JP7698977B2 - Method for manufacturing optical fiber connection structure - Google Patents

Description

The present invention relates to a method for manufacturing an optical fiber connection structure.

As a conventional optical fiber connection structure of this type, one disclosed in Patent Document 1 has been proposed. In Patent Document 1, the optical fiber connection structure includes a multicore fiber and a fiber bundle made of multiple single-core fibers joined together with an adhesive, and the multicore fiber and the fiber bundle are optically coupled.

Here, the multiple cores arranged in the multicore fiber and the fiber bundle are generally formed using glass. Therefore, in Patent Document 1, in order to reduce Fresnel reflection caused by the difference in refractive index between the glass and air at the end faces of the multicore fiber and the fiber bundle, the end faces of the multicore fiber and the fiber bundle are inclined with respect to a plane perpendicular to the central axis.

The multicore fiber and the fiber bundle are then arranged so that the inclination directions of their end faces are opposite to each other (different inclination directions).

JP 2016-061941 A

However, in the conventional technology, the arrangement of the multiple cores at the end faces of the multicore fiber and the fiber bundle is unclear. In other words, in the conventional technology, the orientation of the core arrangement at the end face tilted with respect to the plane perpendicular to the central axis is not strictly specified.

Therefore, there is a risk that variation in the amount of focus deviation will occur depending on the combination of the orientation of the tilted end face and the orientation of the core array. And if variation occurs due to focus deviation, this will result in variation in the coupling loss, so it is desirable to fabricate the fiber so that the core orientation and tilt orientation are constant.

The present invention has been made in consideration of the problems inherent in the conventional techniques, and an object of the present invention is to provide a method for manufacturing an optical fiber connection structure that can suppress variations in coupling loss caused by oblique polishing of the fiber ends and simplifies the adjustment process for optically coupling cores together.

The optical fiber connection structure according to an aspect of the present invention comprises a first optical fiber unit in which a plurality of first cores are arranged, and a second optical fiber unit in which a plurality of second cores are arranged to correspond to each of the plurality of first cores, the end face of the first optical fiber unit is inclined with respect to a plane perpendicular to the central axis of the first optical fiber unit, the end face of the second optical fiber unit is inclined with respect to a plane perpendicular to the central axis of the second optical fiber unit, and the first optical fiber unit and the second optical fiber unit are arranged such that the inclination direction of the end face of the first optical fiber unit and the inclination direction of the end face of the second optical fiber unit are opposite to each other. The first optical fiber unit is arranged so that the central axis is horizontal and the most protruding point of the inclined end face is the upper end, and the uppermost and lowermost cores of the multiple first cores are arranged on a line segment connecting the upper and lower ends of the end face of the first optical fiber unit, and the second optical fiber unit is arranged so that the central axis is horizontal and the most protruding point of the inclined end face is the upper end, and the uppermost and lowermost cores of the multiple second cores are arranged on a line segment connecting the upper and lower ends of the end face of the second optical fiber unit.

A method for manufacturing an optical fiber connection structure according to an aspect of the present invention is a method for manufacturing an optical fiber connection structure in which a first optical fiber unit in which a plurality of first cores are arranged is optically connected to a second optical fiber unit in which a plurality of second cores are arranged to correspond to each of the plurality of first cores. The manufacturing method of the optical fiber connection structure includes a polishing step of polishing an end face of each of the optical fiber units so that the end face of the first optical fiber unit and the end face of the second optical fiber unit are inclined with respect to a plane perpendicular to a central axis of each of the optical fiber units, and an alignment step of opposing the end face of the first optical fiber unit and the end face of the second optical fiber unit to perform optical alignment, the polishing step including a first core orientation adjustment step of adjusting an arrangement of the plurality of first cores so that a relationship between a tilt direction of the end face of the first optical fiber unit and a direction of arrangement of the plurality of first cores is the same, a second core orientation adjustment step of adjusting the arrangement of the plurality of second cores so that a relationship between a tilt direction of the end face of the second optical fiber unit and a direction of arrangement of the plurality of second cores is the same, and a second core orientation adjustment step of adjusting the arrangement of the plurality of first cores so that a relationship between a tilt direction of the end face of the second optical fiber unit and a direction of arrangement of the plurality of second cores is the same after the first core orientation adjustment step is performed. The method includes a first polishing step of polishing the end face of the first optical fiber unit so that the uppermost core and the lowermost core are positioned on a line segment connecting the upper end and the lower end of the end face of the first optical fiber unit, and a second polishing step of polishing the end face of the second optical fiber unit so that the uppermost core and the lowermost core of the multiple second cores are positioned on a line segment connecting the upper end and the lower end of the end face of the second optical fiber unit after the second core orientation adjustment step is performed, with the central axis of the second optical fiber unit being horizontal and the most protruding point of the inclined end face being positioned at the upper end. The alignment step includes a core orientation alignment step of aligning the orientations of the first core and the second core by arranging the end face of the first optical fiber unit and the end face of the second optical fiber unit so that the inclination direction of the end face of the first optical fiber unit and the inclination direction of the end face of the second optical fiber unit are opposite to each other, and an optical axis alignment step of aligning the optical axis after the core orientation alignment step is performed.

According to the present invention , it is possible to provide a manufacturing method for an optical fiber connection structure that can suppress variations in coupling loss between each core and simplify the process of adjusting the optical axis of the core orientation by aligning the fiber end polishing orientation.

