adjacent the first end, one of the plurality of longitudinal waveguides extends outside the coupler housing structure.
39. The optical coupler array of any one of Examples 36-38, wherein one of the plurality of longitudinal waveguides is disposed within the coupler housing structure proximate the first end.
40. The optical coupler array of any one of examples 36-39, wherein the medium is a laterally continuous medium.
41. An optical coupler array as described in any of Examples 36-40, wherein a total volume of the medium in the coupler housing structure is greater than a total volume of all inner cores and outer cores of the at least one lost core waveguide confined within the coupler housing structure.
42. The optical coupler array of any of Examples 36-41, wherein the inner core size, the outer core size, and the spacing between the plurality of longitudinal waveguides decrease simultaneously and gradually from the first end to the second end.
43. An optical coupler array as described in any of Examples 36-42, wherein proximate the second end, the coupler array has substantially no gaps between the coupler housing structure and the plurality of longitudinal waveguides.
44. The optical coupler array of any of Examples 36-43, wherein the at least one hole comprises a single hole and at least one of the plurality of longitudinal waveguides comprises a plurality of longitudinal waveguides.
45. The optical coupler array of example 44, wherein the plurality of longitudinal waveguides are in a hexagonal arrangement.
46. The optical coupler array of any of examples 44-45, wherein the single hole has a circular cross-section.
47. The optical coupler array of any one of Examples 44-45, wherein the single hole has a non-circular cross-section.
48. The optical coupler array of example 47, wherein the non-circular cross-section is hexagonal.
49. The optical coupler array of example 47, wherein the non-circular cross section is D-shaped.
50. The optical coupler array of any one of Examples 44-49, wherein the coupler housing structure has a circular outer cross-section.
51. The optical coupler array of any one of Examples 44-49, wherein the coupler housing structure has a non-circular outer cross-section.
52. The optical coupler array of example 51, wherein the outer cross section is hexagonal.
53. The optical coupler array of example 51, wherein the outer cross section is D-shaped.
54. The optical coupler array of any one of Examples 36-43, wherein the at least one hole comprises a plurality of holes.
55. The optical coupler array of example 54, wherein the plurality of holes are in a hexagonal arrangement.
56. The optical coupler array of example 54, wherein the plurality of holes are in a rectangular arrangement.
57. The optical coupler array of example 54, wherein the plurality of holes are defined by an XY array.
58. The optical coupler array of any of Examples 54-57, wherein one or more of the plurality of holes comprises a non-waveguide material.
59. The optical coupler array of any one of Examples 54-58, wherein one or more of the plurality of holes has a circular cross-section.
60. The optical coupler array of any one of Examples 54-59, wherein one or more of the plurality of holes has a non-circular cross-section.
61. The optical coupler array of example 60, wherein the non-circular cross-section has a D-shape.
62. The optical coupler array of any of Examples 54-61, wherein one or more of the plurality of holes has a different dimension than another one of the holes.
63. The optical coupler array of any of Examples 54-62, wherein one or more of the plurality of holes has a different shape than another one of the holes.
64. The optical coupler array of any one of Examples 54 to 63, wherein the holes are insulated.
65. The optical coupler array of any one of Examples 54 to 63, wherein some of the holes are connected.
66. The optical coupler array of any of Examples 54-65, wherein the at least one missing core waveguide comprises a single mode fiber.
67. The optical coupler array of any of Examples 54-66, wherein the at least one missing core waveguide comprises a multimode fiber.
68. The optical coupler array of any of Examples 54-67, wherein the at least one lost core waveguide comprises a polarization maintaining fiber.
Example Set IV
1. A multi-channel optical coupler for optically coupling a plurality of optical fibers to an optical device, the multi-channel optical coupler comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are spaced apart from one another, each having capacity for at least one optical mode of a predetermined mode field profile, each embedded within the common unitary housing structure, at least one of the plurality of longitudinal waveguides being an lost core optical waveguide;
Each of the at least one missing core waveguides comprises an inner missing core, an outer core, and an outer cladding, the inner missing core having a first refractive index (N-1), a first inner core size (ICS-I) at the first end, an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounding the inner core and having a second refractive index (N-2), a first outer core size (OCS-I) at the first end, an intermediate outer core size (OCS-IN) at the intermediate cross section, and a second inner core size (ICS-3) at the second end. the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3), a first cladding size at the first end and a second cladding size at the second end; the common unitary coupler housing structure has a fourth refractive index (N-4) and comprises a laterally continuous medium surrounding the plurality of longitudinal waveguides, the relative magnitude relationship between the first, second, third and fourth refractive indices (N-1, N-2, N-3 and N-4) having the following magnitude relationship (N-1>N-2>N-3);
a total volume of the medium or common single coupler housing structure is greater than all of the lost core waveguide inner cores and outer cores enclosed within the total volume or common single coupler housing structure, the first inner lost core size (ICS-I), the first outer core size (OCS-I), and the spacing between the plurality of longitudinal waveguides simultaneously and gradually decrease according to a predetermined decreasing profile along the optical element between the first end and the second end until the second inner lost core size (ICS-2) and the second outer core size (OCS-2) are reached, the intermediate inner lost core size (ICS-IN) is selected to be insufficient to guide light therethrough, the intermediate outer core size (OCS-IN) is selected to be sufficient to guide at least one optical mode, and the second outer core size (OCS-2) is selected to be sufficient to guide at least one optical mode, such that
light traveling from the first end to the second end escapes from the inner missing core into the corresponding outer core proximate the intermediate cross section and from the outer core into a coupled waveguide formed by at least two adjacent outer cores proximate the second end;
light traveling from the second end to the first end travels from the coupled waveguide formed by the at least two adjacent outer cores into the outer core proximate the intermediate cross section and from the outer core into the corresponding inner lost core proximate the first end;
a common single coupler housing structure proximate the first end, the common single coupler housing structure having a cross-sectional structure comprising a laterally continuous structure having at least one hole, the at least one hole containing at least one of the plurality of longitudinal waveguides, forming a gap between the coupler housing structure and at least one of the plurality of longitudinal waveguides.
2. A multi-channel optical coupler for optically coupling a plurality of optical fibers to an optical device, the multi-channel optical coupler comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are spaced apart from one another, each having capacity for at least one optical mode, each embedded in the housing structure, at least one of the plurality of longitudinal waveguides being an evanescent core waveguide, each of the at least one evanescent core waveguide comprising:
an inner lost core, an outer core, and an outer cladding, the inner lost core having a first refractive index (N-1), a first inner core size (ICS-I) at the first end and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounding the inner core and having a second refractive index (N-2), a first outer core size (OCS-I) at the first end and a second outer core size (OCS-2) at the second end, the outer cladding being a common single coupler housing structure having a medium longitudinally surrounding the outer core and having a third refractive index (N-3), a first cladding size at the first end and a second cladding size at the second end, the common single coupler housing structure having a fourth refractive index (N-4) and surrounding the plurality of longitudinal waveguides, the relative magnitude relationship between the first, second, third and fourth refractive indices (N-1, N-2, N-3 and N-4) having the following magnitude relationship (N-1>N-2>N-3);
the first inner missing core size (ICS-I), the first outer core size (OCS-1), and the spacing between the plurality of longitudinal waveguides simultaneously and gradually decrease along the optical element between the first end and the second end until the second inner missing core size (ICS-2) and the second outer core size (OCS-2) are reached, the second inner missing core size (ICS-2) being selected to be insufficient to guide light therethrough and the second outer core size (OCS-2) being selected to be sufficient to guide at least one optical mode, such that
light traveling from the first end to the second end escapes from the inner lost core into the corresponding outer core proximate the second end, and light traveling from the second end to the first end travels from the outer core into the corresponding inner lost core proximate the first end;
a coupler housing structure proximate the first end having one of the following cross-sectional shapes: a ring surrounding the plurality of longitudinal waveguides; or a laterally continuous structure having a plurality of holes, at least one of the holes containing at least one of the plurality of longitudinal waveguides.
Example Set V
1. A multi-channel optical coupler for optically coupling a plurality of optical fibers to an optical device, the multi-channel optical coupler comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides each spaced apart from one another, each having capacity for at least one optical mode of a predetermined mode field profile, each embedded in the common unitary housing structure proximate the second end, at least one being an lost core optical guide, the at least one lost core optical guide comprising:
An inner lossy core, an outer core, and an outer cladding;
The inner missing core has a first refractive index (N-1), a first inner core size (ICS-I) at the first end, an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second inner core size (ICS-2) at the second end, and the outer core longitudinally surrounds the inner core and has a second refractive index (N-2), a first outer core size (OCS-I) at the first end, an intermediate outer core size (OCS-IN) at the intermediate cross section, and a second outer core size (OCS- 2), the outer cladding longitudinally surrounds the outer core and has a third refractive index (N-3), a first cladding size at the first end and a second cladding size at the second end, the common unitary coupler housing structure has a fourth refractive index (N-4) and surrounds the plurality of longitudinal waveguides, the relative magnitude relationship between the first, second, third and fourth refractive indices (N-1, N-2, N-3 and N-4) having the following magnitude relationship (N-1>N-2>N-3);
a total volume of the medium or common single coupler housing structure is greater than all of the lost core waveguide inner cores and outer cores enclosed within the total volume or common single coupler housing structure, the first inner lost core size (ICS-I), the first outer core size (OCS-I), and the predetermined spacing between the plurality of longitudinal waveguides simultaneously and gradually decrease according to a predetermined decreasing profile along the optical element between the first end and the second end until the second inner lost core size (ICS-2) and the second outer core size (OCS-2) are reached, the intermediate inner lost core size (ICS-IN) is selected to be insufficient to guide light therethrough, the intermediate outer core size (OCS-IN) is selected to be sufficient to guide at least one optical mode, and the second outer core size (OCS-2) is selected to be insufficient to guide light therethrough, so that
light traveling from the first end to the second end escapes from the inner missing core into the corresponding outer core proximate the second end and from the outer core into a coupling waveguide formed by at least two adjacent outer cores proximate the second end;
at least one waveguide mode of light traveling from the second end to the first end travels from the coupled waveguide formed by at least two adjacent outer cores into the outer core proximate the intermediate cross section and from the outer core into the corresponding inner missing core proximate the first end;
a common single coupler housing structure proximate the first end having a cross-sectional shape, the cross-sectional shape having a laterally continuous structure having at least one hole, the at least one hole containing at least one of the plurality of longitudinal waveguides, forming a gap between the coupler housing structure and at least one of the plurality of longitudinal waveguides.
2. A multi-channel optical coupler, comprising:
Equipped with a long optical element,
the elongated optical element has a first end, an intermediate cross section, and a second end;
The elongated optical element comprises:
a common single coupler housing structure and a plurality of longitudinal waveguides;
the plurality of longitudinal waveguides are spaced apart from one another, each having a capacity for at least one optical mode, each disposed in the housing structure, at least one of the plurality of longitudinal waveguides being an evanescent core waveguide, the at least one evanescent core waveguide comprising:
An inner lossy core, an outer core, and an outer cladding;
The inner missing core has a first refractive index (N-1), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second inner core size (ICS-2) at the second end, the outer core longitudinally surrounds the inner core and has a second refractive index (N-2), a first outer core size (OCS-I) at the first end, an intermediate outer core size (OCS-IN) at the intermediate cross section, and a second outer core size (OCS-2) at the second end, the outer cladding having a first refractive index (N-3), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (OCS-2) at the second end, the outer cladding having a second refractive index (N-4), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (ICS-2) at the second end, the outer cladding having a second refractive index (N-5), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (ICS-2) at the second end, the outer cladding having a second refractive index (N-6), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (ICS-2) at the second end, the outer cladding having a second refractive index (N-7), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (ICS-2) at the second end, the outer cladding having a second refractive index (N-8), an intermediate inner core size (ICS-IN) at the intermediate cross section, and a second outer core size (ICS-2) at the the cladding longitudinally surrounds the outer core and has a third refractive index (N-3), a first cladding size at the first end and a second cladding size at the second end; the common unitary coupler housing structure has a fourth refractive index (N-4) and surrounds the plurality of longitudinal waveguides; and the relative magnitude relationship between the first, second, third, and fourth refractive indices (N-1, N-2, N-3, and N-4) has the following magnitude relationship (N-1>N-2>N-3);
the first inner missing core size (ICS-I), the first outer core size (OCS-I), and the spacing between the plurality of longitudinal waveguides decrease along the optical element between the first end and the second end, the intermediate inner missing core size (ICS-IN) is selected to be insufficient to guide light therethrough, the intermediate outer core size (OCS-IN) is selected to be sufficient to guide at least one optical mode, and the second outer core size (OCS-2) is selected to be insufficient to guide light therethrough, such that
light traveling from the first end to the second end escapes from the inner missing core into the corresponding outer core proximate the intermediate cross section and from the outer core into a coupling waveguide formed by at least two adjacent outer cores proximate the second end;
11. A multi-channel optical coupler, wherein at least one waveguide mode of light traveling from the second end to the first end travels from the coupled waveguide formed by at least two adjacent outer cores into the outer core proximate the intermediate cross section and from the outer core into the corresponding inner lost core proximate the first end.

