Method for manufacturing an optical fiber connection structure

Abstract

To provide an optical fiber connection structure that can suppress variance in coupling loss due to tilting of a fiber end, and a method of manufacturing the optical fiber connection structure that can facilitate an optical axis adjusting process for a core direction by suppressing variance in coupling loss between cores and aligning a fiber end polishing direction.SOLUTION: A state in which optical fiber units 2, 3 are so arranged that most projecting points of inclined end faces 2a, 3a are upper ends 2aa, 3aa with center axes C1, C2 held horizontally is defined as a reference state. In the reference state of the optical fiber units 2, 3, cores 20a, 30a located at uppermost parts and cores 20c, 30c located at lowermost parts among a plurality of cores 20, 30 are arranged on segments L1, L2 connecting upper ends 2aa, 3aa and lower ends 2ab, 3ab of the end faces 2a, 3a of the optical fiber units 2, 3.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention , light relates to a method for manufacturing a fiber connection structure.

Background Art

[0002] As a conventional optical fiber connection structure of this kind, the one disclosed in Patent Document 1 has been proposed. In this Patent Document 1, the optical fiber connection structure includes a multi-core fiber and a fiber bundle in which a plurality of single-core fibers are joined to each other by an adhesive, and the multi-core fiber and the fiber bundle are optically coupled.

[0003] Here, the plurality of cores respectively arranged in the multi-core fiber and the fiber bundle are generally formed using glass. Therefore, in Patent Document 1, in order to reduce Fresnel reflection generated by the refractive index difference between the glass and air at the end faces of the multi-core fiber and the fiber bundle, the end faces of the multi-core fiber and the fiber bundle are inclined with respect to a plane orthogonal to the central axis.

[0004] And the multi-core fiber and the fiber bundle are arranged in a state where the inclination directions of their end faces are opposite to each other (a state where the inclination directions are different).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the prior art, the arrangement state of a plurality of cores at each end face of the multi-core fiber and the fiber bundle is unknown. That is, in the prior art, the orientation of the core array on the end face inclined with respect to the plane orthogonal to the central axis is not strictly defined.

[0007] Therefore, depending on the combination of the orientation of the inclined end face and the orientation of the core array, there is a possibility that variations will occur in the amount of focus deviation. And when variations due to focus deviation occur, variations in coupling loss will occur. Therefore, it is desirable to fabricate the core orientation and the inclination orientation to be constant.

[0008] The present invention has been made in view of such problems of the prior art. And the object of the present invention is , hu to provide a method for manufacturing an optical fiber connection structure capable of suppressing variations in coupling loss due to oblique polishing of the fiber end and simplifying the adjustment process of optically coupling the cores to each other.

Means for Solving the Problems

[0009] The optical fiber connection structure according to an aspect of the present invention includes 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 so as 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 orthogonal to the central axis of the first optical fiber unit, and the end face of the second optical fiber unit is inclined with respect to a plane orthogonal to the central axis of the second optical fiber unit. 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. With the first optical fiber unit arranged such that its central axis is horizontal and the most protruding point of the inclined end face is the upper end, the core located at the uppermost part and the core located at the lowermost part among 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. With the second optical fiber unit arranged such that its central axis is horizontal and the most protruding point of the inclined end face is the upper end, the core located at the uppermost part and the core located at the lowermost part among 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.

[0010] 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 and a second optical fiber unit in which a plurality of second cores are arranged so as to correspond to each of the plurality of first cores are optically connected. The method for manufacturing an optical fiber connection structure includes a polishing step of polishing 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 planes orthogonal to the central axes of the respective optical fiber units, and an alignment step of optically aligning the end face of the first optical fiber unit and the end face of the second optical fiber unit while facing each other. The polishing step includes a first core orientation adjustment step of adjusting the arrangement of the plurality of first cores so that the relationship between the inclination direction of the end face of the first optical fiber unit and the arrangement direction of the plurality of first cores is the same, and a second core orientation adjustment step of adjusting the arrangement of the plurality of second cores so that the relationship between the inclination direction of the end face of the second optical fiber unit and the arrangement direction of the plurality of second cores is the same. After performing the first core orientation adjustment step, with the central axis of the first optical fiber unit being horizontal and the most protruding point of the inclined end face being the upper end, the core located at the uppermost part and the core located at the lowermost part among 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, and a first polishing step of polishing the end face of the first optical fiber unit. After performing the second core orientation adjustment step, with the central axis of the second optical fiber unit being horizontal and the most protruding point of the inclined end face being the upper end, the core located at the uppermost part and the core located at the lowermost part among 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, and a second polishing step of polishing the end face of the second optical fiber unit. The alignment step includes a core orientation alignment step of aligning the orientations of the first core and the second core by arranging 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 to be opposite to each other, and an optical axis alignment step of aligning the optical axis after performing the core orientation alignment step.

Advantages of the Invention

[0011] According to the present invention , each it is possible to provide a method for manufacturing an optical fiber connection structure that can suppress variations in coupling loss between cores and simplify the optical axis adjustment process of the core orientation by aligning the fiber end polishing orientations.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, the optical fiber connection structure according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0014] In addition, the following embodiments and their modifications include similar components. Therefore, hereinafter, the same reference numerals will be given to those similar components, and redundant explanations will be omitted.