1 is a side cross-sectional view showing a schematic diagram of an example of an optical fiber connection structure. FIG. 2 is a side cross-sectional view showing a schematic arrangement of a first optical fiber unit and a second optical fiber unit; 3 is a diagram showing a schematic view of an end face of a first optical fiber unit and an end face of a second optical fiber unit; FIG. 1A to 1C are diagrams illustrating an example of a manufacturing method for an optical fiber connection structure. 10 is a side view showing a schematic example of a method for inclining an end face of the first optical fiber unit. FIG. 10 is a front view showing a schematic example of a method for inclining an end face of the first optical fiber unit. FIG. 11 is a bottom view showing a schematic example of a method for inclining the end face of the first optical fiber unit. FIG. 5A to 5C are side cross-sectional views each showing a schematic example of a method for manufacturing the first fiber collimator. 11 is a side cross-sectional view showing an example of a method for adjusting the distance between the first optical fiber unit and the first lens; FIG. 10 is a side cross-sectional view that illustrates an example of a method for aligning a first fiber collimator and a second fiber collimator. FIG. 10A to 10C are diagrams illustrating another example of a manufacturing method for an optical fiber connection structure. 13 is a side view showing a schematic diagram of another example of a method for inclining the end face of the first optical fiber unit. FIG. 13 is a front view showing a schematic diagram of another example of a method for inclining the end face of the first optical fiber unit. FIG. 13 is a bottom view showing a schematic diagram of another example of a method for inclining the end face of the first optical fiber unit. FIG. 4A and 4B are diagrams for explaining the core pitch and the diagonal core pitch in the first optical fiber unit. 11A and 11B are diagrams for explaining an angular deviation of the first optical fiber unit around the Z axis. 13 is a graph showing the relationship between the angular deviation around the Z axis and the loss rate for each core pitch. 13 is a graph showing the relationship between the core pitch and the angular deviation around the Z axis for each loss ratio. 11A and 11B are diagrams illustrating another example of the end face of the first optical fiber unit.

The optical fiber connection structure according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings have been exaggerated for the sake of explanation and may differ from the actual ratios.

Furthermore, the following embodiments and their variations include similar components. Therefore, in the following, the same reference numerals are used for those similar components, and duplicate explanations will be omitted.

In the following embodiments and their variations, the central axis direction of the first optical fiber unit and the second optical fiber unit is defined as the Z direction (front-rear direction of the optical fiber connection structure). The vertical direction (Y direction) of the optical fiber connection structure is defined in a state in which the most protruding points of the end faces of the first optical fiber unit and the second optical fiber unit are positioned upward. The direction perpendicular to the Z direction and Y direction is defined as the width direction (X direction) of the optical fiber connection structure.

As shown in FIG. 1, the optical fiber connection structure 1 according to this embodiment includes a first optical fiber unit 2 in which a plurality of first cores 20 are arranged, and a second optical fiber unit 3 in which a plurality of second cores 30 are arranged.

In this embodiment, the first optical fiber unit 2 is exemplified by a multicore fiber in which four first cores 20 are arranged at a distance from one another and are covered with one first cladding 21. In this way, by forming the optical fiber connection structure 1 using a multicore fiber, it is possible to further increase the communication transmission capacity. As a result, it is possible to obtain an optical fiber connection structure 1 that can handle the increase in communication transmission capacity due to the rapid spread of IoT and video distribution via the Internet. Note that multicore fibers are optical fibers that are expected to be used as transmission paths in next-generation backbone systems and data centers.

The first cladding 21 can be formed to be flexible using a material such as glass, and has a cord-like shape that is elongated in the Z direction (front-to-back direction). On the other hand, the first core 20 can be formed to be flexible using a material such as glass, and is disposed inside the first cladding 21 in a state in which it is elongated in the Z direction (front-to-back direction).

Furthermore, in this embodiment, the first cladding 21 and the four first cores 20 are formed so that the cross-sectional shape when cut along a plane perpendicular to the central axis C1 is circular.

The four first cores 20 are arranged at equal intervals on a circle centered on the central axis C1 of the first optical fiber unit 2 (see Figure 3).

In this embodiment, the four first cores 20 are numbered. Specifically, in the state shown in FIG. 3, the first core 20 located at the center and upper part in the X direction (width direction) is designated as first core No. 1 20a. Also, in the state shown in FIG. 3, starting from first core No. 1 20a, the first cores are designated as first core No. 2 20b, first core No. 3 20c, and first core No. 4 20d in a clockwise direction. Note that the above numbers are assigned for convenience and are not prescribed by standardization or the like. Therefore, the numbers assigned to the four first cores 20 can be set randomly.

Furthermore, in this embodiment, the end face 2a on one side in the Z direction (front-rear direction) of the first optical fiber unit 2 is inclined with respect to a plane perpendicular to the central axis C1 of the first optical fiber unit 2. This makes it possible to more reliably reduce Fresnel reflection caused by the difference in refractive index between the glass (first core 20) of the end face 2a of the first optical fiber unit 2 and the air.

The end face 2a inclined relative to the plane perpendicular to the central axis C1 can be formed by polishing the end of the first optical fiber unit 2. In this way, by polishing the end of the first optical fiber unit 2 to form the end face 2a inclined relative to the plane perpendicular to the central axis C1, the end face 2a can be more easily and reliably made into a flat inclined surface. As a result, it becomes possible to more reliably reduce Fresnel reflection caused by the difference in refractive index between the glass (first core 20) of the end face 2a of the first optical fiber unit 2 and the air.

Furthermore, in this embodiment, when the end face 2a of the first optical fiber unit 2 is tilted, the relationship between the tilt direction of the end face 2a and the arrangement direction of the four first cores 20 is made the same.

Specifically, when the inclination direction of the end face 2a is set to the lower side in the vertical direction (Y direction) and to one side in the front-to-rear direction (Z direction), the first core No. 1 20a and the first core No. 3 20c are aligned in the vertical direction (Y direction).

In this embodiment, first core No. 1 20a and first core No. 3 20c are two vertices located on a diagonal line when a square is drawn with the four first cores 20 as vertices. In addition, this diagonal line is a line segment passing through the central axis C1 of the first optical fiber unit 2.

In this manner, in this embodiment, in the reference state of the first optical fiber unit 2, the first core No. 1 20a and the first core No. 3 20c are arranged on the line segment L1 connecting the upper end 2aa and the lower end 2ab of the end face 2a of the first optical fiber unit 2. Here, the reference state of the first optical fiber unit 2 refers to a state in which the first optical fiber unit 2 is arranged so that the central axis C1 is horizontal and the most protruding point of the inclined end face 2a is the upper end 2aa. In addition, the first core No. 1 20a is the first core 20 located at the top of the four first cores 20 in the reference state of the first optical fiber unit 2. And the first core No. 3 20c is the first core 20 located at the bottom of the four first cores 20 in the reference state of the first optical fiber unit 2. At this time, the first core No. 2 20b and the first core No. 4 20d are each located at the center in the vertical direction (Y direction) of the end face 2a in the reference state of the first optical fiber unit 2. In other words, the first core No. 2 20b and the first core No. 4 20d are located on a horizontal line passing through the central axis C1 of the first optical fiber unit 2 in the reference state of the first optical fiber unit 2.

