Method for manufacturing optical connection structure

Abstract

To provide an optical connection structure with which it is possible to suppress a temporal degradation in optical characteristics.SOLUTION: An optical connection structure comprises an MCF, a first ferrule, a plurality of optical fibers, and a second ferrule. The MCF has a plurality of first cores and a first clad. The first ferrule has a first inner hole for accommodating the tip portion of the MCF and a first ferrule end face. Each of the plurality of optical fibers optically connected to the MCF has a second core and a second clad. The second ferrule has a second inner hole for accommodating the tip portion of each of the plurality of optical fibers and a second ferrule end face. The second ferrule secures the tip portion of each of the optical fibers in the inside of the second inner hole by a wiring adhesive. The wiring adhesive is charged in such a way that a surface is drawn into the second inner hole beyond the second ferrule end face. A refractive index matching agent is enclosed in a space that is sealed up by the first ferrule end face and second ferrule end face.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to an optical connection structure. [Background technology]

[0002] Patent Document 1 discloses an optical connection structure for optically connecting a multicore fiber and a plurality of optical fibers. In this optical connection structure, the tip end face of the multicore fiber housed in a ferrule is butted against the tip end faces of a plurality of optical fibers housed in another ferrule, thereby optically connecting the two fibers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-113597 [Patent Document 2] U.S. Patent No. 9,599,776 [Patent Document 3] Japanese Patent Application Publication No. 01-262507 [Patent Document 4] Japanese Patent Application Publication No. 01-136904 Summary of the Invention [Problem to be solved by the invention]

[0004] 14 , in the optical connection structure disclosed in Patent Document 1 and the like, a plurality of optical fibers 200 are housed in a ferrule 201 such that the tips 200a of the optical fibers 200 are aligned with the end face 201a of the ferrule 201, and are fixed to the ferrule 201 by an adhesive 202 filled around the optical fibers 200. At this time, the ferrule end face 201a, including the tips of the optical fibers 200 and the adhesive 202, is formed to be flush by polishing or the like. However, among the plurality of optical fibers 200 fixed by the adhesive 202, there is an optical fiber 200A that moves (is retracted) toward the rear end in the longitudinal direction due to thermal influence or the like during continued use. In this case, some of the optical fibers 200A of the plurality of optical fibers 200 are retracted backward from a state in which the plurality of optical fibers 200 are butted against a multi-core fiber 210 held by a ferrule 211, and a gap V is formed between the multi-core fiber 210 and the retracted optical fiber 200A. When the gap V is formed, it deteriorates the return loss and insertion loss between the multicore fiber 210 and the pulled-in optical fiber 200A. Therefore, there is a demand for an optical connection structure that suppresses deterioration of optical characteristics over time.

[0005] An object of the present disclosure is to provide an optical connection structure that suppresses deterioration of optical characteristics over time. [Means for solving the problem]

