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

Abstract

In an optical fiber bundle (200), each of a plurality of optical fibers (40) includes a first diameter part (43), a second diameter part (44) having a diameter larger than the diameter of the first diameter part (43), and a third diameter part (46) having a diameter larger than the diameter of the second diameter part (44) and including a coating. A resin part (70) includes a first resin part (71) connecting the first diameter part (43), the second diameter part (44), and an inner surface (51a) of a first fiber housing part (51), a second resin part (72) connecting the third diameter part (46) and an inner surface (61a) of a second fiber housing part (61), and a third resin part (73) bonded to the second diameter part (44) and connecting the first resin part (71) and the second resin part (72). The third resin part (73) is separated from the inner surface (61a) of the second fiber housing part (61).

Description

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

[0001] The present disclosure relates to an optical fiber bundle, an optical connection structure, and a method for manufacturing an optical fiber bundle. This application claims priority to Japanese Application No. 2023-213627, filed December 19, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] An optical fiber bundle including a plurality of optical fibers and a ferrule is known (see, for example, Patent Document 1). In Patent Document 1, each of the plurality of optical fibers includes a first diameter portion, a second diameter portion having a diameter larger than that of the first diameter portion, and a third diameter portion having a diameter larger than that of the second diameter portion and covered with resin. The ferrule includes a fiber accommodating portion that accommodates the first diameter portion and a portion of the second diameter portion. The plurality of optical fibers are fixed in the fiber accommodating portion with an adhesive.

[0003] JP 2017-181791 A

[0004] An optical fiber bundle according to one aspect of the present disclosure includes a plurality of optical fibers, a ferrule, a flange, and a resin portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a third diameter portion. The second diameter portion has a diameter larger than that of the first diameter portion. The third diameter portion has a diameter larger than that of the second diameter portion and includes a coating. The ferrule includes a first fiber accommodating portion that accommodates the first diameter portion and a portion of the second diameter portion. The flange is connected to the ferrule. The flange includes a second fiber accommodating portion. The second fiber accommodating portion is in communication with the first fiber accommodating portion and accommodates a portion of the second diameter portion and a portion of the third diameter portion. The resin portion fixes the plurality of optical fibers in the first fiber accommodating portion and the second fiber accommodating portion. The resin portion includes a first resin portion, a second resin portion, and a third resin portion. The first resin portion connects the first diameter portion and the second diameter portion to an inner surface of the first fiber accommodating portion. The second resin portion connects the third diameter portion and the inner surface of the second fiber accommodating portion. The third resin portion is adhered to the second diameter portion and connects the first resin portion and the second resin portion. The third resin portion is spaced apart from the inner surface of the second fiber accommodating portion.

[0005] A method for manufacturing an optical fiber bundle according to another aspect of the present disclosure includes preparing a plurality of optical fibers, a ferrule, a flange, and a resin portion, and filling the first fiber accommodating portion and the second fiber accommodating portion with an adhesive so that a first resin portion, a second resin portion, and a third resin portion are formed and the third resin portion is spaced from an inner surface of the second fiber accommodating portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a third diameter portion. The second diameter portion has a diameter larger than that of the first diameter portion. The third diameter portion has a diameter larger than that of the second diameter portion and includes a coating. The ferrule includes a first fiber accommodating portion that accommodates the first diameter portion and a portion of the second diameter portion. The flange is connected to the ferrule. The flange includes a second fiber accommodating portion. The second fiber accommodating portion is in communication with the first fiber accommodating portion and accommodates a portion of the second diameter portion and a portion of the third diameter portion. The first resin portion connects the first and second diameter portions to the inner surface of the first fiber accommodating portion. The second resin portion connects the third diameter portion to the inner surface of the second fiber accommodating portion. The third resin portion is bonded to the second diameter portion and connects the first resin portion to the second resin portion.

[0006] FIG. 1 is a perspective view showing an optical connection structure according to an 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. FIG. 4 is a view showing the tip of a multicore fiber and the end face of a ferrule. FIG. 5 is a view showing the tips of a plurality of optical fibers and the end face of a ferrule. FIG. 6 is a schematic view showing optical fibers. FIG. 7 is a schematic cross-sectional view showing a fiber accommodating portion of a ferrule. FIG. 8 is an enlarged cross-sectional view of an optical fiber bundle. FIG. 9 is a view showing a state in which a plurality of optical fibers and a multicore fiber are connected together, the optical connection structure being provided with the optical connection structure shown in FIG. 1.

[0007] [Problem to be Solved by the Invention] In order to improve the tensile strength of the optical fiber, it is conceivable to provide a flange connected to the ferrule and fix the optical fiber to the flange with an adhesive. For example, the flange has a fiber accommodating portion that communicates with the fiber accommodating portion of the ferrule, and the optical fiber is also fixed to the fiber accommodating portion of the flange with an adhesive.

[0008] However, the resin portion used as the adhesive expands and contracts depending on the temperature and humidity. If the resin portion expands and contracts inside the fiber accommodating portion, a force is applied to the optical fiber, which may cause the optical fiber to break. The larger the volume of the resin portion in the optical fiber accommodating portion, the greater the force applied to the optical fiber due to the expansion and contraction of the resin portion.