In addition, in this embodiment, as described above, the first cladding 21 is formed so that the cross-sectional shape when cut along a plane perpendicular to the central axis C1 is circular. That is, the end face 2a of the first optical fiber unit 2 has a circular contour shape when viewed along the central axis C1. Therefore, the end face 2a, which is inclined with respect to a plane perpendicular to the central axis C1, has an elliptical shape. The line segment L1 connecting the upper end 2aa and the lower end 2ab coincides with the major axis of the elliptical end face 2a, and the horizontal line passing through the central axis C1 of the first optical fiber unit 2 coincides with the minor axis of the elliptical end face 2a.

In addition, in this embodiment, the second optical fiber unit 3 is exemplified by a bundle of four single mode fibers, each of which has a second core 30 covered by a second cladding 31.

The second cladding 31 can be formed to be flexible using a material such as glass, and has a cord-like shape that is elongated in the Z direction (front-to-back direction). On the other hand, the second core 30 can be formed to be flexible using a material such as glass, and is disposed inside the second cladding 31 in a state in which it is elongated in the Z direction (front-to-back direction).

Furthermore, in this embodiment, the second cladding 31 and the second core 30 are formed so that the cross-sectional shape when cut along a plane perpendicular to the central axis C2 is circular.

The four single mode fibers are bundled together such that the four second cores 30 correspond one-to-one to the four first cores 20. The four single mode fibers are then fixed together in a bundled state using an adhesive or the like to form a second optical fiber unit 3 having four second cores 30.

Furthermore, in this embodiment, the four second cores 30 are also arranged at equal intervals on a circle centered on the central axis C2 of the second optical fiber unit 3 (see Figure 3).

Here, in this embodiment, the four second cores 30 are also numbered. Specifically, in the state shown in FIG. 3, the second core 30 located at the center and upper part in the X direction (width direction) is second core No. 1 30a. Also, in the state shown in FIG. 3, starting from second core No. 1 30a, the second cores 30 are numbered counterclockwise as second core No. 2 30b, second core No. 3 30c, and second core No. 4 30d. Note that the above numbers are also assigned for convenience and are not prescribed by standardization or the like. Therefore, the numbers assigned to the four second cores 30 can also be set randomly. In this case, it is preferable to assign the same numbers as those assigned to the corresponding first cores 20.

Furthermore, in this embodiment, the end face 3a on one side in the Z direction (front-rear direction) of the second optical fiber unit 3 is inclined with respect to a plane perpendicular to the central axis C2 of the second optical fiber unit 3. This makes it possible to more reliably reduce Fresnel reflection caused by the difference in refractive index between the glass (second core 30) of the end face 3a of the second optical fiber unit 3 and the air.

The end face 3a that is inclined with respect to a plane perpendicular to the central axis C2 can also be formed by polishing the end of the second optical fiber unit 3.

Furthermore, in this embodiment, even when the end face 3a of the second optical fiber unit 3 is tilted, the relationship between the tilt direction of the end face 3a and the arrangement direction of the four second cores 30 is made the same.

Specifically, when the inclination direction of the end face 3a is set to the lower side in the vertical direction (Y direction) and to one side in the front-to-rear direction (Z direction), the second core No. 1 30a and the second core No. 3 30c are aligned in the vertical direction (Y direction).

In this embodiment, second core No. 1 30a and second core No. 3 30c are two vertices located on a diagonal line when a square is drawn with the four second cores 30 as vertices. In addition, this diagonal line is a line segment passing through the central axis C2 of the second optical fiber unit 3.

In this manner, in this embodiment, in the reference state of the second optical fiber unit 3, the second core No. 1 30a and the second core No. 3 30c are arranged on the line segment L2 connecting the upper end 3aa and the lower end 3ab of the end face 3a of the second optical fiber unit 3. Here, the reference state of the second optical fiber unit 3 refers to a state in which the second optical fiber unit 3 is arranged so that the central axis C2 is horizontal and the most protruding point of the inclined end face 3a is the upper end 3aa. In addition, the second core No. 1 30a is the second core 30 located at the top of the four second cores 30 in the reference state of the second optical fiber unit 3. And the second core No. 3 30c is the second core 30 located at the bottom of the four second cores 30 in the reference state of the second optical fiber unit 3. At this time, the second core No. 2 30b and the second core No. 4 30d are each disposed at the center in the vertical direction (Y direction) of the end face 3a in the reference state of the second optical fiber unit 3. In other words, the second core No. 2 30b and the second core No. 4 30d are disposed on a horizontal line passing through the central axis C2 of the second optical fiber unit 3 in the reference state of the second optical fiber unit 3.

Then, the first optical fiber unit 2 and the second optical fiber unit 3 configured in this way are optically coupled to form the optical fiber connection structure 1.

To realize an optical communication system using a multicore fiber, a fan-in/fan-out (FIFO) device is required to connect each core of the multicore fiber to the core of an existing single mode fiber. In this embodiment, a connection structure formed when manufacturing a fan-in/fan-out (FIFO) device is illustrated as the optical fiber connection structure 1.

One of the connection methods for optically coupling the first optical fiber unit 2 and the second optical fiber unit 3 is a spatial coupling type connection method using lenses. Another method of the spatial coupling type connection method using lenses is a structure in which two single lenses are used to optically couple the propagation core of a multicore fiber with a bundle of multiple single mode fibers.

In this embodiment, the optical fiber connection structure 1 employs a structure in which two single lenses are used to optically couple the propagation core of a multicore fiber with a bundle of multiple single mode fibers. This makes the coupling tolerance in the X and Y directions (up and down, left and right directions) of the first core 20 and the second core 30 looser than when the end faces of the optical fibers must be butted together in close contact, and stabilizes the coupling loss.

That is, in this embodiment, the optical fiber connection structure 1 includes a first lens 212a optically coupled to the end face 2a of the first optical fiber unit 2, and a second lens 312a optically coupled to the end face 3a of the second optical fiber unit 3. In this embodiment, aspheric lenses are used as the first lens 212a and the second lens 312a.

The first lens 212a and the second lens 312a are optically coupled to each other.

Specifically, the first optical fiber unit 2 is inserted and fixed into the collimator pipe 210 holding the first lens 212a, forming the first fiber collimator 200 in which the end face 2a of the first optical fiber unit 2 and the first lens 212a are optically coupled.

