Optical fiber bundle, optical connection structure, and method for manufacturing optical fiber bundle

Abstract

To reduce bending loss in a plurality of optical fibers.SOLUTION: An optical fiber bundle comprises a ferrule 50, a hold part, and a plurality of optical fibers 40. The hold part has a second fiber housing hole. The plurality of optical fibers each have: a glass fiber having a first diameter part 43, a second diameter part 44, and a taper part 45 coupling the first diameter part and the second diameter part; and a covering part 46 formed such that a portion of the glass fiber 41 continuing to the second diameter part is covered by a covering. The respective covering parts of the plurality of optical fibers include a first portion led out through the second fiber housing hole and a second portion positioned apart from the second fiber housing hole. Each of the coverings of the first portions of the plurality of optical fibers is fixed to the covering of the first portion in the covering part of at least one optical fiber among the other optical fibers. An arrangement order of the covering parts of the plurality of optical fibers in the second fiber housing hole is the same as an arrangement order of the plurality of optical fibers in a front end of the ferrule.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to an optical fiber bundle, an optical connection structure, and a method for manufacturing an optical fiber bundle. [Background technology]

[0002] Patent Document 1 and Patent Document 2 disclose an optical fiber bundle in which multiple optical fibers are inserted into a ferrule. In the optical fiber bundle described in Patent Document 1, multiple optical fibers are aligned in a close-packed structure by being twisted inside a ferrule (capillary). In the optical fiber bundle described in Patent Document 2, optical fibers processed to have a small diameter by etching are housed in a ferrule. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-167299 A [Patent Document 2] JP 2013-68891 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical fiber bundle described in Patent Document 2, when multiple optical fibers are inserted into a ferrule, the positions of the multiple optical fibers may shift relative to one another along the longitudinal direction. In this case, it is necessary to determine the insertion amount into the ferrule so that the coating of the optical fiber that is shifted furthest to the rear is positioned inside the ferrule, and the insertion amount of the optical fibers other than that optical fiber into the ferrule becomes excessive. In the case where multiple optical fibers are processed to have a small diameter, if the insertion amount becomes excessive, the optical fiber may hit the inner surface of the hole of the ferrule, increasing the curvature of the optical fiber and increasing the bending loss in the optical fiber.

[0005] Therefore, an object of the present disclosure is to provide an optical fiber bundle, an optical connection structure, and a method for manufacturing an optical fiber bundle that can reduce bending loss in an optical fiber. [Means for solving the problem]

[0006] An optical fiber bundle according to an embodiment of the present disclosure is an optical fiber bundle for optically coupling a plurality of optical fibers to a multi-core optical fiber. The optical fiber bundle includes a ferrule, a holding portion, and a plurality of optical fibers. The ferrule extends along a first direction. The ferrule has a front end in the first direction, a rear end on the opposite side of the front end in the first direction, and a first fiber storage hole. The first fiber storage hole is a hole including a first portion located at the front end, a second portion located at the rear end, and an inner diameter conversion portion connecting the first portion and the second portion. The second portion has an inner diameter larger than that of the first portion. The holding portion has a second fiber storage hole which is a hole extending along the first direction. The second fiber storage hole communicates with the first fiber storage hole at the rear end of the ferrule. The plurality of optical fibers include a glass fiber and a coating portion. The glass fiber includes a first diameter portion, a second diameter portion having a diameter larger than the diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion. At least the first diameter section, the tapered section, and the second diameter section extend along the first direction. The coating section is formed by coating a portion of the glass fiber that is continuous with the second diameter section. The first diameter sections of the optical fibers are inserted into the first section of the first fiber storage hole. The tapered sections of the optical fibers are inserted into the second section of the first fiber storage hole. The boundaries between the second diameter sections and the coating sections of the optical fibers are inserted into the second fiber storage hole. The coating sections of each of the optical fibers include a first section that is led out from the second fiber storage hole and a second section that is separated from the second fiber storage hole. The coating of the first section is fixed to the coating of the first section of the coating section of at least one of the other optical fibers. The arrangement order of the coating sections of the optical fibers in the second fiber storage hole is the same as the arrangement order of the first diameter sections of the optical fibers at the front end of the ferrule. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide an optical fiber bundle, an optical connection structure, and a method for manufacturing an optical fiber bundle that are capable of reducing bending loss in an optical fiber. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an optical connection structure according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the optical connection structure shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III of the optical connection structure shown in FIG. [Figure 4] FIG. 4 is a diagram showing the tip of a multi-core fiber and the end face of a ferrule. [Diagram 5] FIG. 5 is a diagram showing the tips of a plurality of optical fibers and the end face of a ferrule. [Figure 6] FIG. 6 is a schematic diagram showing an optical fiber. [Figure 7] FIG. 7 is a perspective view showing a number of optical fibers extending outside the flange. [Figure 8] FIG. 8 is a perspective view showing a plurality of optical fibers. [Figure 9] FIG. 9 is a schematic cross-sectional view showing an inner hole of a ferrule. [Figure 10] FIG. 10 is a schematic cross-sectional view showing a plurality of optical fibers inserted into the inner hole of the ferrule and the inner hole of the flange. [Figure 11] FIG. 11 is a perspective view showing the configuration of multiple optical fibers in the inner bore of the ferrule and the inner bore of the flange. [Figure 12] FIG. 12 is a flowchart showing a method for manufacturing an optical fiber bundle. [Figure 13] FIG. 13 is a schematic diagram showing a plurality of optical fibers inserted into the inner hole of the ferrule and the inner hole of the flange. [Figure 14]FIG. 14 is a schematic perspective view showing an example of the arrangement of a plurality of optical fibers in an inner hole of a flange. [Figure 15] FIG. 15 is a schematic perspective view showing an example of an arrangement of a plurality of optical fibers at the front end of a ferrule. [Figure 16] FIG. 16 is a schematic perspective view showing an example of the arrangement of a plurality of optical fibers at the front end of a ferrule. [Figure 17] FIG. 17 is a schematic perspective view showing an example of the arrangement of a plurality of optical fibers at the front end of a ferrule. [Figure 18] FIG. 18 is a diagram showing a fan-in fan-out device including the optical connection structure shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0010] [1] An optical fiber bundle according to an embodiment of the present disclosure is an optical fiber bundle for optically coupling a plurality of optical fibers to a multi-core optical fiber. The optical fiber bundle includes a ferrule, a holding portion, and a plurality of optical fibers. The ferrule extends along a first direction. The ferrule has a front end in the first direction, a rear end on the opposite side of the front end in the first direction, and a first fiber storage hole. The first fiber storage hole is a hole including a first portion located at the front end, a second portion located at the rear end, and an inner diameter conversion portion connecting the first portion and the second portion. The second portion has an inner diameter larger than that of the first portion. The holding portion has a second fiber storage hole which is a hole extending along the first direction. The second fiber storage hole communicates with the first fiber storage hole at the rear end of the ferrule. The plurality of optical fibers include a glass fiber and a coating portion. The glass fiber includes a first diameter portion, a second diameter portion having a diameter larger than the diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion. At least the first diameter section, the tapered section, and the second diameter section extend along the first direction. The coating section is formed by coating a portion of the glass fiber that is continuous with the second diameter section. The first diameter sections of the optical fibers are inserted into the first section of the first fiber storage hole. The tapered sections of the optical fibers are inserted into the second section of the first fiber storage hole. The boundaries between the second diameter sections and the coating sections of the optical fibers are inserted into the second fiber storage hole. The coating sections of each of the optical fibers include a first section that is led out from the second fiber storage hole and a second section that is separated from the second fiber storage hole. The coating of the first section is fixed to the coating of the first section of the coating section of at least one of the other optical fibers. The arrangement order of the coating sections of the optical fibers in the second fiber storage hole is the same as the arrangement order of the first diameter sections of the optical fibers at the front end of the ferrule.

[0011] In this optical fiber bundle, the coating of the first portion of the coating of each of the multiple optical fibers is fixed to the coating of the first portion of the coating of at least one of the other optical fibers. With this configuration, the positions of the multiple optical fibers in the first fiber storage hole and the second fiber storage hole are suppressed from being misaligned with each other along the first direction. This prevents the amount of optical fiber inserted into the ferrule from becoming excessive. As a result, an increase in the curvature of the optical fiber is suppressed. In addition, the order of the coatings of the multiple optical fibers in the second fiber storage hole is the same as the order of the first diameter portions of the multiple optical fibers at the front end of the ferrule. With this configuration, the intersection of the multiple optical fibers inside the ferrule is suppressed. From the above, it is possible to reduce bending loss in the multiple optical fibers.

[0012] [2] In the optical fiber bundle of [1] above, first portions of the coatings of the optical fibers may be integrated by fixing the coatings to each other. In second portions of the coatings of the optical fibers, the coatings may be separated from each other. In this way, by integrating the first portions of the coatings, the positional deviation of the optical fibers in the first fiber housing hole and the second fiber housing hole is further suppressed. This further suppresses an increase in the curvature of the optical fibers.