[0006] The present disclosure provides an optical connection structure. The optical connection structure includes a multicore fiber, a first ferrule, multiple optical fibers, and a second ferrule. The multicore fiber has multiple first cores extending in the longitudinal direction, a first cladding covering the multiple first cores, and a first fiber tip surface including each tip of the multiple first cores and the first cladding. The first ferrule has a first inner hole that houses a tip portion of the multicore fiber and a first ferrule end surface where the first fiber tip surface is exposed on the inside. The first ferrule fixes the tip portion of the multicore fiber within the first inner hole. Each of multiple optical fibers optically connected to the multicore fiber has a second core extending along the longitudinal direction, a second cladding covering the second core, and a second fiber tip surface including each tip of the second core and the second cladding. The second ferrule has a second inner hole that houses each tip portion of the multiple optical fibers and a second ferrule end surface where the second fiber tip surface of each of the multiple optical fibers is exposed on the inside. The second ferrule fixes the tip ends of the multiple optical fibers in the second inner hole with a bonding adhesive. The bonding adhesive is filled in the second inner hole so that the surface facing the tip end face of the first fiber is recessed further into the second inner hole than the end face of the second ferrule. A refractive index matching material is sealed in the space sealed by the end faces of the first and second ferrules. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to suppress deterioration of optical properties over time. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an optical connection structure according to an embodiment. [Figure 2] FIG. 2 is an exploded perspective view of the optical connection structure shown in FIG. [Figure 3] 3 is a cross-sectional view taken along line III-III of the optical connection structure shown in FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a region T of the optical connection structure shown in FIG. [Figure 5] FIG. 5 is a diagram showing the tip of the multi-core fiber and the end face of the ferrule. [Figure 6] FIG. 6 is a diagram showing the tips of a plurality of optical fibers and the end face of a ferrule. [Figure 7] FIG. 7 is a perspective view showing an initial state in which a plurality of optical fibers are fixed in a ferrule with a bonding adhesive, with the tip face of each fiber aligned with the end face of the ferrule. [Figure 8] FIG. 8 is a cross-sectional view showing the initial state of FIG. [Figure 9] FIG. 9 is a perspective view showing a state in which some of the optical fibers have been pulled in further from the initial state shown in FIGS. [Figure 10] FIG. 10 is a cross-sectional view showing the retracted state of FIG. [Figure 11] FIG. 11 is a perspective view showing a configuration for fixing the optical connection structure shown in FIG. [Figure 12] FIG. 12 is a perspective view showing another configuration for fixing the optical connection structure shown in FIG. [Figure 13] FIG. 13 is a perspective view showing still another configuration for fixing the optical connection structure shown in FIG. [Figure 14] FIG. 14 is a cross-sectional view for explaining a state in which an optical fiber is pulled in in an optical connection structure. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, the details of the embodiments of the present disclosure will be listed and described. An optical connection structure according to one embodiment includes a multicore fiber, a first ferrule, multiple optical fibers, and a second ferrule. The multicore fiber has multiple first cores extending in the longitudinal direction, a first cladding covering the multiple first cores, and a first fiber tip surface including each tip of the multiple first cores and the first cladding. The first ferrule has a first inner hole that houses a tip portion of the multicore fiber and a first ferrule end surface where the first fiber tip surface is exposed on the inside. The first ferrule fixes the tip portion of the multicore fiber within the first inner hole. Each of multiple optical fibers optically connected to the multicore fiber has a second core extending along the longitudinal direction, a second cladding covering the second core, and a second fiber tip surface including each tip of the second core and the second cladding. The second ferrule has a second inner hole that houses each tip portion of the multiple optical fibers and a second ferrule end surface where the second fiber tip surface of each of the multiple optical fibers is exposed on the inside. The second ferrule fixes the tip ends of the multiple optical fibers in the second inner hole with a bonding adhesive. The bonding adhesive is filled in the second inner hole so that the surface facing the tip end face of the first fiber is recessed further into the second inner hole than the end face of the second ferrule. A refractive index matching material is sealed in the space sealed by the end faces of the first and second ferrules.

[0010] In this optical connection structure, the surface of the bonding adhesive filled in the second ferrule that holds the multiple optical fibers is configured to be pulled into the second inner hole further than the end face of the second ferrule. A refractive index matching material is sealed in the space sealed by the end faces of the first and second ferrules. According to this aspect, even if some of the multiple optical fibers are pulled in due to thermal influences on the optical connection structure, the refractive index matching material moves into the gap and fills the gap. Therefore, with this optical connection structure, even if there are thermal influences, the return loss and insertion loss between the multicore fiber and the pulled-in optical fiber are not degraded, and deterioration of optical properties over time can be suppressed.

[0011] In one embodiment, the maximum retraction amount along the longitudinal direction from the end face of the second ferrule to the surface of the bonding adhesive may be 0.1 μm or more and 5 μm or less. According to this aspect, the space in which the refractive index matching material is sealed is extremely small. Therefore, even if some of the multiple optical fibers are retracted due to thermal influence, the refractive index matching material quickly moves into the gap by capillary action and fills the gap. Therefore, this optical connection structure can easily prevent deterioration of the return loss and insertion loss between the multicore fiber and the retracted optical fiber, and can easily suppress deterioration of optical characteristics over time. The maximum retraction amount along the longitudinal direction from the end face of the second ferrule to the surface of the bonding adhesive may be 3 μm or less.

[0012] In one embodiment, the refractive index matching agent may be sealed in a space defined by the first fiber end face, the second inner hole, the drawn surface of the splicing adhesive, and the exposed end portions of the multiple optical fibers, including the second fiber end faces. According to this aspect, even if some of the multiple optical fibers are drawn in due to thermal influence on the optical connection structure, the refractive index matching agent disposed near the gap quickly moves to fill the gap. Therefore, this optical connection structure can easily prevent deterioration of the return loss and insertion loss between the multicore fiber and the drawn optical fiber, and easily suppress deterioration of optical characteristics over time. Note that a portion of the refractive index matching agent may be sealed so as to be located between the first ferrule end face of the first ferrule and the second ferrule end face of the second ferrule.

