JP5190400B2 - Optical fiber with lens and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical fiber with a lens and a method for manufacturing the same for connecting an optical device and an optical fiber with high efficiency.

OEIC (Optical with functions such as switch, wavelength conversion, phase modulation, etc. on a semiconductor waveguide based on gallium arsenide or a silicon wire waveguide based on a silicon substrate
Research on optical devices such as hybrid optical elements, in which electronic components and optical components (such as Electrical Integrated Circuit) are integrated, is in progress.

  Many of these optical devices often propagate in a core of 1 μm or less under a single mode condition due to the difference in refractive index between the waveguide core and the substrate, and the diameter of the beam, that is, the mode field diameter (Mode Field Diameter). MFD) (hereinafter referred to as MFD) is 1 μm or less. On the other hand, many optical fibers have a core in which a germanium oxide dopant is dispersed in a quartz clad, the core diameter is 10 μm, and the MFD is also about 10 μm. Therefore, in order to connect these with high efficiency, it is necessary to match the spot size of the beam, and it is necessary to arrange an appropriate lens between the optical fiber and the optical device, and to fix after alignment. . Further, since the magnification for conversion is high, it is necessary to form the lens with a material having a high refractive index.

  In such a method of coupling an optical fiber and an optical device through a lens, it is necessary to precisely align and fix the three bodies, and a small optical device configured on a semiconductor integrated circuit is used in a large casing. The glass material used for the lens is restricted in refractive index and does not provide sufficient coupling characteristics, so it is used in actual devices. I did not come.

  In order to solve these problems, for example, as shown in Patent Documents 1 to 3, various optical fibers with a lens in which a lens is formed at the tip of an optical fiber have been proposed. With the attached optical fiber, sufficient coupling efficiency cannot be obtained with respect to the optical device described above.

  For example, FIG. 6 schematically shows the coupling between a conventional silica-based optical fiber a with a lens and a silicon thin-wire waveguide c of an optical device b. The spot diameter of a silica-based optical fiber with a lens for a 1550 nm beam is shown in FIG. The MFD of the silicon thin wire waveguide is φ0.5 μm, and the coupling loss is about 15 dB due to the coupling of about 3% of the whole beam.

  On the other hand, regarding the production of optical fibers with lenses, the method of processing single-mode optical fibers into convex lenses is limited by the refractive index of the quartz material, making it difficult to obtain a sufficient refraction angle for condensing. There are limits to optical properties. In the method of forming a concave surface directly on a single-mode optical fiber by etching and forming a thick film with a high refractive index on the concave surface, the refractive index distribution of the core is constant, so that etching solutions having different etching rates depending on the dopant concentration are used. Even if the selective etching is performed, it is difficult to obtain a concave shape suitable for condensing light, it is necessary to adjust the concave shape, and it is difficult to manufacture with good reproducibility.

  In addition, when considering the use of an optical fiber having a squared refractive index distribution used in a conventional optical fiber with a lens, the beam diameter periodically changes depending on the refractive index distribution in this optical fiber. It was necessary to process the length precisely.

JP 2003-294958 A JP 2004-177826 A JP 2006-276169 A

  The problem to be solved by the present invention is that the conventional optical fiber with a lens cannot obtain a sufficient coupling efficiency with respect to the optical device described above.

In order to solve the above-described problems, the present invention first provides a second mode in which a single mode type optical fiber is provided at an end portion of a single mode type first optical fiber and a refractive index profile is provided in a core. An optical fiber is connected, and a concave surface portion formed according to the refractive index distribution is provided on the tip side of the second optical fiber, with an antireflection film interposed therebetween, so that the refractive index of the core of the second optical fiber An optical fiber with a lens having a high refractive index, in which a lens material for constituting a lens is filled in the concave surface portion, and a lens is constructed by polishing an end surface.

In the present invention, next, the end of the first optical fiber of the single mode type is a multimode optical fiber comprising a multimode optical fiber having an intrinsic MFD equal to the MFD of the first optical fiber and having a square-type refractive index profile. The optical fiber of 2 is connected, and the end surface of the second optical fiber is filled with a lens material having a high refractive index via an antireflection film in a concave surface portion formed in accordance with the refractive index distribution. We propose an optical fiber with a lens that is polished to form a lens. Here, the intrinsic MFD refers to an MFD that propagates through a square type multimode optical fiber having a square type refractive index distribution without changing its beam diameter, and its size 2W is the maximum refractive index of the core of the optical fiber. When n, wavelength is λ, core radius is a, and relative refractive index difference is Δ, 2 {λa / nπ (2Δ) ^1/2 } ^1/2 is expressed. In other words, when a light beam having an MFD given by the equation is incident, the incident beam can propagate through the square multimode optical fiber while maintaining its diameter.