[0015] In the following embodiments and their modifications, the central axis direction of the first optical fiber unit and the second optical fiber unit is defined as the Z direction (the front-back direction of the optical fiber connection structure) for description. Further, in a state where the most protruding points of the end faces of the first optical fiber unit and the second optical fiber unit are arranged upward, the vertical direction (Y direction) of the optical fiber connection structure is defined for description. Then, the direction orthogonal to the Z direction and the Y direction is defined as the width direction (X direction) of the optical fiber connection structure for description.

[0016] As shown in FIG. 1, the optical fiber connection structure 1 according to the present 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.

[0017] In the present embodiment, as the first optical fiber unit 2, a multi-core fiber in which four first cores 20 are arranged apart from each other and covered with one first cladding 21 is exemplified. In this way, if the optical fiber connection structure 1 is formed using a multi-core fiber, the communication transmission capacity can be further increased. As a result, an optical fiber connection structure 1 capable of coping with the increase in communication transmission capacity due to the rapid spread of IoT and video distribution via the Internet can be obtained. Note that the multi-core fiber is an optical fiber expected to be used as a transmission path in next-generation backbone systems and data centers.

[0018] The first cladding 21 can be formed to have flexibility using a material such as glass, and has an elongated cord shape in the Z direction (front-back direction). On the other hand, the first core 20 can be formed to have flexibility using a material such as glass, and is arranged inside the first cladding 21 in a state of being elongated in the Z direction (front-back direction).

[0019] Furthermore, in the present embodiment, the first cladding 21 and the four first cores 20 are formed such that the cross-sectional shape obtained by cutting in a plane orthogonal to the central axis C1 is circular.

[0020] The four first cores 20 are arranged at equal intervals on the circumference centered on the central axis C1 of the first optical fiber unit 2 (see FIG. 3).

[0021] Here, in the present 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 above in the X direction (width direction) is defined as the first core No. 1 20a. Also, in the state shown in FIG. 3, starting from the first core No. 1 20a and clockwise, they are respectively defined as the first core No. 2 20b, the first core No. 3 20c, and the first core No. 4 20d. Note that the above numbers are assigned for convenience and are not defined by standardization or the like. Therefore, the numbers assigned to the four first cores 20 can be set randomly.

[0022] Furthermore, in the present embodiment, one 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 the plane orthogonal to the central axis C1 of the first optical fiber unit 2. By doing so, it is possible to more reliably reduce the Fresnel reflection generated by the refractive index difference between the glass (first core 20) and air at the end face 2a of the first optical fiber unit 2.

[0023] The end face 2a inclined with respect to the plane orthogonal 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 with respect to the plane orthogonal to the central axis C1, it is possible to more easily and reliably make the end face 2a a flat inclined plane. As a result, it is possible to more reliably reduce the Fresnel reflection generated by the refractive index difference between the glass (first core 20) and air at the end face 2a of the first optical fiber unit 2.

[0024] Furthermore, in the present embodiment, when the end face 2a of the first optical fiber unit 2 is inclined, the relationship between the inclination direction of the end face 2a and the arrangement direction of the four first cores 20 is made the same.

[0025] Specifically, when the inclination direction of the end face 2a is the lower side in the vertical direction (Y direction) and one side in the front-rear direction (Z direction), the first core No. 1 20a and the first core No. 3 20c are arranged side by side in the vertical direction (Y direction).

[0026] In the present embodiment, the first core No. 1 20a and the first core No. 3 20c are two vertices located on the diagonal line when a square is drawn with the four first cores 20 as vertices. Further, this diagonal line is a line segment passing through the central axis C1 of the first optical fiber unit 2.

[0027] Thus, in the present 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 a 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 means a state in which the first optical fiber unit 2 is arranged such that the central axis C1 is horizontal and the most protruding point of the inclined end face 2a is the upper end 2aa. Also, the first core No. 1 20a is the first core 20 located at the uppermost part among 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 lowermost part among 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 respectively arranged at the central part in the vertical direction (Y direction) of the end face 2a in the reference state of the first optical fiber unit 2. That is, the first core No. 2 20b and the first core No. 4 20d are arranged 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.

[0028] In addition, in the present embodiment, as described above, the first cladding 21 is formed such that the cross-sectional shape obtained by cutting in a plane orthogonal 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 that is inclined with respect to the plane orthogonal to the central axis C1 has an elliptical shape. And 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.

[0029] In addition, in the present embodiment, as an example of the second optical fiber unit 3, four single-mode fibers each having one second core 30 covered by one second cladding 31 are bundled.

[0030] The second cladding 31 can be formed to have flexibility using a material such as glass, and has an elongated cord shape in the Z direction (front-rear direction). On the other hand, the second core 30 can be formed to have flexibility using a material such as glass, and is arranged inside the second cladding 31 in a state of being elongated in the Z direction (front-rear direction).

[0031] Furthermore, in the present embodiment, the second cladding 31 and the second core 30 are formed such that the cross-sectional shape obtained by cutting in a plane orthogonal to the central axis C2 is circular.

[0032] And the four single-mode fibers are bundled in a state where the four second cores 30 correspond one-to-one to each of the four first cores 20. And by fixing the four single-mode fibers in a bundled state with an adhesive or the like, the second optical fiber unit 3 having four second cores 30 is formed.

[0033] Furthermore, in the present embodiment, the four second cores 30 are also arranged at equal intervals on the circumference centered on the central axis C2 of the second optical fiber unit 3 (see FIG. 3).