[0009] [Effects of the Present Disclosure] 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 can achieve both a reduction in the force applied to the optical fiber due to the expansion and contraction of the resin part and ensuring the tensile resistance of the optical fiber.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. [1] An optical fiber bundle according to an embodiment of the present disclosure includes a plurality of optical fibers, a ferrule, a flange, and a resin portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a third diameter portion. The second diameter portion has a diameter larger than that of the first diameter portion. The third diameter portion has a diameter larger than that of the second diameter portion and includes a coating. The ferrule includes a first fiber accommodating portion that accommodates the first diameter portion and a portion of the second diameter portion. The flange is connected to the ferrule. The flange includes a second fiber accommodating portion. The second fiber accommodating portion is in communication with the first fiber accommodating portion and accommodates a portion of the second diameter portion and a portion of the third diameter portion. The resin portion fixes the plurality of optical fibers in the first fiber accommodating portion and the second fiber accommodating portion. The resin portion includes a first resin portion, a second resin portion, and a third resin portion. The first resin portion connects the first diameter portion and the second diameter portion to the inner surface of the first fiber accommodating portion. The second resin portion connects the third diameter portion to the inner surface of the second fiber accommodating portion. The third resin portion is adhered to the second diameter portion and connects the first resin portion to the second resin portion. The third resin portion is spaced apart from the inner surface of the second fiber accommodating portion.

[0011] In this optical fiber bundle, the third resin portion is bonded to the second diameter portion, connects the first resin portion and the second resin portion, and is spaced apart from the inner surface of the second fiber accommodating portion. In this case, it is possible to reduce the force applied to the optical fiber due to the expansion and contraction of the resin portion while ensuring the tensile strength of the optical fiber.

[0012] [2] In the optical fiber bundle of [1] above, the Shore D hardness of the resin portion may be equal to or greater than 60. In this case, the tensile strength of the plurality of fibers can be further improved.

[0013] [3] In the optical fiber bundle of the above [1] or [2], the second resin portion may be formed of a resin different from that of the first resin portion. In this case, the optical fiber bundle having the above-mentioned resin portion configuration can be more easily manufactured.

[0014] [4] In the optical fiber bundle according to any one of [1] to [3] above, the ferrule may be made of a ceramic material, so that the multi-core fiber and the single-core fiber can be easily physically connected to each other.

[0015] [5] In the optical fiber bundle according to any one of [1] to [4] above, the flange may be made of metal. In this case, radial expansion of the flange inside the flange can be reduced and the rigidity of the optical fiber bundle can be improved.

[0016] [6] In the optical fiber bundle according to any one of [1] to [5] above, the width of the adhesive surface between the resin portion and the inner surface of the second fiber accommodating portion in the longitudinal direction of the flange may be 4 mm or less. In this case, the size of the optical fiber bundle in the longitudinal direction is reduced.

[0017] [7] An optical connection structure according to another embodiment of the present disclosure may include a multicore fiber, the optical fiber bundle according to any one of [1] to [6] above, and a connecting portion that connects the multicore fiber and the plurality of optical fibers so that the multicore fiber and the plurality of optical fibers are optically coupled. In this optical connection structure, it is possible to achieve both a reduction in the force applied to the optical fibers due to the expansion and contraction of the resin portion and ensuring the tensile resistance of the optical fibers.

[0018] [8] A method for manufacturing an optical fiber bundle according to an embodiment of the present disclosure includes preparing a plurality of optical fibers, a ferrule, a flange, and a resin portion, and filling the first fiber accommodating portion and the second fiber accommodating portion with an adhesive so that a first resin portion, a second resin portion, and a third resin portion are formed and the third resin portion is spaced from an inner surface of the second fiber accommodating portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a third diameter portion. The second diameter portion has a diameter larger than that of the first diameter portion. The third diameter portion has a diameter larger than that of the second diameter portion and includes a coating. The ferrule includes a first fiber accommodating portion that accommodates the first diameter portion and a portion of the second diameter portion. The flange is coupled to the ferrule. The flange includes a second fiber accommodating portion. The second fiber accommodating portion is in communication with the first fiber accommodating portion and accommodates a portion of the second diameter portion and a portion of the third diameter portion. The first resin portion connects the first diameter portion and the second diameter portion to the inner surface of the first fiber accommodating portion. The second resin portion connects the third diameter portion to the inner surface of the second fiber accommodating portion. The third resin portion is bonded to the second diameter portion and connects the first resin portion to the second resin portion. In this case, an optical fiber bundle can be manufactured that can achieve both a reduction in the force applied to the optical fiber due to expansion and contraction of the resin portions and ensuring the tensile resistance of the optical fiber.

[0019] [9] In the method for manufacturing an optical fiber bundle according to [8] above, the first diameter portion may include a tip end surface from which the fiber core is exposed. The ferrule may have a first opening. The first opening may be connected to the first fiber accommodating portion. The first opening may expose the tip end surface to the outside of the ferrule. The flange may have a second opening. The second opening may be connected to the second fiber accommodating portion. The second opening may expose a third diameter portion to the outside of the flange. Filling the first fiber accommodating portion and the second fiber accommodating portion with adhesive may include filling the adhesive from the first opening and filling the adhesive from the second opening. In this case, an optical fiber bundle having the above-described resin portion configuration can be more easily manufactured.