In the drawings, like reference characters indicate corresponding or similar elements throughout the various drawings.
FIG. 1A is a schematic side view of a first embodiment of an optical fiber coupler array comprising at least one lost core waveguide (VC waveguide), illustrated herein as a single VC waveguide, and at least one non-VC waveguide, illustrated herein as a plurality of non-VC waveguides disposed symmetrically and proximally to the illustrated single VC waveguide. FIG. 1B is a schematic side view of a second embodiment of an optical fiber coupler array comprising at least one lost core waveguide (VC waveguide), illustrated herein as a single VC waveguide, and at least one non-VC waveguide, illustrated herein as a single non-VC waveguide disposed parallel to and proximal to the illustrated single VC waveguide, a portion of the optical fiber coupler array configured to comprise a channel spacing magnitude at its second (smaller) end that is higher than the corresponding channel spacing magnitude at the second end of the optical fiber coupler array of FIG. 1A . FIG. 1C is a schematic side view of a third embodiment of an optical fiber coupler array comprising a plurality of non-VC waveguides and a plurality of VC waveguides arranged longitudinally and asymmetrically relative to one another, at least some of the non-VC waveguides having different types and/or different characteristics. FIG. 1D is a schematic side view of a fourth embodiment of an optical fiber coupler array configured for fan-in and fan-out connections and including a pair of optical fiber coupler components having a multi-core optical fiber element connected between the second ends (of a smaller size) of the two optical fiber coupler components. FIG. 2A is a schematic side view of a fifth embodiment of an optical fiber coupler array comprising a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure, each of the plurality of VC waveguides being spliced to a corresponding long optical device (such as an optical fiber) at a specific first splice location, at least a portion of which extends a predetermined length outside the single common housing structure, and each specific first splice location being disposed within the single common housing structure. FIG. 2B is a schematic side view of a sixth embodiment of an optical fiber coupler array comprising a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure, each of the plurality of VC waveguides being spliced to a corresponding long-length optical device (such as an optical fiber) at a specific second splice location, at least a portion of which extends a predetermined length outside the single common housing structure, and each specific second splice location being disposed in an outer cross-sectional boundary area of the single common housing structure. 2C is a schematic side view of a seventh embodiment of a fiber optic coupler array comprising a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure, each of the plurality of VC waveguides being spliced to a corresponding long length optical device (such as an optical fiber) at a particular third splice location, at least a portion of which extends a predetermined length outside the single common housing structure, and each particular third splice location being disposed outside the single common housing structure. 2D is a schematic side view of an alternative embodiment of a fiber optic coupler array comprising a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure configured to increase, improve, and/or optimize optical coupling to a free-space based optical device at its second end, which may also have (1) a separate device, such as a lens followed by other optical components as shown in FIG. 2D, or (2) a fusion spliceable device, such as a coreless glass element, at the second end of the coupler. The coreless glass element may act as an end cup for power density reduction at the glass-air interface or as a Talbot mirror for phase locking of the coupler's waveguides in a Talbot cavity geometry. FIG. 3A is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIGS. 1D-2D above, the optical fiber coupler array optionally comprising reference elements operable to provide visual identification of waveguide placement/characteristics (such as alignment) that can be placed into one of several categories of cross-sectional area. FIG. 3B is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIG. 1A, in which at least one VC waveguide, illustrated herein as a single VC waveguide, is arranged along a central longitudinal axis of a single common housing structure and is surrounded by a plurality of parallel non-VC waveguides arranged proximally and symmetrically. FIG. 3C is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIG. 3B above, in which the volume of a single common housing structure medium surrounding all portions of the waveguides embedded therein exceeds the combined volume of the inner and outer cores of the portions of the VC waveguides embedded within the single common housing structure. FIG. 3D is a schematic cross-sectional view of a second alternative embodiment of the optical fiber coupler array of FIG. 3B, in which at least one VC waveguide disposed along a central longitudinal axis of a single common housing structure comprises a plurality of VC waveguides, and the volume of the single common housing structure medium surrounding all portions of the waveguides embedded therein exceeds the combined volume of the inner and outer cores of the portions of the multiple VC waveguides embedded within the single common housing structure. FIG. 3E is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIG. 3D, the optical fiber coupler array comprising a central waveguide channel operable to provide an optical pump function therethrough. FIG. 3F is a schematic cross-sectional view of a second alternative embodiment of the optical fiber coupler array of FIG. 3D in which a VC waveguide disposed along a central longitudinal axis of a single common housing structure is of a different type and/or has different characteristics than the remaining multiple VC waveguides, and if selected to have an enlarged inner core, can be advantageously utilized to increase or optimize optical coupling to different types of optical pump channels of various optical devices. FIG. 3G is a schematic cross-sectional view of a third alternative embodiment of the optical fiber coupler array of FIG. 3B, in which at least one VC waveguide, illustrated in this specification as a single VC waveguide, is arranged as a side channel offset from the central longitudinal axis of a single common housing structure so that it can be easily used as a fiber optical amplifier and/or laser when spliced to a double-clad optical fiber having a non-concentric core to improve the optical pump efficiency of the optical fiber coupler array of this embodiment. FIG. 3H is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIG. 3G above, in which at least one VC waveguide, exemplified herein as a side channel off-center positioned single VC waveguide, has polarization maintaining properties and has a polarization axis aligned relative to its lateral off-center position. FIG. 3I is a schematic cross-sectional view of a fourth alternative embodiment of the optical fiber coupler array of FIG. 3B above, in which a single centrally located VC waveguide and multiple non-VC waveguides each have polarization-maintaining properties (illustrated merely as induced by a rod stress member, and which can be readily and alternately induced by a variety of other stresses or equivalent designs) and corresponding polarization axes, all of which are aligned with each other. FIG. 3J is a schematic cross-sectional view of a first alternative embodiment of the optical fiber coupler array of FIG. 3I above, in which all polarization maintaining properties of the waveguides are due solely to the non-circular cross-sectional shape of the core (or outer core in the case of a VC waveguide) of each waveguide, the non-circular cross-sectional shape being merely exemplified as at least partially elliptical, and optionally comprising at least one waveguide placement indication element disposed in an outer region of the single common housing structure representing a particular cross-sectional geometric arrangement of the waveguides of the optical coupler array, the particular cross-sectional geometric waveguide arrangement being easily identifiable from at least one of visual and physical inspection of the single common coupler housing structure, and the waveguide placement indication element being further operable to facilitate passive alignment of a second end of the optical coupler array to at least one optical device. FIG. 3K is a schematic cross-sectional view of a fifth alternative embodiment of the optical fiber coupler array of FIG. 3B above, in which a single centrally located VC waveguide has polarization-maintaining properties (illustrated merely as induced by a rod stress member, and which could easily and alternately be induced by a variety of other stresses or equivalent designs) and corresponding polarization axis, and optionally includes a plurality of optional waveguide placement indicating elements of the same or different type, as described in connection with FIG. 3J. FIG. 3L is a schematic cross-sectional view of a second alternative embodiment of the optical fiber coupler array of FIG. 3I above, in which the single common housing structure has a cross-section having a non-circular geometric shape (illustrated as a hexagon), and the polarization axes of the waveguides are aligned with each other and with the geometric shape of the single common housing structure cross-section, optionally further comprising a waveguide placement indication element as described in connection with FIG. 3J. FIG. 4 is a schematic isometric view showing an example connection of the second end (i.e., “tip”) of the optical fiber coupler array in the process of connecting to multiple vertical coupling elements of an optical device in a proximal open-air optical coupling alignment configuration, which can also be easily transitioned to a butt coupling configuration via full physical contact between the second end of the optical fiber coupler array and the vertical coupling elements. FIG. 5 is a schematic isometric view showing an example connection of a second end (i.e., “tip”) of an optical fiber coupler array connected to multiple edge coupling elements of an optical device in a butt coupling configuration, which can also be easily transitioned to one of several alternative coupling configurations having a proximal open-air optical coupling alignment configuration and/or an angled alignment coupling configuration. FIG. 6 is a schematic cross-sectional view of a known fiber optic coupler, which has various drawbacks and disadvantages that are readily overcome by the various embodiments of the fiber optic coupler arrays of FIGS. 1A-5. FIG. 7 is a schematic diagram of a flexible reduced pitch optical fiber array (PROFA) in various states. 8 is a schematic cross-sectional view of an example configuration of a housing structure proximate a first end of an optocoupler array, the cross-section being perpendicular to the longitudinal direction or length of the optocoupler array. FIG. 9 is a schematic cross-sectional view of another example configuration of a housing structure proximate a first end of an optical coupler array. FIG. 10 is a schematic diagram of another exemplary optical coupler array in various states. FIG. 11 is a schematic diagram of another exemplary optical coupler array in various states. FIG. 12 is a schematic diagram of an exemplary multi-channel optical combiner that can be used in coherent or incoherent beam combining applications. FIG. 13 is a schematic diagram of an exemplary multi-channel optical combiner having a single polarization mode output. FIG. 14 is a schematic graph illustrating various exemplary refractive index profiles, each with a different back reflection loss reduction scenario corresponding to a particular coupler array configuration. FIG. 15 is a schematic graph illustrating various exemplary refractive index profiles, each with a different back reflection loss reduction scenario corresponding to a particular coupler array configuration.

Various embodiments described herein provide improved fiber arrays, e.g., fiber arrays for use in coherent or incoherent beam combining illumination. Some embodiments can address shortcomings of other beam combining devices, such as (1) the use of back reflectors or fiber Bragg gratings (FBGs) as terminations of individual channels, (2) composite active length adjustment for phase locking, and (3) shortcomings from suppression of competing supermodes. Additionally, some embodiments can be useful in generating a single polarization mode output from a fiber array.

In some examples, improved cross-sectional (or lateral) positioning of the waveguides is desirable in many multi-channel optical coupler arrays. In the present disclosure, some embodiments of the housing structure (e.g., in some examples, a common single coupler housing structure) may allow for a self-aligned waveguide arrangement proximate the first end (e.g., a hexagonal close-packed arrangement of housing structures having circular or hexagonal interior cross sections (as shown in FIG. 8)) and improved cross-sectional positioning of the waveguides (in some examples, precise or near-precise) at the second end.

Packaging of photonic integrated circuits (PICs) with a low vertical profile (perpendicular to the PIC face) is also desirable for a variety of applications including optical communications and sensing. This is easily achievable for edge couplers, but surface couplers may require nearly vertical lengths.

It is therefore advantageous to provide various embodiments of a pitch reduced optical fiber array (PROFA) based flexible optical fiber array component that can be configured and possibly optimized to maintain all channels discrete with sufficiently low crosstalk while providing sufficient flexibility to accommodate low profile packaging. Furthermore, it is desirable to provide a PROFA based flexible optical fiber array component with a flexible portion to provide mechanical isolation of the "PROFA-PIC interface" from the rest of the PROFA, thereby increasing stability against environmental variations including temperature variations and mechanical shock and vibration. Furthermore, it is desirable to provide a PROFA based flexible optical fiber array with multiple coupled arrays, each having multiple optical channels, interdigitated with each other to form an optical multi-port input/output (IO) interface.

Certain embodiments are directed to an optical fiber coupler array and an optical device. The optical fiber coupler array can provide a low-loss, high-coupling coefficient interface between a plurality of optical fibers (or other optical devices) having a first channel spacing with high precision and easy alignment. The optical device has a plurality of waveguide interfaces having a smaller second channel spacing. Advantageously, in various embodiments, the larger and smaller sized ends of the optical fiber coupler array are configurable to have correspondingly different (i.e., larger vs. smaller) channel spacings, respectively. Here, the respective channel spacings at the larger and smaller ends of the optical coupler array can be easily matched to the corresponding respective first channel spacings of the plurality of optical fibers at the larger optical coupler array end and the second channel spacings of the plurality of waveguide interfaces of the optical device at the smaller optical coupler array end.

In various embodiments, the optical coupler array has a plurality of waveguides (at least one of which may optionally be polarization maintaining) with at least one tapered "vanishing core fiber" at least partially embedded within a common housing structure. Alternatively, in various additional embodiments, the coupler array may be configured to be utilized with at least one of an optical fiber amplifier and an optical fiber laser.

The various embodiments of the optical coupler array each advantageously include at least one "vanishing core" (VC) fiber waveguide, as described below in connection with, for example, the VC waveguide 30A of the optical coupler array 10A of FIG. 1A.

It should also be noted that the term "optical device," as used generally herein, applies to virtually any single-channel or multi-channel optical device, or any type of optical fiber, including, but not limited to, standard/conventional optical fibers. For example, optical devices to which a coupler array may be advantageously coupled may include, but are not limited to, one or more of the following:
A free-space based optical device; an optical circuit having at least one input/output edge-coupled port;
an optical circuit having at least one optical port with a vertical coupling element;
- Multimode (MM) optical fiber,
・Double clad optical fiber,
- Multi-core (MC) optical fiber,
Large mode area (LMA) fibre,
- Double-clad multi-core optical fiber,
Standard/conventional optical fiber,
Custom optical fibers, and/or Additional optical coupler arrays

Furthermore, it should be noted that although the term "fusion splice" is utilized in the various descriptions of exemplary embodiments of coupler arrays provided below with reference to the interconnections between the various optical coupler array components and between the various optical coupler array components and optical devices, any other form of waveguide or other coupler array component connection technique or method can be readily selected and utilized as a matter of design choice or need without departing from the spirit of the present invention, including, but not limited to, mechanical connections.

Now referring to FIG. 1A, a first embodiment of an optical fiber coupler array is shown as optical coupler array 10A. Optical coupler array 10A includes a common housing structure 14A (described below), at least one VC waveguide, illustrated in FIG. 1A as a single VC waveguide 30A, and at least one non-VC waveguide, illustrated in FIG. 1A as a pair of non-VC waveguides 32A-1, 32A-2. Each of the pair of non-VC waveguides 32A-1, 32A-2 is symmetrically positioned proximal to one of the sides of the illustrated single VC waveguide 30A. The portion of VC waveguide 30A located between positions B and D in FIG. 1A is embedded within common housing structure 14A.

Before describing the coupler array 10A and its components in more detail, it is useful to provide a detailed overview of the VC waveguide 30A, exemplary and alternative embodiments of which are advantageously utilized in each of the various embodiments of the coupler arrays of Figures 1A-5.

The VC waveguide 30A has a larger end (proximal to position B shown in FIG. 1A) and a smaller tapered end (proximal to position C shown in FIG. 1A), and comprises an inner core 20A (comprising a material with an effective refractive index N-1), an outer core 22A (comprising a material with an effective refractive index N-2 less than N-1), and a cladding 24A (comprising a material with an effective refractive index N-3 less than N2).

Advantageously, the outer core 22A serves as an effective cladding at the large end of the VC waveguide 30A where the VC waveguide 30A supports the "M1" spatial propagation mode in the inner core 20A, where M1 is greater than 0. The refractive indices N-1 and N-2 are preferably selected such that the numerical aperture (NA) at the large end of the VC waveguide 30A matches the NA of the optical device (e.g., optical fiber). The optical device is, for example, optical device 34A-1, comprising a standard/conventional optical fiber connected to the VC waveguide 30A at splice location 36A-1 (e.g., by fusion splice, mechanical connection, or other fiber connection design). Meanwhile, the dimensions of the inner and outer cores (20A, 22A) are selected such that the connected optical device (e.g., optical device 34A-1) has approximately the same mode field dimension (MFD). Here and below, the mode field dimension is used instead of the commonly used mode field diameter (MFD) because the cross section of a VC or non-VC waveguide may not be circular, resulting in a non-circular mode profile. Thus, the mode field dimension has both the mode size and the mode shape, and is equal to the mode field diameter in the case of a circularly symmetric mode.

During the manufacture of the coupler array 10A from a suitably configured preform (comprising a VC waveguide 30A preform with corresponding inner cores 20A, 22A, and cladding 24A), the coupler array 10A preform is tapered according to at least one predetermined reduction profile, so that the inner core 20A becomes too small to support all M1 modes. The number of spatial modes supported by the inner core at the second (tapered) end is M2, where M2<M1. For a single mode waveguide, here M1=1 (corresponding to two polarization modes) and M2=0, meaning that the inner core is too small to support light propagation. The VC waveguide 30A then acts to comprise a fiber with a single core of effective index close to N-2 surrounded by a cladding of lower index N-3.

During fabrication of the coupler array 10A, the channel spacing S-1 at the larger end of the coupler array 10A (position B, FIG. 1A) decreases in value to the channel spacing S-2 at the smaller end of the coupler array 10A (position C, FIG. 1A) in proportion to the stretch ratio selected for fabrication. Meanwhile, the MFD value (or the inverted NA value of the VC waveguide 30A) can be decreased, increased, or maintained depending on the selected difference in refractive index, (N-1-N-2) and (N-2-N-3), depending on the desired application of the optical coupler array 10A, as described below.

The ability to independently control the channel spacing and MFD values at each end of the optical coupler array is a highly advantageous feature of certain embodiments. In addition, the ability to match MFD and NA values by the size and shape of the inner core 20A and outer core 22A and the corresponding selection of values of N-1, N-2, and N-3 allows the optical coupler array to be utilized to couple to various waveguides without the use of lenses.

In its various embodiments, as the diameter of the VC waveguide becomes significantly smaller, the property of the VC waveguide that allows light to continue to propagate through the waveguide core along its length advantageously reduces light loss from interfacial defects or contamination and enables the use of a wider range of materials (described below) for the medium 28A of the common housing structure 14A, including but not limited to the above.
(a) a non-optical material (because the light is concentrated inside the waveguide core);
(b) a material with a refractive index greater than that of a standard/conventional fiber or absorption or scattering of the material to reduce or increase crosstalk between channels;
(c) Pure Silica (e.g., the same material used for most standard/conventional fiber claddings, to facilitate splicing into multicore, double-clad, or multimode fibers).

Preferably, according to a particular embodiment, the desired relative values of NA-1 and NA-2 (each of which corresponds to a corresponding end of the coupler array 10A, e.g., NA-1 corresponding to a large end of the coupler array 10A, and NA-2 corresponding to a small end of the coupler array 10A), and, optionally, the desired value of each of NA-1 and NA-2 may be determined by selecting values of the refractive indices N1, N2 and N3 of the coupler array 10A and configuring them according to at least one of the following relationships, which are selected based on the magnitude of the desired relative numerical aperture at each end of the coupler array 10A:

In general, the NA of any type of fiber is determined by the following formula:

where n _core and n _clad are the refractive indices of the fiber core and cladding, respectively.

Note that when using the above formula, the relationship between NA and the acceptance angle of a fiber is only an approximation. In particular, fiber manufacturers often express the "NA" of single-mode (SM) fibers based on the above formula, even though the acceptance angle of single-mode fibers is quite different and cannot be determined from the refractive index alone.

According to an embodiment, as used herein, the various NA values are preferably determined using the effective refractive index for both n _core and n _cladding , since the effective refractive index determines the light propagation and is more meaningful in the case of structured waveguides utilized in various embodiments. Also, the transverse refractive index profile inside the waveguide may not be smooth, but rather may vary around the values N1, N2, N3, or N4. Furthermore, the transition between the regions with refractive index N1, N2, N3, and N4 may not be as abrupt as a step function due to dopant diffusion, or some other intentional or unintentional factor, but may be a smooth function connecting the values of N1, N2, N3, and N4. The coupling design or optimization may also vary both the values of N1, N2, N3, and N4, and the size and shape of the regions with the respective indices.

Returning now to Figure 1A, the common coupling structure 14A comprises a medium 28A in which is embedded the portion of the VC waveguide 30A located between positions B and D in Figure 1A. The medium may include, but is not limited to, at least one of the following materials:
- materials that have properties that impede the propagation of light,
- a material having light absorbing properties; - a material having light scattering properties; - a material having optical properties selected such that the fourth refractive index (N-4) is greater than the third refractive index (N-3); and/or - a material having optical properties selected such that the fourth refractive index (N-4) is approximately equal to the third refractive index (N-3).

At the large end of the optical coupler array 10A (near position B in FIG. 1A), the VC waveguides 30A are spliced at specific splice locations 36A-1 (shown as an example positioned inside the common housing structure 14A) to portions of corresponding respective long optical devices 34A-1 (e.g., optical fibers) that extend a predetermined length 12A outside the common housing structure 14A. Meanwhile, the non-VC waveguides 32A-1, 32A-2 are spliced at specific splice locations 36A-2, 36A-3 (each positioned outside the common housing structure 14A) to corresponding respective long optical devices 34A-2, 34A-3 (e.g., optical fibers) that extend a predetermined length 12A outside the common housing structure 14A.