At this time, since the first optical fiber unit 2 is flexible, the first optical fiber unit 2 is inserted into the cylindrical first ferrule 22 made of ceramic or metal and fixed by adhesive, and is then inserted into the collimator pipe 210. In this embodiment, the first ferrule 22 is fixed to the side where the end face 2a of the first optical fiber unit 2 is formed.

Furthermore, in this embodiment, the collimator pipe 210 includes a cylindrical main body 211 into which the first optical fiber unit 2 is inserted, and a lens holding tube 212 that holds the first lens 212a. Then, the lens holding tube 212 holding the first lens 212a is fixed to the cylindrical main body 211 to form the collimator pipe 210 with the first lens 212a.

The first ferrule 22 (first optical fiber unit 2) and the cylindrical main body 211 are fixed together after the first optical fiber unit 2 is manufactured.

Similarly, the second optical fiber unit 3 is inserted and fixed into the collimator pipe 310 holding the second lens 312a, forming a second fiber collimator 300 in which the end face 3a of the second optical fiber unit 3 and the second lens 312a are optically coupled.

At this time, since the second optical fiber unit 3 is also flexible, the second optical fiber unit 3 is inserted into the cylindrical second ferrule 32 made of ceramic or metal and fixed by adhesive, and is then inserted into the collimator pipe 310. In this embodiment, the second ferrule 32 is fixed to the side where the end face 3a of the second optical fiber unit 3 is formed.

Furthermore, in this embodiment, the collimator pipe 310 includes a cylindrical main body 311 into which the second optical fiber unit 3 is inserted, and a lens holding tube 312 that holds the second lens 312a. The first lens 212a and the second lens 312a are optically coupled to each other to form the optical fiber connection structure 1. Note that this embodiment illustrates an optical fiber connection structure 1 in which the first fiber collimator 200 and the second fiber collimator 300 are fixed by a cylindrical adapter 41 and a fixing ring 42.

The first optical fiber unit 2 and the second optical fiber unit 3 are arranged so that the inclination direction of the end face 2a of the first optical fiber unit 2 and the inclination direction of the end face 3a of the second optical fiber unit 3 are opposite to each other. In other words, the inclination direction of the end face 2a is downward in the vertical direction (Y direction) and on one side in the front-to-back direction (Z direction), while the inclination direction of the end face 3a is downward in the vertical direction (Y direction) and on the other side in the front-to-back direction (Z direction).

The first optical fiber unit 2 and the second optical fiber unit 3 are arranged such that the central axis C1 of the first optical fiber unit 2 and the central axis C2 of the second optical fiber unit 3 are aligned (see Figure 2).

Next, an example of a manufacturing method for the optical fiber connection structure 1 according to this embodiment will be described with reference to Figures 4 to 10.

Note that Figures 5 to 7 show an example of a method for polishing the end face 2a of the first optical fiber unit 2, but the end face 3a of the second optical fiber unit 3 can also be polished in a similar manner.

In addition, FIG. 8 shows an example of a method for manufacturing the first fiber collimator 200, but the second fiber collimator 300 can also be manufactured in a similar manner.

Figure 9 shows an example of a method for adjusting the relationship between the first optical fiber unit 2 and the first lens 212a, but the relationship between the second optical fiber unit 3 and the second lens 312a can also be adjusted in a similar manner.

The optical fiber connection structure 1 according to this embodiment can be manufactured through the process shown in FIG.

First, the end 2a of the first optical fiber unit 2 is polished so that the end face 2a of the first optical fiber unit 2 is an inclined surface that is inclined with respect to a plane perpendicular to the central axis C1 of the first optical fiber unit 2 (fiber processing end face polishing process: polishing process).

Specifically, the end of the first optical fiber unit 2 is polished using a polishing jig 50. At this time, since the first optical fiber unit 2 is fibrous and flexible, there is a risk that it may bend while polishing the end, making it impossible to polish the end surface uniformly. Therefore, the side of the first optical fiber unit 2 on which the end surface 2a is formed is adhesively fixed to the first ferrule 22, and the end surface of the first optical fiber unit 2 is polished together with the first ferrule 22.

In this embodiment, the polishing jig 50 includes a main body 51 having a V-shaped groove 51a formed therein in which the first optical fiber unit 2 adhesively fixed to the first ferrule 22 is placed. Furthermore, the polishing jig 50 includes a pressing plate 52 that presses the first optical fiber unit 2 adhesively fixed to the first ferrule 22 so that it does not rotate around the central axis C1 when the first optical fiber unit 2 is placed in the groove 51a.

The V-shaped groove 51a is angled in advance so that when the first optical fiber unit 2 adhesively fixed to the first ferrule 22 is placed in the groove 51a, the angle between the central axis C1 of the first optical fiber unit 2 and the horizontal plane is angle θ. This angle θ can be, for example, 76 degrees to 84 degrees.

Then, after the first optical fiber unit 2 adhesively fixed to the first ferrule 22 is set on the polishing jig 50, the arrangement direction of the four first cores 20 is adjusted to a predetermined direction using a microscope or the like before the end face is polished (core orientation confirmation is performed). This core orientation confirmation method can be performed, for example, by using the crosshairs R of a microscope or the like and the reference planes P1 and P2 of the polishing jig 50 to adjust the arrangement direction of the four first cores 20 to a predetermined direction. In this embodiment, the method shown in FIG. 7 is exemplified. In FIG. 7, the first core No. 1 20a is observed using the crosshairs R of a microscope or the like, and the first optical fiber unit 2 is rotated so that the reference plane P2 extending in the horizontal direction passes through the maximum diameter of the first core No. 1 20a, thereby adjusting the arrangement direction of the four first cores 20.

Next, the first fiber collimator 200 is manufactured using the first optical fiber unit 2 in which the end face 2a is inclined so that the relationship between the inclination direction of the end face 2a and the arrangement direction of the first cores 20 is the same (fiber collimator manufacturing process).

Specifically, first, the first optical fiber unit 2 is inserted into the collimator pipe 210 holding the first lens 212a. Then, with the first optical fiber unit 2 inserted into the collimator pipe 210, the first optical fiber unit 2 is moved relatively in the forward and backward directions (the direction of the arrow A in Figures 8 and 9). In this way, the distance between the first optical fiber unit 2 and the first lens 212a is adjusted so that the focal position is optimized.