The present invention proposes an optical fiber with a lens in which, in the above configuration, the end surface of the lens material is polished into a convex surface or a concave surface in addition to a flat surface.

In the present invention, next, a step of fusion splicing a second optical fiber having a single mode type and a refractive index distribution in the core to the end of the single mode type first optical fiber; A step of forming a concave portion at the end of the second optical fiber by selective etching using an etchant having different etching rates depending on the concentration of the dopant corresponding to the rate distribution, and reflection on the concave portion of the second optical fiber. A step of filling a lens material for constituting a lens in the concave portion with a refractive index higher than the refractive index of the core of the second optical fiber through a prevention film, and forming a thick film on the end face; A method of manufacturing an optical fiber with a lens, comprising a step of polishing a thick film having a high refractive index formed on the end face of the optical fiber 2 to form a lens having a desired optical characteristic.

In the present invention, a square multimode having a square refractive index profile at the end of the single-mode first optical fiber and having the same intrinsic MFD as the MFD of the first optical fiber. A concave surface is formed at the end of the second optical fiber by fusion splicing of the second optical fiber made of the fiber and selective etching using an etchant having an etching rate different depending on the concentration of the dopant corresponding to the refractive index distribution. Forming a lens, and forming a lens on the concave surface with a refractive index higher than the refractive index of the core of the second optical fiber via an antireflection film on the concave surface of the second optical fiber . Filling the lens material and forming a thick film on the end face; and polishing the high refractive index thick film formed on the end face of the second optical fiber to form a lens with desired optical characteristics. Optical lens with lens We propose a method for manufacturing a driver.

  In the optical fiber with a lens according to the present invention, the second optical fiber fusion-bonded to the end portion of the single-mode first optical fiber has a refractive index distribution in the core. A hemispherical concave surface portion can be obtained by performing selective etching using etching solutions having different speeds. Therefore, a lens suitable for condensing is manufactured with good reproducibility by filling the concave surface portion with a high refractive index lens material through an antireflection film and polishing the end surface into a flat surface, convex surface or concave surface. be able to.

  The second optical fiber is a single mode type optical fiber having a refractive index distribution in the core, or a multimode graded index type, and its intrinsic MFD is equal to the MFD of the first single mode optical fiber. Since the fiber is used, the periodic behavior of the beam propagating through the fiber is eliminated, and the length adjustment is unnecessary, so that productivity is improved. Furthermore, since the core diameter can be made larger than when a single mode fiber is used as the second fiber, the diameter of the lens formed at the tip can be made larger, so that the light beam can be transmitted while avoiding the peripheral portion of the lens. As a result, there is an effect that the aberration at the time of condensing can be reduced.

It is explanatory drawing which shows the structure and manufacturing process of 1st Embodiment of the optical fiber with a lens of this invention. It is explanatory drawing which shows the structure and manufacturing process of 2nd Embodiment of the optical fiber with a lens of this invention. It is a schematic diagram which shows the light intensity distribution and phase distribution in the edge part of the 2nd optical fiber in the optical fiber with a lens of this invention. It is explanatory drawing which shows the normalization intensity | strength (solid line) and relative phase (dashed line) of the light in the condensing position in an analysis example. It is a schematic diagram which shows the coupling state of the optical fiber with a lens of this invention, and a silicon | silicone thin wire | line waveguide. It is a schematic diagram which shows the coupling | bonding state of the conventional optical fiber with a quartz-type lens, and a silicon | silicone thin wire | line waveguide.

FIG. 1 and FIG. 2 are explanatory views showing configurations and manufacturing steps of the first and second embodiments of the optical fiber with a lens according to the present invention, and the optical fibers of Example 1 and Example 2 described later, respectively. It corresponds to the dimensions.
In these drawings, reference numeral 1 denotes a single-mode first optical fiber, and reference numerals 1a and 1b denote a cladding and a core, respectively. As shown in (a) of the figure, a second optical fiber 2 having a refractive index distribution, that is, a squared refractive index distribution, is fusion spliced to the end of the first optical fiber 1 so as to have an appropriate length. Disconnect.

  Next, selective etching is performed on the end portion of the second optical fiber 2 using an etchant having different etching rates depending on the concentration of the dopant corresponding to the refractive index distribution, as shown in FIG. A concave surface portion 3 is formed at the end of the second optical fiber 2.