[0034] Here, in the present 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 above in the X direction (width direction) is defined as the second core No. 1 30a. Further, in the state shown in FIG. 3, starting from the second core No. 1 30a and in the counterclockwise direction, they are respectively defined as the second core No. 2 30b, the second core No. 3 30c, and the second core No. 4 30d. Note that the above numbers are also assigned for convenience and are not defined by standardization or the like. Therefore, the numbers assigned to the four second cores 30 can also be set randomly. At this time, it is preferable to assign the same number as the number assigned to the corresponding first core 20.

[0035] Furthermore, in the present embodiment, one 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 the plane orthogonal to the central axis C2 of the second optical fiber unit 3. By doing so, it is possible to more reliably reduce the Fresnel reflection generated by the refractive index difference between the glass (second core 30) and air on the end face 3a of the second optical fiber unit 3.

[0036] Note that the end face 3a inclined with respect to the plane orthogonal to the central axis C2 can also be formed by polishing the end of the second optical fiber unit 3.

[0037] Furthermore, in the present embodiment, when the end face 3a of the second optical fiber unit 3 is inclined, the relationship between the inclination direction of the end face 3a and the arrangement direction of the four second cores 30 is made the same.

[0038] Specifically, when the inclination direction of the end face 3a is the lower side in the vertical direction (Y direction) and one side in the front-rear direction (Z direction), the second core No. 1 30a and the second core No. 3 30c are arranged in the vertical direction (Y direction).

[0039] In this embodiment, the second core No. 1 30a and the second core No. 3 30c are two vertices located on the diagonal when a square is drawn with the four second cores 30 as vertices. Further, this diagonal is a line segment passing through the central axis C2 of the second optical fiber unit 3.

[0040] As described above, 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 means a state in which the second optical fiber unit 3 is arranged such that the central axis C2 is horizontal and the most protruding point of the inclined end face 3a is the upper end 3aa. Also, the second core No. 1 30a is the second core 30 located at the uppermost position among 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 lowermost position among 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 respectively arranged at the central portions in the vertical direction (Y direction) of the end face 3a in the reference state of the second optical fiber unit 3. That is, the second core No. 2 30b and the second core No. 4 30d are arranged on the 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.

[0041] Then, by optically coupling the first optical fiber unit 2 and the second optical fiber unit 3 configured as described above, the optical fiber connection structure 1 is formed.

[0042] In addition, in order to realize an optical communication system using a multi-core fiber, a fan-in / fan-out (FIFO) device is required to connect each core of the multi-core fiber to the core of an existing single-mode fiber. In this embodiment, as the optical fiber connection structure 1, an example of a connection structure formed when manufacturing a fan-in / fan-out (FIFO) device is illustrated.

[0043] By the way, as one of the connection methods for optically coupling the first optical fiber unit 2 and the second optical fiber unit 3, there is a spatial coupling type connection method using a lens. Further, as one means of the spatial coupling type connection method using a lens, there is a structure in which two single lenses are used to optically couple the propagation core of a multi-core fiber and a bundle of a plurality of single-mode fibers.

[0044] In this embodiment, as the optical fiber connection structure 1, a structure is adopted in which two single lenses are used to optically couple the propagation core of a multi-core fiber and a bundle of a plurality of single-mode fibers. By doing so, the coupling tolerance in the X and Y directions (vertical and horizontal directions) in the first core 20 and the second core 30 becomes looser than in the case of a configuration where the end faces of the optical fibers need to be butted and adhered to each other, and the coupling loss is stabilized.

[0045] 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, aspherical lenses are used as the first lens 212a and the second lens 312a.

[0046] And the first lens 212a and the second lens 312a are optically coupled to each other.

[0047] Specifically, by inserting and fixing the first optical fiber unit 2 into the collimator pipe 210 holding the first lens 212a, a first fiber collimator 200 is formed in which the end face 2a of the first optical fiber unit 2 and the first lens 212a are optically coupled.

[0048] At this time, since the first optical fiber unit 2 has flexibility, the first optical fiber unit 2 is inserted into the collimator pipe 210 in a state of being inserted into and adhesively fixed to a cylindrical first ferrule 22 formed of ceramic or metal. 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.

[0049] Furthermore, in this embodiment, the collimator pipe 210 includes a cylindrical main body portion 211 into which the first optical fiber unit 2 is inserted and a lens holding cylinder 212 that holds the first lens 212a. Then, by fixing the lens holding cylinder 212 holding the first lens 212a and the cylindrical main body portion 211, the collimator pipe 210 with the first lens 212a is formed.

[0050] Note that the first ferrule 22 (first optical fiber unit 2) and the cylindrical main body portion 211 are fixed after the production of the first optical fiber unit 2.

[0051] Similarly, by inserting and fixing the second optical fiber unit 3 into the collimator pipe 310 holding the second lens 312a, a second fiber collimator 300 is formed in which the end face 3a of the second optical fiber unit 3 and the second lens 312a are optically coupled.

[0052] At this time, since the second optical fiber unit 3 also has flexibility, the second optical fiber unit 3 is inserted into the collimator pipe 310 in a state of being inserted into and adhesively fixed to a cylindrical second ferrule 32 formed of ceramic or metal. 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.