In this embodiment, as described above, the end surface 2a is an inclined surface that is inclined with respect to a plane perpendicular to the central axis C1 of the first optical fiber unit 2. Therefore, a difference occurs in the focal distance between each first core 20 and the first lens 212a. Therefore, in this embodiment, the focal distances of all the first cores 20 are averaged. Specifically, as shown in FIG. 9, the light emitted from one first core 20 of the first optical fiber unit 2 is passed through the first lens 212a to form a collimated beam. Then, by placing a total reflection mirror 60 at the position of the beam waist A1 and maximally coupling it to the first core 20 located diagonally, the difference in distance between the two first cores 20 and the first lens 212a can be averaged. Here, in this embodiment, in the reference state of the first optical fiber unit 2, the first core No. 1 20a and the first core No. 3 20c are arranged on the line segment L1 connecting the upper end 2aa and the lower end 2ab of the end surface 2a of the first optical fiber unit 2. Therefore, in this embodiment, the combination of first core #1 20a and first core #3 20c is the combination with the largest core-lens distance difference. Therefore, first core #1 20a is treated as one first core 20, and first core #3 20c is treated as the first core 20 located diagonally, and maximum coupling is performed between these two first cores 20. In this way, all core-lens distances are averaged. At this time, the core-lens distance between first core #2 20b and first core #4 20d is exactly between first core #1 20a and first core #3 20c, which is the average distance.

Then, after adjusting the distance between the first optical fiber unit 2 and the first lens 212a, the first ferrule 22 (first optical fiber unit 2) and the cylindrical main body 211 are fixed. In this way, the first fiber collimator 200 is manufactured. Note that when the fiber collimator is constructed, it is housed inside the lens and the metal pipe, and it is no longer possible to observe the core orientation.

Next, the first fiber collimator 200 and the second fiber collimator 300 are placed opposite each other and optical alignment is performed (collimator opposing system alignment process: alignment process).

As described above, in this embodiment, the relationship between the inclination direction of the end face 2a of the first optical fiber unit 2 and the arrangement direction of the first cores 20 is made the same for each product. Similarly, the relationship between the inclination direction of the end face 3a of the second optical fiber unit 3 and the arrangement direction of the second cores 30 is made the same for each product. In this embodiment, the first optical fiber unit 2 and the second optical fiber unit 3 are arranged so that the inclination direction of the end face 2a of the first optical fiber unit 2 and the inclination direction of the end face 3a of the second optical fiber unit 3 are opposite to each other.

Therefore, the core orientations are roughly aligned by simply visually checking and setting the first fiber collimator 200 and the second fiber collimator 300 so that the inclination directions (polishing orientations) of the end faces 2a and 3a are opposite to each other (core orientation alignment process). In this way, if the core arrangement is roughly aligned first when forming the optical fiber connection structure 1, the alignment work can be performed without spending time on subsequent adjustments. In particular, in this embodiment, since the core arrangement and polishing orientation are known in advance, there is no need to check the core arrangement, which can only be observed with a microscope, so the core arrangement can be aligned easily and quickly. Then, after the core arrangement is roughly aligned, the optical axis is aligned to maximize coupling (the optical axis alignment process is performed), and the core arrangement orientation is finely aligned so that each core has minimum loss (core orientation precision alignment process and X, Y, θx, θy optical axis adjustment process).

In this way, by manufacturing the optical fiber connection structure 1 using the method shown in this embodiment, there is no need to check the core orientation before the fiber collimator manufacturing process or the collimator opposing system alignment process. As a result, it becomes possible to manufacture the optical fiber connection structure 1 (optically connect the first optical fiber unit 2 and the second optical fiber unit 3) with high precision (low loss) and in a short time.

The optical fiber connection structure 1 can also be manufactured using the method shown in Figures 11 to 18.

Below, other examples of the manufacturing method for the optical fiber connection structure 1 will be described with reference to Figures 11 to 18.

Note that Figures 12 to 14 show other examples of methods for polishing the end face 2a of the first optical fiber unit 2, but the end face 3a of the second optical fiber unit 3 can also be polished in a similar manner.

The optical fiber connection structure 1 can be manufactured through the process shown in Figure 11.

First, the end of the first optical fiber unit 2 is polished so that the end face 2a of the first optical fiber unit 2 is an inclined surface that is inclined with respect to a plane perpendicular to the central axis C1 of the first optical fiber unit 2 (fiber processing end face polishing process: polishing process).

This fiber processing end face polishing process is basically performed in the same manner as the method shown in the above embodiment. That is, the end of the first optical fiber unit 2 with the first ferrule 22 attached is polished while the first optical fiber unit 2 is fixed using a polishing jig 50. The configuration of the polishing jig 50 is the same as the polishing jig 50 used in the method shown in the above embodiment.

Here, in the method shown in Figs. 12 to 14, a marking M1 is provided on the rear end of the first ferrule 22, which allows the inclination direction of the end face 2a to be aligned with the core arrangement. By providing such a marking M1 on the first ferrule 22, the polishing orientation can be known at the polishing stage. In this way, even if the polishing orientation of the end face 2a cannot be visually observed from the outside due to the first lens 212a or the collimator pipe 210 when manufacturing the first fiber collimator 200, the marking M1 can be used as a reference in a later process. Note that when performing the marking formation process of providing the marking M1 on the rear end of the first ferrule 22, it is preferable to perform the process with the first optical fiber unit 2 with the first ferrule 22 set on the polishing jig 50. In this way, the marking can be easily and accurately added compared to the case where the first optical fiber unit 2 with the first ferrule 22 is removed from the polishing jig 50 and then the core orientation is observed and then the marking is added.

Next, the first fiber collimator 200 is manufactured using the first optical fiber unit 2 in which the end face 2a is inclined so that the relationship between the inclination direction of the end face 2a and the arrangement direction of the first cores 20 is the same (fiber collimator manufacturing process).

This fiber collimator fabrication process is performed in the same manner as in the embodiment described above. That is, the first optical fiber unit 2 is inserted into the collimator pipe 210 holding the first lens 212a. Then, with the first optical fiber unit 2 inserted into the collimator pipe 210, the first optical fiber unit 2 is moved relatively in the forward and backward directions (the direction of arrow A in Figures 8 and 9). In this way, the distance between the first optical fiber unit 2 and the first lens 212a is adjusted so that the focal position is optimized.