[0013] [3] In the optical fiber bundle of [1] above, the first portions of the coatings of the optical fibers may be two-dimensionally arranged in a cross section intersecting with the central axes of the optical fibers. In the second portions of the coatings of each of the optical fibers, the coating may be fixed to the coating of the second portions of the coatings of at least one of the other adjacent optical fibers. In this way, the first portions of the coatings are two-dimensionally arranged, which makes it easier to optically couple the optical fibers to the cores of the multi-core optical fiber.

[0014] [4] In the optical fiber bundle of [1] above, the coatings of the optical fibers may further include a connecting portion connecting the first portion and the second portion. The coatings of the first portions of the coatings of the optical fibers may be fixed to each other so that the first portions of the coatings of the optical fibers are arranged two-dimensionally in a cross section intersecting the central axes of the optical fibers. The coatings of the second portions of the coatings of the optical fibers may be fixed to each other so that the second portions of the coatings of the optical fibers are arranged one-dimensionally in a cross section intersecting the central axes of the optical fibers. In this way, the first portions of the coatings are arranged two-dimensionally, which makes it easier to optically couple the optical fibers to the cores of the multi-core optical fiber. Furthermore, the second portions of the coatings are arranged one-dimensionally, which prevents the optical fibers from scattering and becoming entangled with each other. As a result, when a measurement or the like is performed using the optical fiber bundle, it is possible to improve the workability of the measurement or the like.

[0015] [5] The optical fiber bundle of [4] above may further include a protective member for protecting at least a boundary between the joint portion and the second portion of the coating of each of the optical fibers. In this case, unintentional separation of the coatings of the second portions of the optical fibers is suppressed.

[0016] [6] In the optical fiber bundle of [3] or [5] above, the second portions of the coatings of the optical fibers may form a single ribbon fiber. In this case, the optical fibers are further prevented from becoming disjointed and entangled with each other.

[0017] [7] In the optical fiber bundle of [6] above, the ribbon core wire may have another coating that collectively surrounds the coating of the second portion of the coating of the multiple optical fibers. The average thickness of the other coating may be 0.01 mm or more and 0.25 mm or less. With this configuration, since the thickness of the other coating is 0.01 mm or more, separation of the coatings of the second portions constituting the ribbon core wire is suppressed by the sufficient strength of the other coating. Furthermore, since the thickness of the other coating is 0.25 mm or less, removal of the other coating when forming the first portion of the coating is facilitated.

[0018] [8] In the optical fiber bundle according to any one of [1] to [7] above, the coatings of the first portions of the coatings of the optical fibers may be bonded to each other by an adhesive. In this case, the coatings can be easily bonded to each other.

[0019] [9] Any one of the optical fiber bundles [1] to [7] above may further include a cylinder extending along the first direction. The first portions of the coatings of the optical fibers may be inserted into the cylinder, and the coatings of the first portions of the coatings may be fixed to the cylinder by an adhesive. In this case, the coatings of the first portions of the coatings of the optical fibers can be firmly fixed to each other.

[0020]

[10] Any one of the optical fiber bundles [1] to [7] above may further include a cylindrical shrink tube extending along the first direction. The first portions of the coatings of the multiple optical fibers may be housed in the shrink tube and held together. In this case, the coatings of the first portions of the coatings of the multiple optical fibers can be firmly fixed to each other.

[0021]

[11] In the optical fiber bundle according to any one of [1] to

[10] above, the appearance of the coating of each of the optical fibers may include a different color or coloring for each optical fiber. In this case, the optical fibers can be easily distinguished from each other.

[0022]

[12] In any one of the optical fiber bundles [1] to

[11] above, the positional deviation between the tapered portions of the optical fibers in the first direction may be 1 mm or less. In this case, an increase in the insertion amount of the optical fiber into the ferrule can be suppressed. This suppresses an increase in the curvature of the optical fiber. As a result, bending loss in the optical fiber can be reduced.

[0023]

[13] An optical connection structure according to an aspect of the present disclosure may include a multi-core optical fiber including multiple cores extending along a first direction and a cladding covering the multiple cores, a first optical connector having a ferrule for holding a tip of the multi-core optical fiber, and a second optical connector which is an optical connector having any one of the optical fiber bundles of [1] to

[12] above. When the second optical connector is connected to the first optical connector, each core of the multiple optical fibers may be optically coupled to each of the multiple cores of the multi-core optical fiber. With this optical connection structure, it is possible to reduce bending loss in the multiple optical fibers.

[0024]

[14] A method for manufacturing an optical fiber bundle according to an embodiment of the present disclosure is a method for manufacturing an optical fiber bundle for optically coupling a plurality of optical fibers to a multi-core optical fiber, the method including the steps of preparing a ferrule, preparing a holding portion, preparing a plurality of optical fibers, inserting, and fixing. The ferrule extends along a first direction. In the step of preparing the ferrule, the ferrule has a front end in the first direction, a rear end opposite to the front end in the first direction, and a first fiber storage hole. The first fiber storage hole is a hole including a first portion located at the front end, a second portion located at the rear end and having an inner diameter larger than the first portion, and an inner diameter conversion portion connecting the first portion and the second portion. In the step of preparing the holding portion, the holding portion has a second fiber storage hole that is a hole extending along the first direction and communicates with the first fiber storage hole at the rear end of the ferrule. In the step of preparing a plurality of optical fibers, the plurality of optical fibers include a glass fiber and a coating portion. The glass fiber includes a first diameter portion, a second diameter portion having a diameter larger than that of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion. At least the first diameter portion, the tapered portion, and the second diameter portion extend along a first direction. The coating portion is formed by coating a portion of the glass fiber that is continuous with the second diameter portion. In the inserting step, the first diameter portions of the optical fibers are inserted into a first portion of the first fiber storage hole, the tapered portions of the optical fibers are inserted into a second portion of the first fiber storage hole, and the boundaries between the second diameter portions and the coating portions of the optical fibers are inserted into the second fiber storage hole. In the fixing step, the optical fibers are fixed to the ferrule by an adhesive. In the step of preparing the optical fibers, the coating portions of the optical fibers each include a first portion that is led out of the second fiber storage hole and a second portion that is separated from the second fiber storage hole. The coating of the first portion is fixed to the coating of the first portion of the coating portion of at least one of the other optical fibers. In the fixing step, the arrangement order of the coatings of the optical fibers in the second fiber housing hole is the same as the arrangement order of the first diameter portions of the optical fibers in the front end of the ferrule.

[0025] In this method for manufacturing an optical fiber bundle, the coating of the first portion of the coating of each of the optical fibers is fixed to the coating of the first portion of the coating of at least one of the other optical fibers. With this configuration, the positions of the optical fibers in the first fiber storage hole and the second fiber storage hole are prevented from being misaligned with each other along the first direction. This prevents the amount of optical fiber inserted into the ferrule from becoming excessive. As a result, an increase in the curvature of the optical fiber is prevented. In addition, the order of the coatings of the optical fibers in the second fiber storage hole is the same as the order of the first diameter portions of the optical fibers at the front end of the ferrule. With this configuration, the crossing of the optical fibers inside the ferrule is prevented. From the above, an optical fiber bundle in which the bending loss of the optical fibers is reduced can be manufactured.

[0026]

[15] In the inserting step of the method for producing an optical fiber bundle according to

[14] above, the coatings of the optical fibers may be arranged in a jig to align and temporarily fix the optical fibers in a predetermined arrangement, and the jig may be removed after the optical fibers are inserted into the ferrules. In this case, the coatings are prevented from scattering and becoming entangled with each other, improving the workability of the inserting step.

[0027]

[16] In the method for manufacturing an optical fiber bundle according to any one of

[14] or

[15] above, the step of preparing the optical fibers may include the steps of: separating the optical fibers from each other over a length of 10 mm or more from the tip of a ribbon fiber formed by integrating the optical fibers; and forming the first diameter portion and the tapered portion by chemically etching the tip of the glass fiber of each optical fiber. In this case, the first diameter portion and the tapered portion of the optical fibers can be easily formed.

[0028] [Details of the embodiment of the present disclosure] Specific examples of the optical fiber bundle, optical connection structure, and manufacturing method of the optical fiber bundle according to the present embodiment will be described with reference to the drawings as necessary. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, the same elements in the description of the drawings will be given the same reference numerals, and duplicated descriptions will be omitted.

[0029] Fig. 1 is a perspective view showing an optical connection structure according to one embodiment. Fig. 2 is an exploded perspective view of the optical connection structure shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line III-III of the optical connection structure shown in Fig. 1. As shown in Figs. 1 to 3, the optical connection structure 1 includes a first optical connector 10, a second optical connector 20, and a split sleeve 30 (sleeve).

[0030] The first optical connector 10 includes a structure 100 having a multicore fiber 12 (hereinafter also referred to as "MCF 12"), a ferrule 14, and a flange 16. The second optical connector 20 includes an optical fiber bundle 200 having a plurality of optical fibers 40, a ferrule 50, and a flange 60 (holding portion). The optical fiber bundle 200 is configured to optically couple the plurality of optical fibers 40 to the MCF 12. When the first optical connector 10 is connected to the second optical connector 20, each core of the plurality of optical fibers 40 is optically coupled to each of the plurality of cores of the MCF 12. The split sleeve 30 is a member that holds and aligns the ferrule 14 and the ferrule 50 from the outside so that the central axis of the ferrule 14 of the first optical connector 10 coincides with the central axis of the ferrule 50.