[0053] Furthermore, in the present embodiment, the collimator pipe 310 includes a cylindrical main body portion 311 into which the second optical fiber unit 3 is inserted, and a lens holding cylinder 312 that holds the second lens 312a. By optically coupling the first lens 212a and the second lens 312a to each other, the optical fiber connection structure 1 is formed. In the present embodiment, 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 is illustrated.

[0054] The first optical fiber unit 2 and the second optical fiber unit 3 are arranged such 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. That is, while the inclination direction of the end face 2a is the lower side in the vertical direction (Y direction) and one side in the front-rear direction (Z direction), the inclination direction of the end face 3a is the lower side in the vertical direction (Y direction) and the other side in the front-rear direction (Z direction).

[0055] Also, the first optical fiber unit 2 and the second optical fiber unit 3 are arranged in a state where 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 FIG. 2).

[0056] Next, an example of a manufacturing method of the optical fiber connection structure 1 according to the present embodiment will be described with reference to FIGS. 4 to 10.

[0057] Although FIGS. 5 to 7 show an example of a polishing method for the end face 2a of the first optical fiber unit 2, the end face 3a of the second optical fiber unit 3 can also be polished in the same manner.

[0058] Also, FIG. 8 shows an example of a manufacturing method of the first fiber collimator 200, but the second fiber collimator 300 can also be manufactured in the same manner.

[0059] FIG. 9 shows an example of an adjustment method between the first optical fiber unit 2 and the first lens 212a. The adjustment between the second optical fiber unit 3 and the second lens 312a can be performed in the same manner.

[0060] The optical fiber connection structure 1 according to this embodiment can be manufactured through the steps shown in FIG. 4.

[0061] First, the end portion 2a of the first optical fiber unit 2 is polished so that the end face 2a of the first optical fiber unit 2 becomes an inclined surface inclined with respect to the plane orthogonal to the central axis C1 of the first optical fiber unit 2 (fiber processing end face polishing step: polishing step).

[0062] Specifically, the end portion of the first optical fiber unit 2 is polished using the 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 during the polishing of the end portion, resulting in uneven end face polishing. Therefore, the side where the end face 2a of the first optical fiber unit 2 is formed is adhesively fixed to the first ferrule 22, and the end face of the first optical fiber unit 2 is polished together with the first ferrule 22.

[0063] In this embodiment, the polishing jig 50 includes a main body portion 51 in which a V-shaped groove 51a is formed on which the first optical fiber unit 2 adhesively fixed to the first ferrule 22 is placed. Further, 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 the first optical fiber unit 2 does not rotate about the central axis C1 in a state where the first optical fiber unit 2 is placed in the groove 51a.

[0064] The V-shaped groove 51a is pre-angled so that when the first optical fiber unit 2 adhesively fixed to the first ferrule 22 is placed in the groove 51a, the angle formed between the central axis C1 of the first optical fiber unit 2 and the horizontal plane is the angle θ. This angle θ can be, for example, 76 degrees to 84 degrees.

[0065] Then, after setting the first optical fiber unit 2 adhesively fixed to the first ferrule 22 on the polishing jig 50, before performing end face polishing, the arrangement direction of the four first cores 20 is adjusted (core orientation confirmation is performed) so as to be in a predetermined direction using a microscope or the like. This core orientation confirmation method can be, for example, adjusted so that the arrangement direction of the four first cores 20 is in a predetermined direction by using the crosshair R of a microscope or the like and the reference planes P1 and P2 of the polishing jig 50. In the present embodiment, the method shown in FIG. 7 is exemplified. In FIG. 7, the first core No. 20a is observed using the crosshair 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. 20a, thereby adjusting the arrangement direction of the four first cores 20.

[0066] Next, the first fiber collimator 200 is manufactured (fiber collimator manufacturing step) 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 core 20 is the same.

[0067] Specifically, first, the first optical fiber unit 2 is inserted into the collimator pipe 210 in which the first lens 212a is held. Then, with the first optical fiber unit 2 inserted into the collimator pipe 210, the first optical fiber unit 2 is relatively moved in the front-rear direction (the direction of arrow A in FIGS. 8 and 9). By doing so, the distance between the first optical fiber unit 2 and the first lens 212a is adjusted so that the focal position becomes optimal.

[0068] In this embodiment, as described above, the end face 2a is an inclined face that is inclined with respect to the plane orthogonal to the central axis C1 of the first optical fiber unit 2. Therefore, a difference in focal length occurs between each first core 20 and the first lens 212a. Thus, in this embodiment, the focal lengths 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, a total reflection mirror 60 is disposed at the position of the beam waist A1 and maximally coupled to the first core 20 located diagonally, so that 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 face 2a of the first optical fiber unit 2. Therefore, in this embodiment, the combination of the first core No. 1 20a and the first core No. 3 20c has the largest difference in the core-lens distance. Thus, the first core No. 1 20a is regarded as one first core 20, the first core No. 3 20c is regarded as the first core 20 located diagonally, and maximum coupling is performed between these two first cores 20. By doing so, the distances between all the cores and the lens are averaged. At this time, the core-lens distance between the first core No. 2 20b and the first core No. 4 20d becomes the average distance by being exactly in the middle between the first core No. 1 20a and the first core No. 3 20c.