[0020] [Details of the embodiments of the present disclosure] Specific examples of the embodiments of the present disclosure will be described below with reference to the drawings. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted as appropriate.

[0021] First, the optical connection structure according to this embodiment will be described in more detail with reference to Figures 1 to 7. Figure 1 is a perspective view showing an optical connection structure according to one embodiment. Figure 2 is an exploded perspective view of the optical connection structure shown in Figure 1. Figure 3 is a cross-sectional view of the optical connection structure shown in Figure 1 taken along line III-III. As shown in Figures 1 to 3, the optical connection structure 1 includes a first optical connector 10, a second optical connector 20, and a split sleeve 30 (connecting portion).

[0022] The first optical connector 10 includes an MCF unit 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, a flange 60, and a resin portion 70. The optical fiber bundle 200 is configured to optically couple the plurality of optical fibers 40 to the MCF 12. By connecting the first optical connector 10 and the second optical connector 20, each core of the plurality of optical fibers 40 and the plurality of cores of the MCF 12 are optically coupled to each other.

[0023] 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. The split sleeve 30 connects the MCF 12 and the plurality of optical fibers 40 of the optical fiber bundle 200 so that the MCF 12 of the MCF unit 100 and the plurality of optical fibers 40 are optically coupled.

[0024] Fig. 4 is a diagram schematically illustrating 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 (fiber cores) and a cladding 12b that collectively covers the plurality of cores 12a. The plurality of cores 12a and the cladding 12b extend along the longitudinal direction D shown in Figs. 1 and 2.

[0025] The MCF 12 has a tip surface 12c. The tip surface 12c is composed of the tips of the multiple cores 12a and the tips of the cladding 12b. The cores 12a mainly contain silica glass doped with a dopant such as germanium to increase the refractive index. The cladding 12b mainly contains silica glass doped with a dopant such as fluorine to decrease the refractive index. The compositions of the cores 12a and the cladding 12b and the combination of dopants can be selected as appropriate. In such an MCF 12, an optical signal can be propagated through each core 12a.

[0026] In a cross section perpendicular to the central axis of the MCF 12, the cores 12a are arranged, for example, two-dimensionally. In the example shown in this embodiment, the MCF 12 has four cores 12a. The MCF 12 may have seven, eight, or nineteen cores 12a. The number of cores 12a in the MCF 12 is not limited to these. In the example shown in FIG. 4 , four cores 12a are arranged in a square lattice pattern of two rows and two columns. The mode field diameter (MFD) of light emitted from each core 12a may be, for example, 10 μm or less, or may be 5 μm or less. The MFD 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 the 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, or 50 μm or more.

[0027] The ferrule 14 holds the tip portion 12d of the MCF 12. The ferrule 14 includes a fiber accommodating portion 14a that accommodates the tip portion 12d of the MCF 12. The ferrule 14 has, for example, a cylindrical shape. The ferrule 14 has an end face 14b, and the tip portion 12d of the MCF 12 is fixed to the fiber accommodating portion 14a so that the tip face 12c of the MCF 12 is exposed at the end face 14b. The inner diameter of the fiber accommodating portion 14a is the same as or slightly larger than the outer diameter of the MCF 12. The tip portion 12d of the MCF 12 is inserted into the fiber accommodating portion 14a to be fitted into the fiber accommodating portion 14a. The ferrule 14 has a length of, for example, 6 mm to 8 mm, and is made of a ceramic material such as zirconia, glass, or metal.

[0028] As shown in Fig. 3, the flange 16 is connected to the ferrule. The flange 16 holds the rear end portion of the ferrule 14 and accommodates the MCF 12 therein. The flange 16 has, for example, a cylindrical shape. The portion of the MCF 12 accommodated in the flange 16 is fixed to the flange 16 with an adhesive. The flange 16 is made of, for example, metal. As a modification of this embodiment, the flange 16 may be made of resin.

[0029] The optical fibers 40 are optical fibers that are 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 (fiber core) and a cladding 40b that covers the core 40a. Each optical fiber 40 extends in the longitudinal direction D.

[0030] Each optical fiber 40 has a tip surface 40c. At the tip surface 40c of each optical fiber 40, the core 40a is exposed. The tip surface 40c is composed of the tip of the core 40a and the tip of the cladding 40b. The core 40a mainly contains silica glass doped with a dopant such as germanium to increase the refractive index. The cladding 40b mainly contains silica glass doped with a dopant such as fluorine to decrease the refractive index. The compositions of the core 40a and the cladding 40b and the combination of dopants can be selected as appropriate. Such an optical fiber 40 can propagate an optical signal through each core 40a.

[0031] The optical fiber 40 is, for example, a single-core fiber. In this case, the refractive index profile 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 profile is unimodal. The optical loss when light having a wavelength of 1.55 μm and light having a wavelength of 1.625 μm passes through the optical fiber 40 may be 0.15 dB / km or less and 0.45 dB / km or less, respectively. The refractive index profile in the radial direction of the optical fiber 40 may also be unimodal.