Then, after adjusting the distance between the first optical fiber unit 2 and the first lens 212a, the first ferrule 22 (first optical fiber unit 2) and the cylindrical main body 211 are fixed. In this way, the first fiber collimator 200 is manufactured.

Next, the first fiber collimator 200 and the second fiber collimator 300 are placed opposite each other and optical alignment is performed (collimator opposing system alignment process: alignment process).

At this time, the core arrangement is roughly aligned using the marking M1 made in the previous process as a reference. This makes it possible to align the core orientation during subsequent adjustments without spending a lot of time.

For example, if the first fiber collimator 200 and the second fiber collimator 300 are positioned so that the marking M1 is located on the upper side, the inclination directions (polishing orientations) of the end faces 2a, 3a can be made to be opposite. In this way, even with the method shown in Figures 11 to 18, the core orientations can be roughly aligned simply by visually checking and setting the first fiber collimator 200 and the second fiber collimator 300.

Furthermore, in the method shown in Figures 11 to 18, the relationship between the angle deviation θz around the central axis C1 (around the Z-axis) and the amount of loss (loss increase) is calculated before manufacturing, thereby clarifying the angle deviation θz and the amount of loss relative to the core pitch d1 (diagonal core pitch d2).

As shown in FIG. 15, the core pitch d1 is the distance between two adjacent cores in the circumferential direction, and the diagonal core pitch d2 is the distance between two cores facing each other across the central axis C1, as shown in FIG. 15. The angular deviation θz represents the amount of rotation around the central axis C1 (around the Z-axis) relative to the reference state (see FIG. 16).

Figure 17 shows the results of calculating the coupling efficiency at an angle pitch of 0.07 degrees when the spot size radius is 5.5 μm and the wavelength λ is 1550 nm. Figure 18 shows an example of the relationship between the loss amount and the angle deviation θz.

From the graph in Figure 17, for example, in the case of a core pitch of 40 μm (diagonal core pitch of 56.6 μm), it is possible to keep the loss (increase) within 0.2 dB by setting the deviation between the polishing orientation and the core orientation to 3 degrees or less. In other words, it is possible to keep the loss (increase) within 0.2 dB by setting the relative angle deviation between the cores to ±1.5 degrees or less.

This process can be adapted to other core pitches, and makes it possible to specify the angle deviation range based on the results of pre-calculation. Furthermore, by using the results of Figure 17, the relationship between the core pitch and angle deviation for a desired amount of loss can be obtained as shown in Figure 18, making it possible to specify the core pitch d1 and angle deviation θz for the desired amount of loss. As a result, it becomes possible to manufacture FIFO devices more simply and in a shorter time according to the required amount of loss (specifications) of the FIFO device.

In this way, by using the method shown in Figures 11 to 18, for example, it is possible to form an optical fiber connection structure 1 with a loss increase of less than 0.2 dB without requiring precise alignment work.

In addition, the manufacturing time can be shortened according to the amount of loss (specifications) required for the FIFO device. In other words, it becomes possible to form the optical fiber connection structure 1 in an appropriate manufacturing time according to the required performance.

As described above, by manufacturing the optical fiber connection structure 1 using the method shown in Figures 11 to 18, it is possible to omit the core orientation precision alignment process performed in the method shown in the above embodiment. As a result, it becomes possible to manufacture the optical fiber connection structure 1 (optically connect the first optical fiber unit 2 and the second optical fiber unit 3) with high precision (low loss) and in a short time.

As shown in FIG. 19, the first optical fiber unit 2 can also be a multi-core fiber in which seven first cores 20 are spaced apart from one another and covered with one first clad 21. In FIG. 19, the first clad 21 and the seven first cores 20 are also formed so that the cross-sectional shape cut along a plane perpendicular to the central axis C1 is circular.

The seven first cores 20 are arranged such that one first core 20 is located in the center, and the other six first cores 20 are arranged at equal intervals on a circumference centered on the central axis C1 of the first optical fiber unit 2.

Here, in FIG. 19, seven first cores 20 are numbered. Specifically, in the state shown in FIG. 19, the first core 20 located at the center and upper part in the X direction (width direction) is designated as first core No. 1 20a. In addition, in the state shown in FIG. 19, the first core 20 arranged to include the central axis C1 of the first optical fiber unit 2 is designated as first core No. 2 20b, and the first core 20 located at the center and lower part in the X direction (width direction) is designated as first core No. 3 20c. Then, in the state shown in FIG. 19, the remaining four first cores 20 are designated as first core No. 4 20d, first core No. 5 20e, first core No. 6 20f, and first core No. 7 20g, respectively, in a counterclockwise direction starting from first core No. 1 20a. Note that the above numbers are assigned to the topmost and bottommost first cores 20 in accordance with the above embodiment, but the numbers are not limited to this and the seven first cores 20 can be assigned randomly.

When the end face 2a of the first optical fiber unit 2 shown in FIG. 19 is made an inclined face, the end face 2a is inclined so that the first core No. 1 20a, the first core No. 2 20b, and the first core No. 3 20c are positioned on the line segment L1 in the reference state of the first optical fiber unit 2.

In the case of the first optical fiber unit 2 shown in FIG. 19, the second optical fiber unit 3 is a bundle of seven single mode fibers, each of which has one second core 30 covered by one second cladding 31. Specifically, one single mode fiber is placed in the center, and six single mode fibers are bundled around it at equal intervals. In this way, the seven second cores 30 of the seven single mode fibers correspond one-to-one to each of the seven first cores 20.

Then, the first optical fiber unit 2 and the second optical fiber unit 3 having such a configuration are optically coupled to form the optical fiber connection structure 1.

[Action and Effects]
The following describes the characteristic configurations of the optical fiber connection structure and the manufacturing method of the optical fiber connection structure shown in the above embodiment and its modified example, and the effects obtained thereby.

The optical fiber connection structure 1 shown in the above embodiment and its modified example includes a first optical fiber unit 2 in which a plurality of first cores 20 are arranged, and a second optical fiber unit 3 in which a plurality of second cores 30 are arranged to correspond to each of the plurality of first cores 20.

In addition, the end face 2a of the first optical fiber unit 2 is inclined with respect to a plane perpendicular to the central axis C1 of the first optical fiber unit 2, and the end face 3a of the second optical fiber unit 3 is inclined with respect to a plane perpendicular to the central axis C2 of the second optical fiber unit 3.