[0031] FIG. 4 is a diagram showing a schematic view of the tip of the MCF 12 and the end face of the ferrule 14. As shown in FIG. 4, the MCF 12 has a plurality of cores 12a extending along the longitudinal direction A (see FIGS. 1 to 3), and a cladding 12b extending along the longitudinal direction A and covering the plurality of cores 12a collectively. The MCF 12 also has a tip face 12c. The tip face 12c is composed of the tips of the plurality of cores 12a and the tips of the cladding 12b. The cores 12a mainly include silica glass to which a dopant such as germanium is added to increase the refractive index. The cladding 12b mainly includes silica glass to which a dopant such as fluorine is added to decrease the refractive index. The composition of the cores 12a and the cladding 12b and the combination of the dopants can be appropriately selected. Such an MCF 12 can propagate an optical signal for each core 12a by each core 12a.

[0032] In a cross section perpendicular to the central axis of the MCF 12, the cores 12a are arranged, for example, two-dimensionally. In this embodiment, the MCF 12 has four cores 12a. The MCF 12 may have seven cores 12a, eight cores 12a, or 19 cores 12a. The number of cores 12a of the MCF 12 is not limited to these. In the example shown in FIG. 4, four cores 12a are arranged in a square lattice shape with two rows and two columns. The diameter (core diameter) of each core 12a may be, for example, 10 μm or less, or 5 μm or less. The diameter (core diameter) of each core 12a may be 1 μm or more. The core pitch (center-to-center distance) between adjacent cores 12a may be, for example, 10 μm or more and 50 μm or less. The diameter of cladding 12b (cladding diameter) may be, for example, 200 μm or less, 125 μm or less, 100 μm or less, or 80 μm or less, and the diameter of cladding 12b (cladding diameter) may be 50 μm or more.

[0033] The ferrule 14 is a cylindrical member that holds the tip portion 12d of the MCF 12 (see FIG. 3), and has an inner hole 14a that is a through hole that houses the tip portion 12d of the MCF 12, and an end face 14b. The ferrule 14 fixes the tip portion 12d of the MCF 12 in the inner hole 14a so that the tip face 12c of the MCF 12 is exposed at the end face 14b. The inner diameter of the inner hole 14a is the same as or slightly larger than the outer diameter of the MCF 12, and the tip portion 12d of the MCF 12 is inserted into the inner hole 14a to be fitted into the inner hole 14a. The ferrule 14 has a length of, for example, 6 mm or more and 8 mm or less, and is made of a ceramic material such as zirconia.

[0034] 3, the flange 16 is a cylindrical member that holds the rear end portion of the ferrule 14 and houses the MCF 12 therein. The portion of the MCF 12 that is housed in the flange 16 may be fixed to the inside of the flange 16 by an adhesive. The flange 16 is made of, for example, metal or resin.

[0035] The optical fibers 40 are optical fibers optically coupled to the MCF 12. FIG. 5 is a diagram showing the tips of the optical fibers 40 and the end face of the ferrule 50. As shown in FIG. 5, each optical fiber 40 has a core 40a extending in a longitudinal direction A (see FIGS. 1 to 3), and a cladding 40b extending in the longitudinal direction A and covering the core 40a. Each optical fiber 40 also has a tip face 40c. The tip face 40c is composed of the tip of the core 40a and the tip of the cladding 40b. The core 40a mainly includes silica glass doped with a dopant such as germanium to increase the refractive index. The cladding 40b mainly includes silica glass doped with a dopant such as fluorine to decrease the refractive index. The composition of the core 40a and the cladding 40b and the combination of the dopants can be appropriately selected. Such an optical fiber 40 propagates an optical signal through each core 40a.

[0036] The optical fiber 40 is, for example, a single mode fiber. In this case, the refractive index distribution in the radial direction of the optical fiber 40 is trench type. This reduces the optical loss when the optical fiber 40 is bent, compared to when the refractive index distribution is single-peaked. The optical losses when light having a wavelength of 1.55 μm and light having a wavelength of 1.625 μm are passed through the optical fiber 40 may be 0.15 dB or less and 0.45 dB or less, respectively. The refractive index distribution in the radial direction of the optical fiber 40 may be single-peaked.

[0037] The optical fibers 40 are arranged two-dimensionally in a cross section perpendicular to the longitudinal direction A. In the example shown in FIG. 5, four optical fibers 40 are arranged in a square lattice of two rows and two columns. The second optical connector 20 has four optical fibers 40 in this embodiment. The second optical connector 20 may have seven optical fibers 40, eight optical fibers 40, or nineteen optical fibers 40. The number of optical fibers in the second optical connector 20 is not limited to the above. The number and arrangement of the optical fibers 40 in the second optical connector 20 correspond one-to-one to the number and arrangement of the cores 12a of the MCF 12 in the first optical connector 10. In other words, the arrangement of the optical fibers 40 matches the arrangement of the cores 12a of the MCF 12. However, the number and arrangement of the multiple optical fibers 40 do not need to completely match the number and arrangement of the MCF 12, and a configuration in which at least one of the multiple optical fibers 40 is not optically connected to the core 12a may be used, or a configuration in which at least one of the multiple cores 12a is not optically connected to the optical fiber 40 may be used. The multiple optical fibers 40 are optically coupled to each core 12a of the MCF 12 of the first optical connector 10 by being rotated and adjusted around the central axis of the ferrule 50.

[0038] The diameter (core diameter) of each core 40a may be, for example, 10 μm or less, or 5 μm or less. The diameter (core diameter) of each core 40a may be, for example, 1 μm or more. The core pitch (center-to-center distance) between adjacent cores 40a may be, for example, 10 μm or more and 50 μm or less. The diameter (cladding diameter) of the cladding 40b may be, for example, 80 μm or more and 125 μm or less outside the ferrule 50 described later, and is made thinner inside the ferrule 50 than the outside of the ferrule 50. The circumscribing circle of the bundle of the multiple claddings 40b made thinner matches the cladding diameter of the MCF 12.

[0039] The outer diameter of the cladding 40b is converted to be thinner inside the ferrule 50 from the outer diameter outside the ferrule 50. Such an optical fiber can be realized by etching the tip portion with hydrofluoric acid or the like. FIG. 6 is a schematic diagram showing an optical fiber 40 as viewed in a direction intersecting the longitudinal direction A. Each optical fiber 40 has a glass fiber 41 made of glass and a coating 42 made of resin. The glass fiber 41 includes a first diameter portion 43, a second diameter portion 44, and a tapered portion 45 connecting the first diameter portion 43 and the second diameter portion 44. The portion of the glass fiber 41 that is continuous with the second diameter portion 44 is covered and coated with the coating 42. The portion of the glass fiber 41 that is continuous with the second diameter portion 44 and the coating 42 constitute a coating portion 46. The coating 42 is usually made of an organic resin material, and furthermore, an ultraviolet-curable resin or a thermosetting resin is used.

[0040] The first diameter portion 43 includes a tip surface 40c. The first diameter portion 43 extends from the tip surface 40c along the longitudinal direction A. The diameter of the first diameter portion 43 is, for example, 40 μm. The tapered portion 45 is continuous with the first diameter portion 43 and extends along the longitudinal direction A. The length of the tapered portion 45 along the longitudinal direction A is, for example, 0.1 mm or more and 0.5 mm or less. The diameter of the tapered portion 45 increases from the first diameter portion 43 toward the second diameter portion 44. The second diameter portion 44 is continuous with the tapered portion 45 and extends along the longitudinal direction A. In other words, the tapered portion 45 is located between the first diameter portion 43 and the second diameter portion 44 in the longitudinal direction A. The second diameter portion 44 has a diameter larger than that of the first diameter portion 43. The diameter of the second diameter portion 44 is, for example, 80 μm or more and 125 μm or less. The coating 42 covers the periphery of the glass fiber 41 at a coating portion 46. The positional deviation between the tapered portions 45 of the optical fibers 40 in the longitudinal direction A may be 1 mm or less.

[0041] 7 and 8 are perspective views showing the optical fibers 40 on the outside of the ferrule 50 and the flange 60. As shown in FIG. 7, the optical fibers 40 extend from the rear end 60b of the flange 60 to the rear of the flange 60. The coating 46 includes a first portion 46a that is continuous with the second diameter portion 44 and is led out of the inner hole 61, a second portion 46b that is separated from the inner hole 61, and a connecting portion 46c that connects the first portion 46a and the second portion 46b. The first portion 46a is two-dimensionally arranged in a cross section that intersects with the central axes of the optical fibers 40. The second portion 46b is one-dimensionally arranged (in a row) in a cross section that intersects with the central axes of the optical fibers 40.