[0032] The multiple optical fibers 40 are arranged two-dimensionally in a cross section perpendicular to the longitudinal direction D. In the example shown in FIG. 5 , four optical fibers 40 are arranged in a square lattice pattern of two rows and two columns. In the example shown in this embodiment, the second optical connector 20 has four optical fibers 40. 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 multiple cores 12 a of the MCF 12 in the first optical connector 10. In other words, in a cross section perpendicular to the longitudinal direction D, the arrangement of the multiple optical fibers 40 matches the arrangement of the multiple cores 12 a of the MCF 12. However, the number and arrangement of the multiple optical fibers 40 do not need to exactly match the number and arrangement of the MCF 12, and a configuration may be adopted in which at least one of the multiple optical fibers 40 is not optically connected to the core 12a, or a configuration in which at least one of the multiple cores 12a is not optically connected to the optical fiber 40. 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.

[0033] The MFD of the light emitted from each core 40a may be, for example, 10 μm or less, or may be 5 μm or less. The MFD of the light emitted from each core 40a may also 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 80 μm or more and 125 μm or less outside the ferrule 50 described below, and is thinner inside the ferrule 50 than outside the ferrule 50. The circumscribing circle of the bundle of the thinner claddings 40b matches the cladding diameter of the MCF 12.

[0034] The outer diameter of the cladding 40b inside the ferrule 50 is smaller than the outer diameter outside the ferrule 50. Such an optical fiber is formed by etching the tip portion with buffered hydrofluoric acid or the like.

[0035] 6 is a schematic diagram showing optical fibers 40 viewed from a direction intersecting the longitudinal direction D. Each optical fiber 40 has a glass fiber 41 made of glass and a coating 42 made of resin. Each optical fiber 40 includes a first diameter portion 43, a second diameter portion 44, and a third diameter portion 46.

[0036] 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 second diameter portion 44 has a diameter larger than that of the first diameter portion 43. The portion of the glass fiber 41 that continues to the second diameter portion 44 is covered with a coating 42. The third diameter portion 46 includes the portion of the glass fiber 41 that continues to the second diameter portion 44 and the coating 42. The third diameter portion 46 has a diameter larger than that of the second diameter portion 44. The coating 42 is typically made of an organic resin material, and may further include an ultraviolet-curable resin or a thermosetting resin.

[0037] The first diameter portion 43 has a tip surface 40c. The first diameter portion 43 extends from the tip surface 40c along the longitudinal direction D. 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 D. The length of the tapered portion 45 along the longitudinal direction D 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 D. 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 D. 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 in the third diameter portion 46. The positional deviation between the tapered portions 45 of the plurality of optical fibers 40 in the longitudinal direction D may be 1 mm or less.

[0038] The ferrule 50 collectively holds the tip portions 22d of the multiple optical fibers 40. The ferrule 50 includes a first fiber accommodating portion 51 that accommodates the tip portions 22d of the multiple optical fibers 40. The ferrule 50 has, for example, a cylindrical shape. The ferrule 50 has a front end 50a in the longitudinal direction D and a rear end 50b on the opposite side of the front end 50a in the longitudinal direction D. The first fiber accommodating portion 51 is a through hole that extends from the rear end 50b to the front end 50a. An opening 55 is formed in the front end 50a, and an opening 56 is formed in the rear end 50b. The openings 55 and 56 are in communication with the first fiber accommodating portion 51.

[0039] The ferrule 50 has an end face 50c at the front end 50a. An opening 55 is formed in the end face 50c. The ferrule 50 secures the tip portions 22d of the multiple optical fibers 40 in the first fiber accommodating portion 51 so that the tip faces 40c are exposed outside the ferrule 50 at the opening 55. The multiple optical fibers 40 extend from the opening 56 to the outside of the ferrule 50. The ferrule 50 is formed of, for example, a ceramic material such as zirconia, glass, or metal.

[0040] 7 is a cross-sectional view schematically illustrating the first fiber housing portion 51. The first fiber housing portion 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 D.

[0041] 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 a circumscribing circle of the bundle of 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 transition portion 54 is continuous with the first portion 52 and extends along the longitudinal direction D. The inner diameter of the inner diameter transition portion 54 matches 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 matches the inner diameter of the second portion 53 at the boundary with the second portion 53. The inner diameter transition portion 54 may have a tapered shape or may have a curvature in its cross section. The second portion 53 is continuous with the inner diameter transition portion 54 and extends along the longitudinal direction D. In other words, in the longitudinal direction D, the inner diameter conversion portion 54 is located between the first portion 52 and the second portion 53. The inner diameter of the second portion 53 is, for example, not less than 300 μm and not more than 400 μm. The length of the ferrule 50 in the longitudinal direction D is, for example, not less than 6 mm and not more than 8 mm.

[0042] 8 is an enlarged cross-sectional view of the optical fiber bundle 200. The ferrule 50 holds the first diameter portion 43, the tapered portion 45, and the second diameter portion 44. The first fiber accommodating portion 51 accommodates the first diameter portion 43 and a portion of the second diameter portion 44. The first portion 52 and the inner diameter converting portion 54 of the first fiber accommodating portion 51 accommodate a portion of the first diameter portion 43 of the multiple optical fibers 40. The second portion 53 of the first fiber accommodating portion 51 accommodates a portion of the first diameter portion 43, the tapered portion 45, and a portion of the second diameter portion 44 of the multiple optical fibers 40.