The first optical fiber unit 2 and the second optical fiber unit 3 are arranged so that the inclination direction of the end face 2a of the first optical fiber unit 2 and the inclination direction of the end face 3a of the second optical fiber unit 3 are opposite to each other.

Here, the state in which the first optical fiber unit 2 is arranged so that the central axis C1 is horizontal and the most protruding point of the inclined end face 2a is the upper end 2aa is defined as the reference state of the first optical fiber unit 2. Also, the state in which the second optical fiber unit 3 is arranged so that the central axis C2 is horizontal and the most protruding point of the inclined end face 3a is the upper end 3aa is defined as the reference state of the second optical fiber unit 3.

In the reference state of the first optical fiber unit 2, the uppermost core 20a and the lowermost core 20c among the multiple first cores 20 are arranged on the line segment L1 connecting the upper end 2aa and the lower end 2ab of the end face 2a of the first optical fiber unit 2.

Furthermore, in the reference state of the second optical fiber unit 3, the uppermost core 30a and the lowermost core 30c among the multiple second cores 30 are arranged on the line segment L2 connecting the upper end 3aa and the lower end 3ab of the end face 3a of the second optical fiber unit 3.

The manufacturing method of the optical fiber connection structure 1 shown in the above embodiment and its modified example includes a polishing process for polishing the end faces 2a, 3a of the first and second optical fiber units 2, 3. This polishing process polishes the end faces 2a, 3a of the first and second optical fiber units 2, 3 so that they are inclined with respect to a plane perpendicular to the central axes C1, C2 of the optical fiber units 2, 3.

The manufacturing method of the optical fiber connection structure 1 also includes an alignment process in which the end face 2a of the first optical fiber unit 2 and the end face 3a of the second optical fiber unit 3 are opposed to each other to perform optical alignment.

The polishing process includes a first core orientation adjustment process for adjusting the arrangement of the multiple first cores 20 so that the relationship between the tilt direction of the end face 2a of the first optical fiber unit 2 and the arrangement direction of the multiple first cores 20 is the same. It also includes a second core orientation adjustment process for adjusting the arrangement of the multiple second cores 30 so that the relationship between the tilt direction of the end face 3a of the second optical fiber unit 3 and the arrangement direction of the multiple second cores 30 is the same.

Furthermore, after the first core orientation adjustment process, a first polishing process is performed to polish the end face 2a of the first optical fiber unit 2. In this first polishing process, the uppermost core 20a and the lowermost core 20c of the multiple first cores 20 are polished to be positioned on the line segment L1 connecting the upper end 2aa and the lower end 2ab of the end face 2a of the first optical fiber unit 2 in the above-mentioned reference state.

Then, after the second core orientation adjustment process, there is a second polishing process in which the end face 3a of the second optical fiber unit 3 is polished. In this second polishing process, in the above-mentioned reference state, the uppermost core 30a and the lowermost core 30c among the multiple second cores 30 are polished so that they are positioned on the line segment L2 connecting the upper end 3aa and the lower end 3ab of the end face 3a of the second optical fiber unit 3.

The alignment process further includes a core orientation alignment process in which the orientation of the first core 20 and the second core 30 are aligned by arranging the end face 2a of the first optical fiber unit 2 and the end face 3a of the second optical fiber unit 3 so that their inclination directions are opposite to each other.

The alignment process includes an optical axis alignment process for aligning the optical axis after the core orientation alignment process.

With such an optical fiber connection structure 1 and a manufacturing method for an optical fiber connection structure, the end face 2a of the first optical fiber unit 2 and the end face 3a of the second optical fiber unit 3 can be inclined while the arrangement direction of the first core 20 and the second core 30 is specified. Therefore, it is possible to make the relationship between the inclination direction of the end faces 2a, 3a and the arrangement direction of the first core 20 and the second core 30 the same.

As a result, when optically coupling the first optical fiber unit 2 and the second optical fiber unit 3 (when manufacturing and assembling the optical fiber connection structure 1), the manufacturing process can be simplified, and the manufacturing time can be further shortened. Furthermore, when connecting the first optical fiber unit 2 and the second optical fiber unit 3 (performing the alignment work), the error and variation in the insertion loss of the first core 20 and the second core 30 can be reduced, and the time for the alignment work can be further shortened.

By making the relationship between the inclination direction of the end faces 2a, 3a and the arrangement direction of the first core 20 and the second core 30 the same, it becomes possible to suppress variation in the coupling loss in the first core 20 and the second core 30.

In this way, by using the configurations shown in the above embodiment and its modified examples, it is possible to obtain an optical fiber connection structure 1 and a method for manufacturing an optical fiber connection structure that can perform optical connections with high precision (low loss) and in a short time.

The first optical fiber unit 2 and the second optical fiber unit 3 may also be arranged such that the central axis C1 of the first optical fiber unit 2 and the central axis C2 of the second optical fiber unit 3 are aligned.

The multiple first cores 20 may be arranged at equal intervals on a circle centered on the central axis C1 of the first optical fiber unit 2. The multiple second cores 30 may be arranged at equal intervals on a circle centered on the central axis C2 of the second optical fiber unit 3.

In this way, even if the two first cores 20 and second cores 30 that face each other across the central axes C1 and C2 are arbitrarily selected, the arrangement state of the first cores 20 and second cores 30 at the end faces 2a and 3a can be made substantially the same. Therefore, when the first optical fiber unit 2 and the second optical fiber unit 3 are optically coupled, it is possible to more reliably suppress the variation in the positions of the corresponding first cores 20 and second cores 30 at the end faces 2a and 3a. As a result, it is possible to further reduce the coupling loss in the first cores 20 and second cores 30.

A first ferrule 22 that suppresses bending of the first optical fiber unit 2 may be fixed to the side where the end face 2a of the first optical fiber unit 2 is formed. Furthermore, a second ferrule 32 that suppresses bending of the second optical fiber unit 3 may be fixed to the side where the end face 3a of the second optical fiber unit 3 is formed. And, the first ferrule 22 and the second ferrule 32 may be formed with markings M1 that can align the inclination direction of the respective end faces 2a, 3a with the core arrangement.