[0069] Then, after adjusting the distance between the first optical fiber unit 2 and the first lens 212a, the first ferrule 22 (the first optical fiber unit 2) and the cylindrical main body portion 211 are fixed. By doing so, the first fiber collimator 200 is manufactured. Note that when a fiber collimator is configured, since it is housed inside a lens and a metal pipe, it becomes impossible to observe the core orientation thereafter.

[0070] Next, the first fiber collimator 200 and the second fiber collimator 300 are opposed to each other for optical alignment (collimator opposed system alignment step: alignment step).

[0071] In this embodiment, as described above, 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 core 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 core 30 is made the same for each product. And in this embodiment, the first optical fiber unit 2 and the second optical fiber unit 3 are arranged such 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.

[0072] Therefore, just by 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, the core orientations are roughly aligned (core orientation centering process). In this way, when forming the optical fiber connection structure 1, if the core arrays are roughly aligned first, the centering operation can be performed without spending time during subsequent adjustment. In particular, in this embodiment, since the core array and the polishing orientation are known in advance, there is no need to check the core array that can only be observed with a microscope, so the core arrays can be easily and quickly aligned. And after roughly aligning the core arrays, after centering the optical axes for maximum coupling (performing the optical axis adjustment process), the core array orientation may be finely adjusted so that each core has the minimum loss (core orientation precision centering process and X, Y, θx, θy optical axis adjustment process).

[0073] In this way, if the optical fiber connection structure 1 is manufactured by the method shown in this embodiment, there is no need to perform the operation of checking the core orientation before the fiber collimator manufacturing process or before the collimator facing system centering process. As a result, the optical fiber connection structure 1 can be manufactured with high precision (low loss) and in a short time (optically connecting the first optical fiber unit 2 and the second optical fiber unit 3).

[0074] Note that the optical fiber connection structure 1 can also be manufactured by the methods shown in FIGS. 11 to 18.

[0075] Next, another example of the manufacturing method of the optical fiber connection structure 1 will be described with reference to FIGS. 11 to 18.

[0076] Although FIGS. 12 to 14 show other examples of the polishing method of the end face 2a of the first optical fiber unit 2, the end face 3a of the second optical fiber unit 3 can also be polished in the same manner.

[0077] The optical fiber connection structure 1 can be manufactured by going through the steps shown in FIG. 11.

[0078] 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 becomes an inclined surface inclined with respect to the plane orthogonal to the central axis C1 of the first optical fiber unit 2 (fiber processing end face polishing step: polishing step).

[0079] This fiber processing end face polishing step is basically performed in the same manner as the method shown in the above embodiment. That is, with the polishing jig 50 used to fix the first optical fiber unit 2 with the first ferrule 22, the end of the first optical fiber unit 2 is polished. The configuration of the polishing jig 50 has the same configuration as the polishing jig 50 used in the method shown in the above embodiment.

[0080] Here, in the methods shown in FIGS. 12 to 14, a marking M1 capable of aligning the inclination direction of the end face 2a with the core arrangement is provided at the rear end portion of the first ferrule 22. By providing such a marking M1 on the first ferrule 22, the polishing orientation can be known at the polishing stage. In this way, when manufacturing the first fiber collimator 200, even if the polishing orientation of the end face 2a cannot be visually observed from the appearance due to the first lens 212a or the collimator pipe 210, this marking M1 can be used as a reference in the subsequent process. When performing the marking formation process of providing the marking M1 at the rear end portion of the first ferrule 22, it is preferably performed with the first optical fiber unit 2 with the first ferrule 22 set on the polishing jig 50. In this way, compared with the case where the first optical fiber unit 2 with the first ferrule 22 is removed from the polishing jig 50 and then microscopic observation is performed to observe the core orientation and the marking is made, the marking can be made more accurately and simply.

[0081] 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 core 20 is the same (fiber collimator manufacturing step).

[0082] This fiber collimator manufacturing step is performed in the same manner as the method shown in the above embodiment. That is, the first optical fiber unit 2 is inserted into the collimator pipe 210 in which the first lens 212a is held. Then, with the first optical fiber unit 2 inserted into the collimator pipe 210, the first optical fiber unit 2 is relatively moved in the front-rear direction (the direction of arrow A in FIGS. 8 and 9). By doing so, the distance between the first optical fiber unit 2 and the first lens 212a is adjusted so that the focal position becomes optimal.

[0083] After adjusting the distance between the first optical fiber unit 2 and the first lens 212a, the first ferrule 22 (the first optical fiber unit 2) and the cylindrical main body portion 211 are fixed. By doing so, the first fiber collimator 200 is manufactured.

[0084] Next, the first fiber collimator 200 and the second fiber collimator 300 are opposed to each other for optical alignment (collimator opposing system alignment step: alignment step).

[0085] At this time, the core arrays are roughly aligned with reference to the marking M1 provided in the previous step. By doing so, the alignment operation of the core orientation can be performed without spending time during subsequent adjustment.

[0086] For example, if the first fiber collimator 200 and the second fiber collimator 300 are arranged such that the marking M1 is located on the upper side, the inclination directions (polishing orientations) of the end faces 2a and 3a can be made opposite to each other. In this way, even with the methods shown in FIGS. 11 to 18, just by visually checking and setting the first fiber collimator 200 and the second fiber collimator 300, the core orientations can be roughly aligned.