[0043] The flange 60 is connected to the ferrule 50. The flange 60 includes a rear end 60b opposite the connection portion with the ferrule 50. The flange 60 includes a second fiber accommodating portion 61 at the rear end 50b of the ferrule 50, which communicates with the first fiber accommodating portion 51 of the ferrule 50. The second fiber accommodating portion 61 has a through hole extending along the longitudinal direction D. An opening 65 is formed at the rear end 60b. The opening 65 communicates with the second fiber accommodating portion 61. The flange 60 exposes the third diameter portion 46 to the outside of the flange 60 at the opening 65. The multiple optical fibers 40 extend from the opening 65 to the outside of the flange 60.

[0044] The first fiber accommodating section 51 and the second fiber accommodating section 61 share the same central axis L1. The second fiber accommodating section 61 accommodates the boundaries between the second diameter section 44 and the third diameter section 46 of the optical fibers 40. That is, the second fiber accommodating section 61 accommodates a portion of the second diameter section 44 and a portion of the third diameter section 46. When four optical fibers 40 each having a coating 42 with an outer diameter of 250 μm are bundled and inserted into the second fiber accommodating section 61, the diameter of the circumscribed circle of the bundle is 604 μm. Therefore, the inner diameter of the second fiber accommodating section 61 is 604 μm or more. The flange 60 is made of, for example, metal. As a variation of this embodiment, the flange 60 is made of glass, metal, or resin.

[0045] The resin portion 70 fixes the multiple optical fibers 40 in the first fiber housing portion 51 and the second fiber housing portion 61. The resin portion 70 includes a first resin portion 71, a second resin portion 72, and a third resin portion 73. The Shore D hardness of the resin portion 70 is 60 or higher. The first resin portion 71, the second resin portion 72, and the third resin portion 73 are, for example, integrally formed. The resin portion 70 corresponds to an adhesive. The resin portion 70 is, for example, a thermosetting resin, a room temperature curing resin, or a resin that is cured by both ultraviolet curing and thermosetting. If a material that is transparent to ultraviolet light is used for the ferrule or flange, an ultraviolet curing resin can also be used. For example, the second resin portion 72 and the first resin portion 71 are formed of different types of resin. For example, the first resin part 71 is a thermosetting resin, such as an epoxy resin, and the second resin part 72 is a combined ultraviolet curing and thermosetting resin, such as an epoxy resin or an acrylic resin.

[0046] The first resin portion 71 secures the multiple optical fibers 40 in the first fiber accommodating portion 51 of the ferrule 50. Specifically, the first resin portion 71 secures the first diameter portion 43, the tapered portion 45, and the second diameter portion 44 to the first fiber accommodating portion 51 so that the tip surfaces 40c of the multiple optical fibers 40 are exposed at the end surface 50c of the ferrule 50. The first resin portion 71 connects the first diameter portion 43, the tapered portion 45, and the second diameter portion 44 to the inner surface 51a of the first fiber accommodating portion 51. The first resin portion 71 is injected into gaps between the first diameter portion 43, the tapered portion 45, and the second diameter portion 44 and the inner surface 51a of the first fiber accommodating portion 51, and when hardened, adhesively secures the first diameter portion 43, the tapered portion 45, and the second diameter portion 44 to the inner surface 51a. For example, the first resin portion 71 covers the entire inner surface 51a of the first fiber housing portion 51. The first resin portion 71 corresponds to an adhesive.

[0047] The second resin portion 72 secures the multiple optical fibers 40 in the second fiber accommodating portion 61 of the flange 60. Specifically, the second resin portion 72 secures the third diameter portion 46 to the second fiber accommodating portion 61. The second resin portion 72 connects the third diameter portion 46 to the inner surface 61a of the second fiber accommodating portion 61. The second resin portion 72 is injected into the gap between the third diameter portion 46 and the inner surface 61a of the second fiber accommodating portion 61 and, upon hardening, adhesively secures the third diameter portion 46 to the inner surface 61a. The second resin portion 72 covers a portion of the inner surface 61a of the second fiber accommodating portion 61. In the longitudinal direction D of the flange 60, the width of the adhesive surface 72a between the inner surface 61a of the second fiber accommodating portion 61 and the second resin portion 72 is 4 mm or less. The adhesive surface 72a of the second resin portion 72 extends from the opening 65 of the flange 60 in the longitudinal direction D. The second resin portion 72 corresponds to an adhesive.

[0048] The third resin portion 73 is adhered to the second diameter portion 44 and connects the first resin portion 71 and the second resin portion 72. The third resin portion 73 is spaced apart from the inner surface 61a of the second fiber accommodating portion 61. The third resin portion 73 connects the second diameter portions 44 of the multiple optical fibers 40 to each other. The third resin portion 73 is disposed inside the second fiber accommodating portion 61 of the flange 60. The third resin portion 73 corresponds to an adhesive.