[0042] The multiple connecting portions 46c include an arrangement change portion 47. The multiple optical fibers 40 are arranged at the arrangement change portion 47 at a certain distance from the rear end 60b of the flange 60, and are arranged at the arrangement change portion 47 from a two-dimensional arrangement to a one-dimensional arrangement. The portion of the multiple optical fibers 40 behind the arrangement change portion 47 (i.e., the second portion 46b) constitutes a four-core ribbon core wire. The ribbon core wire has a second coating 49b that collectively surrounds the coatings 42 of the second portions 46b of the multiple optical fibers 40. The average thickness of the second coating 49b is, for example, 0.01 mm or more and 0.25 mm or less. The multiple optical fibers 40 are separated into two two-core ribbon core wires by tearing the second coating 49b at a boundary 48 between the connecting portion 46c and the second portion 46b, and are further separated into single cores at the first portion 46a in front of the connecting portion 46c by removing the second coating 49b. The first portions 46a of the multiple optical fibers 40 are aligned in a two-dimensional array near the flange 60, and the coatings 42 of the first portions 46a are fixed to one another. In the example shown in Fig. 7, the multiple first portions 46a separated from the single fibers and aligned in a two-dimensional array are inserted into an inner hole 61 of the flange 60 (see Fig. 3).

[0043] A protective member that collectively protects the multiple boundaries 48 may be provided at the boundaries 48 of the multiple optical fibers 40. The protective member may collectively protect the multiple connecting portions 46c and the multiple boundaries 48, may collectively protect the multiple second portions 46b, the multiple connecting portions 46c, and the multiple boundaries 48, or may collectively protect the multiple first portions 46a, the multiple second portions 46b, the multiple connecting portions 46c, and the multiple boundaries 48.

[0044] Fig. 8 shows the vicinity of the ends of the multiple optical fibers 40. As shown in Fig. 8, each of the multiple optical fibers 40 further includes an end face 40d opposite to the tip face 40c. In the example shown in Fig. 8, the four end faces 40d are arranged one-dimensionally (in a row).

[0045] The coating 42 of each of the optical fibers 40 includes a tip portion 42a (see FIG. 6) adjacent to the second diameter portion 44 and a terminal portion 42b (see FIG. 8) opposite to the tip portion 42a. The tip portion 42a constitutes an outer peripheral portion of the tip of the first portion 46a. The terminal portion 42b constitutes an outer peripheral portion of the tip of the second portion 46b. The coating 42 of each optical fiber 40 is fixed to the coating 42 of at least one of the other optical fibers 40. The tip portions 42a are fixed to each other. The terminal portions 42b are fixed to each other, so that the second portions 46b constitute a ribbon core wire. The tip portions 42a are fixed to each other by an adhesive. The terminal portion 42b may be fixed by an adhesive or by the second coating 49b.

[0046] In the illustrated example, the coatings 42 of the joint portions 46c of the upper two optical fibers 40 among the four optical fibers 40 are further covered with a second coating 49b, and thus the two optical fibers 40 are fixed to each other, thereby forming a tape (integrated). The coatings 42 of the joint portions 46c of the lower two optical fibers 40 among the four optical fibers 40 are further covered with a second coating 49b, and thus the two optical fibers 40 are fixed to each other, thereby forming a tape (integrated). The coatings 42 of the second portions 46b of the four optical fibers 40 are further covered with a second coating 49b, and thus formed into a tape (integrated). As a result, in the second portions 46b of the multiple optical fibers 40, all of the multiple optical fibers 40 are tape (integrated) up to the vicinity of the ends.

[0047] The coating 42 has a different appearance for each optical fiber 40. Specifically, in each of the multiple optical fibers 40, the appearance of the tip portion 42a of the coating 42 and the appearance of the end portion 42b of the coating 42 each include a color or coloring. In each of the multiple optical fibers 40, the color or coloring of the tip portion 42a and the color or coloring of the end portion 42b correspond to each other (for example, match). The color or coloring of the coating 42 is different for each optical fiber 40. As an example, the coatings 42 of the four optical fibers 40 each include gray, pink, green, and orange. The coating 42 does not have to be formed from a single material. In a cross section perpendicular to the longitudinal direction of the optical fiber 40, the coating 42 may be formed to form a plurality of concentric layers with the central axis of the optical fiber 40 as the axis, and the color or coloring of the coating 42 located at the outermost layer of each optical fiber 40 may be different for each optical fiber 40.

[0048] As shown in Fig. 3, the ferrule 50 extends along the longitudinal direction A. The ferrule 50 is a cylindrical member made of, for example, ceramic such as zirconia, glass, or metal. The ferrule 50 holds the tip portions of the multiple optical fibers 40 together. The ferrule 50 has a front end 50a in the longitudinal direction A, a rear end 50b on the opposite side of the front end 50a in the longitudinal direction A, an end face 50c located at the front end 50a, and an inner hole 51 (first fiber storage hole). The inner hole 51 is a through hole that extends from the rear end 50b to the front end 50a, and stores the multiple optical fibers 40 as shown in Fig. 5.

[0049] FIG. 9 is a cross-sectional view showing a schematic view of the inner hole 51. The inner hole 51 includes a first portion 52 located at the front end 50a, a second portion 53 located at the rear end 50b, and an inner diameter conversion portion 54 connecting the first portion 52 and the second portion 53. The first portion 52 extends from the front end 50a along the longitudinal direction A. The inner diameter of the first portion 52 is smaller than the inner diameter of the second portion 53. The inner diameter of the first portion 52 is equal to or slightly larger than the diameter of the circumscribing circle of the bundle of the first diameter portions 43 of the multiple optical fibers 40. The inner diameter of the first portion 52 is, for example, 90 μm or more and 100 μm or less. The inner diameter conversion portion 54 is continuous with the first portion 52 and extends along the longitudinal direction A. The inner diameter of the inner diameter conversion portion 54 coincides with the inner diameter of the first portion 52 at the boundary with the first portion 52, expands from the first portion 52 toward the second portion 53, and coincides with the inner diameter of the second portion 53 at the boundary with the second portion 53. The inner diameter conversion portion 54 may have a tapered shape or may have a curvature in the cross section. The second portion 53 is continuous with the inner diameter conversion portion 54 and extends along the longitudinal direction A. In other words, the inner diameter conversion portion 54 is located between the first portion 52 and the second portion 53 in the longitudinal direction A. The inner diameter of the second portion 53 is, for example, 300 μm or more and 400 μm or less.

[0050] 10 is a schematic cross-sectional view showing multiple optical fibers 40 inserted into an inner hole 51 of a ferrule 50 and an inner hole 61 (described later) of a flange 60. The ferrule 50 holds a first diameter section 43, a tapered section 45, and a second diameter section 44. A portion of the first diameter section 43 of the multiple optical fibers 40 is inserted into a first portion 52 and an inner diameter conversion section 54 of the inner hole 51. A remaining portion of the first diameter section 43, the tapered section 45, and a portion of the second diameter section 44 of the multiple optical fibers 40 are inserted into a second portion 53 of the inner hole 51.

[0051] A plurality of optical fibers 40 are fixed to the ferrule 50 by an adhesive. Specifically, the first diameter portion 43, the tapered portion 45, and the second diameter portion 44 are fixed to the inner hole 51 by the adhesive 28 (see FIG. 5) so that the tip faces 40c of the plurality of optical fibers 40 are exposed at the end face 50c of the ferrule 50. The first diameter portion 43, the tapered portion 45, and the second diameter portion 44 are bonded and fixed to each other by the adhesive 28 injected into the gap between the inner hole 51. The adhesive 28 is, for example, a thermosetting epoxy adhesive, and the adhesive 28 can be hardened by heating after the adhesive 28 is injected into a predetermined position. The length of the ferrule 50 in the longitudinal direction A is, for example, 6 mm or more and 8 mm or less. In addition, when the ferrule 50 is made of glass, the adhesive 28 may be an ultraviolet-curing epoxy adhesive or an ultraviolet-curing acrylic adhesive.

[0052] As shown in FIG. 10, the flange 60 is a cylindrical member that holds the rear end portion of the ferrule 50 and stores a plurality of optical fibers 40 therein. The flange 60 has an inner hole 61 (second fiber storage hole) that is a through hole extending along the longitudinal direction A. The inner hole 61 communicates with the inner hole 51 at the rear end 50b of the ferrule 50. The inner hole 51 and the inner hole 61 have the same central axis L1. The boundaries between the second diameter portion 44 and the coating portion 46 of the plurality of optical fibers 40 are inserted into the inner hole 61. That is, the remaining portion of the second diameter portion 44 and a part of the coating portion 46 are inserted into the inner hole 61. The portion of the second diameter portion 44 stored in the inner hole 61 and the coating 42 of the portion of the coating portion 46 stored in the inner hole 61 may be fixed in the flange 60 by an adhesive. The flange 60 is made of, for example, glass, metal, or resin. When four optical fibers 40 with coatings 42 having an outer diameter of 250 μm are bundled and inserted into inner hole 61, the diameter of the circumscribed circle of the bundle is 604 μm. Therefore, in this case, the inner diameter of inner hole 61 is 604 μm or more.