[0013] In one embodiment, the refractive index matching agent may have a refractive index that deviates from the refractive index of the second core by 3% or less. According to this aspect, it is possible to more reliably prevent deterioration in the return loss and insertion loss between the multicore fiber and the inserted optical fiber, and more reliably suppress deterioration of the optical properties over time.

[0014] As one embodiment, the arrangement of the multiple first cores in a planar direction along the tip surface of the first fiber may match the arrangement of the second cores in a planar direction along the tip surface of the second fiber. According to this aspect, it is possible to further optimize the optical connection between the multicore fiber and the multiple optical fibers. Note that the cores of the multicore fiber and the cores of the multiple optical fibers may all be arranged to correspond to each other, or some may not. Furthermore, the cores of the multicore fiber and the cores of the multiple optical fibers may be rotationally adjusted so that their arrangements correspond to each other.

[0015] In one embodiment, the first ferrule and the second ferrule may be pressed against each other by a pressing member so that the end faces of the first ferrule and the second ferrule are sealed. According to this aspect, with a simple configuration, the state in which the refractive index matching material is sealed in the space defined by the end faces of the first ferrule and the second ferrule can be maintained.

[0016] In one embodiment, the first ferrule and the second ferrule may be adhesively fixed so that the end faces of the first ferrule and the second ferrule are kept in close contact with each other. This aspect allows the refractive index matching material to be sealed in the space defined by the end faces of the first ferrule and the second ferrule with a simple configuration.

[0017] As an embodiment, the optical connection structure according to any of the above aspects may further include a sleeve that holds the first ferrule and the second ferrule from the outside so as to align the optical axes of the plurality of first cores with the optical axes of the second cores. The first ferrule, the second ferrule, and the sleeve may be adhesively fixed so that the end faces of the first ferrule and the second ferrule are maintained in close contact with each other. According to this aspect, with a simple configuration, it is possible to maintain the state in which the refractive index matching material is sealed in the space defined by the end faces of the first ferrule and the second ferrule.

[0018] As one embodiment, the end face of the first ferrule and the end face of the second ferrule may at least partially have a spherical shape with a curvature radius of 1 mm or more and 50 mm or less. According to this aspect, when the first ferrule and the second ferrule are butted together, the tips of the two ferrules are likely to come into close contact with each other, and therefore, the tip face of the multicore fiber and the tip faces of the multiple optical fibers can be easily directly joined, for example, connected by physical contact (PC).

[0019] In another aspect, the present disclosure relates to a method for fabricating an optical connection structure having any of the above-described aspects. The fabrication method includes the steps of inserting tip portions of multiple optical fibers into a second inner hole of a second ferrule and fixing the multiple optical fibers to the second ferrule with a bonding adhesive, polishing the second ferrule end face of the second ferrule to which the multiple optical fibers are fixed, and performing additional heat treatment on the member containing the bonding adhesive after the polishing step. In this method for fabricating an optical connection structure, the additional heat treatment causes the surface of the bonding adhesive to be recessed further into the second inner hole than the second ferrule end face. This fabrication method makes it possible to easily form a space for disposing an index matching agent to be injected between the multicore fiber and the multiple optical fibers.

[0020] [Details of the embodiments of the present disclosure] Specific examples of 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 of the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0021] 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 of the optical connection structure shown in FIG. 1 taken along line III-III. 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. The first optical connector 10 includes a multicore fiber 12 (hereinafter also referred to as "MCF 12"), a ferrule 14 (first ferrule), and a flange 16. The second optical connector 20 includes a plurality of optical fibers 22, a ferrule 24 (second ferrule), and a flange 26. The split sleeve 30 (sleeve) is a member that holds and aligns the ferrules 14 and 24 from the outside so as to align the optical axes of the cores of the MCF 12 of the first optical connector 10 with the optical axes of the cores of the plurality of optical fibers 22 (see also FIG. 4).

[0022] As shown in FIGS. 3 to 5, the MCF 12 has multiple cores 12a (first cores) extending in the longitudinal direction A, a cladding 12b (first cladding) extending in the longitudinal direction A and collectively covering the multiple cores 12a, and a tip surface 12c (first fiber tip surface). FIG. 4 is an enlarged cross-sectional view of a region T of the optical connection structure 1. FIG. 5 is a diagram showing the tip of the MCF 12 and the end face of the ferrule 14. The tip surface 12c is composed of the tips of the multiple cores 12a and the tip of the cladding 12b. The cores 12a may be made of silica glass doped with a dopant such as germanium to increase the refractive index, and the cladding 12b may be made of silica glass doped with a dopant such as fluorine to decrease the refractive index. The combination of materials, dopants, and the like can be selected appropriately. In such an MCF 12, an optical signal of a predetermined wavelength can be propagated through each core 12a.