[0049] The second resin portion 72 and the third resin portion 73 form a void S in the second fiber accommodating portion 61. A portion of the void S is defined by the inner surface 61a of the second fiber accommodating portion 61, and the inner surface 61a has a region R that is not in contact with the resin portion 70. The void S is filled with, for example, air. As a modification of this embodiment, the void S may be filled with a substance having a thermal expansion coefficient lower than that of the resin portion 70.

[0050] Next, a method for manufacturing the above-described optical fiber bundle 200 will be described. A second optical connector 20 including the optical fiber bundle 200 is manufactured. The method for manufacturing the optical fiber bundle 200 will be described below. First, a ferrule 50 having a front end 50a, a rear end 50b, and a first fiber accommodating portion 51 is prepared. Next, a flange 60 having a second fiber accommodating portion 61 is prepared. 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.

[0051] Next, a plurality of optical fibers 40 are prepared. The process of preparing the plurality of optical fibers 40 includes a process of forming a first diameter portion 43 and a tapered portion 45 by reducing the diameter of the glass fibers of the optical fibers 40. 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 fiber formed by integrating a plurality of optical fibers 40, and the tip of the glass fiber 41 of each optical fiber 40 is chemically etched. As an example, only the tip portion of a ribbon fiber formed by a plurality of optical fibers 40 is separated into single fibers, and the tip portion is immersed in an etchant and chemically etched. The etchant is, for example, buffered hydrofluoric acid.

[0052] Next, the plurality of optical fibers 40 are inserted into the second fiber accommodating portion 61 of the flange 60 and the first fiber accommodating portion 51 of the ferrule 50. In this step, the plurality of optical fibers 40 are inserted all at once into the second fiber accommodating portion 61 of the flange 60 and the first fiber accommodating portion 51 of the ferrule 50, and the plurality of optical fibers 40 are arranged in the first fiber accommodating portion 51 of the ferrule 50. Specifically, first, the third diameter portions 46 of the plurality of optical fibers 40 are placed in a jig, thereby aligning and temporarily fixing the plurality of optical fibers 40 in a predetermined arrangement.

[0053] Next, the first diameter portions 43 of the multiple optical fibers 40 are inserted into the first portions 52 of the first fiber accommodating portions 51 of the ferrule 50. At the same time, the tapered portions 45 of the multiple optical fibers 40 are inserted into the second portions 53 of the first fiber accommodating portions 51 of the ferrule 50. At the same time, the boundaries between the second diameter portions 44 and the third diameter portions 46 of the multiple optical fibers 40 are inserted into the second fiber accommodating portions 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 in a cross section perpendicular to the longitudinal direction D. At this time, the optical fibers 40 are arranged so that the claddings 40b of the optical fibers 40 are in contact with each other and also in contact with the first fiber accommodating portions 51 of the ferrule 50. Thereafter, the jig is removed from the multiple optical fibers 40.

[0054] Next, the optical fibers 40 are fixed to the ferrule 50 and the flange 60 with an adhesive. Specifically, a first resin portion 71, a second resin portion 72, and a third resin portion 73 are formed, and the adhesive is filled into the first fiber accommodating portion 51 and the second fiber accommodating portion 61 so that the third resin portion 73 is separated from the inner surface 61 a of the second fiber accommodating portion 61. The adhesive is, for example, a resin material with high fluidity.

[0055] First, adhesive is injected through the opening 55 of the ferrule 50 into the gap between the first fiber accommodating portion 51 of the ferrule 50 and the plurality of optical fibers 40. At this time, the adhesive is injected sufficiently to cover the tip surfaces 40c of the optical fibers 40 and the end surface 50c of the ferrule 50. The adhesive is then thermally cured, for example, by heating. This fixes the plurality of optical fibers 40 to the ferrule 50.

[0056] Next, adhesive is injected through the opening 56 of the flange 60 into the gap between the second fiber accommodating portion 61 of the flange 60 and the plurality of optical fibers 40. At this time, enough adhesive is injected so that the adhesive protrudes from the rear end 60b to the outside of the flange 60. The adhesive is then thermally cured, for example, by heating. This fixes the plurality of optical fibers 40 to the flange 60. 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 50c is removed, exposing the tip faces 40c and 50c.

[0057] In this way, 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).

[0058] Next, the effects obtained from the optical fiber bundle, the optical connection structure, and the method for manufacturing the optical fiber bundle according to the embodiment will be described.

[0059] The optical fiber bundle 200 includes a resin portion 70 that fixes the optical fibers 40 in the first fiber accommodating portion 51 and the second fiber accommodating portion 61. The resin portion 70 includes a first resin portion 71, a second resin portion 72, and a third resin portion 73. The first resin portion 71 connects the first diameter portion 43 and the second diameter portion 44 to the inner surface 51a of the first fiber accommodating portion 51. The second resin portion 72 connects the third diameter portion 46 to the inner surface 61a of the second fiber accommodating portion 61. The third resin portion 73 is bonded to the second diameter portion 44 and connects the first resin portion 71 and the second resin portion 72, and is separated from the inner surface 61a of the second fiber accommodating portion 61. In this case, it is possible to achieve both a reduction in the force applied to the optical fibers 40 due to expansion and contraction of the resin portion 70 and ensuring the tensile strength of the optical fibers 40. The resin portion 70 corresponds to an adhesive.