[0053] 11 is a perspective view showing the configuration of the optical fibers 40 in the inner hole 51 and the inner hole 61. The arrangement order of the coatings 46 in the inner hole 61 is the same as the arrangement order of the first diameter portions 43 of the optical fibers 40 at the front end 50a of the ferrule 50. That is, the first diameter portions 43 of each optical fiber 40 do not intersect with the first diameter portions 43 of other optical fibers 40 in the inner hole 51 of the ferrule 50. Here, the intersection means that the relative positional relationship of the first diameter portions 43 of the optical fibers 40 changes between one end and the other end of the first diameter portions 43 in the longitudinal direction A. The intersection means, for example, that the optical fibers 40 are entangled like a braid. Furthermore, the arrangement of the tip faces 40c of the multiple optical fibers 40 at the front end 50a of the ferrule 50 is not misaligned in the circumferential direction about the central axis L1 of the inner holes 51, 61 with respect to the arrangement of the coatings 46 of the multiple optical fibers 40 in the inner hole 61 of the flange 60, or if there is any misalignment, the misalignment is an angle of less than 90 degrees around the central axis L1. Note that, if permissible as a required characteristic of the product, either the intersection of the first diameter portions 43 or the above-mentioned misalignment of 90 degrees or more may occur.

[0054] Next, a method for manufacturing the above-mentioned optical connection structure 1 will be described. First, the first optical connector 10 including the structure 100 is manufactured. Specifically, first, the MCF 12, the ferrule 14, and the flange 16 are prepared. In the MCF 12, the cores 12a are arranged in a predetermined manner (for example, four cores 12a are arranged in a square).

[0055] Next, the MCF 12 is inserted into the inner hole of the flange 16 and the inner hole 14a of the ferrule 14, and the tip portion 12d of the MCF 12 is fitted into the inner hole 14a of the ferrule 14. At this time, the tip surface 12c of the MCF 12 may be aligned with the end surface 14b of the ferrule 14, or the tip surface 12c of the MCF 12 may be polished together with the end surface 14b of the ferrule 14 after fitting. For example, when polishing so as to be connected by PC (Physical Contact), the radius of curvature of the end surface 14b of the ferrule 14 is, for example, 1 mm or more and 50 mm or less. The structure 100 is prepared by accommodating the ferrule 14 and the flange 16 in a housing not shown. Then, the first optical connector 10 is prepared by accommodating the ferrule 14 and the flange 16 in a housing not shown.

[0056] Next, the second optical connector 20 including the optical fiber bundle 200 is manufactured. The manufacturing method of the optical fiber bundle 200 will be described below. FIG. 12 is a flowchart showing the manufacturing method of the optical fiber bundle 200. First, a ferrule 50 having a front end 50a, a rear end 50b, and an inner hole 51 is prepared (step S01: step of preparing a ferrule). Next, a flange 60 having an inner hole 61 is prepared (step S02: step of preparing a holding portion). Note that the preparation of the flange 60 may be performed before the preparation of the ferrule 50, or these preparations may be performed in parallel.

[0057] Next, a plurality of optical fibers 40 each having a glass fiber 41 and a coating 42 are prepared (step S03: preparing a plurality of optical fibers). The process of preparing a plurality of optical fibers 40 includes a process of forming a first diameter portion 43 and a tapered portion 45 by processing the glass fiber of the optical fiber 40 to have a small diameter (forming the first diameter portion 43 and the tapered portion 45). In the process of forming the first diameter portion 43 and the tapered portion 45, the plurality of optical fibers 40 are separated from each other over a length of 10 mm or more from the tip of a ribbon core wire in which a plurality of optical fibers 40 are integrated, and the tip of the glass fiber 41 of each optical fiber 40 is chemically etched. As an example, only the tip portion of the ribbon core wire made of a plurality of optical fibers 40 is separated into a single fiber, and the tip portion is immersed in an etchant for chemical etching. The etchant is, for example, hydrofluoric acid. In this way, by separating only the tip portion of the ribbon core wire into a single core and leaving the remaining portion as a ribbon core wire, the unevenness and entanglement of the optical fibers 40 from the step of inserting the optical fibers 40 (step S04) to the step of fixing the optical fibers (step S07) are suppressed, and workability is improved. In addition, in the step of preparing the optical fibers 40, the coating 42 of the first portion 46a of each of the optical fibers 40 is fixed to the coating 42 of the first portion 46a of at least one (e.g., all) of the other optical fibers 40 by, for example, an adhesive, in a state in which the first portions 46a of the optical fibers 40 are arranged in a predetermined order corresponding to the arrangement of the cores 12a of the MCF 12. The preparation of the optical fibers 40 may be performed before the preparation of one or both of the flange 60 and the ferrule 50, or may be performed in parallel with the preparation of one or both of the flange 60 and the ferrule 50. In addition, the step of preparing the optical fibers 40 (step S03) may include a step of changing the appearance of the coating 42. The modifying step may involve changing the appearance of the coating 42 by painting the coating 42 with a pen or the like.

[0058] Next, the optical fibers 40 are inserted into the inner hole 61 of the flange 60 and the inner hole 51 of the ferrule 50 (step S04: inserting step). In this step, the optical fibers 40 are inserted into the inner hole 61 of the flange 60 and the inner hole 51 of the ferrule 50 at once, and the optical fibers 40 are arranged in the inner hole 51 of the ferrule 50. Specifically, first, the coatings 46 of the optical fibers 40 are arranged on a jig, so that the optical fibers 40 are aligned in a predetermined arrangement and temporarily fixed. Next, as shown in FIG. 10, the first diameter portions 43 of the optical fibers 40 are inserted into the first portion 52 of the inner hole 51 of the ferrule 50. At the same time, the tapered portion 45 of the optical fibers 40 is inserted into the second portion 53 of the inner hole 51 of the ferrule 50. At the same time, the boundary between the second diameter portion 44 and the coatings 46 of the optical fibers 40 is inserted into the inner hole 61 of the flange 60. At this time, the multiple optical fibers 40 are arranged in the ferrule 50 so as to correspond to the arrangement of the cores 12a of the MCF 12 (for example, two-dimensionally in a cross section intersecting with the longitudinal direction A). At this time, the optical fibers 40 are arranged so that the clads 40b are in contact with each other and also in contact with the inner hole 51 of the ferrule 50. Thereafter, the jig is removed from the multiple optical fibers 40.

[0059] FIG. 13 is a diagram showing a state in the middle of inserting a plurality of optical fibers 40 into the ferrule 50. As shown in FIG. 13, when the plurality of optical fibers 40 are inserted deep into the inner hole 51 of the ferrule 50, the optical fibers 40 come into contact with the inner diameter conversion portion 54 of the ferrule 50. At this time, the optical fibers 40 cannot move toward the front end 50a (see FIG. 10) of the ferrule 50 and stop. In this state, the bending of the first diameter portion 43 of the optical fiber 40 becomes large in the inner diameter conversion portion 54, and bending loss and breakage may occur in the first diameter portion 43. Therefore, in the above-mentioned inserting step, as shown in FIG. 13, the optical fiber 40 is inserted until it hits the inner diameter conversion portion 54, and then, as shown in FIG. 10, the optical fiber 40 is pulled back a certain distance. As a result, the first diameter portion 43 can be inserted into the first portion 52 while bending the first diameter portion 43 with a small curvature in the second portion 53 of the inner hole 51 of the ferrule 50 and the inner diameter conversion portion 54. As a result, bending loss and breakage in the first diameter portion 43 can be suppressed.

[0060] Next, the arrangement of the optical fibers 40 at the front end 50a of the ferrule 50 is confirmed (step S05: confirmation step). Specifically, the arrangement of the optical fibers 40 at the front end 50a of the ferrule 50 is confirmed by conducting light from the end face 40d of each of the optical fibers 40 and observing the tip face 40c of each of the optical fibers. That is, the light is conducted from the end face 40d of each of the optical fibers 40 to confirm the correspondence between the end face 40d and the tip face 40c of each of the optical fibers 40. As an example, a red laser light is incident on the end face 40d of the optical fiber 40. In this case, the red laser light is emitted from the core 40a of the optical fiber 40 at the front end 50a of the ferrule 50. At this time, the tip faces 40c of the optical fibers are magnified and observed with a microscope or the like to record the position where the red laser light is emitted. This makes it possible to confirm the correspondence between the end face 40d and the tip face 40c of each of the optical fibers 40. The light incident on the optical fiber 40 may be visible light.

[0061] Next, it is determined whether or not one or both of intersection and misalignment have occurred (step S06: determining step). An intersection is an intersection between the first diameter portion 43 of one optical fiber 40 and the first diameter portion 43 of another optical fiber 40 among the multiple optical fibers 40 in the inner hole 51 of the ferrule 50. A misalignment is a misalignment between the arrangement of the multiple optical fibers 40 at the front end 50a of the ferrule 50 and the arrangement of the multiple optical fibers 40 in the inner hole 61. The misalignment is a misalignment of a predetermined angle or more in the circumferential direction centered on the central axis L1 of the inner hole 51. The predetermined angle is, for example, 90 degrees. A misalignment that occurs when the multiple optical fibers 40 rotate together is called a twist.

[0062] The determination step (step S06) will be described in more detail below. First, based on the appearance of the coating 42 of the optical fiber 40, the correspondence between the coating portions 46 of the optical fibers 40 at the rear end 50b of the ferrule 50 and the end faces 40d of the optical fibers 40 is confirmed. Next, the correspondence between the end face 40d and the tip face 40c confirmed in step S05 is applied to the correspondence between the coating portions 46 of the flange 60 and the end face 40d, thereby confirming the correspondence between the coating portions 46 of the flange 60 and the tip face 40c of the front end 50a of the ferrule 50.