[0087] Furthermore, in the methods shown in FIGS. 11 to 18, by calculating in advance the relationship between the angular deviation amount θz around the central axis C1 (around the Z axis) and the loss amount (loss increase amount) before manufacturing, the angular deviation amount θz and the loss amount with respect to the core pitch d1 (diagonal core pitch d2) are clarified.

[0088] As shown in FIG. 15, the core pitch d1 is the distance between two adjacent cores in the circumferential direction, and as shown in FIG. 15, the diagonal core pitch d2 is the distance between two cores facing each other across the central axis C1. Also, the angular deviation amount θz represents how much rotation has occurred around the central axis C1 (around the Z axis) with respect to the reference state (see FIG. 16).

[0089] Also, FIG. 17 shows the results of calculating the coupling efficiency at an angular pitch interval of 0.07 deg when the spot size radius is 5.5 μm and the wavelength λ is 1550 nm. FIG. 18 shows an example of the relationship between the loss amount and the angular deviation amount θz.

[0090] From the graph of Fig. 17, for example, in the case of a core pitch of 40 μm (diagonal core pitch of 56.6 μm), it can be seen that by specifying the deviation between the polishing orientation and the core orientation to be 3° or less, the loss (increase) amount can be kept within 0.2 dB. That is, it can be seen that if the angular deviation between the cores is specified to be ±1.5° or less in relative angle, the loss (increase) amount can be kept within 0.2 dB.

[0091] This process can also be applied to other core pitches, and it becomes possible to specify the angular deviation range based on the previously calculated results. Furthermore, by using the results of Fig. 17, the relationship between the core pitch and the angular deviation for a desired loss amount can be obtained as shown in Fig. 18, and it becomes possible to specify the core pitch d1 and the angular deviation amount θz for a desired loss amount. As a result, it becomes possible to manufacture the FIFO device more simply and in a shorter time according to the required loss amount (specification) of the FIFO device.

[0092] Thus, by using the methods shown in Figs. 11 to 18, for example, it is possible to form the optical fiber connection structure 1 without requiring precise centering work and with a loss increase amount within 0.2 dB.

[0093] Also, the manufacturing time can be shortened according to the required loss amount (specification) of the FIFO device. That is, it becomes possible to form the optical fiber connection structure 1 in an appropriate manufacturing time according to the required performance.

[0094] From the above, if the optical fiber connection structure 1 is manufactured by the methods shown in Figs. 11 to 18, the core orientation precision centering process performed by the method shown in the above embodiment can be omitted. As a result, it becomes possible to manufacture the optical fiber connection structure 1 with high precision (low loss) and in a short time (optically connect the first optical fiber unit 2 and the second optical fiber unit 3).

[0095] Also, as shown in FIG. 19, the first optical fiber unit 2 can be a multi-core fiber in which seven first cores 20 are arranged apart from each other and covered by one first cladding 21. Also in FIG. 19, the first cladding 21 and the seven first cores 20 are formed such that the cross-sectional shape obtained by cutting in a plane orthogonal to the central axis C1 is circular.

[0096] And, one of the seven first cores 20 is arranged at the center, and the six first cores 20 are arranged at equal intervals on the circumference centered on the central axis C1 of the first optical fiber unit 2.

[0097] Here, in FIG. 19, the seven first cores 20 are numbered. Specifically, in the state shown in FIG. 19, the first core 20 located at the center and above in the X direction (width direction) is defined as the first core No. 1 20a. Also, in the state shown in FIG. 19, the first core 20 arranged so as to include the central axis C1 of the first optical fiber unit 2 is defined as the first core No. 2 20b, and the first core 20 located at the center and below in the X direction (width direction) is defined as the first core No. 3 20c. And, in the state shown in FIG. 19, the remaining four first cores 20 are defined as the first core No. 4 20d, the first core No. 5 20e, the first core No. 6 20f, and the first core No. 7 20g, respectively, starting from the first core No. 1 20a and rotating counterclockwise. Note that the above numbers are assigned so as to match the numbers of the first core 20 located at the uppermost part and the first core 20 located at the lowermost part in the above embodiment, and not limited thereto, and the numbers of the seven first cores 20 can be set randomly.

[0098] And, when the end face 2a of the first optical fiber unit 2 shown in FIG. 19 is an inclined surface, in the reference state of the first optical fiber unit 2, 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 arranged on the line segment L1.

[0099] When the first optical fiber unit 2 shown in FIG. 19 is used, the second optical fiber unit 3 is formed by bundling seven single-mode fibers each having one second core 30 covered by one second cladding 31. Specifically, one single-mode fiber is arranged in the center, and six single-mode fibers are arranged around it at equal intervals and then bundled. By doing so, the seven second cores 30 of the seven single-mode fibers correspond one-to-one to each of the seven first cores 20.

[0100] Then, by optically coupling the first optical fiber unit 2 and the second optical fiber unit 3 having such a configuration, the optical fiber connection structure 1 is formed.

[0101] [Operation and Effect] Hereinafter, 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 examples, and the effects obtained thereby will be described.

[0102] The optical fiber connection structure 1 shown in the above embodiment and its modified examples 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 so as to correspond to each of the plurality of first cores 20.

[0103] Also, the end face 2a of the first optical fiber unit 2 is inclined with respect to a plane orthogonal 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 orthogonal to the central axis C2 of the second optical fiber unit 3.

[0104] The first optical fiber unit 2 and the second optical fiber unit 3 are arranged such 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.