[0023] In the MCF 12, for example, the cores 12a are arranged two-dimensionally. As shown in FIG. 5, the MCF 12 may have, for example, four cores 12a, seven cores 12a, eight cores 12a, or 19 cores 12a, but is not limited thereto. In the example shown in FIG. 5, four cores 12a are arranged in a square. The diameter (core diameter) of each core 12a may be, for example, 10 μm or less, 5 μm or less, or 1 μm or more. The core pitch (center-to-center distance) of each core 12a may be, for example, 10 μm or more and 50 μm or less. The diameter (cladding diameter) of the cladding 12b may be, for example, 200 μm or less, 125 μm or less, 100 μm or less, 80 μm or less, or 50 μm or more.

[0024] The ferrule 14 is a cylindrical member that holds the tip portion 12d of the MCF 12 and has an inner hole 14a (first inner hole) that is a through hole that accommodates the tip portion 12d of the MCF 12, and an end face 14b of the ferrule 14. The ferrule 14 secures 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 inside 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 therewith. The ferrule 14 has a length of, for example, 6 mm to 8 mm and is made of a ceramic material such as zirconia.

[0025] 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 housed in the flange 16 may be fixed to the inside of the flange 16 with an adhesive or the like. The flange 16 is made of, for example, metal or resin.

[0026] The optical fibers 22 are optical fibers optically connected to the MCF 12. As shown in FIGS. 3, 4, and 6, each optical fiber 22 has a core 22a (second core) extending in the longitudinal direction A, a cladding 22b (second cladding) extending in the longitudinal direction A and covering the core 22a, and a tip end face 22c (second fiber tip end face). FIG. 6 is a diagram showing the tips of the optical fibers 22 and the end face of the ferrule 24. The tip end face 22c is composed of the tip of the core 22a and the tip of the cladding 22b. The core 22a may be made of silica glass doped with a dopant such as germanium to increase the refractive index, and the cladding 22b may be made of silica glass doped with a dopant such as fluorine to decrease the refractive index. The combination of materials, dopants, etc. can be selected appropriately. In such an optical fiber 22, an optical signal of a predetermined wavelength is propagated through each core 22a. The plurality of optical fibers 22 may be, for example, a bundle of fibers or individual optical fibers.

[0027] In the second optical connector 20, the optical fibers 22 are arranged two-dimensionally. As shown in FIG. 6, the second optical connector 20 may have, for example, four, seven, eight, or nineteen optical fibers 22, but is not limited thereto. The number and arrangement of the optical fibers 22 in the second optical connector 20 correspond 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 22 is similar to (matches) the arrangement of the cores 12a of the MCF 12. However, the number and arrangement of the optical fibers 22 do not need to completely match the number and arrangement of the MCF 12, and some may not be optically connected. The optical fibers 22 in the second optical connector 20 are configured to be optically coupled to the cores 12a of the MCF 12 in the first optical connector 10 by rotationally adjusting the ferrule 24 about the central axis thereof.

[0028] The diameter (core diameter) of each core 22a may be, for example, 10 μm or less, 5 μm or less, or 1 μm or more. The core pitch (center-to-center distance) of each core 22a may be, for example, 10 μm or more and 50 μm or less. The diameter (cladding diameter) of the cladding 22b may be 80 μm or more and 125 μm or less outside the ferrule 24 described below, and may be thinned inside the ferrule 24 to correspond to the MCF 12. The circumscribing circle of the thinned optical fiber 22 (corresponding to the inner diameter of the inner hole 24a of the ferrule 24) corresponds to the cladding diameter of the MCF 12 and may be, for example, 200 μm or less, 125 μm or less, 100 μm or less, 80 μm or less, or 50 μm or more. The cladding 22b may be converted to a thin diameter inside the ferrule 24 from a typical outer diameter of 125 μm or 80 μm. Such an optical fiber can be realized by etching the tip portion with hydrofluoric acid, etc. In this case, the inner diameter of the ferrule 24 that houses the multiple optical fibers 22 may be different between the portion that houses the small-diameter optical fiber portion and the portion that houses the optical fiber with a normal outer diameter.