[0063] Next, based on the correspondence between the coatings 46 in the flange 60 and the tip face 40c at the front end 50a of the ferrule 50, the arrangement of the coatings 46 of the multiple optical fibers 40 in the inner hole 61 (hereinafter referred to as the "coating arrangement") is compared with the arrangement of the multiple optical fibers 40 at the front end 50a of the ferrule 50 (hereinafter referred to as the "tip face arrangement"). Finally, based on the comparison result between the coating arrangement and the tip face arrangement, it is determined whether or not one or both of a misalignment and an intersection have occurred.

[0064] FIG. 14 is a diagram showing an example of a covering portion arrangement. FIG. 15 to FIG. 17 are diagrams showing an example of a tip surface arrangement. In the example shown in FIG. 14, covering portions 46(1), 46(2), 46(3), and 46(4) are arranged in this order in a clockwise direction. In the example shown in FIG. 15, tip surfaces 40c(1), 40c(2), 40c(3), and 40c(4) are arranged in this order in a clockwise direction. In the example shown in FIG. 16, tip surfaces 40c(1), 40c(2), 40c(3), and 40c(4) are arranged in the clockwise direction in the order of tip surfaces 40c(1), 40c(4), 40c(3), and 40c(2). In the example shown in FIG. 17, the tip faces 40c(1), 40c(2), 40c(3), and 40c(4) are arranged clockwise in the order of tip faces 40c(4), 40c(1), 40c(2), and 40c(3).

[0065] For example, when the covering portion arrangement shown in FIG. 14 is compared with the tip face arrangement shown in FIG. 15, the clockwise arrangement of the covering portions 46 matches the clockwise arrangement of the tip faces 40c. In this case, it can be determined that no intersection occurs in the inner hole 51 of the ferrule 50. In addition, when the covering portion arrangement shown in FIG. 14 is compared with the tip face arrangement shown in FIG. 15, no misalignment occurs between the tip face 40c and the covering portion 46 in the circumferential direction about the central axis L1 of the inner hole 51 (in other words, the angular misalignment between the tip face 40c and the covering portion 46 is 0 degrees). In this case, it can be determined that no misalignment occurs between the tip face 40c and the covering portion 46 in the circumferential direction about the central axis L1 in the inner hole 51 of the ferrule 50. In this example, there is no intersection between the multiple optical fibers 40, and no misalignment between the tip face 40c and the coating portion 46, so the radius of curvature of the first diameter portion 43 in the inner hole 51 of the ferrule 50 is a large value, for example, 32.5 mm or more.

[0066] Also, for example, when comparing the coating arrangement shown in FIG. 14 with the tip face arrangement shown in FIG. 16, the clockwise arrangement order of the coatings 46 does not match the clockwise arrangement order of the tip faces 40c. In this case, it can be determined that the multiple optical fibers 40 cross each other in the inner hole 51 of the ferrule 50. When comparing the coating arrangement shown in FIG. 14 with the tip face arrangement shown in FIG. 16, there is no misalignment in the circumferential direction around the central axis L1 of the inner hole 51 between the tip face 40c and the coating 46 (in other words, the misalignment between the tip face 40c and the coating 46 is 0 degrees). In this case, it can be determined that there is no misalignment in the circumferential direction around the central axis L1 between the tip face 40c and the coating 46 in the inner hole 51 of the ferrule 50. In this example, since there is an intersection between the multiple optical fibers 40, the radius of curvature of the first diameter portion 43 in the inner hole 51 of the ferrule 50 is a small value, for example, 17.0 mm or less.

[0067] Furthermore, for example, when comparing the coating arrangement shown in FIG. 14 with the tip face arrangement shown in FIG. 17, the clockwise arrangement order of the coatings 46 matches the clockwise arrangement order of the tip faces 40c. In this case, it can be determined that no intersection occurs between the multiple optical fibers 40 in the inner hole 51 of the ferrule 50. However, when comparing the coating arrangement shown in FIG. 14 with the tip face arrangement shown in FIG. 17, a deviation of an angle θ occurs between the tip face 40c and the coatings 46 along the circumferential direction centered on the central axis L1 of the inner hole 51. The angle θ is an angle formed by a straight line B1 passing through the center of the inner hole 61 and the center of a certain tip face 40c in FIG. 14 and a straight line B2 passing through the center of the inner hole 51 and the center of the tip face 40c in FIG. 17. When the angle θ is less than a predetermined angle (for example, less than 90 degrees), it can be determined that no deviation occurs between the tip face 40c and the coatings 46 in the inner hole 51 of the ferrule 50. When the angle θ is equal to or larger than a predetermined angle (e.g., equal to or larger than 90 degrees), it can be determined that there is a misalignment between the tip face 40c and the covering portion 46 in the inner hole 51 of the ferrule 50. When there is a misalignment of 90 degrees or more, the radius of curvature of the first diameter portion 43 in the inner hole 51 of the ferrule 50 is a small value, for example, equal to or smaller than 17.0 mm.

[0068] If it is determined that one or both of the intersection and the misalignment have occurred (step S06: YES), the inserting step (step S04), the checking step (step S05), and the determining step (step S06) are executed again. In this case, in the inserting step, the multiple optical fibers 40 may be inserted again into the ferrule 50, or the multiple optical fibers 40 may be vibrated or moved along the longitudinal direction A without being removed from the ferrule 50. If it is determined that neither the intersection nor the misalignment have occurred (step S06: NO), the process proceeds to the fixing step (step S07).

[0069] In the determining step (step S06), it may be determined whether or not an intersection has occurred. If it is determined that an intersection has occurred (step S06: YES), the inserting step (step S04), the checking step (step S05), and the determining step (step S06) are executed again. If it is determined that an intersection has not occurred (step S06: NO), the process proceeds to the fixing step (step S07). In the determining step (step S06), it may be determined whether or not a deviation has occurred. If it is determined that a deviation has occurred (step S06: YES), the inserting step (step S04), the checking step (step S05), and the determining step (step S06) are executed again. If it is determined that a deviation has not occurred (step S06: NO), the process proceeds to the fixing step (step S07).

[0070] Next, the optical fibers 40 are fixed to the ferrule 50 by adhesive (step S07: fixing process). Specifically, first, the adhesive 28 is injected into the gap between the inner hole 51 of the ferrule 50 and the optical fibers 40. At this time, the adhesive 28 is injected sufficiently to cover the tip faces 40c of the optical fibers 40 and the end face 50c of the ferrule 50. Then, the adhesive 28 is thermally cured, for example, by heating. As a result, the optical fibers 40 are fixed to the ferrule 50 such that the arrangement order of the coating parts 46 in the inner hole 61 is the same as the arrangement order of the first diameter parts 43 of the optical fibers 40 at the front end 50a of the ferrule 50. Then, the end face 50c of the ferrule 50 is polished together with the tip faces 40c of the optical fibers 40. By polishing, the adhesive on the tip faces 40c and the end faces 50c is removed, and the tip faces 40c and the end faces 50c are exposed. When polishing for PC connection, the radius of curvature of the end face 50c of the ferrule 50 is, for example, 1 mm or more and 50 mm or less, as described above. In this manner, the optical fiber bundle 200 is prepared. Then, the second optical connector 20 is prepared by accommodating the ferrule 50 and the flange 60 in a housing (not shown).

[0071] Next, the split sleeve 30 is prepared. Then, the first optical connector 10 and the second optical connector 20 are connected to each other so that the end face 14b of the ferrule 14 and the end face 50c of the ferrule 50 abut against each other within the split sleeve 30. Next, one or both of the ferrule 14 and the ferrule 50 are rotated and aligned within the split sleeve 30 so that each core 12a of the MCF 12 and each corresponding core 40a of the multiple optical fibers 40 are optically coupled to each other.

[0072] Next, after the alignment is completed, the first optical connector 10 and the second optical connector 20 are fixed in a state in which they are pressed against each other. At this time, a pressing member may be used to press the ferrule 14 and the ferrule 50 by friction with the split sleeve 30, or the ferrule 14 and the ferrule 50 may be bonded and fixed with an adhesive. In this manner, the optical connection structure 1 can be manufactured.

[0073] Next, a method for determining the state of the optical fibers 40 in the inner hole 51 of the ferrule 50 when the optical fibers 40 are inserted into the inner hole 51 of the ferrule 50 from the rear end 50b of the ferrule 50 will be described. First, the arrangement of the optical fibers 40 at the front end 50a of the ferrule 50 is confirmed (step S05: confirming step). Then, it is determined whether or not one or both of intersection and misalignment have occurred (step S06: determining step).

[0074] The following describes the effects and advantages obtained by the optical fiber bundle 200, the optical connection structure 1, and the manufacturing method for the optical fiber bundle 200 according to the present embodiment described above. In a conventional optical fiber bundle, when multiple optical fibers are inserted into a ferrule, the optical fibers may be misaligned in the longitudinal direction. In this case, it is necessary to increase the amount of optical fiber inserted into the ferrule, which may increase the curvature of the multiple optical fibers and increase the bending loss in the multiple optical fibers.