[0060] The adhesive strength of the coating 42 to the cladding 40b of the optical fiber 40 is relatively weak, and when the optical fiber 40 is pulled in a configuration in which only the coating 42 is fixed to the flange 60, the tensile force is likely to also affect the optical fiber 40 inside the flange 60. The third resin portion 73 is adhered to the second diameter portion 44, and the cladding 40b of the optical fiber 40 is indirectly fixed to the inner surface 61a of the flange 60 via the second resin portion 72 and the third resin portion 73. Therefore, the effect of the tensile force on the optical fiber 40 can be suppressed.

[0061] In the example shown in this embodiment, the Shore D hardness of the resin portion 70 is equal to or greater than 60. In this case, the tensile resistance of the plurality of fibers can be further improved.

[0062] In the example shown in this embodiment, the second resin portion 72 is formed of a different type of resin from the first resin portion 71. In this case, an optical fiber bundle having the above-described configuration of the resin portion 70 can be more easily manufactured. For example, when the second resin portion 72 is formed after the first resin portion 71, if an adhesive with a relatively high viscosity is used to form the second resin portion 72, excessive flow of the adhesive into the second fiber accommodating portion 61 can be suppressed. For example, when the second resin portion 72 is formed after the first resin portion 71 is formed, if the second resin portion 72 is an ultraviolet-curable resin, temporary curing by irradiation with ultraviolet light can suppress excessive flow of the adhesive into the second fiber accommodating portion 61. If the adhesive is a combination of ultraviolet-curable and heat-curable adhesive, it can be sufficiently cured even inside the flange, which is not exposed to ultraviolet light.

[0063] In the example shown in this embodiment, the ferrule 50 is made of a ceramic material, which allows the MCF 12 and the multiple optical fibers 40 to be easily physically connected to each other.

[0064] In the example shown in this embodiment, the flange 60 is formed of metal in the optical fiber bundle 200. In this case, radial expansion of the flange 60 inside the flange 60 is reduced, and the rigidity of the optical fiber bundle 200 can also be improved.

[0065] In the example shown in this embodiment, the width of the adhesive surface between the resin portion 70 and the inner surface 61 a of the second fiber accommodating portion 61 is 4 mm or less in the longitudinal direction D of the flange 60. In this case, the size of the optical fiber bundle 200 in the longitudinal direction D is suppressed.

[0066] As in this embodiment, the optical connection structure 1 optically couples the MCF 12 and multiple optical fibers 40. That is, the optical connection structure 1 is a fan-in / fan-out (FIFO) device for the MCF 12. FIG. 9 is a diagram showing the connection state between multiple optical fibers 40A, 40B, and the MCF 12. The optical connection structure 1 includes multiple connectors 81, multiple optical fibers 40A, an optical connection structure 1A, an MCF 12, an optical connection structure 1B, multiple optical fibers 40B, and multiple connectors 82. Multiple optical fibers 40A are connected to the multiple connectors 81, respectively. The multiple optical fibers 40A are optically coupled to the MCF 12 in the optical connection structure 1A. The MCF 12 is optically coupled to multiple optical fibers 40B in the optical connection structure 1B. The multiple optical fibers 40B are optically coupled to the multiple connectors 82. A signal input from the connector 81 propagates through the optical fiber 40A, the MCF 12, and the optical fiber 40B, and is output from the connector 82.

[0067] The optical connection structures 1A and 1B have the same configuration as the optical connection structure 1. This facilitates the alignment process, which involves aligning the core of the MCF 12 with the core of the optical fibers 40A and 40B and fixing them at a position where optical loss is minimized. Furthermore, connectors 81 and 82 are attached to the optical connection structures 1A and 1B via multiple optical fibers 40A and 40B. This configuration facilitates repeated IL (insertion loss) measurements when inspecting the overall connection state after the alignment process.

[0068] Connectors 81, 82, which are single-core connectors or multi-core connectors, are provided at the ends of the optical fibers 40A, 40B. When connecting to other optical fibers using a multi-core connector, multiple optical fibers 40A, 40B can be connected in a single operation. In this case, the operation time can be reduced compared to connecting using single-core connectors. Furthermore, when the multiple optical fibers 40A, 40B are ribbon core wires, multiple connectors 81, 82 can be easily provided at the ends of the multiple optical fibers 40A, 40B.

[0069] The method for manufacturing the optical fiber bundle 200 includes forming a first resin portion 71, a second resin portion 72, and a third resin portion 73, and filling the first fiber accommodating portion 51 and the second fiber accommodating portion 61 with adhesive so that the third resin portion 73 is spaced from the inner surface 61 a of the second fiber accommodating portion 61. In this case, the optical fiber bundle 200 can be manufactured in which the force applied to the optical fiber 40 due to expansion and contraction of the resin portion 70 can be reduced while ensuring the tensile resistance of the optical fiber 40.