Optionally, the coupler array 10A can also have a generally uniform diameter tip 16A (shown between positions C and D in FIG. 1A) for coupling with the optical waveguide device 40A interface 42A at the array interface 18A. A uniform diameter tip 16A can be useful in certain interface applications, for example, as shown in FIGS. 1D, 5. Alternatively, the coupler array 10A can be manufactured without the tip 16A (or the tip 16A can be removed after manufacturing) such that coupling with the optical device interface 42A occurs at the coupler array 10A interface at position C in FIG. 1A.

In an alternative embodiment, when the optical device 40A comprises a double-clad fiber, when the small end of the coupler array 10A is coupled (e.g., fusion spliced) to the optical device interface 42A, at least a portion of the common housing structure 14A proximal to the splice location (e.g., at least a portion of the tip 16A) may be coated with a low index medium (not shown) and extend over the splice location and to the outer cladding of the double-clad fiber optical device 40A (optionally extending over a portion of the outer cladding of the double-clad fiber optical device 40A proximal to the splice location).

Now, referring to FIG. 1B, a second embodiment of the optical fiber coupler array is shown as coupler array 10B. The coupler array 10B comprises a common housing structure 14B, at least one VC waveguide, illustrated in FIG. 1B as a single VC waveguide 30B, and at least one non-VC waveguide, illustrated in FIG. 1B as a single non-VC waveguide 32B. The non-VC waveguide 32B is arranged in parallel proximal to the VC waveguide 30B. Here, a portion of the optical coupler array 10B is configured at its small end to have a channel spacing value S2' that is larger than the corresponding channel spacing value S2 at the small end of the optical coupler array 10A in FIG. 1A. This configuration can be easily achieved by cutting the optical fiber array 10A laterally at position C'. Thus, a common housing structure 14B can be manufactured that is shorter than the common housing structure 14A, resulting in a new and larger diameter array interface 18B with a larger channel spacing value S2'.

Now referring to FIG. 1C, a third embodiment of an optical fiber coupler array is shown as coupler array 10C. Coupler array 10C comprises a plurality of VC waveguides, shown in FIG. 1 as VC waveguides 30C-1, 30C-2, and a plurality of non-VC waveguides, shown in FIG. 1C as non-VC waveguides 32C-1, 32C-2, 32C-a. These are all arranged longitudinally and asymmetrically with respect to one another, and at least some of the plurality of non-VC waveguides are of different types and/or have different characteristics (e.g., single mode or multimode or polarization maintaining), e.g., non-VC waveguides 32C-1, 32C-2 are of a different type or have different characteristics than non-VC waveguide 32C-a. In addition, any VC or non-VC waveguide (e.g., non-VC waveguide 32C-a) can easily extend any desired length beyond the common housing structure of the coupler array 10C and need only be spliced in close proximity to the optical device.

Referring now to FIG. 1D, a fourth embodiment of an optical fiber coupler array configured for multicore fan-in and fan-out connections and shown as coupler array 50 is shown. The coupler array 50 comprises a pair of optical fiber coupler array components (10D-1, 10D-2) having a multicore optical fiber element 52. The multicore optical fiber element 52 is connected (e.g., by a fusion splice at locations 54-1, 54-2) between the second (smaller sized) ends of the two optical fiber coupler array components (10D-1, 10D-2). Preferably, at least one of the VC waveguides in each of the coupler array components (10D 1, 10D-2) is configured to increase or maximize optical coupling to a corresponding selected core of the multicore fiber element 52 while reducing or minimizing optical coupling to all of its other cores.

2A, a fifth embodiment of an optical fiber coupler array is shown as coupler array 100A. Coupler array 100A comprises a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure 104A, exemplified as a plurality of VC waveguides 130A-1, 130A-2. Each of the plurality of VC waveguides 130A-1, 130A-2 is spliced to a corresponding respective long optical device 134A-1, 134A-2 (e.g., optical fiber) at a specific splice location 132A-1, 132A-2, at least a portion of which extends a predetermined length 102A outside of the common housing structure 104A, and the specific splice location 132A-1, 132A-2, respectively, is disposed within the common housing structure 104A.

Now referring to FIG. 2B, a sixth embodiment of an optical fiber coupler array is shown as coupler array 100B.

The coupler array 100B comprises a plurality of longitudinal proximal VC waveguides at least partially embedded within a single common housing structure 104B, exemplified as a plurality of VC waveguides 130B-1, 130B-2. The plurality of VC waveguides 130B-1, 130B-2 are each spliced to a corresponding respective long-length optical device 134B-1, 134B-2 (e.g., optical fiber) at a specific splice location 132B-1, 132B-2, at least a portion of which extends a predetermined length 102B outside the common housing structure 104B, and the specific splice location 132B-1, 132B-2, respectively, are disposed in an outer cross-sectional boundary region of the common housing structure 104B.

Now referring to FIG. 2C, a seventh embodiment of an optical fiber coupler array is shown as coupler array 100C.

The coupler array 100C comprises a plurality of elongated proximal VC waveguides, as illustrated by a plurality of VC waveguides 130C-1, 130C-2, at least partially embedded within a single common housing structure 104C. The plurality of VC waveguides 130C-1, 130C-2 are each spliced to a corresponding respective elongated optical device 134C-1, 134C-2 (e.g., optical fiber) at a specific splice location 132C-1, 132C-2, at least a portion of which extends a predetermined length 102C outside the common housing structure 104C, and the specific splice location 132C-1, 132C-2, respectively, are disposed outside the common housing structure 104C.

2D, an alternative embodiment of the optical fiber coupler array is shown as a coupler array 150. The coupler array 150 comprises a plurality of longitudinal proximal VC waveguides. The longitudinal proximal VC waveguides are at least partially embedded in a single common housing structure configured at their second ends to increase or optimize optical coupling to a free-space-based optical device 152. The free-space-based optical device 152 may comprise a lens 154 followed by additional optical device components 156. They may comprise, as an example, a MEMS mirror or a volume Bragg grating. The combination of the coupler and the free-space-based optical device 152 may be used as an optical switch or WDM device for spectral combining or splitting of optical signals 160b (representative of the output signal 160a of the optical coupler array 150 after the optical signal 160a has passed through the lens 154). In this case, one of the fibers may be used as an input and all the others for the output, or vice versa. In another embodiment, the free space based device 152 can be fusion spliced to the end of the second coupler. This element can be a coreless glass element. It can act as an end cup for power density drop at the glass air interface. In another variation, the coreless element can act as a Talbot mirror for phase locking of the coupler waveguides in a Talbot cavity geometry.

Before describing in detail the various embodiments shown in Figures 3A-3L, whenever "plurality" or "at least one" coupler component/element is referred to below, it should be understood that the particular quantity of such coupler components/elements that may be provided in the corresponding embodiment of the coupler array may be selected as a matter of need or design choice (e.g., based on the intended industrial application of the coupler array) without departing from the spirit of the present invention. Thus, in the various Figures 3A-3L, single or individual coupler array components/elements are identified by a single reference number, while multiple coupler array components/elements are each identified by a reference number following "(1..n)." "n" is the desired number of multiple coupler components/elements (which may have different values in any particular coupler array embodiment described below).

Also, all waveguides VC and non-VC are shown with circular cross sections of the inner and outer cores and cladding by way of example. Other shapes of cross sections of the inner and outer cores and cladding (e.g., hexagonal, rectangular, or square) may be utilized without departing from the invention. The particular choice of shape is based on various requirements such as the channel shape, channel location geometry (e.g., hexagonal, rectangular, or square lattice), or axial polarization alignment mode of the optical device.

Similarly, unless otherwise noted below, the exemplary sizes, relative sizes, relative positions, and compositional material choices described below in connection with the detailed description of the coupler array embodiments of FIGS. 3A-3L are not limited to the exemplary sizes, relative sizes, relative positions, and compositional material choices described below in connection with the detailed description of the coupler array embodiments of FIGS. 3A-3L, so long as the various relationships described below (e.g., the relative capacitance relationships described below in connection with each of the optical coupler arrays 200C, 200D of FIGS. 3C and 3D, and the features described below in connection with the coupler array 200H of FIG. 3H, in which the PM VC waveguide 204H is laterally and vertically offset from the central longitudinal axis of the coupler array 200H) are adhered to. However, they may be selected by one of ordinary skill in the art as a matter of convenience or design choice without departing from the spirit of the present invention.

Finally, it should be noted that the various single common housing structural components 202A-202L of the various coupler arrays 200A-200L of Figures 3A-3L each have a value of refractive index N-4 according to an applicable one of the above relationships with the values of refractive indexes N-1, N-2, N-3 of the other coupler array components, and can be constructed from a medium having properties and characteristics selected from the various possible exemplary medium composition parameters described above in connection with medium 28A of Figure 1A.

3A, a first alternative embodiment of the optical fiber coupler array embodiment of FIGS. 1D-2D is shown as coupler array 200A, where all of the waveguides are VC waveguides. Coupler array 200A comprises a single common housing 202A and a plurality of VC waveguides 204A-(1-n), where n is equal to 19, by way of example. The plurality of VC waveguides 204A are centrally disposed along a central longitudinal axis of housing 202A.
The combiner array 200A may comprise at least one optional reference element 210A operable to provide the combiner array with one or more useful characteristics, including but not limited to the following:
- Allowing for visual identification of the coupler array waveguide arrangement (at least one of the ends of the coupler array); and - Facilitating passive alignment of at least one of the ends of the coupler array to at least one optical device.

Furthermore, when deployed in an optical coupler array embodiment comprising at least one polarization-maintaining VC waveguide (such as the optical coupler array embodiment described below in connection with Figures 3H-3L), the reference element can further operate as follows.
- allowing visual identification of a particular polarization axis alignment mode of an optical coupler array (described below in connection with Figures 3H-3L); and - serving as a geometrically positioned reference point for alignment of one or more polarization axes of a PM waveguide in a particular optical coupler array with respect to the optical coupler array.

The reference element 210A may comprise any of a variety of types of reference elements known in the art, selected as a matter of design choice or convenience, without departing from the spirit of the invention. For example, it may be a dedicated elongated element disposed longitudinally within the common housing structure 202A at one of a variety of cross-sectional locations (e.g., locations X or Y shown in FIG. 3A). Alternatively, the reference element 210A may comprise a dedicated channel not used for non-reference purposes, e.g., replacing one of the waveguides 204A-(1..n) illustrated at location Z in FIG. 3A.

Referring now to FIG. 3B, a first alternative embodiment of the optical fiber coupler array 10A of FIG. 1A above is shown as coupler array 200B. The coupler array 200B comprises a single housing structure 202B, at least one VC waveguide, illustrated in FIG. 3B as VC waveguide 204B, and a plurality of non-VC waveguides 206B-(1..n), where n is equal to 18, for example. The VC waveguide 204B is positioned along the longitudinal central axis of the common housing structure 202B and is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed non-VC waveguides 206B-(1..n).

3C, a first alternative embodiment of the optical fiber coupler array 200B of FIG. 3B above is shown as coupler array 200C. The coupler array 200C comprises a single housing structure 202C, a VC waveguide 204C, and a plurality of non-VC waveguides 206C-(1..n), where n is equal to 18, for example. The VC waveguide 204C is positioned along a longitudinal central axis of the common housing structure 202C and is circumferentially and symmetrically surrounded by a plurality of parallel, proximally disposed non-VC waveguides 206C-(1..n). The coupler array 200C is configured such that the capacity of the common housing structure 202C medium surrounding all portions of the waveguides embedded therein (i.e., the VC waveguide 204C and the multiple non-VC waveguides 206C-(1..n)) exceeds the combined capacity of the inner and outer cores of the portions of the VC waveguide 204C embedded within a single common housing structure 202C.

3D, a first alternative embodiment of the optical fiber coupler array 200C of FIG. 3C above is shown as coupler array 200D. The coupler array 200D comprises a single housing structure 202D, a plurality of VC waveguides 204D-(1..N) (e.g., n equals 7), and a plurality of non-VC waveguides 206D-(1..n) (e.g., n equals 12). The plurality of VC waveguides 204D-(1..N) are arranged along a longitudinal central axis of the common housing structure 202D and are circumferentially and symmetrically surrounded by a plurality of parallel and proximally arranged non-VC waveguides 206D-(1..n). The coupler array 200D is configured such that the capacity of the common housing structure 202D medium surrounding all portions of the waveguides embedded therein (e.g., multiple VC waveguides 204D-(1..N) and multiple non-VC waveguides 206D-(1..n)) exceeds the total capacity of the inner and outer cores of the portions of multiple VC waveguides 204D-(1..N) embedded within a single common housing structure 202D.

Referring to FIG. 3E, a first embodiment of the optical fiber coupler array 200D of FIG. 3D above is shown as coupler array 200E. The coupler array 200E comprises a single housing structure 202E, a plurality of VC waveguides 204E-(1..N) (e.g., N equals 6), a plurality of non-VC waveguides 206E-(1..n) (e.g., n equals 12), and a separate single non-VC waveguide 206E'. The non-VC waveguide 206E' is preferably operable to provide an optical pump function therethrough, and is disposed along a longitudinal central axis of the common housing structure 202E, circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed VC waveguides 204E-(1..N), which in turn is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed non-VC waveguides 206E-(1..n).

3F, a second alternative embodiment of the optical fiber coupler array 200B of FIG. 3B above is shown as coupler array 200F. The coupler array 200F comprises a single housing structure 202F, a plurality of VC waveguides 204F-(1 ..N) (e.g., N equals 6), a separate single VC waveguide 204F', and a plurality of non-VC waveguides 206F-(1 ..n) (e.g., n equals 12). The plurality of non-VC waveguides 206 each preferably comprises an enlarged inner core of sufficient diameter to increase or optimize optical coupling to different types of optical pump channels of various optical devices to which the coupler array 200F can be advantageously coupled. The VC waveguide 204F' is disposed along the longitudinal central axis of the common housing structure 202F and is circumferentially and symmetrically surrounded by a plurality of parallel, proximally arranged VC waveguides 204F-(1..N), which in turn is circumferentially and symmetrically surrounded by a plurality of parallel, proximally arranged non-VC waveguides 206F-(1..n).

Now referring to FIG. 3G, a third alternative embodiment of the optical fiber coupler array 200B of FIG. 3B above is shown as coupler array 200G. The coupler array 200G comprises a single housing structure 202G, at least one VC waveguide, illustrated in FIG. 3G as VC waveguide 204G, and a plurality of non-VC waveguides 206G-(1..n) (e.g., n equal to 18). The VC waveguides 204G are arranged as side channels offset from the longitudinal central axis of the single common housing structure 202G, so that the optical fiber coupler array 200G can be easily used as a fiber optical amplifier and/or laser when spliced to a double clad optical fiber (not shown) having a non-concentric core to improve optical pump efficiency. It should be noted that since a double-clad fiber is a fiber in which both the core and the inner cladding have light-guiding properties, most optical fiber types, such as SM, MM, LMA, or MC (multicore), with or without polarization maintenance, and even standard (e.g., conventional) single-mode optical fibers, can be converted to double-clad fibers by coating (or recoating) the fiber with a low-index medium (forming the outer cladding).

Optionally, when the second end of the coupler array 200G is spliced to a double-clad fiber (not shown), at least a portion of the common housing structure 202G proximate the splice point with the double-clad fiber (not shown) may be coated with a low refractive index medium that extends beyond the splice point to the outer cladding of the double-clad fiber (optionally extending beyond a portion of the outer cladding proximate the splice point).

3H-3L, in various alternative embodiments of optical couplers, at least one of the VC waveguides utilized therein, and in certain embodiments, optionally at least one of the non-VC waveguides, may have polarization-maintaining (PM) properties. By way of example, the PM properties of a VC waveguide may result from a pair of longitudinal stress rods disposed within the VC waveguide on the outside of its inner core and either inside or outside of the outer core (or via other stress elements), or the PM properties may result from a non-circular inner or outer core shape, or from other PM-inducing optical fiber configurations (e.g., bowtie or elliptical clad PM fiber). Various embodiments of optical fibers in which at least one PM waveguide (VC and/or non-VC) is utilized may include axial alignment of the PM waveguide (or waveguides) with a particular polarization axis alignment mode.

According to certain embodiments, the polarization axis alignment mode may include, but is not limited to, at least one of the following:
Axial alignment of the polarization axis of the PM waveguide with respect to the polarization axes of other PM waveguides in the optical coupler; for off-center placement of PM waveguides: axial alignment of the polarization axis of the PM waveguide with respect to its cross-sectional (geometric) position in the optical coupler;
When the single common housing structure of the optical coupler has a non-circular geometry (e.g., as illustrated in FIG. 3L): axial alignment of the polarization axes of the PM waveguides to the geometric features of the outer shape of the common housing structure;
In an optical coupler comprising one or more waveguide alignment indicators as described below in connection with Figures 3J-3L: axial alignment of the polarization axis of the PM waveguide with at least one geometric characteristic;
In an embodiment of the optical coupler comprising at least one reference element 210A as described above in relation to FIG. 3A: axial alignment of the polarization axis of the PM waveguide with respect to the geometric position of the at least one reference element 210A.