[0075] In the optical fiber bundle 200 according to the present embodiment, the coating 42 of the first portion 46a of the coating portion 46 of each of the optical fibers 40 is fixed to the coating 42 of the first portion 46a of the coating portion 46 of at least one of the other optical fibers 40. With this configuration, the positions of the optical fibers 40 in the inner hole 51 and the inner hole 61 are prevented from being misaligned with each other along the longitudinal direction A. This prevents the insertion amount of the optical fibers 40 into the ferrule 50 from becoming excessive. As a result, an increase in the curvature of the optical fiber 40 is prevented. In addition, the order of the coating portions 46 of the optical fibers 40 in the inner hole 61 is the same as the order of the first diameter portions 43 of the optical fibers 40 at the front end 50a of the ferrule 50. With this configuration, the intersection of the optical fibers 40 inside the ferrule 50 is prevented. From the above, the bending loss in the optical fibers 40 can be reduced.

[0076] As in this embodiment, the coating portion 46 of the optical fibers 40 includes a connecting portion 46c that connects the first portion 46a and the second portion 46b. The coatings 42 of the first portions 46a of the optical fibers 40 are fixed to each other so that the first portions 46a of the optical fibers 40 are arranged two-dimensionally in a cross section intersecting the central axes of the optical fibers 40. The coatings 42 of the second portions 46b of the optical fibers 40 are fixed to each other so that the second portions 46b of the optical fibers 40 are arranged one-dimensionally in a cross section intersecting the central axes of the optical fibers 40. In this way, the first portions 46a of the coating portion 46 are arranged two-dimensionally, which makes it easier to optically couple the optical fibers 40 to the cores 12a of the MCF 12. In addition, the second portions 46b of the coating portion 46 are arranged one-dimensionally, which prevents the optical fibers 40 from scattering and becoming entangled with each other. As a result, when a measurement or the like is performed using the optical fiber bundle 200, it is possible to improve the workability of the measurement or the like.

[0077] As in the present embodiment, the optical fiber bundle 200 may include a protective member that protects at least the boundary 48 between the connecting portion 46c and the second portion 46b of each of the multiple optical fibers 40. In this case, unintentional separation of the coatings 42 of the second portions 46b of the multiple optical fibers 40 is suppressed.

[0078] As in the present embodiment, the second portions 46b of the coatings 46 of the multiple optical fibers 40 form one ribbon fiber. In this case, the multiple optical fibers 40 are further prevented from becoming scattered and entangled with each other.

[0079] As in this embodiment, the ribbon core wire has a second coating 49b that collectively surrounds the coatings 42 of the second portions 46b of the multiple optical fibers 40. The average thickness of the second coating 49b is 0.01 mm or more and 0.25 mm or less. With this configuration, since the thickness of the second coating 49b is 0.01 mm or more, the second coating 49b has sufficient strength to prevent the coatings 42 of the second portions 46b that constitute the ribbon core wire from being separated from each other. Furthermore, since the thickness of the second coating 49b is 0.25 mm or less, the second coating 49b can be easily removed when separating the first portions 46a of the coating portion 46 into individual fibers.

[0080] In this embodiment, the coatings 42 of the first portions 46a are fixed to each other by an adhesive, so that the coatings 42 can be easily fixed to each other.

[0081] As in this embodiment, the appearance of the coatings 42 of the multiple optical fibers 40 includes different colors or hues for each optical fiber 40. In this case, the multiple optical fibers 40 can be easily distinguished from one another.

[0082] As in the present embodiment, the positional deviation between the tapered portions 45 of the optical fibers 40 in the longitudinal direction A is 1 mm or less. In this case, it is possible to suppress an increase in the insertion amount of the optical fibers 40 into the ferrule 50. This suppresses an increase in the curvature of the optical fiber 40. As a result, it is possible to reduce bending loss in the optical fiber 40.

[0083] The optical connection structure 1 according to this embodiment includes an MCF 12 including a plurality of cores 12a extending along a longitudinal direction A and a cladding 12b covering the plurality of cores 12a, a first optical connector 10 having a ferrule 14 that holds a tip portion 12d of the MCF 12, and a second optical connector 20 having an optical fiber bundle 200. When the second optical connector 20 is connected to the first optical connector 10, the cores 40a of the plurality of optical fibers 40 are optically coupled to the plurality of cores 12a of the MCF 12, respectively. With this optical connection structure 1, it is possible to reduce bending loss in the plurality of optical fibers 40.

[0084] As in this embodiment, the optical connection structure 1 optically couples the MCF 12 and a plurality of optical fibers 40. With this configuration, the optical connection structure 1 can constitute a fan-in / fan-out device (Fan-In / Fan-Out: FIFO) of the MCF 12. FIG. 18 is a diagram showing a FIFO 70. The FIFO 70 has a plurality of connectors 71, a plurality of optical fibers 40A, an optical connection structure 1A, an MCF 12, an optical connection structure 1B, a plurality of optical fibers 40B, and a plurality of connectors 72. A plurality of optical fibers 40A are connected to the plurality of connectors 71, respectively. The plurality of optical fibers 40A are optically coupled to the MCF 12 in the optical connection structure 1A. The MCF 12 is optically coupled to a plurality of optical fibers 40B in the optical connection structure 1B. The plurality of optical fibers 40B are optically coupled to the plurality of connectors 72. In this FIFO 70, a signal input from a connector 71 is propagated through an optical fiber 40A, an MCF 12, and an optical fiber 40B, and is output from a connector 72.

[0085] The optical connection structures 1A and 1B have the same configuration as the optical connection structure 1. This facilitates the alignment process, which is the process of aligning the cores of the MCF 12 and the cores of the optical fibers 40A and 40B and fixing them at a position where the optical loss is minimized. In addition, the optical connection structures 1A and 1B are attached with the connectors 71 and 72 via the multiple optical fibers 40A and 40B. This configuration facilitates repeated IL measurement (insertion loss measurement) when inspecting the FIFO 70 after the alignment process.

[0086] The connectors 71, 72 are fused to the optical fibers 40A, 40B by single-core fusion or multiple-core fusion. When fusion is performed by multiple-core fusion, the multiple connectors 71, 72 can be connected to the multiple optical fibers 40A, 40B in one operation. In this case, the operation time can be shortened compared to single-core fusion. Furthermore, when the multiple optical fibers 40A, 40B are ribbon core wires, the multiple connectors 71, 72 can be easily fused to the multiple optical fibers 40A, 40B. Since it is not necessary to line up and fusion the optical fibers 40A, 40B individually, the fusion operation is simplified, which reduces the manufacturing cost of the FIFO 70 and suppresses a decrease in fusion accuracy.

[0087] In the manufacturing method of the optical fiber bundle 200 according to the present embodiment, the coating 42 of the first portion 46a of each of the optical fibers 40 is fixed to the coating 42 of the first portion 46a of at least one of the other optical fibers 40. With this configuration, the positions of the optical fibers 40 in the inner hole 51 and the inner hole 61 are prevented from being misaligned with each other along the longitudinal direction A. This prevents the insertion amount of the optical fiber 40 into the ferrule 50 from becoming excessive. As a result, an increase in the curvature of the optical fiber 40 is prevented. In addition, the order of the coating portions 46 of the optical fibers 40 in the inner hole 61 is the same as the order of the first diameter portions 43 of the optical fibers 40 at the front end 50a of the ferrule 50. With this configuration, the intersection of the optical fibers 40 inside the ferrule 50 is prevented. From the above, the optical fiber bundle 200 in which the bending loss of the optical fibers 40 is reduced can be manufactured.

[0088] As in the present embodiment, in the insertion step (step S04), the coating portions 46 of the multiple optical fibers 40 are arranged in a jig, so that the multiple optical fibers 40 are aligned and temporarily fixed in a predetermined arrangement, and the jig is removed after the multiple optical fibers 40 are inserted into the ferrule 50. In this case, the multiple coating portions 46 are prevented from scattering and becoming entangled with each other, improving the workability of the insertion step (step S04).

[0089] As in this embodiment, the process of preparing the multiple optical fibers 40 includes a process of separating the multiple optical fibers 40 from each other over a length of 10 mm or more from the tip of a ribbon core formed by integrating the multiple optical fibers 40, and chemically etching the tip of the glass fiber 41 of each optical fiber 40 to form the first diameter portion 43 and the tapered portion 45. In this case, the first diameter portion 43 and the tapered portion 45 of the multiple optical fibers 40 can be easily formed.

[0090] The optical fiber bundle 200, the optical connection structure 1, and the manufacturing method of the optical fiber bundle 200 according to the present disclosure are not limited to the above-mentioned embodiment, and various other modifications are possible. In the above-mentioned embodiment, the coating 42 of the second portion 46b of each of the optical fibers 40 is fixed to the coating 42 of the second portion 46b of the other optical fibers 40, but this is not limited. For example, the coatings 42 of the second portions 46b of the optical fibers 40 may be separated from each other. Even in this case, the first portions 46a of the optical fibers 40 are fixed to each other, so that the positions of the optical fibers 40 are prevented from shifting from each other along the longitudinal direction. This prevents an increase in the curvature of the optical fibers 40.