[0070] In the example shown in this embodiment, the first diameter portion 43 includes the tip surface 40c from which the core 40a is exposed. The ferrule 50 has a first opening 55. The first opening 55 may be connected to the first fiber accommodating portion 51. The opening 55 exposes the tip surface 40c to the outside of the ferrule 50. The flange 60 has an opening 65. The second opening 65 may be connected to the second fiber accommodating portion 61. The second opening 65 exposes the third diameter portion 46 to the outside of the flange 60. Filling the first fiber accommodating portion 51 and the second fiber accommodating portion 61 with adhesive includes filling the adhesive from the first opening 55 and filling the adhesive from the second opening 65. In this case, the optical fiber bundle 200 having the above-described configuration of the resin portion 70 can be more easily manufactured.

[0071] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments and can be applied to various embodiments. In the above example, the number of cores 12a and the number of cores 40a are four. However, the number of cores is not limited to this. The number of cores 12a and the number of cores 40a may differ from each other.

[0072] REFERENCE SIGNS LIST 1, 1A, 1B...optical connection structure 10...first optical connector 12...MCF 12a, 40a...core 12b, 40b...clad 12c, 40c...tip surface 12d, 22d...tip portion 14, 50...ferrule 14a, 51, 61...fiber accommodating section 14b, 50c...end surface 16, 60...flange 20...second optical connector 30...split sleeve 40, 40A, 40B...optical fiber 40a...core 40b...clad 40c...tip surface 41...glass fiber 42...coating 43...first diameter section 44...second diameter section 45...tapered section 46...third diameter section 50a...front end 50b, 60b...rear end 51...first fiber accommodating section 51a...inner surface 52...first section 53... Second portion 54... Inner diameter conversion portion 55, 56, 65... Opening 60... Flange 60b... Rear end 61... Second fiber accommodating portion 61a... Inner surface 70... Resin portion 71... First resin portion 72... Second resin portion 72a... Adhesion surface 73... Third resin portion 81... Connector 82... Connector 100... MCF unit 200... Optical fiber bundle D... Longitudinal direction L1... Central axis R... Region S... Gap

Claims

1. A plurality of optical fibers, each of which includes a first diameter portion, a second diameter portion having a diameter larger than that of the first diameter portion, and a third diameter portion having a diameter larger than that of the second diameter portion and including a coating; a ferrule including a first fiber accommodating portion accommodating the first diameter portion and a portion of the second diameter portion; a flange connected to the ferrule, communicating with the first fiber accommodating portion, and including a second fiber accommodating portion accommodating a portion of the second diameter portion and a portion of the third diameter portion; and resin portions for fixing the plurality of optical fibers in the first fiber accommodating portion and the second fiber accommodating portion, the resin portions including a first resin portion connecting the first diameter portion and the second diameter portion to an inner surface of the first fiber accommodating portion, a second resin portion connecting the third diameter portion to an inner surface of the second fiber accommodating portion, and a third resin portion bonded to the second diameter portion and connecting the first resin portion to the second resin portion, The third resin portion is spaced apart from an inner surface of the second fiber accommodating portion.

2. The optical fiber bundle according to claim 1, wherein the Shore D hardness of the resin portion is 60 or more.

3. An optical fiber bundle as described in claim 1 or 2, wherein the second resin portion is formed from a different type of resin from that of the first resin portion.

4. The optical fiber bundle according to any one of claims 1 to 3, wherein the ferrule is made of a ceramic material.

5. The optical fiber bundle according to any one of claims 1 to 4, wherein the flange is formed of metal.

6. An optical fiber bundle according to any one of claims 1 to 5, wherein the width of the adhesive surface between the resin portion and the inner surface of the second fiber accommodating portion in the longitudinal direction of the flange is 4 mm or less.

7. An optical connection structure comprising: a multicore fiber; an optical fiber bundle according to any one of claims 1 to 6; and a connecting portion that connects the multicore fiber and the plurality of optical fibers so that the multicore fiber and the plurality of optical fibers are optically coupled.

8. A method for manufacturing an optical fiber bundle, comprising: preparing a plurality of optical fibers, each of which includes a first diameter portion, a second diameter portion having a diameter larger than that of the first diameter portion, and a third diameter portion having a diameter larger than that of the second diameter portion and including a coating; a ferrule including a first fiber accommodating portion accommodating the first diameter portion and a portion of the second diameter portion; and a flange connected to the ferrule, communicating with the first fiber accommodating portion, and having a second fiber accommodating portion accommodating a portion of the second diameter portion and a portion of the third diameter portion; and filling the first fiber accommodating portion and the second fiber accommodating portion with an adhesive so that a first resin portion is formed which connects the first diameter portion and the second diameter portion to an inner surface of the first fiber accommodating portion, a second resin portion is formed which connects the third diameter portion to an inner surface of the second fiber accommodating portion, and a third resin portion is bonded to the second diameter portion and connects the first resin portion to the second resin portion, and the third resin portion is formed so that the third resin portion is separated from the inner surface of the second fiber accommodating portion.

9. A method for manufacturing an optical fiber bundle as described in claim 8, wherein the first diameter portion includes a tip surface from which a fiber core is exposed, the ferrule has a first opening communicating with the first fiber accommodating portion and exposing the tip surface to the outside of the ferrule, the flange has a second opening communicating with the second fiber accommodating portion and exposing the third diameter portion to the outside of the flange, and filling the first fiber accommodating portion and the second fiber accommodating portion with adhesive includes filling the adhesive from the first opening and filling the adhesive from the second opening.

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