The selection of a particular type of polarization axis alignment mode for various embodiments of the optical coupler is preferably governed by at least one axis alignment criterion, which may include, but is not limited to, polarization axis alignment of the PM waveguides in a geometry that increases or maximizes PM properties and/or satisfies at least one requirement of one or more intended industrial applications of the coupler array.

Now referring to FIG. 3H, a first alternative embodiment of the optical fiber coupler array 200G of FIG. 3G above is shown as coupler array 200H. The coupler array 200H comprises a single housing structure 202H, at least one VC waveguide, illustrated in FIG. 3H as PM VC waveguide 204H having polarization maintaining properties, and a plurality of non-VC waveguides 206H-(1..n) (e.g., n equal to 18). The PM VC waveguide 204H is positioned as a side channel offset from the longitudinal center axis of the single common housing structure 202H, e.g., with a polarization axis aligned with respect to a position offset laterally from the center of the PM VC waveguide 204H.

Now, referring to FIG. 3I, a fourth alternative embodiment of the optical fiber coupler array 200B of FIG. 3B above is shown as coupler array 200I. The coupler array 200I comprises a single housing structure 202I, at least one VC waveguide, illustrated in FIG. 3I as PM VC waveguide 204I having polarization-maintaining properties, and a plurality of PM non-VC waveguides 206I-(1..n) (e.g., n equal to 18). Each of the plurality of PM non-VC waveguides has polarization-maintaining properties. The PM VC waveguide 204I is disposed along the longitudinal central axis of the common housing structure 202I and is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed PM non-VC waveguides 206I-(1..n). By way of example, the coupler array 200I has a polarization axis alignment mode in which the polarization axes of the PM VC waveguide 204I and the multiple PM non-VC waveguides 206I-(1..n) are aligned with each other. The PM properties of the PM VC waveguide 204I and the multiple PM non-VC waveguides 206I-(1..n) are illustrated as being induced by a rod stress member (which can be easily and alternately induced by a variety of other stress or equivalent designs).

Now referring to FIG. 3J, a first alternative embodiment of the optical fiber coupler array 200I of FIG. 3I above is shown as coupler array 200J. The coupler array 200J comprises a single housing structure 202J, at least one VC waveguide, illustrated in FIG. 3J as PM VC waveguide 204J having polarization-maintaining properties, and a plurality of PM non-VC waveguides 206J-(1..n) (e.g., n equal to 18). Each of the plurality of PM non-VC waveguides also has polarization-maintaining properties. The PM VC waveguide 204J is disposed along the longitudinal central axis of the common housing structure 202J and is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed PM non-VC waveguides 206J-(1..n). The PM characteristics of the PM VC waveguide 204 and the multiple PM non-VC waveguides 206J-(1..n) are illustrated as resulting from a circular cross-sectional shape (illustrated as at least partially elliptical) of each of the multiple PM non-VC waveguides 206J-(1..n) cores (and resulting from the non-circular cross-sectional shape of the outer core of the PM VC waveguide 204J).

The coupler array 200J optionally includes at least one waveguide placement indicator element 208J. The waveguide placement indicator element is disposed in an outer region of the common housing structure 202J. The common housing structure 202J represents a particular cross-sectional geometric arrangement of the optical coupler array 200J waveguides (i.e., the PM VC waveguide 204J and the plurality of PM non-VC waveguides 206J-(1..n)). Thereby, the particular cross-sectional geometric waveguide arrangement can be easily identified from at least one of visual and physical inspection of the common coupler housing structure 202J. This inspection is sufficient to check the waveguide placement indicator element 208J. Preferably, the waveguide placement indicator element 208J may be further operatively configured to facilitate passive alignment of the second end of the optical coupler array 200J to at least one optical device (not shown).

The waveguide placement indicator element 208J is applied to the exterior surface of the common housing structure 202J and may comprise one or more of, but is not limited to, a color marking and/or a physical marking (such as a groove or other modification of the exterior surface of the common housing structure 202J, or an element or other member disposed thereon). Alternatively, the waveguide placement indicator element 208J may actually include a specific modification or definition to the cross-sectional geometry of the common housing structure 202J (e.g., the hexagonal shape, underside, or another geometry of the common housing structure 202L of FIG. 3L, etc.).

As an example, the coupler array 200J can have a polarization axis alignment mode in which the polarization axes of the PM VC waveguide 204J and each of the multiple PM non-VC waveguides 206J-(1..n) are aligned with each other or with the waveguide placement indicator element 208J.

Now referring to FIG. 3K, a fifth alternative embodiment of the optical fiber coupler array 200B of FIG. 3B above is shown as coupler array 200K. The coupler array 200K comprises a single housing structure 202K, at least one VC waveguide, illustrated in FIG. 3K as PM VC waveguide 204K having polarization-maintaining properties, and a plurality of non-VC waveguides 206K-(1..n) (e.g., n equal to 18). The PM VC waveguide 204K is disposed along the longitudinal central axis of the common housing structure 202K and is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed PM non-VC waveguides 206K-(1..n). The PM properties of the PM VC waveguide 204K are illustrated as being induced by a rod stress member (which can be readily and alternately induced by various other stresses, or equivalent approaches). The coupler array 200K may also optionally include a plurality of waveguide placement indicator elements, exemplified as waveguide placement indicator elements 208K-a, 208K-b. These elements may be the same or different types as those described above in connection with the waveguide placement indicator element 208J of FIG. 3J.

Now referring to FIG. 3L, a second alternative embodiment of the optical fiber coupler array 200I of FIG. 3I above is shown as coupler array 200L. The coupler array 200L comprises a single housing structure 202L having a cross section of a non-circular geometric shape (illustrated as a hexagon), at least one VC waveguide exemplified in FIG. 3L as a PM VC waveguide 204L having polarization-maintaining properties, and a plurality of PM non-VC waveguides 206L-(1..n) (e.g., n equal to 18), each having polarization-maintaining properties. The PM VC waveguide 204L is disposed along the longitudinal central axis of the common housing structure 202L and is circumferentially and symmetrically surrounded by a plurality of parallel and proximally disposed PM non-VC waveguides 206L-(1..n).

By way of example, the coupler array 200L includes a polarization axis alignment mode in which the polarization axes of the PM VC waveguide 204L and the plurality of PM non-VC waveguides 206L-(1..n) are aligned with each other and with the cross-sectional geometry of the common housing structure 202L. The PM properties of the PM VC waveguide 204L and the plurality of PM non-VC waveguides 206L-(1..n) are illustrated as being induced by a rod stress member (which could easily and alternately be induced by a variety of other stresses, or equivalent designs). The coupler array 200K may also optionally include a waveguide placement indicator element 208L-a. The element may include any of the configurations described above in connection with the waveguide placement indicator element 208J of FIG. 3J.

Referring now to FIG. 4, the second end 302 (i.e., "tip") of the optical fiber coupler array is illustrated as being in the process of connecting to a plurality of vertical coupling elements 306 of an optical device 304 in a proximal open-air optical coupling alignment configuration. This alignment configuration can also be easily transferred to a butt coupling configuration with full physical contact between the second end 302 of the optical fiber coupler array and the vertical coupling elements 306.

Referring now to FIG. 5, a second end 322 (i.e., "tip") of the optical fiber coupler array is illustrated as being in the process of connecting to a plurality of edge coupling elements 326 of an optical device 324 in a butt coupling configuration. This butt coupling configuration can also be easily transitioned to one of several alternative coupling configurations. These alternative coupling configurations include a proximal open air optical coupling alignment configuration and/or an angled alignment coupling configuration.

In at least one alternative embodiment, the optical coupler array (e.g., optical coupler arrays 200D-200L of FIGS. 3C-3L) may be readily configured to pump optical fiber lasers and/or optical fiber amplifiers (or equivalent devices). In a preferred embodiment, the pumpable coupler array comprises a central channel (i.e., waveguide) configured to transmit a signal (i.e., serves as a "signal channel") that is then amplified or utilized to generate a laser. The pumpable coupler array further comprises at least one additional channel (i.e., waveguide) configured to provide an optical pump function (i.e., each serves as a "pump channel"). In various exemplary alternative embodiments, the pumpable coupler array may also comprise the following in any desired combination:
- at least one of the following signal channels: a single-mode signal channel configured to increase or optimally couple into a single-mode amplifying fiber at at least one predetermined signal or laser wavelength; a multimode signal channel configured to increase or optimally couple into a multimode amplifying fiber at at least one predetermined signal or laser wavelength; and - at least one of the following pump channels: a single-mode pump channel configured to increase or optimally couple into a single-mode pump source at at least one predetermined pump wavelength; a multimode pump channel configured to increase or optimally couple into a multimode pump source at at least one predetermined pump wavelength.

Optionally, to increase or maximize pump efficiency, the pumpable combiner array may be configured to selectively utilize less than all available pump channels. It should also be noted that, as a matter of design choice, without departing from the spirit of the invention, the pumpable combiner array may be configured to comprise:
a at least one signal channel, each disposed at a predetermined desired position in the combiner array structure;
b at least one pump channel, each disposed at a predetermined desired position in the coupler array structure;
c Optionally, at least one additional waveguide for at least one additional purpose other than signal transmission or pump (eg, alignment, fault detection, fiducial marker for data transmission).

Advantageously, the pump channel can be positioned at any lateral location within the coupler along the central longitudinal axis. The pump channel can also comprise, but is not limited to, at least one of the following optical fiber types: SM, MM, LMA, or VC waveguide. Optionally, all optical fibers utilized as optical pump channels within the coupler (regardless of fiber type) can have polarization-maintaining properties.

In another embodiment, the pumpable coupler array can be configured to be optimized to couple to a double-clad fiber. In this case, the signal channels of the coupler array are configured or optimized to couple to the signal channels of the double-clad fiber, while at least one pump channel is each configured or optimized to couple to the inner cladding of the double-clad fiber.

In essence, the optical coupler arrays illustrated in the various embodiments can also be readily implemented as high density, multi-channel, optical input/output (I/O) for fiber-to-chip and fiber-to-optical waveguides. The optical fiber couplers can readily comprise at least the following features:
Significantly reduced channel spacing and device footprint (compared to known solutions)
Scalable channel count All-glass optical path Easily butt-coupled or spliced with high density surfaces without the need for lenses, air gaps, or beam spreading media Can be manufactured by semi-automated manufacturing processes Wide range of customizable parameters: wavelength, mode field size, channel spacing, array configuration, fiber type

Fiber optic couplers may be advantageously utilized in at least the following applications, as a matter of design choice or convenience, without departing from the spirit of the present invention:
Coupling to a waveguide:
PIC or PCB based (single mode or multimode)
Multicore fiber Chip edge (1D) or chip face (2D) coupling Application optimized NA, factoring:
Package alignment required Chip processing required/waveguide up taper Polarization maintaining properties can be easily configured Chip based devices: e.g. VCSELs, photodiodes, coupling to vertical coupling gratings Laser diode coupling High density device input/output (I/O)

Thus, when implemented, the various exemplary embodiments of the fiber optic coupler provide at least the following advantages over currently available competing solutions:
-Unprecedented density -Low loss coupling (≦0.5 dB)
・Operational stability ・Form factor support ・Spectral broadband ・Matching NA
- Scalable channel count - Polarization maintenance

Referring now to FIG. 7, at least one exemplary embodiment of a flexible optical coupler array is shown as a flexible pitch reduced optical fiber array (PROFA) coupler 450. Various features of an exemplary PROFA coupler may be described with reference to FIG. 7, however, any of the features described above may be implemented in any combination with a flexible PROFA coupler. For example, the features described with reference to FIGS. 1A-5 may be utilized in a flexible PROFA coupler. Additionally, any of the features described with reference to FIGS. 1A-5 may be combined with any of the features described with reference to FIG. 7.

Continuing to refer to FIG. 7, the exemplary flexible PROFA coupler 450 shown in FIG. 7 can be configured for use in applications where an interconnect with low crosstalk and sufficient flexibility to accommodate low profile packages is desired. The disappearing core approach described herein and in U.S. Patent Application Publication No. 2013/0216184, entitled "CONFIGURABLE PITCH REDUCING OPTICAL FIBER ARRAY," incorporated herein in its entirety, enables, for example, a pitch reduced optical fiber array (PROFA) coupler/interconnect operable to optically couple a plurality of optical fibers to an optical device (e.g., a PIC), which can be butt-coupled to an array of vertical grating couplers (VGCs). As described herein and in U.S. Patent Application Publication No. 2013/0216184, if the cross-sectional structure of coupler 450 has an additional layer of refractive index N-2A even lower than N2, the vanishing core approach can once again be utilized to further reduce the outer diameter without substantially compromising channel crosstalk. This further reduction can advantageously provide certain embodiments having a flexible region with a reduced cross-section between the first and second ends.

In some preferred embodiments, when light is guided by an additional layer with a refractive index of N-2A, the difference (N-2A-N-3) is greater than the difference (N-2-N-2A) or (N-1-N-2), resulting in a high NA bend-insensitive waveguide. Also, in some preferred embodiments, after the outer diameter of the coupler 450 is reduced along its longitudinal length from one end to form a flexible region, the outer diameter can then be expanded along its longitudinal length toward the second end. This results in a lower NA waveguide with a larger coupling surface area at the second end.

For example, as shown in FIG. 7, a particular embodiment of the optical coupler array 450 can include an elongated optical element 1000 having a first end 1010, a second end 1020, and a flexible portion 1050 therebetween. The optical element 1000 can have a coupler housing structure 1060 and a plurality of longitudinal waveguides 1100 embedded within the housing structure 1060. The waveguides 1100 can be arranged relative to one another in a cross-sectional geometry waveguide arrangement. In FIG. 7, an exemplary cross-sectional geometry waveguide arrangement of the waveguide 1100 is shown for the first end 1010, the second end 1020, and a position within the flexible portion 1050. A cross-sectional geometry waveguide arrangement of the waveguide 1100 for an intermediate position 1040 between the first end 1010 and the flexible portion 1050 is also shown. As indicated by the shaded areas in the cross section and described herein, light can be guided through the optical element 1000 from the first end 1010 through the flexible portion 1050 to the second end 1020. As also shown in FIG. 7, this can result in a structure that keeps all channels discrete with sufficiently low crosstalk while providing sufficient flexibility (e.g., via the flexible portion 1050) to accommodate a low profile package.

The level of crosstalk and/or flexibility may depend on the application of the array. For example, in some embodiments, low crosstalk may be considered to be in the range of -45 dB to -35 dB, and in other embodiments, low crosstalk may be considered to be in the range of -15 dB to -5 dB. Thus, the level of crosstalk is not particularly limited. In some embodiments, the crosstalk may be -55 dB, -50 dB, -45 dB, -40 dB, -35 dB, -30 dB, -25 dB, -20 dB, -15 dB, -10 dB, 0 dB, or any value therebetween (e.g., -37 dB, -27 dB, -5 dB or less). In some embodiments, the crosstalk can be in a range formed from -50 dB to -40 dB, -40 dB to -30 dB, -30 dB to -20 dB, -20 dB to -10 dB, -10 dB to 0 dB, -45 dB to -35 dB, -35 dB to -25 dB, -25 dB to -15 dB, -15 dB to -5 dB, -10 dB to 0 dB, any combination of these ranges, or any value from -55 dB to 0 dB (e.g., -52 dB to -37 dB, -48 dB to -32 dB).

Flexibility can also depend on the application of the array. For example, in some embodiments, good flexibility of the flexible portion 1050 can include at least a 90 degree bend, and in other embodiments, at least a 50 degree bend is acceptable. Thus, flexibility is not particularly limited. In some embodiments, flexibility can be at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, 120 degrees, or at least any value therebetween. In some embodiments, the flexible portion 1050 can bend in a range formed by any of these values, such as 45-55 degrees, 50-60 degrees, 60-70 degrees, 70-80 degrees, 80-90 degrees, 90-100 degrees, 100-110 degrees, 110-120 degrees, or any combination of these ranges, or any range formed by any value in these ranges (e.g., 50-65 degrees, 50-85 degrees, 65-90 degrees). In other embodiments, the flexible portion 1050 can bend more or less than these values. Bending can generally be associated with light scattering. However, various embodiments can be configured to bend as described herein (e.g., in one of the ranges above) and achieve relatively low crosstalk as described herein (e.g., in one of the ranges above).