[0091] In the above embodiment, the first portions 46a are arranged two-dimensionally in a cross section intersecting with the central axes of the optical fibers 40, and the second portions 46b are arranged one-dimensionally in a cross section intersecting with the central axes of the optical fibers 40, but the present invention is not limited thereto. For example, the entire coatings 46 of the optical fibers 40 may be arranged two-dimensionally in a cross section intersecting with the central axes of the optical fibers 40. The coating 42 of each of the optical fibers 40 may be fixed to the coating 42 of at least one of the other optical fibers 40 adjacent to each other. Even in this case, the positions of the optical fibers 40 are prevented from shifting from one another along the longitudinal direction A. This further prevents an increase in the curvature of the optical fibers 40.

[0092] In the above embodiment, the optical fiber bundle 200 may further include a cylinder extending along the longitudinal direction A. The first portions 46a of the optical fibers 40 may be inserted into the cylinder, and the coatings 42 of the first portions 46a may be fixed to the cylinder by an adhesive. In this case, the coatings 42 of the first portions 46a can be firmly fixed to each other.

[0093] In the above embodiment, the optical fiber bundle 200 may further include a cylindrical shrink tube extending along the longitudinal direction A. The first portions 46a of the multiple optical fibers 40 may be housed in the shrink tube and held together. In this case, the coatings 42 of the multiple first portions 46a can be firmly fixed to each other.

[0094] In the above embodiment, the appearance of the coating of the multiple optical fibers 40 includes different colors or shades for each optical fiber, but may include the same color or shades for each optical fiber. [Explanation of symbols]

[0095] 1, 1A, 1B...Optical connection structure 10…First optical connector 12...MCF 12a…Core 12b…Clad 12c…Tip surface 12d…Tip part 14…Ferrule 14a...Inner hole 14b...end face 16...Flange 20…Second optical connector 28…Glue 30…Split sleeve 40, 40A, 40B...Optical fiber 40a…Core 40b…Clad 40c…Tip surface 40d...terminal surface 41...Glass fiber 42…Covering 42a…Tip 42b…Terminal part 43…First diameter section 44…Second diameter section 45…Tapered section 46…Covering part 46a...first part 46b…Second part 46c...Connection part 47…Array change section 48...Border 49b…Second coating 50…Ferrule 50a…front end 50b…rear end 50c...end face 51…Inner hole 52…Part 1 53…Second part 54…Inner diameter conversion part 60...Flange 60b…rear end 61…Inner hole 70…FIFO 71,72…Connector 100...Structure 200...Optical fiber bundle A…Longitudinal direction B1…straight line B2…straight line L1…center axis θ…Angle

Claims

1. An optical fiber bundle for optically coupling a plurality of optical fibers to a multi-core optical fiber, comprising: a ferrule extending along a first direction, the ferrule having a front end in the first direction, a rear end opposite the front end in the first direction, a first portion located at the front end, a second portion located at the rear end and having an inner diameter larger than that of the first portion, and a first fiber storage hole which is a hole including an inner diameter conversion portion connecting the first portion and the second portion; a holding portion having a second fiber housing hole which is a hole extending along the first direction and communicates with the first fiber housing hole at the rear end of the ferrule; a plurality of optical fibers each including a glass fiber including a first diameter portion, a second diameter portion having a diameter larger than a diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion, and wherein at least the first diameter portion, the tapered portion, and the second diameter portion extend along the first direction; and a coated portion in which a portion of the glass fiber connected to the second diameter portion is coated with a coating; the first diameter portions of the optical fibers are inserted into the first portion of the first fiber housing hole, the tapered portions of the optical fibers are inserted into the second portions of the first fiber receiving holes, The second fiber housing hole is inserted into the second diameter portion of each of the optical fibers at a boundary between the second diameter portion and the coating portion, the coating portion of each of the plurality of optical fibers includes a first portion extending from the second fiber housing hole and a second portion distant from the second fiber housing hole, and the coating of the first portion is fixed to the coating of the first portion of the coating portion of at least one of the other optical fibers; an arrangement order of the coating portions of the optical fibers in the second fiber housing hole is the same as an arrangement order of the first diameter portions of the optical fibers in the front end of the ferrule.

2. The first portions of the coatings of the optical fibers are integrated together by bonding the coatings to each other, 2. The optical fiber bundle of claim 1, wherein the coatings are separated from one another in the second portions of the coatings of the optical fibers.

3. the first portions of the coatings of the optical fibers are two-dimensionally arranged in a cross section intersecting with central axes of the optical fibers, 2. The optical fiber bundle according to claim 1, wherein the coating of the second portion of the coating of each of the plurality of optical fibers is fixed to the coating of the second portion of the coating of at least one of the other adjacent optical fibers.

4. The coating portions of the optical fibers further include a connecting portion that connects the first portion and the second portion to each other, the coatings of the first portions of the coating portions of the optical fibers are fixed to each other such that the first portions of the coating portions of the optical fibers are two-dimensionally arranged in a cross section intersecting with central axes of the optical fibers; 2. The optical fiber bundle according to claim 1, wherein the coatings of the second portions of the coating portions of the optical fibers are fixed to each other so that the second portions of the optical fibers are arranged one-dimensionally in a cross section intersecting with the central axes of the optical fibers.

5. 5. The optical fiber bundle according to claim 4, further comprising a protection member for protecting at least a boundary between the coupling portion and the second portion of the coating of each of the plurality of optical fibers.

6. 5. The optical fiber bundle according to claim 4, wherein the second portions of the coatings of the optical fibers constitute one ribbon fiber.

7. the ribbon fiber has another coating that collectively surrounds the coating of the second portion of the coating portion of the plurality of optical fibers, 7. The optical fiber bundle according to claim 6, wherein an average thickness of the second coating is not less than 0.01 mm and not more than 0.25 mm.

8. 8. The optical fiber bundle according to claim 1, wherein the coatings of the first portions of the coating portions of the optical fibers are fixed to each other by an adhesive.

9. The device further includes a cylinder extending along the first direction, 8. The optical fiber bundle according to claim 1, wherein the first portions of the coatings of the optical fibers are inserted into the cylindrical body, and the coatings of the first portions of the coatings are fixed to the cylindrical body by an adhesive.

10. a cylindrical shrink tube extending along the first direction, 8. The optical fiber bundle according to claim 1, wherein the first portions of the coatings of the optical fibers are housed and held together in the shrink tube.

11. 8. The optical fiber bundle according to claim 1, wherein the appearance of the coating of the plurality of optical fibers includes a different color or hue for each of the optical fibers.

12. 8. The optical fiber bundle according to claim 1, wherein the positional deviation between the tapered portions of the plurality of optical fibers in the first direction is 1 mm or less.

13. a first optical connector having a multi-core optical fiber including a plurality of cores extending along the first direction and a cladding covering the plurality of cores, and a ferrule that holds a tip of the multi-core optical fiber; a second optical connector having the optical fiber bundle according to any one of claims 1 to 7; an optical connection structure, wherein when the second optical connector is connected to the first optical connector, each core of the plurality of optical fibers is optically coupled to each of the plurality of cores of the multi-core optical fiber.

14. A method for manufacturing an optical fiber bundle for optically coupling a plurality of optical fibers to a multi-core optical fiber, comprising the steps of: preparing a ferrule extending along a first direction, the ferrule having a front end in the first direction, a rear end opposite the front end in the first direction, a first portion located at the front end, a second portion located at the rear end and having an inner diameter larger than that of the first portion, and a first fiber storage hole which is a hole including an inner diameter conversion portion connecting the first portion and the second portion; preparing a holding portion having a second fiber-housing hole extending along the first direction and communicating with the first fiber-housing hole at the rear end of the ferrule; preparing a plurality of optical fibers each having a glass fiber including a first diameter portion, a second diameter portion having a diameter larger than a diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion, and in which at least the first diameter portion, the tapered portion, and the second diameter portion extend along the first direction; and a coating portion in which a portion of the glass fiber connected to the second diameter portion is covered with a coating; inserting the first diameter portions of the optical fibers into the first portion of the first fiber housing hole, the tapered portions of the optical fibers into the second portion of the first fiber housing hole, and the boundaries between the second diameter portions and the coating portions of the optical fibers into the second fiber housing hole; and fixing the plurality of optical fibers to the ferrule with an adhesive, In the step of preparing the plurality of optical fibers, the coating portion of each of the plurality of optical fibers includes a first portion extending from the second fiber housing hole and a second portion distant from the second fiber housing hole, and the coating of the first portion is fixed to the coating of the first portion of the coating portion of at least one of the other optical fibers, a first diameter portion of the optical fiber bundle that is arranged in a first direction and a second direction of the optical fiber bundle that is arranged in a first direction, the first diameter portion of the optical fiber bundle being arranged in a first direction and a second direction of the optical fiber bundle being arranged in a second ... first direction and a

15. 15. The method for manufacturing an optical fiber bundle according to claim 14, wherein in the inserting step, the coating portions of the plurality of optical fibers are placed in a jig to align and temporarily fix the plurality of optical fibers in a predetermined arrangement, and the jig is removed after the plurality of optical fibers are inserted into the ferrule.

16. 16. The method for manufacturing an optical fiber bundle according to claim 14 or 15, wherein the step of preparing the plurality of optical fibers includes the steps of: separating the plurality of optical fibers from each other over a length of 10 mm or more from a tip of a ribbon core formed by integrating the plurality of optical fibers; and forming the first diameter portion and the tapered portion by chemically etching a tip of the glass fiber of each of the optical fibers.

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