The polishing process may also include a marking formation process. In this marking formation process, a marking M1 that can align the inclination direction of the end face 2a of the first optical fiber unit 2 with the core arrangement of the first cores 20 is formed on the first ferrule 22 to which the first optical fiber unit 2 is fixed. Furthermore, a marking M1 that can align the inclination direction of the end face 3a of the second optical fiber unit 3 with the core arrangement of the second cores 30 is formed on the second ferrule 32 to which the second optical fiber unit 3 is fixed.

In this way, even if the polishing orientation of the end faces 2a, 3a cannot be visually observed from the outside, the marking M1 can be used as a reference in subsequent processes. In other words, the core arrangement can be roughly aligned using the marking M1 as a reference. In this way, it becomes possible to perform the core orientation alignment work without spending a lot of time during subsequent adjustments.

In addition, in the core orientation alignment process, the orientations of the first core 20 and the second core 30 may be aligned based on the relationship between the amount of loss and the angle deviation θz around the central axis C1 that is calculated in advance.

In this way, it becomes possible to determine the allowable range of angle deviation based on the results of prior calculations, and it becomes possible to manufacture the optical fiber connection structure 1 more simply and in a shorter time according to the required amount of loss (specifications).

[others]
Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

For example, it is possible to combine the configurations and methods shown in the above embodiments and their variations as appropriate.

In addition, in the above embodiment and its modified examples, four and seven first cores 20 and second cores 30 are exemplified, but the number of first cores 20 and second cores 30 may be two or more, and is not limited to four or seven. In this case, it is preferable that at least two cores are arranged on a line segment passing through the central axis of the optical fiber unit.

In addition, in the above embodiment and its modified example, a spatial coupling type connection method using a lens is exemplified as the optical fiber connection structure 1, but this is not limited to this.

In the above embodiment and its modified example, a multicore fiber is exemplified as the first optical fiber unit 2, and a bundle of single mode fibers is exemplified as the second optical fiber unit 3, but this is not limited to this. For example, the present invention can be applied to optical coupling between multicore fibers, or to optical coupling between bundles of single mode fibers. It is also possible for either the first optical fiber unit 2 or the second optical fiber unit 3 to be a multicore fiber, and for the other to be a bundle of multicore fibers or single mode fibers. It is also possible for both the first optical fiber unit 2 and the second optical fiber unit 3 to be multimode fibers.

In addition, the collimator pipe, adapter, and other detailed specifications (shape, size, layout, etc.) can also be changed as appropriate.

REFERENCE SIGNS LIST 1 Optical fiber connection structure 2 First optical fiber unit 20 First core 2a End face 2aa Upper end 2ab Lower end 22 First ferrule L1 Line segment C1 Central axis M1 Marking 3 Second optical fiber unit 30 Second core 3a End face 3aa Upper end 3ab Lower end 32 Second ferrule L2 Line segment C2 Central axis

Claims (3)

A method for manufacturing an optical fiber connection structure, in which a first optical fiber unit in which a plurality of first cores are arranged and a second optical fiber unit in which a plurality of second cores are arranged to correspond to the plurality of first cores, are optically connected to each other, comprising:
a polishing step of polishing the end faces of the first optical fiber unit and the second optical fiber unit so that the end faces of the first optical fiber unit and the second optical fiber unit are inclined with respect to a plane perpendicular to a central axis of each optical fiber unit;
a first fiber collimator fabrication step of forming a first fiber collimator by inserting the first optical fiber unit into a collimator pipe holding a first lens;
a second fiber collimator fabrication step of forming a second fiber collimator by inserting the second optical fiber unit into a collimator pipe holding a second lens;
an alignment step of optically aligning an end face of the first optical fiber unit and an end face of the second optical fiber unit by opposing each other;
Equipped with
The polishing step includes:
a first core orientation adjustment step of adjusting an arrangement of the plurality of first cores so that a relationship between an inclination direction of the end face of the first optical fiber unit and an arrangement direction of the plurality of first cores is the same;
a second core orientation adjustment step of adjusting the arrangement of the plurality of second cores so that a relationship between a tilt direction of the end face of the second optical fiber unit and a direction in which the plurality of second cores are arranged is the same;
a first polishing step of polishing the end face of the first optical fiber unit after the first core orientation adjustment step, in a state in which the central axis of the first optical fiber unit is horizontal and the most protruding point of the inclined end face is arranged to be the upper end, so that the uppermost core and the lowermost core of the plurality of first cores are arranged on a line segment connecting the upper end and the lower end of the end face of the first optical fiber unit;
a second polishing step of polishing the end face of the second optical fiber unit after the second core orientation adjustment step, in a state in which the central axis of the second optical fiber unit is horizontal and the most protruding point of the inclined end face is arranged to be the upper end, so that the uppermost core and the lowermost core of the plurality of second cores are arranged on a line segment connecting the upper end and the lower end of the end face of the second optical fiber unit;
having
The aligning step includes:
a core orientation centering step of centering the orientations of the first core and the second core by arranging the first optical fiber unit and the second optical fiber unit so that the inclination direction of the end face of the first optical fiber unit and the inclination direction of the end face of the second optical fiber unit are symmetrical with respect to a plane perpendicular to a central axis of the first optical fiber unit and a central axis of the second optical fiber unit;
an optical axis aligning step of aligning an optical axis after the core orientation aligning step is performed;
having
In the first fiber collimator fabrication step, a total reflection mirror is disposed at a beam waist position to perform maximum coupling between the uppermost core and the lowermost core among the plurality of first cores;
In the second fiber collimator fabrication step, a total reflection mirror is disposed at a position of a beam waist to perform maximum coupling between the uppermost core and the lowermost core among the plurality of second cores.
A method for manufacturing an optical fiber connection structure. the polishing step includes a marking forming step of forming a marking on a first ferrule to which the first optical fiber unit is fixed, the marking enabling the alignment of a tilt direction of an end face of the first optical fiber unit with a core arrangement of the first cores, and forming a marking on a second ferrule to which the second optical fiber unit is fixed, the marking enabling the alignment of a tilt direction of an end face of the second optical fiber unit with a core arrangement of the second cores,
In the core orientation aligning step, orientations of the first core and the second core are aligned based on markings formed on the first ferrule and the second ferrule.
A method for manufacturing the optical fiber connection structure according to claim 1. In the core orientation aligning step, orientations of the first core and the second core are aligned based on a relationship between an amount of loss and an amount of angular deviation about a central axis that is calculated in advance.
A method for manufacturing the optical fiber connection structure according to claim 1 or 2.

Images