In various applications, the flexible portion 1050 may not bend during use, but flexibility may be desirable to isolate the first end 1010 or the second end 1020 from other portions of the coupler array 450. For example, the flexible portion 1050 of a flexible PROFA coupler 450 can provide mechanical isolation of the first end 1010 (e.g., the PROFA-PIC interface) from the remainder of the PROFA, resulting in increased stability with respect to environmental variations, including temperature variations and mechanical shock and vibration.

In the example shown in FIG. 7, the coupler array 450 is operable to optically couple to a plurality of optical fibers 2000 and/or optical devices 3000. The optical fibers 2000 and the optical devices 3000 can have any of those described herein. The coupler array 450 can couple to the optical fibers 2000 at the first end 1010 via a plurality of waveguides 1100. Additionally, the coupler array 450 can couple to the optical devices 3000 at the second end 1020 via a plurality of waveguides 1100. As described herein, the plurality of waveguides 1100 can also have at least one VC waveguide 1101. FIG. 7 shows all of the waveguides 1100 as waveguides. However, one or more non-VC waveguides can also be used. Additionally, while FIG. 7 shows seven VC waveguides, any number of VC and/or non-VC waveguides can be used.

Also, as shown in cross section, each of the waveguides 1100 can be positioned at an individual corresponding cross-sectional geometric location relative to the other waveguides of the plurality of waveguides 1100. Although FIG. 7 shows a waveguide surrounded by six other waveguides, the cross-sectional geometric waveguide arrangement is not limited and can have any arrangement known by those skilled in the art or yet to be developed, including any of those shown in FIGS. 3A-3L.

As described herein, the VC waveguide 1101 may also have an inner core (e.g., inner vanishing core) 1110, an outer core 1120, and an outer cladding 1130, each having refractive indexes N-1, N-2, and N-3, respectively. As shown in FIG. 7, the VC waveguide 1101 may also have a second outer core 1122 (e.g., between the outer core 1120 and the outer cladding 1130) having a refractive index N-2A. The outer core 1120 may longitudinally surround the inner core 1110, such that the second outer core 1122 may longitudinally surround the outer core 1120 with the outer cladding 1130 longitudinally surrounding the second outer core 1122. In various embodiments, the relationship between the refractive indices of the inner core 1110, the outer core 1120, the second outer core 1122, and the outer cladding 1130 may advantageously be N-1>N-2>N2-A>N-3. Such a relationship allows the surrounding layer to function as an effective cladding for the layer within it (e.g., the outer core 1120 may function as an effective cladding for the inner core 1110, and the second outer core 1122 may function as an effective cladding for the outer core 1120). Thus, the use of the second outer core 1122 may provide an additional set of cores and claddings.

By having a second outer core 1122 with a refractive index N-2A, certain embodiments can achieve a higher NA (e.g., compared to the absence of the second outer core 1122). In various embodiments, the difference (N-2A-N-3) can be greater than the difference (N-2-N-2A) or (N-1-N-2), resulting in a relatively high NA. By increasing the NA, the MFD can be reduced, allowing the channels (e.g., waveguides 1100) to be closer to each other (e.g., closer spacing between the waveguides 1100) without compromising crosstalk. Thus, the coupler array 450 can further reduce its cross section (e.g., compared to the absence of the second outer core 1122) to provide a reduced area when light is guided by the second outer core 1122. By providing a reduced area between the first end 1010 and the second end 1020, certain embodiments can have a flexible portion 1050 that can be more flexible than the proximal regions of the first end 1010 and the second end 1020.

For example, the size of the inner core 1110, the size of the outer core 1120, and the spacing between the waveguides 1100 can be decreased (e.g., simultaneously and gradually, in some examples) along the optical element 1000 from the first end 1010 to the intermediate position 1040. As a result, at the intermediate position 1040, the size of the inner core 1110 is insufficient to guide light therethrough, and the size of the outer core 1120 is sufficient to guide at least one optical mode. In certain embodiments, each waveguide 1100 can have capacity for at least one optical mode (e.g., single mode or multimode). For example, at the first end 1010, the VC waveguide 1101 can support multiple spatial modes (M1) in the inner core 1110. At the intermediate position 1040, in various embodiments, the inner core 1110 cannot support all M1 modes (e.g., cannot support optical propagation). However, in some such embodiments, at the intermediate position 1040, the outer core 1120 can support all M1 modes (and in some examples can support additional modes). In this example, light traveling in the inner core 1110 from the first end 1010 to the intermediate position 1040 can escape from the inner core 1110 into the outer core 1120 such that light traveling in the inner core 1110 from the first end 1010 to the intermediate position 1040 can propagate in both the inner core 1110 and the outer core 1120.

In addition, the size of the outer core 1120, the size of the second outer core 1122, and the spacing between the waveguides 1100 can be reduced (e.g., simultaneously and gradually, in some examples) along the optical element 1000, for example, from the intermediate position 1040 to the flexible portion 1050. As a result, at the flexible portion 1050, the size of the outer core 1120 is insufficient to guide light therethrough, and the size of the second outer core 1122 is sufficient to guide at least one optical mode therethrough. In certain embodiments, at the intermediate position 1040, the VC waveguide 1101 can support all M1 modes within the outer core 1120. At the flexible portion 1050, in various embodiments, the outer core 1120 can no longer support all M1 modes (e.g., cannot support optical propagation). However, in some such embodiments, at the flexible portion 1050, the second outer core 1122 can support all M1 modes (and in some examples, can support additional modes). In this example, light traveling in the outer core 1120 from the intermediate position 1040 to the flexible portion 1050 can escape from the outer core 1120 into the second outer core 1122 so that it can propagate through the inner core 1110, the outer core 1120, and the second outer core 1122.

Additionally, the size of the outer core 1120, the size of the second outer core 1122, and the spacing between the waveguides 1100 can expand (e.g., simultaneously and gradually, in some examples) along the optical element 1000 from the flexible portion 1050 to the second end 1020. As a result, at the second end 1020, the size of the second outer core 1122 is insufficient to guide light therethrough, and the size of the outer core 1120 is sufficient to guide at least one optical mode therethrough. In certain embodiments, at the second end 1020, in various embodiments, the second outer core 1122 cannot support all M1 modes (e.g., cannot support optical propagation). However, in some such embodiments, at the second end 1020, the outer core 1120 can support all M1 modes (and in some examples, can support additional modes). In this example, light propagating within the second outer core 1122 from the flexible portion 1050 to the second end 1020 can return and propagate only within the inner core 1110 and the outer core 1120.

It will be appreciated that light traveling from the second end 1020 to the first end 1010 can operate in the opposite manner. For example, the size of the outer core 1120, the size of the second outer core 1122, and the spacing between the waveguides 1100 can decrease (e.g., simultaneously and gradually, in some examples) along the optical element 1000 from the second end 1020 to the flexible portion 1050. As a result, at the flexible portion 1050, the size of the outer core 1120 is insufficient to guide light therethrough, and the size of the second outer core 1122 is sufficient to guide at least one optical mode therethrough.

The reduction in cross-sectional core and cladding size can advantageously provide stiffness and flexibility in the coupler array 450. Stiffness at the first end 1010 and the second end 1020 is desirable because the optical fiber 2000 and/or the optical device 3000 can be fused to the ends 1010, 1020 of the coupler array 450. However, it is also desirable for the coupler array to be flexible so that it can be bent to interface with low-profile integrated circuits. In certain embodiments, the flexible portion 1050 between the first end 1010 and the second end 1020 can make the first end 1010 and the second end 1020 relatively stiff and provide a flexible portion 1050 therebetween. The flexible portion can extend the length of the optical element 1000 and mechanically separate the first end 1010 and the second end 1020. For example, the flexible portion 1050 can mechanically isolate the first end 1010 from the area between the flexible portion 1050 and the second end 1020. As another example, the flexible portion 1050 can mechanically isolate the second end 1020 from the area between the first end 1010 and the flexible portion 1050. Such mechanical isolation can provide stability to the first end 1010 and the second end 1020 with respect to environmental variations including, for example, temperature variations and mechanical shock and vibration. The length of the flexible portion 1050 is not particularly limited and can depend on the application. In some examples, the length can be any range formed from 2-7 mm, 3-8 mm, 5-10 mm, 7-12 mm, 8-15 mm, any combination of these ranges, or any value between 2-20 mm (e.g., 3-13 mm, 4-14 mm, 5-17 mm, etc.). In other examples, the length of the flexible portion 1050 may be shorter or longer.

At the same time, the flexible portion 1050 can provide flexibility. In many cases, the flexible portion 1050 can have a substantially similar cross-sectional size (e.g., the cross-sectional size of the waveguide 1100) that extends over the length of the flexible portion 1050. In certain embodiments, the cross-sectional size at the flexible portion 1050 can be smaller than the cross-sectional size at the first end 1010 and the second end 1020. Because of the smaller cross-sectional size, the flexible portion 1050 can be more flexible than the regions proximate the first end 1010 and the second end 1020. The smaller cross-sectional size can result in smaller core and cladding sizes. An optional post-etch step may be desirable to further reduce the diameter of the flexible length of the flexible PROFA coupler 450.

In some embodiments, the flexible portion 1050 can be more flexible than a standard SMF28 fiber. In some embodiments, the flexible portion 1050 can bend at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, 120 degrees, or at least any value therebetween. In some embodiments, the flexible portion 1050 can bend in a range formed by any of these values, for example, 45-55 degrees, 50-60 degrees, 60-70 degrees, 70-80 degrees, 80-90 degrees, 90-100 degrees, 100-110 degrees, 110-120 degrees, or any combination of these ranges, or any range formed by any value within these ranges (e.g., 50-65 degrees, 50-85 degrees, 65-90 degrees). In other embodiments, the flexible portion 1050 can bend more or less than these values. As described herein, in various applications, the flexible portion 1050 may not bend during use, but flexibility may be desirable to separate the first end 1010 or the second end 1020 from other portions of the coupler array 450.

The coupler array 450 can have a coupler housing structure 1060. For example, the coupler housing structure 1060 can have a common single coupler housing structure. In certain embodiments, the coupler housing structure 1060 can have a medium 1140 (e.g., having a refractive index N-4) surrounding the waveguides 1100. In some examples, N-4 is greater than N-3. In other examples, N-4 is equal to N-3. The medium 1140 can include any medium described herein (e.g., pure silica). The medium can also include glass, such that the coupler array 450 can be an all-glass coupler array. The waveguides 1100 can be embedded within the medium 1040 of the housing structure 1060. In some examples, the total volume of the medium 1140 of the coupler housing structure 1060 can be greater than the total volume of all the inner and outer cores 1110, 1120, 1122 of the VC waveguides confined within the coupler housing structure 1060.

In some embodiments, each waveguide can be coupled to an optical fiber 2000 and/or optical device 3000 at a location inside, outside, or at a boundary region of the coupler housing structure 1060, as shown, for example, in FIGS. 1A-2D. Since the optical fiber 2000 and the optical device 3000 can be different at each end, the first end 1010 and the second end 1020 can be configured relative to the optical fiber 2000 or optical device 3000 to which it is coupled. For example, the MFD of the VC waveguide at the first end 1010 and/or the second end 1020 can be configured to match or substantially match the MFD of the optical fiber 2000 or optical device 3000 to which it is coupled (e.g., using the core size). Additionally, the NA of the VC waveguide at the first end 1010 and/or second end 1020 can be configured (e.g., using refractive index) to match or substantially match the NA of the optical fiber 2000 or optical device 3000 to which it is coupled. The refractive index can be modified by any method known in the art (e.g., doping the waveguide glass) or yet to be developed. In various embodiments, the difference (N-1-N-2) can be greater than the difference (N-2-N-2A) such that the NA at the first end 1010 is greater than the NA at the second end 1020, as described herein. In other embodiments, the difference (N-1-N-2) can be less than the difference (N-2-N-2A) such that the NA at the first end 1010 is less than the NA at the second end 1020. In yet other embodiments, the difference (N-1-N-2) can be equal to (N-2-N-2A) such that the NA at the first end 1010 is equal to the NA at the second end 1020. The VC waveguide can have any of the fiber types described herein, including, but not limited to, single mode fiber, multimode fiber, and/or polarization maintaining fiber.

The core and cladding (1110, 1120, 1122, 1130) sizes (e.g., outer cross-sectional diameter if circular or outer cross-sectional dimension if not circular) are not particularly limited. In some embodiments, the inner core 1110 and/or outer core 1120 size can be any range formed from 1-3 microns, 2-5 microns, 4-8 microns, 5-10 microns, any combination of these ranges, or any value between 1-10 microns (e.g., 2-8 microns, 3-9 microns). However, the size can be larger or smaller. For example, the inner core 1110 and/or outer core 1120 size can range from submicrons to microns to tens of microns to hundreds of microns, depending on, for example, the wavelength and/or number of desired modes.

Furthermore, the difference in refractive index (eg, between N-1 and N-2, between N-2 and N-2A, and/or between N-2A and N-3) is not particularly limited. In some examples, the refractive index difference can range from 1.5×10 ⁻³ to 2.5×10 ⁻³ , 1.7×10 ⁻³ to 2.3×10 ⁻³ , 1.8×10 ⁻³ to 2.2×10 ⁻³ , 1.9×10 ⁻³ to 2.1×10 ⁻³ , 1.5×10 ⁻³ to 1.7×10 ⁻³ , 1.7×10 ⁻³ to 1.9×10 ⁻³ , 1.9×10 ⁻³ to 2.1×10 ⁻³ , 2.1×10 ⁻³ to 2.3×10 ⁻³ , 2.3×10 ⁻³ to 2.5×10 ⁻³ , any combination of these ranges, or from 1.5×10 ⁻³ to 2.5×10 ⁻³ . In other examples, the refractive index difference can be greater or less.

As described herein, the optical device 3000 may include a PIC.
A PIC can have an array of VGCs. Also, as described in U.S. Patent Application Publication No. 2012/0257857, entitled "HIGH DENSITY OPTICAL PACKAGING HEADER APPARATUS," which is incorporated herein, multiple flexible PROFA couplers (such as coupler 450), each having multiple optical channels, can be combined to advantageously form an optical multi-port input/output (IO) interface. As such, an optical multi-port IO interface can have multiple optical coupler arrays, at least one of which can include optical coupler array 450, as described herein.

8 and 9, exemplary cross-sectional views of a housing structure proximate a first end of a multi-channel optical coupler array are shown. The cross-sectional views are orthogonal to the longitudinal direction or length of the optical coupler array. Some such configurations have improved cross-sectional or lateral (or side) positioning of the waveguides at the first end and improved (in some cases, precise or near-precise) cross-sectional positioning of the waveguides at the second end. The positioning at the first end allows for a self-aligned waveguide arrangement proximate the first end (e.g., a circular (as shown in FIG. 8) or hexagonal close-packed arrangement in a housing structure having a hexagonal interior cross-section). Such a configuration may provide alignment during manufacturing so that the cross-sectional positioning of the waveguides at the second end can be more precisely positioned as desired.

Various features of the exemplary optical combiner array may be described with respect to Figures 8 and 9, however, any of the features described above (e.g., with respect to any of the above figures or embodiments) may be implemented in any combination with a multi-channel optical combiner array. For example, any of the features described with respect to Figures 1A-5, 7 may be utilized in a multi-channel optical combiner array and may be combined with any of the features described with respect to Figures 8 and 9.

For example, referring to the embodiment shown in Figures 1A-2D, there are two ends of the coupler array: a first (larger) end and a second (smaller) end. The two ends are spaced apart longitudinally (along the z-direction). For example, in Figure 1A, the first end is proximal to position B and the second end is proximal to positions C and D.

In certain embodiments, one of the functions of the first end (proximal to position B) is to encapsulate the waveguides 30A, 32A-1, 32A-2 with enhanced or approximate positioning accuracy. For example, the coupler housing structure 14A proximal to the first end (proximal to position B) may, for example, circumferentially surround a portion of the length of the waveguides 30A, 32A-1, 32A-2, but not necessarily completely surround the ends of the waveguides 30A, 32A-1, 32A-2. In such cases, the waveguides 30A, 32A-1, 32A-2 may or may not extend (e.g., longitudinally) outside the coupler housing structure 14A. In FIG. 1A, adjacent to the first end, the end of the waveguide 30A is disposed within the coupler housing structure 14A, but the ends of the waveguides 32A-1 and 32A-2 extend, for example, vertically (parallel to the z-direction) outside the coupler housing structure 14A. In FIG. 2B, adjacent to the first end, the ends of the waveguides 130B-1 and 130B-2 are disposed in the outer cross-sectional boundary region of the coupler housing structure 14A and do not extend vertically (parallel to the z-direction) outside the coupler housing structure 14A.