  Next, after the antireflection film 4 is formed on the concave surface portion 3 of the second optical fiber 2, a high refractive index lens material is filled, and a thick film 5 is formed on the end surface.

  Next, the high refractive index thick film formed on the end face of the second optical fiber 2 is polished while confirming the optical characteristics, and the lens 6 having the desired optical characteristics as shown in FIG. It can be configured with good reproducibility. The operation as a lens is as shown in FIG. 3 showing the light intensity distribution and phase distribution at the end of the second optical fiber.

  If the end face of the optical fiber 2 is polished to a flat surface, a so-called planoconvex lens 6 is formed. As shown in FIG. 5, the silicon thin wire waveguide 8 of the optical device 7 is, for example, the lens 6. Alignment and fixing can be easily performed using an adhesive having a refractive index close to that of the constituent material. In addition, the end surface of the optical fiber 2 can be polished into a convex surface or a concave surface depending on circumstances.

  Thus, by using the optical fiber with a lens of the present invention, the package for coupling with the optical device 7 can be reduced in size, and the apparatus used for alignment is also a two-body alignment, so that the three-body alignment is performed. Compared with the apparatus, the configuration can be greatly simplified, and the time for fixing the alignment can be shortened, so that an improvement in productivity can be expected.

Next, an embodiment of the present invention will be described.
1. The first optical fiber 1 is Corning SMF-28 (cladding diameter: 125 μm, core diameter: 8.4 μm), and the second optical fiber 2 has a relative refractive index difference between the core 2 b and the cladding 2 a. A single-mode optical fiber having a square refractive index profile of 1%, clad diameter: 125 μm, core diameter: 7.5 μm was used.
2. As shown in FIG. 1A, the second optical fiber 2 was fused and connected to the end of the first optical fiber 1 and cut to a length of 10 mm. The tip was immersed in a 9% strength hydrofluoric acid aqueous solution at 25 ° C. as an etchant, and selective etching was performed for 30 minutes.
3. By this selective etching, as shown in (b), a hemispherical concave surface portion 3 having a conical periphery and a radius of curvature of 7 μm at the center was formed.
4). Next, a quarter-wave film was formed from silicon and a silicon oxide film layer by a high-frequency sputtering apparatus, and the antireflection film 4 was obtained.
5. Subsequently, an amorphous silicon thick film 5 was formed to a thickness of about 20 μm by a high frequency sputtering apparatus.
6). Next, this end was temporarily fixed to a ferrule, and polishing was performed while confirming optical characteristics by polishing. As a result, a spot diameter of 0.8 μm was obtained at a wavelength of 1550 nm. At this time, the thickness of the thick film 5 was about 10 μm from the center of the concave portion 3. Thus, when a thin silicon wire waveguide having a core width of 0.5 μm and a core height of 0.5 μm was connected to the optical fiber with a lens, a coupling efficiency of about 50% could be obtained.

1. The first optical fiber 1 is SMF-28 manufactured by Corning, as in Example 1. The second optical fiber 2 has a relative refractive index difference of 1% between the core and the cladding, and a cladding diameter. A graded index optical fiber having a square refractive index profile of 125 μm and a core diameter of 22.7 μm was used. The second optical fiber 2 has a fundamental mode beam diameter of 10.4 μm at 1550 nm, and the fundamental mode propagates with the same mode field diameter as that of the single mode.
2. As shown in FIG. 2A, the second optical fiber 2 was fused and connected to the end of the first optical fiber 1 and cut to a length of 10 mm. The tip was immersed in a 9% strength hydrofluoric acid aqueous solution at 25 ° C. as an etchant, and selective etching was performed for 30 minutes.
3. By this selective etching, as shown in (b), a hemispherical concave surface portion 3 having a conical shape at the periphery and a radius of curvature of 10 μm at the center was formed.
4). Next, a quarter-wave film was formed from silicon and a silicon oxide film layer by a high-frequency sputtering apparatus, and the antireflection film 4 was obtained.
5. Subsequently, an amorphous silicon thick film 5 was formed to a thickness of about 20 μm by a high frequency sputtering apparatus.
6). Next, this end was temporarily fixed to a ferrule, and polishing was performed while confirming optical characteristics by polishing. As a result, a spot diameter of 0.8 μm was obtained at a wavelength of 1550 nm. At this time, the thickness of the thick film 5 was about 10 μm from the center of the concave portion 3. Thus, when a thin silicon wire waveguide having a core width of 0.5 μm and a core height of 0.5 μm was connected to the optical fiber with a lens, a coupling efficiency of about 50% could be obtained.