[0105] Here, a state where the first optical fiber unit 2 is arranged such 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. Further, a state where the second optical fiber unit 3 is arranged such 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.

[0106] And in the reference state of the first optical fiber unit 2, the core 20a located at the uppermost part and the core 20c located at the lowermost part among the plurality of first cores 20 are arranged on a 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.

[0107] Furthermore, in the reference state of the second optical fiber unit 3, the core 30a located at the uppermost part and the core 30c located at the lowermost part among the plurality of second cores 30 are arranged on a 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.

[0108] Also, the manufacturing method of the optical fiber connection structure 1 shown in the above embodiment and its modification includes a polishing step of polishing the end faces 2a and 3a of the first and second optical fiber units 2 and 3. This polishing step polishes the end faces 2a and 3a of the first and second optical fiber units 2 and 3 such that the end faces 2a and 3a of the first and second optical fiber units 2 and 3 are inclined with respect to the planes orthogonal to the central axes C1 and C2 of the respective optical fiber units 2 and 3.

[0109] Also, the manufacturing method of the optical fiber connection structure 1 includes an alignment step of performing optical alignment with the end face 2a of the first optical fiber unit 2 and the end face 3a of the second optical fiber unit 3 facing each other.

[0110] Here, the polishing process includes a first core orientation adjustment step of adjusting the arrangement of the plurality of first cores 20 such that the relationship between the inclination direction of the end face 2a of the first optical fiber unit 2 and the arrangement direction of the plurality of first cores 20 is the same. Further, it includes a second core orientation adjustment step of adjusting the arrangement of the plurality of second cores 30 such that the relationship between the inclination direction of the end face 3a of the second optical fiber unit 3 and the arrangement direction of the plurality of second cores 30 is the same.

[0111] Furthermore, after performing the first core orientation adjustment step, it has a first polishing step of polishing the end face 2a of the first optical fiber unit 2. In this first polishing step, in the above reference state, the core 20a located at the uppermost part and the core 20c located at the lowermost part among the plurality of first cores 20 are polished so as to be arranged on a 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.

[0112] And after performing the second core orientation adjustment step, it has a second polishing step of polishing the end face 3a of the second optical fiber unit 3. In this second polishing step, in the above reference state, the core 30a located at the uppermost part and the core 30c located at the lowermost part among the plurality of second cores 30 are polished so as to be arranged on a 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.

[0113] Furthermore, the centering process includes a core orientation centering step of centering the orientations of the first core 20 and the second core 30 by arranging 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 to be opposite to each other.

[0114] And the centering process includes an optical axis centering step of centering the optical axis after performing the core orientation centering step.

[0115] With such an optical fiber connection structure 1 and a method for manufacturing the optical fiber connection structure, the end faces 2a of the first optical fiber unit 2 and 3a of the second optical fiber unit 3 can be inclined while defining the arrangement directions of the first core 20 and the second core 30. Therefore, it becomes possible to make the relationship between the inclination directions of the end faces 2a and 3a and the arrangement directions of the first core 20 and the second core 30 the same.

[0116] As a result, when optically coupling the first optical fiber unit 2 and the second optical fiber unit 3 (during the manufacturing and assembly of 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 centering operation), 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 centering operation can be further shortened.

[0117] And by making the relationship between the inclination directions of the end faces 2a and 3a and the arrangement directions of the first core 20 and the second core 30 the same, the variation in the coupling loss in the first core 20 and the second core 30 can be suppressed.

[0118] Thus, with the configurations shown in the above embodiments and their modifications, an optical fiber connection structure 1 and a method for manufacturing the optical fiber connection structure capable of performing optical connection with high precision (low loss) and in a short time can be obtained.

[0119] Also, the first optical fiber unit 2 and the second optical fiber unit 3 may be arranged in a state where 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.

[0120] Also, a plurality of first cores 20 may be arranged at equal intervals on a circumference centered on the central axis C1 of the first optical fiber unit 2. And a plurality of second cores 30 may be arranged at equal intervals in a circumferential shape centered on the central axis C2 of the second optical fiber unit 3.

[0121] In this way, even if two first cores 20 and second cores 30 facing each other with the central axes C1 and C2 interposed therebetween are arbitrarily selected, the arrangement states of the first cores 20 and second cores 30 on the end faces 2a and 3a can be made substantially the same. Therefore, when optically coupling the first optical fiber unit 2 and the second optical fiber unit 3, variations in the positions of the end faces 2a and 3a of the mutually corresponding first cores 20 and second cores 30 can be more reliably suppressed. As a result, the coupling loss in the first cores 20 and second cores 30 can be further reduced.

[0122] Also, a first ferrule 22 for suppressing the 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. Further, a second ferrule 32 for suppressing the 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 a marking M1 capable of aligning the inclination direction of each of the end faces 2a and 3a with the core arrangement may be formed on the first ferrule 22 and the second ferrule 32.

[0123] Also, the polishing process may include a marking formation process. In this marking formation process, a marking M1 capable of aligning the inclination direction of the end face 2a of the first optical fiber unit 2 with the core arrangement of the first core 20 is formed on the first ferrule 22 to which the first optical fiber unit 2 is fixed. Further, a marking M1 capable of aligning the inclination direction of the end face 3a of the second optical fiber unit 3 with the core arrangement of the second core 30 is formed on the second ferrule 32 to which the second optical fiber unit 3 is fixed.