In various embodiments, one of the functions of the second ends (proximate positions C and D) is to embed the waveguides 30A, 32A-1, 32A-2 within a housing structure (e.g., in some examples, a common housing structure) with improved cross-sectional positioning (in some examples, precisely or nearly so). For example, the waveguides 30A, 32A-1, 32A-2 may be embedded proximate the second ends (proximate positions C and D) and may be, for example, circumferentially surrounded by the adjacent coupler housing structure 14A. In FIG. 1A, proximate the second ends, the ends of the waveguides 30A, 32A-1, 32A-2 are longitudinally disposed in the outer cross-sectional boundary region of the coupler housing structure 14A. In some embodiments, proximate the second ends, one or more ends of the waveguides may be longitudinally disposed within the coupler housing structure 14A.

To achieve improved positioning, some embodiments can have an exemplary cross-sectional configuration of the housing structure shown in FIG. 8 proximate the first end. The cross-section is orthogonal to the longitudinal direction or length of the optical coupler array. As shown in FIG. 8, the coupler array 800 can have a housing structure 801. The housing structure 801 has a lateral (or side) configuration of a ring surrounding a plurality of longitudinal waveguides 805 longitudinally proximate the first end. A gap, e.g., an air gap, can separate the plurality of longitudinal waveguides 805 from the surrounding ring. Some such configurations can allow for a self-aligned waveguide arrangement proximate the first end (e.g., a hexagonal close-packed arrangement in a housing structure having a circular (shown in FIG. 8) or hexagonal interior cross-section).

In the example configuration shown in FIG. 8, the waveguides 805 are arranged in a hexagonal configuration. Other configurations are possible, e.g., square, rectangular, etc.

The ring can also have an inner cross section 801a (lateral, i.e., perpendicular to the longitudinal direction or length of the optical coupler array) that is circular or non-circular. For example, the inner cross section 801a can be circular, elliptical, D-shaped, square, rectangular, hexagonal, pentagonal, octagonal, other polygonal shapes, etc. The inner cross section 801a does not necessarily follow the arrangement of the waveguides 805. For example, four waveguides in a square arrangement can be confined within the inner circular cross section. As another example, as shown in FIG. 8, the inner cross section 801a is circular and the waveguides 805 are arranged in a hexagon. In some embodiments, a circular inner cross section, as shown in FIG. 8, may be a preferred shape that can enable a close hexagonal arrangement. Other inner cross section shapes, such as square or rectangular, can also be used, which can enable a non-hexagonal waveguide arrangement. In some examples, the inner cross section 801a may be similar to the arrangement of the waveguides 805 to reduce free space. For example, in the case of a hexagonally arranged waveguide 805, the inner cross section 801a of the ring may be hexagonal to reduce the empty space between the inner cross section 801a and the waveguide 805.

The outer cross-section 801b (e.g., transversely orthogonal to the longitudinal or length of the optical coupler array) may be circular or non-circular. For example, the outer cross-section 801b may be circular, elliptical, hexagonal, D-shaped (e.g., to provide passive axial alignment of the couplers, since flat surfaces allow for easy rotational alignment), square, rectangular, pentagonal, octagonal, other polygonal shapes, etc. In FIG. 8, the outer cross-section 801b (e.g., circular) follows the shape (e.g., circular) of the inner cross-section 801a. However, in some embodiments, the outer cross-section 801b need not be similar to the inner cross-section 801a. One function of the inner cross-section shape is to allow for improved lateral positional accuracy close to the second end, while one function of the outer cross-section shape is to allow for passive axial alignment of the couplers (e.g., alignment can be performed without launching light into the coupler). In some configurations, it may be preferable to substantially maintain the outer cross-sectional shape from the first end to the second end to facilitate passive alignment at one or both ends of the coupler array.

9 shows other exemplary cross-sectional configurations of the housing structure proximate the first end. As shown in FIG. 9, the coupler array 850 can have a housing structure 851 having a configuration of a structure (e.g., a possibly adjacent structure) with a plurality of holes 852. At least one of the holes 852 can include at least one of the longitudinal waveguides 855. A gap, e.g., an air gap, can also separate the plurality of longitudinal waveguides 855 from the surrounding housing structure 851. As with the description related to the example shown in FIG. 8, the outer cross section can be circular, elliptical, hexagonal, D-shaped, square, rectangular, pentagonal, octagonal, other polygonal shapes, etc. Some of such configurations can allow passive alignment at one or both ends of the coupler array. While the exemplary configuration shown in FIG. 8 allows for easier manufacturing in some examples, the exemplary configuration shown in FIG. 9 can also allow for any lateral waveguide positioning.

9 shows an example configuration having six holes 852, although other numbers of holes are possible. The holes 852 in this example configuration may be isolated, or some or all of the holes 852 may be connected. For example, as shown in FIG. 9, a first hole 852-1 is isolated from a second hole 852-2. However, in some configurations, a first hole 852-1 may be connected to at least one second hole 852-2. The arrangement of the holes 852 is shown as a 3×2 array, although other arrangements are possible. For example, the arrangement pattern of the holes may be hexagonal, square, rectangular, or may be defined by an XY array that defines the location of the holes in the cross-section.

FIG. 9 shows all holes 852 with waveguides 855 shown as vanishing core (VC) waveguides. However, while at least one of the waveguides in this example is a VC waveguide, one or more of the holes 852 can also have a non-vanishing core (non-VC) waveguide. The VC or non-VC waveguide 855 can have any of the waveguides described herein, e.g., single mode fiber, multimode fiber, polarization maintaining fiber. In some embodiments, one or more of the holes 852 may be empty or filled with other (e.g., non-waveguide) materials, e.g., to function as a reference mark. One or more of the holes 852 may be filled with a single waveguide 855 (some preferred configurations) or multiple waveguides 855, as shown in FIG. Depending on the design, one or more of the holes 852 can be the same or different from another hole 852, for example, to accommodate waveguides 855 of different shapes and dimensions (e.g., cross-sectional shape, diameter, major/minor elliptical dimensions). The cross-section of the hole 852 may be circular or non-circular. For example, the cross-section may be circular, elliptical, hexagonal, or D-shaped (e.g., to provide passive axial alignment of polarization-maintaining (PM) channels), square, rectangular, pentagonal, octagonal, other polygonal shapes, etc. As shown, in many cases, the cross-section of the hole 852 proximate the first end is larger than the cross-section of the waveguide 855, such that a gap is disposed between the inner surface 851a of the coupler housing structure 851 and the waveguide 855.

The coupler housing structure (e.g., 801 in FIG. 8 or 851 in FIG. 9) can include a medium from a wide range of materials as described herein. As described herein, the medium of the coupler housing structure 801, 851 can have a refractive index (N-4). The medium may be a laterally continuous medium. This can allow for a robust housing structure with improved lateral positioning accuracy in some embodiments. In some embodiments, the total volume of the medium of the coupler housing structure 801, 851 can be greater than the total volume of all the inner and outer cores of the VC waveguides confined within the coupler housing structure 801, 851, providing that in some embodiments all the VC waveguides are securely embedded within the housing structure enabling stable performance.

In certain embodiments, the exemplary configurations shown in FIGS. 8 and 9 may also enable improved manufacturability of the device, for example, due to improved cross-sectional (lateral) positioning of the waveguide at the second end. This lateral position may be defined, for example, in the x and/or y directions, while z is the direction along the length of the coupler array (e.g., from the first end to the second end). In various manufacturing approaches, an assembly comprising a waveguide (e.g., 805 in FIG. 8 and 855 in FIG. 9) and a coupler housing structure (e.g., 801 in FIG. 8 or 851 in FIG. 9) may be heated and drawn to form the second end, as shown in the cross-sectional views shown in FIGS. 3A-3L. Referring to FIG. 8, the waveguide 805 may be inserted into a coupler housing structure 801 having a ring configuration (e.g., in a cross-section perpendicular to the longitudinal direction or length of the optical coupler array, in the illustrated xy plane). As described above, a gap such as an air gap can be disposed between the coupler housing structure 801 and the waveguide 805 to allow lateral (x and/or y) movement of the waveguide relative to the coupler housing structure 801. With reference to FIG. 9, one or more waveguides 855 can be inserted into a coupler housing structure 851 having a plurality of holes 852 (e.g., as seen in a cross section perpendicular to the longitudinal or length of the optical coupler array in the xy plane), and the waveguide 855 can be passively aligned within the housing structure 851. A gap such as an air gap can be disposed between the coupler housing structure 851 and the waveguide 855 to allow lateral (x and/or y) movement of the waveguide relative to the coupler housing structure 851. In the case of a close waveguide arrangement (e.g., hexagonal), this movement capability can result in more precise cross-sectional positioning at the second end after fabrication.

With reference to FIG. 1A, the coupler array can include a plurality of longitudinal waveguides 30A, 32A-1, 32A-2 having at least one VC waveguide 30A having an inner core 20A and an outer core 22A. The spacing between the inner core 20A, the outer core 22A, and the plurality of waveguides 30A, 32A-1, 32A-2 can be reduced (e.g., simultaneously and gradually, in some cases) from the first end (proximal to position B) to the second end (proximal to positions C and D), for example, from S-1 to S-2. In various embodiments, the cross-sectional configuration at the first end (proximal position B) can be as shown in FIG. 8 or FIG. 9, and the cross-sectional configuration at the second end (proximal positions C and D) can be as shown in FIG. 3A-3L or FIG. 7. In some embodiments, there are substantially no gaps between the coupler housing structure and the waveguide proximate the second end, some gaps are filled by the housing material, and some gaps are filled by the waveguide cladding material. As a result of the described cross-sectional configuration at the first end, the cross-sectional or lateral positioning of the waveguide at the second end can be improved. Thus, the waveguide at the second end can be properly aligned laterally (e.g., in the x and/or y directions) with the optical device.

10 and 11, further exemplary embodiments of the optical coupler array 4000, 5000 are shown. The coupler array 4000, 5000 can be constructed from multiple optical fibers to couple with multiple optical fibers, e.g., multiple optical fibers having different mode fields and/or core sizes. In some examples, the coupler array 4000, 5000 can be configured to provide coupling between a set of individual optical fibers 2000 and an optical device 3000 having at least one optical channel that allows the propagation of one or more optical modes. In some preferred embodiments, all the individual optical fibers 2000 can be identical (and in some examples different), and the optical device 3000 can also have at least one few-mode fiber, multimode fiber, multicore single-mode fiber, multicore few-mode fiber, and/or multicore multimode fiber. Compared to the specific embodiments described herein with respect to FIGS. 1A-5, the various embodiments 4000, 5000 can further reduce the taper diameter, which can allow light to escape the outer core 4120, 5120 and propagate in the coupled waveguide 4150, 5150 formed by at least two adjacent cores. Thus, the various embodiments described herein can be configured to optically couple between fibers having different mode fields and/or core shapes or sizes. Advantageously, some embodiments of the coupler array can improve and/or optimize optical coupling between one or more of single mode fiber, few mode fiber, multimode fiber, multicore single mode fiber, multicore few mode fiber, and/or multicore multimode fiber.

Although various features of the exemplary coupler array are described herein with respect to Figures 10 and 11, any of the features described can be implemented in any combination with the coupler arrays described with respect to Figures 1A-5 and 7. Additionally, any of the features described with respect to Figures 1A-5 and 7 can be combined with any of the features described with respect to Figures 10 and 11. For example, coupler arrays 4000, 5000 are illustrated utilizing housing structures 4060, 5060 similar to housing structures 801, 851 shown in Figures 8-9. In these embodiments, the cross-sectional configuration of the housing structures 4060, 5060 may include a structure having multiple holes (e.g., multi-hole), as shown in Figure 10, or may include one hole (e.g., a single hole surrounded by a ring), as shown in Figure 11. However, other housing structures can be used. For example, the housing structures described with respect to Figures 1A-5 and 7 can be used.

Referring to FIG. 10, a particular embodiment of a multi-channel optical coupler array 4000 can have an elongated optical element 4001 having a first end 4010, an intermediate position or cross section 4050, and a second end 4020. The optical element 4001 can have a coupler housing structure 4060 and a plurality of longitudinal waveguides 4100 disposed within the housing structure 4060. The waveguides 4100 can be disposed relative to one another in a cross-sectional geometry waveguide arrangement. In FIG. 10, the cross-sectional geometry waveguide arrangement of the waveguides 4100 relative to the first end 4010, the intermediate cross section 4050, and the second end 4020 is illustrated. As illustrated by the shaded areas in the cross section and described herein, light can be guided through the optical element 4001 from the first end 4010, through the intermediate cross section 4050, to the second end 4020.

10, proximal (e.g., adjacent) to the first end 4010, the housing structure 4060 (e.g., a possibly common single coupler housing structure) can have a cross-sectional configuration of a structure (e.g., a possibly laterally adjacent structure) having multiple holes 4062. FIG. 10 illustrates a configuration having three circular holes 4062-1, 4062-2, 4062-3. However, the shape of the holes, the number of holes, and/or the arrangement of the holes are not particularly limited and can have any other shape, number, and/or arrangement, including those described with respect to FIG. 9. At least one of the holes 4062 may include at least one of the longitudinal waveguides 4100. A gap, e.g., an air gap, can also separate the multiple longitudinal waveguides 4100 from the surrounding housing structure 4060 proximal to the first end 4010. In some embodiments, there may be substantially no gap between the coupler housing structure 4060 and the waveguide 4100 at the intermediate location 4050 and/or the second end 4020. For example, one or more gaps may be filled by the housing material and/or the waveguide cladding material. As described herein, in some embodiments, there may be a gap between the coupler housing structure 4060 and the waveguide 4100 proximate the first end 4010, but substantially no gap between the coupler housing structure 4060 and the waveguide 4100 proximate the second end 4020 (or vice versa). In some embodiments, there may be substantially no gap between the coupler housing structure 4060 and the waveguide 4100 proximate the first end 4010, the intermediate location 4050, and/or the second end 4020.

As described herein, the coupler array 4000 is operable to optically couple to a plurality of optical fibers 2000 and/or optical devices 3000. The coupler array 4000 can couple to the optical fibers 2000 via a plurality of waveguides 4100 proximal to the first end 4010 (e.g., via fusion splices 2001) and/or can couple to the optical devices 3000 via a plurality of waveguides 4100 proximal to the second end 4020 (e.g., via fusion splices not shown). In FIG. 10, three waveguides 4100 are shown in each of the three holes 4062-1, 4062-2, 4062-3. However, any number of waveguides 4100 can be used in each of the holes 4062. In some embodiments, the number of waveguides 4100 can be equal to the number of optical fibers 2000 (e.g., nine waveguides coupling to nine optical fibers). In some other embodiments, the number of waveguides 4100 in at least one hole may be equal to the number of optical modes supported by the corresponding few-mode or multimode waveguides of the device 3000 (e.g., three waveguides in each of three holes that couple to three mode cores of a multicore fiber). In various embodiments, the waveguides 4100 may be spaced apart from one another within each hole 4062 (e.g., a predetermined spacing in some examples). In some preferred embodiments of the multihole configuration, each hole 4062-1, 4062-2, 4062-3 may include all the waveguides (e.g., fibers) that are intended to couple to at least one particular core of the few-mode, multimode, and/or multicore fiber of the optical device. In some other embodiments, one or more other additional fibers and/or dummy fibers (e.g., that may not guide light) may be utilized to create a particular geometry of active light guiding fiber waveguides.

In various embodiments, the plurality of waveguides 4100 can have capacity for at least one optical mode (e.g., in some examples, a predetermined mode field profile). The plurality of waveguides 4100 can have at least one vanishing core (VC) waveguide 4101. FIG. 10 illustrates all of the waveguides 4100 as VC waveguides. However, one or more non-VC waveguides can also be used. As described herein, the VC waveguide 4101 can also have an inner core (e.g., an inner vanishing core) 4110, an outer core 4120, and an outer cladding 4130, each having refractive indices N-1, N-2, and N-3, respectively. The outer core 4120 can longitudinally surround the inner core 4110, and the outer cladding 4130 can longitudinally surround the outer core 4120. As described herein, the relative magnitude relationship between the refractive indices of the inner core 4110, the outer core 4120, and the outer cladding 4130 may advantageously be N-1>N-2>N-3.

In various embodiments, the housing structure 4060 can surround the waveguide 4100. The coupler housing structure 4060 can have a medium 4140 having a refractive index N-4. The medium 4140 can have any of those described herein. In some examples, the total volume of the medium 4140 of the coupler housing structure 4060 can be greater than the total volume of all the inner cores 4110 and outer cores 4120 of the VC waveguides confined within the coupler housing structure 4060. In some examples, the waveguide 4100 can be embedded within the housing structure 4060 (e.g., proximal to the second end 4020).