As an analysis example, it is assumed that the shape of the lens is an aspherical shape represented by the following formula, and the result of analysis by the two-dimensional time domain difference (FDTD) method is as follows. As shown in FIG. 4, the field distribution at the condensing position is obtained, and a beam diameter of 0.56 μm is obtained.
Z = (r ² / R) / [1+ {1− (1 + k) r ² / R ² } ^1/2 ]
Here, Z is an optical fiber axial distance, r is a radial distance from the optical fiber axis, R is a curvature of the optical fiber axis, and k is a conic constant.

  The optical fiber with a lens of the present invention is connected to an optical device such as a light emitting element, a light receiving element or a waveguide element, a filter or a switch, and can be used for optical communication, optical control, optical recording, a sensor, etc. The high refractive index plano-convex lens (or convex lens, convex-concave lens) formed on the end face of the optical fiber 2 can be coupled with the optical device with high efficiency.

DESCRIPTION OF SYMBOLS 1 1st optical fiber 1a clad 1b core 2 2nd optical fiber 2a clad 2b core 3 Concave surface part 4 Antireflection film 5 Thick film 6 Lens 7 Optical device 8 Silicon wire waveguide

Claims (6)

A single-mode type second optical fiber having a refractive index distribution at the core is connected to an end of the single-mode type first optical fiber, and a refractive index is provided on the tip side of the second optical fiber. The concave surface portion formed according to the distribution is filled with a lens material having a refractive index higher than the refractive index of the core of the second optical fiber via the antireflection film, and constituting the lens in the concave surface portion. And an optical fiber with a lens whose end face is polished to form a lens. The mode field diameter that propagates through the square multimode optical fiber having the squared refractive index profile, without changing the beam diameter , at the end of the first optical fiber of the single mode type is designated as follows. A multimode type second optical fiber having an eigenmode field diameter equal to the mode field diameter of the first optical fiber and having a square-shaped refractive index distribution is connected, and the second optical fiber is refracted at the tip side. The concave portion formed according to the refractive index distribution is filled with a lens material to form a lens in the concave portion with a refractive index higher than the refractive index of the core of the second optical fiber through an antireflection film. And an optical fiber with a lens whose end face is polished to form a lens.
Eigenmode field diameter (MFD) = 2 {λa / nπ (2Δ) ^1/2 } ^1/2
Where n is the maximum refractive index of the core of the optical fiber, λ is the wavelength, a is the radius of the core, and Δ is the relative refractive index difference. The optical fiber with a lens according to claim 1, wherein an end surface of the lens material is polished into a flat surface. The optical fiber with a lens according to claim 1 or 2, wherein an end surface of the lens material is polished into a convex surface or a concave surface. A step of fusion-bonding a second optical fiber having a single-mode type and a refractive index distribution at the core to the end of the single-mode first optical fiber; and a dopant corresponding to the refractive index distribution A step of forming a concave surface portion at the end of the second optical fiber by selective etching using an etching solution having an etching rate different depending on the concentration; and the second optical fiber via the antireflection film on the concave surface portion of the second optical fiber . A step of filling the concave surface portion with a lens material having a refractive index higher than the refractive index of the core of the optical fiber, and forming a thick film on the end surface, and forming on the end surface of the second optical fiber A method of manufacturing a lensed optical fiber comprising polishing a thick film having a high refractive index to form a lens having desired optical characteristics. The mode field diameter that propagates through the square multimode optical fiber having the squared refractive index profile, without changing the beam diameter , at the end of the first optical fiber of the single mode type is designated as follows. A step of fusion-splicing a multimode type second optical fiber having an eigenmode field diameter equal to the mode field diameter of the first optical fiber and having a square-shaped refractive index distribution; and a dopant corresponding to the refractive index distribution Forming a concave surface portion at the end of the second optical fiber by selective etching using an etchant having an etching rate that varies depending on the concentration of the second optical fiber, and the antireflection film on the concave surface portion of the second optical fiber . a high refractive index than the refractive index of the core of the second optical fiber, filled with lens material for the lens to the concave portion, forming a thick film on the end face, the The method for producing a high refractive index formed on the end face thick polished to a desired lensed optical fiber comprising a step of composing the lens of the optical characteristics of the optical fiber.
Eigenmode field diameter (MFD) = 2 {λa / nπ (2Δ) ^1/2 } ^1/2
Where n is the maximum refractive index of the core of the optical fiber, λ is the wavelength, a is the radius of the core, and Δ is the relative refractive index difference.

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