[0124] In this way, even if the polishing orientation of the end faces 2a and 3a cannot be visually observed from the appearance, this marking M1 can be used as a reference in the subsequent process. That is, the core arrangements can be roughly aligned with reference to the marking M1. In this way, the centering operation of the core orientation can be performed without taking time during the subsequent adjustment.

[0125] Also, in the core 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 angular deviation θz around the central axis C1 calculated in advance and the loss amount.

[0126] In this way, it becomes possible to define the allowable range of angular deviation based on the result calculated in advance, and it becomes possible to manufacture the optical fiber connection structure 1 more simply and in a shorter time according to the required loss amount (specification).

[0127] [Others] As described above, the present embodiment has been described, but the present embodiment is not limited to these, and various modifications are possible within the scope of the gist of the present embodiment.

[0128] For example, it is possible to appropriately combine the configurations and methods shown in the above-described embodiment and its modifications.

[0129] Also, in the above-described embodiment and its modifications, the numbers of the first core 20 and the second core 30 are exemplified as four and seven, but the numbers of the first core 20 and the second core 30 may be two or more and are not limited to four or seven. In this case, it is preferable that at least two cores are arranged on the line segment passing through the central axis of the optical fiber unit.

[0130] Also, in the above-described embodiment and its modifications, the space coupling type connection method using a lens is exemplified as the optical fiber connection structure 1, but it is not limited thereto.

[0131] In the above-described embodiments and their modifications, a multi-core fiber is exemplified as the first optical fiber unit 2, and a bundled single-mode fiber is exemplified as the second optical fiber unit 3. However, the present invention is not limited thereto. For example, the present invention can be applied to optical coupling between multi-core fibers, and the present invention can also be applied to optical coupling between bundled single-mode fibers. Further, either one of the first optical fiber unit 2 and the second optical fiber unit 3 may be a few-mode fiber, and the other may be a bundled multi-core fiber or single-mode fiber. Further, both the first optical fiber unit 2 and the second optical fiber unit 3 may be few-mode fibers.

[0132] Also, the collimator pipe, adapter, and other detailed specifications (shape, size, layout, etc.) can be appropriately changed.

Explanation of Reference Numerals

[0133] 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

1. 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 so as to correspond to each of the plurality of first cores are optically connected, a polishing step of polishing end faces of the first optical fiber unit and the second optical fiber unit so that the end faces of the respective optical fiber units are inclined with respect to a plane orthogonal to the central axis of each optical fiber unit; a first fiber collimator manufacturing step of inserting the first optical fiber unit into a collimator pipe holding a first lens to form a first fiber collimator; a second fiber collimator manufacturing step of inserting the second optical fiber unit into a collimator pipe holding a second lens to form a second fiber collimator; an alignment step of performing optical alignment with the end face of the first optical fiber unit and the end face of the second optical fiber unit facing each other; comprising: the polishing step includes: a first core orientation adjustment step of adjusting the arrangement of the plurality of first cores so that the relationship between the inclination direction of the end face of the first optical fiber unit and the 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 the relationship between the inclination direction of the end face of the second optical fiber unit and the arrangement direction of the plurality of second cores is the same; after performing the first core orientation adjustment step, with the central axis of the first optical fiber unit being horizontal and in a state where the most protruding point of the inclined end face is at the upper end, the core located at the uppermost part and the core located at the lowermost part among 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, and a first polishing step of polishing the end face of the first optical fiber unit; after performing the second core orientation adjustment step, with the central axis of the second optical fiber unit being horizontal and in a state where the most protruding point of the inclined end face is at the upper end, the core located at the uppermost part and the core located at the lowermost part among 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, and a second polishing step of polishing the end face of the second optical fiber unit; having: the alignment step is: By arranging 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 to be symmetric with respect to a plane orthogonal to the central axis of the first optical fiber unit and the central axis of the second optical fiber unit, a core azimuth alignment step of aligning the azimuths of the first core and the second core is performed. After performing the core azimuth alignment step, an optical axis alignment step of aligning the optical axis is performed. It has In the first fiber collimator manufacturing step, a total reflection mirror is arranged at the position of the beam waist to perform maximum coupling between the core located at the uppermost part and the core located at the lowermost part among the plurality of first cores. In the second fiber collimator manufacturing step, a total reflection mirror is arranged at the position of the beam waist to perform maximum coupling between the core located at the uppermost part and the core located at the lowermost part among the plurality of second cores. A method for manufacturing an optical fiber connection structure.

2. The polishing step includes a marking formation step of forming, on the first ferrule to which the first optical fiber unit is fixed, a marking capable of aligning the inclination direction of the end face of the first optical fiber unit and the core arrangement of the first core, and forming, on the second ferrule to which the second optical fiber unit is fixed, a marking capable of aligning the inclination direction of the end face of the second optical fiber unit and the core arrangement of the second core. In the core azimuth alignment step, the azimuths of the first core and the second core are aligned based on the markings formed on the first ferrule and the second ferrule. The method for manufacturing an optical fiber connection structure according to claim 1.

3. In the core azimuth alignment step, the azimuths of the first core and the second core are aligned based on the relationship between the angle deviation amount and the loss amount around the central axis calculated in advance. The method for manufacturing an optical fiber connection structure according to claim 1 or claim 2.

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