In certain embodiments, the waveguide dimensions of the inner core 4110, the waveguide dimensions, refractive index, and/or numerical aperture (NA) of the outer core 4120 are selected to increase and/or optimize coupling to the respective fiber 2000. In various embodiments, the waveguide dimensions, refractive index, NA, and/or cladding 4130 dimensions of the outer core 4120 are selected to increase and/or optimize coupling to the optical device 3000. Various embodiments described herein may also have the reflection reduction features of pitch reduced optical fiber arrays described in U.S. Patent Application No. 14/677,810, entitled "OPTIMIZED CONFIGURABLE PITCH REDUCING OPTICAL FIBER COUPLER ARRAY," which is incorporated herein in its entirety. For polarization control, some of the outer cores 4120 can be fabricated with non-circular cross-sections (e.g., elliptical as shown in FIG. 10) and specific orientations of the outer cores 4120 can be used to increase and/or optimize light coupling. Various embodiments described herein can also have any of the features of the polarization mode couplers described in U.S. Patent Application No. 15/617,84, entitled "CONFIGURABLE POLARIZATION MODE COUPLER," which is incorporated herein in its entirety.

In some embodiments, the size of the inner core 4110, the size of the outer core 4120, the size of the cladding 4130, and/or the spacing between the waveguides 4100 can be reduced (e.g., simultaneously and gradually, in some examples) along the optical element 4001 from the first end 4010 to an intermediate position or cross section 4050. In some embodiments, a predetermined reduction profile can be used. In the example shown in FIG. 10, at the intermediate position 4050, the inner core 4110 can be insufficient to guide light therethrough and the outer core 4120 can be sufficient to guide at least one optical mode (e.g., a spatial mode).

In some embodiments, each core of the waveguide 4100 can have capacity for at least one optical mode (e.g., single mode, few modes, or multiple modes). For example, at the first end 4010, the VC waveguide 4101 can support a number of spatial modes (M1) in the inner core 4110. At the intermediate position 4050, in various embodiments, the inner core 4110 may no longer be able to support all M1 modes (e.g., unable to support optical propagation). However, in some such embodiments, at the intermediate position 4050, the outer core 4120 can support all M1 modes (and in some examples, can support additional modes). In this example, light traveling in the inner core 4110 from the first end 4010 to the intermediate position 4050 can escape from the inner core 4110 into the outer core 4120 so that it can propagate in the outer core 4120.

In some implementations, the size of the inner core 4110, the size of the outer core 4120, the size of the cladding 4130, and/or the spacing between the waveguides 4100 may decrease further (e.g., simultaneously and gradually, in some examples) along the optical element 4001 from the intermediate position 4050 to the second end 4020. In the example shown in FIG. 10, at the second end 4020, the outer core 4120 may be insufficient to guide light therethrough.

In certain embodiments, at the intermediate position 4050, the VC waveguide 4101 can support all M1 modes in the outer core 4120. At the second end 4020, the outer core 4120 may not be able to support all M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the second end 4020, the combined core 4150 of at least two cores can support all M1 modes of all combined waveguides 4101 (and in some examples can support additional modes). In this example, light traveling in the outer core 4120 from the intermediate position 4050 to the second end 4020 can escape from the outer core 4120 into a combined waveguide 4150 formed by at least two outer cores (e.g., two or more adjacent cores) so that it can propagate in the combined core. In the example shown in FIG. 10, the combined waveguides 4150 are each formed by three outer cores. However, in some embodiments, the coupled waveguide 4150 may be formed with a different number of outer cores.

Light traveling from the second end 4020 to the first end 4010 can behave in an inverse manner. For example, in some embodiments, light can travel from a coupled waveguide 4150 formed by at least two adjacent outer cores into at least one outer core 4120 proximal to the intermediate cross section 4050, and from the outer core 4120 into a corresponding inner core 4110 proximal to the first end 4010. In the example shown in FIG. 10, the combined waveguides 4150 can each support three propagation modes. Traveling from the second end 4020 to the first end 4010, each propagation mode can be coupled to a corresponding outer core 4120 proximal to the intermediate cross section 4050 and travel from the outer core 4120 to a corresponding inner core 4110 proximal to the first end 4010.

11, the exemplary embodiment 5000 has similar features to the exemplary embodiment 4000 shown in FIG. 10. One difference is that the cross-sectional configuration of the housing structure 5060 has a structure with a single hole 5062 instead of multiple holes 4062. Similar to the exemplary embodiment 4000 shown in FIG. 10, the optical element 5001 can have a coupler housing structure 5060 (e.g., having a medium 5140) and multiple longitudinal waveguides 5100 disposed in the housing structure 5060. The waveguides 5100 can be disposed relative to each other in a cross-sectional geometry waveguide arrangement within the hole 5062. As shown, light can be guided through the optical element 5001 from a first end 5010, through an intermediate cross section 5050, to a second end 5020.

As described herein, gaps may also separate the multiple longitudinal waveguides 5100 from the surrounding housing structure 5060. In some embodiments, the gaps may be substantially absent between the coupler housing structure 5060 and the waveguides 5100 proximal to the intermediate location 5050 and/or the second end 5020. For example, in FIG. 11, the gaps are shown proximate to the second end 5020, but in preferred embodiments, the gaps may be substantially absent between the coupler housing structure 5060 and the waveguides 5100. In some embodiments, the gaps may be substantially absent between the coupler housing structure 5060 and the waveguides 5100 proximate to the first end 5010, the intermediate location 5050, and/or the second end 5020.

In various embodiments, the plurality of waveguides 5100 can have at least one VC waveguide 5101. FIG. 11 shows all 37 waveguides 5100 as VC waveguides 5101 in a hexagonal arrangement. However, any arrangement can be used. Additionally, any number of VC waveguides, non-VC waveguides, and/or dummy fibers can be used. As described herein, one or more dummy fibers can be utilized to provide a particular geometric arrangement of the active optical fiber waveguide. As described herein, the VC waveguide 5101 can have an inner missing core 5110, an outer core 5120, and an outer cladding 5130.

In certain embodiments, the inner core 5110 waveguide dimensions, outer core 5120 waveguide dimensions, cladding 5130 dimensions, refractive index, and/or numerical aperture (NA) can be selected to increase and/or optimize coupling to individual fibers 2000 and/or optical devices 3000. In some embodiments, the inner core 5110 size, outer core 5120 size, cladding 5130 size, and/or spacing between the waveguides 5100 can decrease along the optical element 5001 from the first end 5010 to the second end 5020. In the example shown in FIG. 11, at the intermediate position 5050, the inner core 5110 of a particular waveguide 5100 can be insufficient to guide light therethrough, and the outer core 5120 of a particular waveguide 5100 can be sufficient to guide at least one optical mode (e.g., a spatial mode). In this example, close to the second end 5020, the outer core 5120 may be insufficient to guide light therethrough. Thus, in some embodiments, light traveling in the outer core 5120 from the intermediate position 5050 to the second end 5020 may escape the outer core 5120 into a combined waveguide 5150 formed by at least two outer cores (e.g., two or more adjacent cores) so that it can propagate in the combined core. In the example shown in FIG. 11, each of the combined waveguides 5150 is formed by three outer cores, but the combined waveguides 5150 may be formed by another number of outer cores. The remaining cores (e.g., cores of waveguides or dummy fibers) may or may not guide light. Light traveling from the second end 5020 to the first end 5010 may behave in the opposite manner.

Optical fiber arrays can be used for coherent or incoherent beam combining applications. The various multi-channel optical combiners with fiber arrays described herein can address one or more of the following shortcomings of other beam combining devices:
1. Coherent combined multi-lasers can use multiple individual back reflectors. The reflectors can be fabricated as a single broad-area reflector housing multiple channels, or as terminations of individual channels. These can be made by placing mirrors on the face of the fiber, or by fabricating fiber Bragg gratings (FBGs) within the fiber. Reflectors are costly, have some deviations from 100% reflectivity, and can degrade or become damaged due to exposure to high optical power.
2. Different channels may have different optical lengths, which may require the use of a composite active length adjustment for phase synchronization.
3. The combined cavity can have multiple competing supermodes, some of which may have to be suppressed.

Figure 12 illustrates a schematic of a multi-channel optical combiner 6000 that can be used for coherent or incoherent beam combining applications. An example of a multi-channel optical combiner 6000 can have an output optical combiner array 6010 and a number of optical fibers 6034 (e.g., 6034-1, 6034-2, 6034-3, 6034-4, 6034-5, 6034-6, 6034-7, 6034-8, 6034-9, 6034-10). At least two of the optical fibers (e.g., 6034-1 and 6034-4; 6034-5 and 6034-8; and 6034-6 and 6034-10) can be connected together at ends opposite the output optical combiner array 6010.

In various implementations, the output optical combiner array 6010 can include any optical combiner array known in the art or yet to be developed. The output optical combiner array can include any optical combiner array described herein, such as any of the optical combiner arrays in Figures 1A-11. As an example, in one example, the output optical combiner array can include a pitch reduced optical fiber array (PROFA), as described herein.

The output optical coupler array 6010 can have a first end 6010A and a second end 6010B. In some examples, the output optical coupler array 6010 can have a tapered shape (e.g., a decrease or increase in cross-sectional area) from the first end 6010A to the second end 6010B. With reference to FIG. 12, the output optical coupler array 6010 can be optically connected to a plurality of optical fibers 6034 at the first end 6010A. The output optical coupler array 6010 can be configured to receive light from the optical fibers 6034 at the first end 6010A and output light 6040 at the second end 6010B. In this example, one of three cases can be implemented based on the desired output. (1) the light can remain separated in different channels of the array, (2) the array channels can be weakly coupled, and (3) the array channels can be strongly coupled. As described herein, the light 6040 from the plurality of optical fibers 6034 can be sent to an optical device. Also, the output optical coupler array 6010 can receive light (e.g., from the optical device) at the second end 6010B and output light at the first end 6010A to the optical fibers 6034. In some examples, the output optical coupler array 6010 can be optically coupled to the optical fibers 6034 at the second end 6010B and can receive light from at least one of the optical fibers 6034 and output light at the first end 6010A.

12, ten optical fibers (e.g., 6034-1, 6034-2, 6034-3, 6034-4, 6034-5, 6034-6, 6034-7, 6034-8, 6034-9, 6034-10) are shown, however, the number of optical fibers is not particularly limited (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 40, 50, 75, 80, 90, 100, or any range formed by any such value). The optical fiber 6034 can be any optical fiber known or yet to be developed in the art. For example, the optical fiber 6034 can have single mode fiber, few mode fiber, multimode fiber, polarization maintaining fiber, and/or any combination thereof. As shown in FIG. 12, the optical fiber 6034 can have one or more gain blocks 6050 configured to enable optical amplification. In some designs, the gain block 6050 can be comprised of a section of pump fiber 6051, e.g., active or doped fiber (single or double clad). The gain block 6050 can further include at least one pump-signal combiner 6052, and at least one pump source 6053, e.g., at the end of the pump fiber 6051. In the example of FIG. 12, a pair of pump-signal combiners 6052 with corresponding pump sources 6053 are shown at either end of the pump fiber 6051 for one or more (in some examples, each) of the gain blocks 6050.

The optical fibers 6034 can have a first end 6034A and a second end 6034B. In FIG. 12, the first end 6034A is optically connected to the first end 6010A of the output optical coupler array 6010. In various embodiments, at least two of the optical fibers 6034 can be connected to each other (e.g., forming a connection 6036) at opposite ends of the output optical coupler array 6010 (e.g., ends proximate the second end 6034B of the optical fiber 6034). In FIG. 12, the optical fibers 6034-1 and 6034-4 are connected to each other, the optical fibers 6034-5 and 6034-8 are connected to each other, and the optical fibers 6034-6 and 6034-10 are connected to each other proximate the rear end 6034B 6036. In some examples, the optical fibers can be connected to each other via a fusion splice, or portions of similar types of fibers can be used for the connection. In some examples, one or more fibers may form a loop.

In various embodiments, by being connected together, the individual fibers can form channels that do not have a fiber reflector on the backside of the connected channel 6036. In some examples, wavelength selection elements such as fiber Bragg gratings (FBGs) can be used in the connected channels. In some examples, modulation elements such as amplitude or phase modulators (fiber-based or chip-based) for Q-switching can be used in the connected channels. In some examples, the output optical coupler array 6010 (e.g., PROFA) can have a reflector (e.g., a Talbot mirror) to form a connected Talbot cavity, as described in U.S. Patent No. 9,851,510, entitled “PHASE LOCKING OPTICAL FIBER COUPLER,” issued on December 26, 2017, which is incorporated herein by reference in its entirety. For example, a reflective surface or reflector can be included in the second end 6010B of the optical coupler array 6010. The reflective surface or mirror may comprise a common reflector, reflective surface, or mirror that is common to multiple channels and cores or that is included in multiple channels or cores.

In some embodiments, one or more optical fibers (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., or any range formed by any such values) may not be connected to another optical fiber at the opposite end 6034B of the optical coupler array 6010. The unconnected fibers are suitable for passive or active phase locking. For example, reflectors, wavelength selection elements (e.g., FBGs), and/or modulation elements may be used at the unconnected end 6034B. However, terminating the rear end of the fiber array at a connection 6036 may enable the following advantages:
1. The number of reflectors can be reduced: In some embodiments, reflectors can be eliminated entirely, such as when there is an even number of channels, all of which are interconnected.
2. In some instances, replacing the back reflector with a splice can effectively accommodate significantly higher efficiency (e.g., substantially 100% efficiency) with virtually no optical loss. Furthermore, the power handling limits may be similar (e.g., in some instances, nearly identical) to the fiber itself. For example, optical power exposure levels would not be limited by levels that could degrade the reflector.
3. In some instances, by connecting several channels together, the properties of the laser cavity can be changed, making it more similar to a Sagnac loop rather than a Fabry-Perot resonator.
In general, a Sagnac interferometer can be more stable with respect to phase fluctuations compared to a Fabry-Perot interferometer.
4. With the prospect of phase locking, the effective number of channels to be locked can be reduced since the connected channels can have the same optical length in some instances. This can result in either less complex electronics in the case of active phase locking, or more efficient devices in the case of passive phase locking. For example, the number of channels with different lengths can be reduced by a factor of two when the array is fully connected, since the connected channels have the same optical length. Thus, if there is a passive phase locking element that can normally lock N channels, some embodiments can lock 2N channels. The complexity of the active phase locking electronics can also be reduced by a factor of two, since it is proportional to the number of channels.
5. The connectivity map can be selected in a way that undesired cavity supermodes can be reduced, substantially suppressed, and/or eliminated. In many applications, single-mode, e.g., all coherent, phase-locked operation is highly desirable. Achieving this mode over a large pump power range allows for a large threshold difference between the desired (e.g., in-phase) supermode and all unwanted (e.g., out-of-phase) supermodes to be used. Since different supermodes have different phase and/or amplitude variations across the channel, a properly selected connectivity map can favor preselected desired supermodes and suppress undesired modes.
6. Various implementations do not require that all connected channels be useful and are compatible with the technology developed. For example, the unconnected channel(s) can be used for wavelength selectivity or modulation.

In some embodiments, a single polarization mode output can be advantageously generated from the fiber array. For example, in some examples, one or more polarizing beam splitters and/or isolators can be used in the connecting channels. FIG. 13 illustrates a multi-channel optical combiner 7000 that generates a single polarization mode output. The illustrated multi-channel optical combiner 7000 can have an output optical combiner array 7010. The output optical combiner array 7010 can have any polarization maintaining (PM) combiner array. In some examples, the PM combiner array can have a PM PROF as described herein. In some examples, the output optical combiner array 7010 can have a tapered shape. The combiner array 7010 can output light of a certain polarization mode. With reference to FIG. 13, an exemplary combiner array 7010 is shown to allow only right-hand circularly polarized light (RCP) to exit at the second end 7010-2. The reflected portion of this light (e.g., via Fresnel reflection) becomes left-handed circularly polarized light (LCP) and exits at the first end 7010-1.

The coupler array 7010 can be connected to multiple optical fibers 7034. For simplicity, this example shows only two optical fibers 7034 forming two channels, although additional optical fibers/channels can be used. The optical fibers 7034 can have one or more polarization converters 7045 (e.g., circular-to-linear or linear-to-circular converters), gain blocks 7050, polarizing beam splitters 7060, and/or isolators 7065. The optical fibers 7034 can be connected together at ends opposite the optical coupler array 7010 to form a connection 7036, for example. In some examples, the optical fibers 7034 can be connected with a 90 degree splice.

Continuing to refer to FIG. 13, the circularly polarized light from the optical coupler array 7010 can be converted to linearly polarized light by a polarization converter 7045 (e.g., a circular to linear converter). The light of a particular linear polarization mode (e.g., fast) can pass through the gain block 7050, the polarizing beam splitter 7060, and the isolator 7065. The linearly polarized light can be converted to another polarization mode (e.g., slow) due to a connection 7036 (e.g., a 90 degree splice), where it can again pass through the polarizing beam splitter 7060, the gain block 7050, the converter 7045, and the coupler array 7010. Upon exiting the PM coupler array 7010, only a single polarization mode can be output (e.g., RCP light in this example). In some such examples, the multi-channel optical combiner 7000 can advantageously generate a single polarization mode without axial channel alignment, as described, for example, in U.S. Patent Application Publication No. 2017/0219774, entitled "POLARIZATION MAINTAINING OPTICAL FIBER ARRAY," which is incorporated by reference in its entirety. Other examples are possible.

Now referring to FIG. 14, a set of refractive index profiles 500 is illustrated. The set of refractive index profiles includes different back reflection loss reduction scenario-optimized refractive index profiles "ORIP" (ORIP-a through ORIP-c) each corresponding to a specific coupler array configuration. ORIP-a through ORIP-c are illustrated, for example, as a coupler array 502 disposed between a number of optical fibers 504 and an optical device 506. The coupler array 502 has interfaces shown as interface 1 and interface 2 at each end.

The profile designated as ORIP-a provides substantial back reflection at interface 1 and suppressed back reflection at interface 2. The profile designated as ORIP-b provides no substantial back reflection at interface 1 and significant back reflection at interface 2. The profile designated as ORIP-c provides reduced, e.g., optimized total back reflection from both interfaces 1 and 2, and balances the reduction in back reflection at each interface, interfaces 1 and 2 (e.g., with the goal of reducing maximum back reflection for higher reflection, or with the goal of reducing the sum of reflections from interfaces 1 and 2).

In some examples, to achieve the results shown in profiles ORIP-b or ORIP-c, the vanishing core waveguide refractive index N-3 of the coupler array 502 can be made lower than the refractive index _N of the cladding of the plurality of optical fibers 504. Thus, for example, if the cladding of the plurality of optical fibers 504 is made of pure silica, N-3 can be made lower than the refractive index of pure silica, and the outer cladding of the vanishing core waveguide longitudinally surrounding the outer core can comprise another material, for example, fluorine-doped silica.

It should be noted that although the baseline refractive index N _of is shown to be the same for the multiple optical fibers 504 and the optical device 506, the value _of the baseline refractive index N of the multiple optical fibers 504 can be different from the baseline refractive index value N of the optical device 506.

The above design, e.g., optimization techniques, can be readily and advantageously applied to various embodiments of coupler arrays such as those shown in Figures 1A-2D, 4, 5 (where interface-1 and interface-2 corresponding to optimization profile set 500 are shown as INT-1 and INT-2, respectively), and Figures 1, 10, and 11.

15 illustrates an exemplary set of refractive index profiles 600. Other examples are possible. As illustrated in FIG. 15, a coupler array 602 having at least one missing core waveguide can be coupled at a first end to an optical fiber 604 and at a second end to an optical device 606. The optical fiber 604 can have a propagation mode with a core refractive index NcoreFiber, a cladding refractive index NcladdingFiber, and an effective refractive index NeffFiber. The optical device 606 can have a mode propagating in a waveguide with a core refractive index NcoreDevice, a cladding refractive index NcladdingDevice, and an effective refractive index NeffDevice. The missing core waveguide of the coupler array 602 can have an inner missing core with a first refractive index (N-1), an outer core with a second refractive index (N-2), and an outer cladding with a third refractive index (N-3). The vanishing core waveguide can have an effective refractive index Neff1 at the first end and an effective refractive index Neff2 at the second end. In various designs, the vanishing core waveguide can have a refractive index profile with a first refractive index (N-1), a first inner core size, a second inner core size, a second refractive index (N-2), a first outer core size, a second outer core size, and a third refractive index (N-3) configured to reduce back reflections at the optical fiber interface and/or the optical device interface of light traveling in a first direction from the plurality of optical fibers to the optical device and/or in a second direction from the optical device to the plurality of optical fibers.

As shown for index profile a, Neff2 can be approximately equal to NeffDevice. In various embodiments, approximately equal with respect to the index can mean that the two index values are within 5% of each other (e.g., within 1%, 2%, 3%, 4%, or 5% of each other, depending on the application). For example, in some designs, Neff2 can be within 1%, 2%, 3%, 4%, or 5% of NeffDevice. In some examples, Neff1 may not be equal to NeffFiber. In various embodiments, the two index values may not be approximately equal if they differ from each other by at least 5% (e.g., differ from each other by at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, or at least 10%, depending on the application). For example, in some designs, Neff1 can differ by at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, or at least 10% of NeffFiber. In some designs, the two index values may be unequal. For example, the two index values may be unequal to each other by at least 1%, at least 2%, at least 3%, or at least 4%. In some examples, Neff1 may be unequal to at least 1%, at least 2%, at least 3%, or at least 4% of NeffFiber.

In some implementations, Neff1 may be greater than NeffFiber. In some examples, N3 may be approximately equal to NcladdingFiber, N-2 may be approximately equal to NcoreDevice, and N1 may be approximately equal to (N-2)+(NcoreFiber-NcladdingFiber). In various designs, the disappearing core waveguide may have a refractive index profile with a first refractive index (N-1), a first inner core size, a second inner core size, a second refractive index (N-2), a first outer core size, a second outer core size, and a third refractive index (N-3) configured to reduce back reflections at the optical device interface of light traveling in a first direction from the plurality of optical fibers to the optical device and/or light traveling in a second direction from the optical device to the plurality of optical fibers.

As shown for index profile b, Neff1 can be approximately equal to NeffFiber, while Neff2 is not equal (e.g., at least 1% unequal) or approximately equal (e.g., within 5%) to NeffDevice. For example, in some examples, Neff2 may be less than NeffDevice. In some examples, the third refractive index (N3) in at least one of the vanishing core waveguides can be lower than NcladdingFiber. N-1 is approximately equal to NcoreFiber, N-2 is approximately equal to NcladdingFiber, and N-3 is approximately equal to (N-2)-(NcoreDevice-NcladdingDevice). In various designs, the vanishing core waveguides can have a refractive index profile. The refractive index profile is configured such that the first refractive index (N-1), the first inner core size, the second inner core size, the second refractive index (N-2), the first outer core size, the second outer core size, and the third refractive index (N-3) are configured to reduce back reflections at the optical fiber interface of light traveling in a first direction from the plurality of optical fibers to the optical device and/or back reflections of light traveling in a second direction from the optical device to the plurality of optical fibers.

As shown for index profile c, Neff1 can be greater than NeffFiber and Neff2 can be less than NeffDevice. In some examples, the third refractive index (N-3) in at least one of the vanishing core waveguides can be less than NcladdingFiber. In some examples, N-3 can be less than NcladdingFiber, N-2 can be approximately equal to (N-3) + (NcoreDevice - NcladdingDevice), and N-1 can be approximately equal to (N-2) + (NcoreFiber - NcladdingFiber). In some designs, the vanishing core waveguides can have a refractive index profile. The refractive index profile can be configured such that the first refractive index (N-1), the first inner core size, the second inner core size, the second refractive index (N-2), the first outer core size, the second outer core size, and the third refractive index (N-3) reduce the total back reflection of light traveling in a second direction from the multiple optical fibers to the optical device and/or from the optical device to the multiple optical fibers at the optical fiber interface and the optical device interface.

In various embodiments, the coupler array 602 can be configured to increase the optical coupling to the optical device 606 at the second end. In some examples, the optical device 606 can comprise a free space based optical device, an optical circuit having at least one input/output end coupling port, or an optical circuit having at least one optical port with a vertical coupling element. In some examples, the optical device 606 can comprise a multimode optical fiber, a double clad optical fiber, a multicore optical fiber, a large mode area fiber, a double clad multicore optical fiber, a standard/conventional optical fiber, or a custom optical fiber. In some examples, the coupler array 604 can have additional coupler arrays.

Thus, while the basic novel features of the invention as applied to the preferred embodiments thereof have been shown, described and pointed out, it will be understood that various omissions and substitutions and changes in the form and details of the illustrated devices and methods, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, all combinations of the above elements and/or method steps which perform substantially the same functions in substantially the same manner to achieve the same results will clearly be within the scope of the invention. It is therefore intended to be limited only as indicated by the scope of the claims appended hereto.

Claims (30)

1. A multi-channel optical coupler array for optically coupling a plurality of optical fibers to an optical device, the multi-channel optical coupler array comprising:
an elongated optical element having a first end operable to optically couple to the plurality of optical fibers and a second end operable to optically couple to the optical device;
The elongated optical element comprises:
a common single coupler housing structure;
a plurality of longitudinal waveguides each extending in a longitudinal direction of the multi-channel optical coupler array ;
an outer cladding;
the plurality of longitudinal waveguides each being spaced apart from one another, each having capacity for at least one optical mode, each embedded in the common unitary housing structure proximate the second end, at least one configured to be coupled to one of the plurality of optical fibers at the first end, and a lost core optical guide configured to be coupled to the optical device at the second end, wherein the plurality of optical fibers have a propagation mode having an effective refractive index NeffFiber, the optical device has a mode having an effective refractive index NeffDevice, and the at least one lost core waveguide is forwardly coupled to the first end. the at least one missing core waveguide comprises an inner missing core and an outer core, the inner missing core having a first refractive index (N-1), a first inner core size (ICS-1) at the first end and a second inner core size (ICS-2) at the second end, the outer core surrounding the inner core along a longitudinal direction of the multi-channel optical coupler array and having a second refractive index (N-2), a first outer core size (OCS-1) at the first end and a second outer core size (OCS-2) at the second end;
the outer cladding surrounds the outer core along a longitudinal direction of the multi-channel optical coupler array and has a third refractive index (N-3), a first cladding size at the first end, and a second cladding size at the second end;
the common unitary coupler housing structure has a fourth refractive index (N-4) and comprises a laterally continuous medium of the multi-channel optical coupler array surrounding the plurality of longitudinal waveguides, the relative magnitude relationship between the first, second, and third refractive indices (N-1, N-2, and N-3) having the following magnitude relationship (N-1>N-2>N-3), a total volume of the medium of the common unitary coupler housing structure is greater than a total volume of all of the lost core waveguide inner cores and the outer cores confined within the common unitary coupler housing structure, and the first inner lost core size (ICS) is greater than the total volume of all of the lost core waveguide inner cores and the outer cores confined within the common unitary coupler housing structure. said first outer core size (OCS-1), said first outer core size (OCS-1), and said spacing between said plurality of longitudinal waveguides are simultaneously and gradually reduced according to a reducing profile along said elongated optical element between said first end and said second end until said second inner missing core size (ICS-2) and said second outer core size (OCS-2) are reached, said second inner missing core size (ICS-2) being selected to be insufficient to guide light therethrough and said second outer core size (OCS-2) being selected to be sufficient to guide at least one optical mode, such that
light traveling in a first direction from the first end to the second end escapes from the inner lost core into the corresponding outer core proximate the second end;
light traveling in a second direction from the second end to the first end travels from the outer core into the corresponding inner lost core proximate the first end;
the common unitary coupler housing structure proximate the first end has a cross-sectional shape;
the cross-sectional shape comprises a laterally continuous structure of the multi-channel optical coupler array having at least one hole, the at least one hole containing at least one of the plurality of longitudinal waveguides and creating a gap between the coupler housing structure and at least one of the plurality of longitudinal waveguides;
The relationship between Neff1, Neff2, NeffFiber, and NeffDevice is:
(1) Neff2 is within 5% of NeffDevice and Neff1 is greater than NeffFiber;
(2) Neff1 is within 5% of NeffFiber and Neff2 is less than NeffDevice;
(3) A multi-channel optical combiner array, where Neff1 is greater than NeffFiber and Neff2 is less than NeffDevice. At least one of the lost core waveguides comprises a refractive index profile;
In the refractive index profile,
the first refractive index (N-1);
the first inner core size (ICS-1);
the second inner core size (ICS-2);
the second refractive index (N-2),
the first outer core size (OCS-1);
the second outer core size (OCS-2), and the third refractive index (N-3),
10. The multi-channel optical coupler array of claim 1, configured to reduce back reflections of light traveling in at least one of the first direction from the plurality of optical fibers to the optical device or the second direction from the optical device to the plurality of optical fibers at an optical fiber interface and/or an optical device interface. 2. The multi-channel optical coupler array of claim 1, wherein Neff1 is greater than NeffFiber and Neff2 is within 5% of NeffDevice. 4. The multi-channel optical coupler array of claim 3, wherein the one of the optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, the optical device has a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice, and the N-3 is within 5% of NcladdingFiber, N-2 is within 5% of NcoreDevice, and N-1 is within 5% of (N-2) + (NcoreFiber - NcladdingFiber). 2. The multi-channel optical coupler array of claim 1, wherein Neff1 is within 5% of NeffFiber and Neff2 is less than NeffDevice. The multichannel optical coupler array of claim 5, wherein the one of the optical fibers has a cladding refractive index NcladdingFiber, and the third refractive index (N3) in at least one of the lost core waveguides is less than NcladdingFiber. the one of the optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, the optical device having a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice;
6. The multi-channel optical coupler array of claim 5, wherein N-1 is within 5% of NcoreFiber, N-2 is within 5% of NcladdingFiber, and N-3 is within 5% of (N-2)-(NcoreDevice-NcladdingDevice). The multi-channel optical coupler array of claim 1, wherein Neff1 is greater than NeffFiber and Neff2 is less than NeffDevice. The multichannel optical coupler array of claim 8, wherein the one of the plurality of optical fibers has a cladding refractive index NcladdingFiber, and the third refractive index (N-3) in at least one of the disappearing core waveguides is less than NcladdingFiber. the one of the optical fibers has a core refractive index NcoreFiber and a cladding refractive index NcladdingFiber, the optical device having a mode with a core refractive index NcoreDevice and a cladding refractive index NcladdingDevice;
9. The optical coupler array of claim 8, wherein N-3 is smaller than NcladdingFiber, N-2 is within 5% of ( N-3 ) + (NcoreDevice - NcladdingDevice), and N-1 is within 5% of ( N-2 ) + (NcoreFiber - NcladdingFiber). At least one of the lost core waveguides comprises a refractive index profile;
In the refractive index profile,
the first refractive index (N-1);
the first inner core size (ICS-1);
the second inner core size (ICS-2);
the second refractive index (N-2),
the first outer core size (OCS-1);
9. The multi-channel optical coupler array of claim 8, wherein the second outer core size (OCS-2) and the third refractive index (N-3) are configured to reduce a sum of back reflections of light traveling in at least one of the first direction from the plurality of optical fibers to the optical device or the second direction from the optical device to the plurality of optical fibers at an optical fiber interface and an optical device interface. the optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device being a free space based optical device;
10. The multi-channel optical coupler array of claim 1 comprising one of: an optical circuit having at least one input/output end coupling port; or an optical circuit having at least one optical port comprising a vertical coupling element. The optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device comprising:
Multimode optical fiber,
Double clad optical fiber,
Multi-core optical fiber,
Large mode area fiber,
Double-clad multi-core optical fiber,
The multi-channel optical coupler array of claim 1 comprising one of: a standard/conventional optical fiber; or a custom optical fiber. The multichannel optical coupler array of claim 1, wherein the optical coupler array is configured to increase optical coupling to the optical device at the second end, the optical device comprising an additional optical coupler array. The multi-channel optical coupler array of claim 1, wherein N-3≦N-4. The multi-channel optical coupler array of claim 1, wherein adjacent the second end, the coupler array has substantially no gap between the coupler housing structure and the plurality of longitudinal waveguides. The multichannel optical coupler array of claim 1, wherein the cross-sectional shape comprises a ring surrounding the plurality of longitudinal waveguides. The multichannel optical coupler array of claim 17, wherein the plurality of longitudinal waveguides are arranged in a hexagonal configuration. The multi-channel optical coupler array of claim 17, wherein the ring has a circular inner cross-section. The multi-channel optical coupler array of claim 17, wherein the ring has a non-circular inner cross-section. The multi-channel optical coupler array of claim 17, wherein the ring has a circular outer cross-section. The multi-channel optical coupler array of claim 17, wherein the ring has a non-circular outer cross-section. The multichannel optical coupler array of claim 1, wherein the cross-sectional shape comprises a structure having a plurality of holes. The multi-channel optical coupler array of claim 23, wherein the holes are arranged in a hexagonal pattern. The multi-channel optical coupler array of claim 23, wherein the holes are arranged in a rectangular configuration. The multi-channel optical coupler array of claim 23, wherein the plurality of holes are defined in an XY array. 24. The multi-channel optical coupler array of claim 23, wherein at least one hole has a circular cross-section. 24. The multi-channel optical coupler array of claim 23, wherein at least one hole has a non-circular cross-section. 24. The multi-channel optical coupler array of claim 23, wherein at least one of the holes has a different dimension than another of the holes. 24. The multi-channel optical coupler array of claim 23, wherein at least one of the holes has a different shape than another of the holes.