[0029] The ferrule 24 is a cylindrical member that collectively holds the tip portions 22d of the multiple optical fibers 22. The ferrule 24 has an inner hole 24a (second inner hole) that is a through hole that accommodates the tip portions of the multiple optical fibers 22, and an end face 24b (second ferrule end face). The ferrule 24 fixes the tip portions 22d of the multiple optical fibers 22 in the inner hole 24a with a bonding adhesive 28 so that the tip faces 22c of the multiple optical fibers 22 are exposed inside the end face 24b of the ferrule 24. The inner diameter of the inner hole 24a is the same as or slightly smaller than the outer diameter of the bundle of multiple optical fibers 22. The tip portions 22d of the multiple optical fibers 22 are inserted into the inner hole 24a and bonded and fixed thereto with the bonding adhesive 28 that is injected into the gaps between them. The bonding adhesive 28 is, for example, a thermosetting adhesive, and can be hardened by heating the bonding adhesive 28 after it is injected into a predetermined location. Like the ferrule 14, the ferrule 24 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.

[0030] 3, the flange 26 is a cylindrical member that holds the rear end portion of the ferrule 24 and houses the plurality of optical fibers 22 therein. The portions of the plurality of optical fibers 22 housed in the flange 26 may be fixed to the inside of the flange 26 with an adhesive or the like. The flange 26 is made of, for example, metal or resin.

[0031] Here, the relationship between the end face 24b of the ferrule 24, the tip face 22c of the optical fiber 22 and the exposed tip portion 22e including the tip face 22c, and the surface 28a of the bonding adhesive 28 in the second optical connector 20 of the optical connection structure 1 will be described with reference to Figs. 7 to 10. Fig. 7 is a perspective view showing an initial state in which multiple optical fibers are fixed in the ferrule with the bonding adhesive, with the tip face of each fiber coinciding with the end face of the ferrule. Fig. 8 is a cross-sectional view showing the initial state of Fig. 7. Fig. 9 is a perspective view showing a state in which some optical fibers have been retracted from the initial state shown in Figs. 7 and 8. Fig. 10 is a cross-sectional view showing the retracted state of Fig. 9.

[0032] As shown in FIGS. 7 and 8 , in the second optical connector 20, the bonding adhesive 28 is filled in the inner bore 24a so that the surface 28a is recessed further into the inner bore 24a than the end face 24b of the ferrule 24. The surface 28a of the bonding adhesive 28 faces the front end face 12c of the MCF 12. The recession amount along the longitudinal direction A from an imaginary plane along the end face 24b of the ferrule 24 to the surface 28a of the bonding adhesive 28 is not particularly limited. For example, the recession amount may be a maximum of 0.1 μm to 5 μm, or may be 3 μm or less. Note that the surface 28a may be flat as shown in FIG. 7 or may have an irregular surface. In the case of an irregular surface, the recession amount may be the shortest distance from the imaginary plane along the end face 24b of the ferrule 24 to the most recessed region of the surface 28a. This distance can be measured, for example, using a surface height measuring instrument or a laser microscope that utilizes the principle of white light interferometry.

[0033] In the second optical connector 20 according to this embodiment, a refractive index matching agent 40 is injected into the space S formed by the recessed surface 28a of the bonding adhesive 28. This space S is a region (gap) defined by the distal end surface 12c of the MCF 12, the inner hole 24a, the recessed surface 28a of the bonding adhesive 28, and the exposed distal end portions 22e including the distal end surfaces 22c of the multiple optical fibers 22. The refractive index matching agent 40 has a refractive index substantially similar to that of the core 12a of the MCF 12 or the core 22a of the optical fiber 22, for example, a refractive index that deviates by 3% or less from the refractive index of the core 12a or the core 22a, and is composed of a liquid that is transparent at wavelengths used in optical communications. The refractive index matching agent 40 may be, for example, silicone oil or the like that has a predetermined refractive index and transmits light. The refractive index matching agent 40 may be a gel-like material, but is preferably an oil-like material considering the rapid mobility of the refractive index matching agent 40. The viscosity of the refractive index matching material 40 is, for example, 1 mPa·s or more and 10,000 mPa·s or less, and preferably 3,000 mPa·s or less. The end face 14b of the ferrule 14 and the end face 24b of the ferrule 24 seal the space S, thereby sealing the wire bonding adhesive 28 injected into the space S. In other words, the wire bonding adhesive 28 is prevented from leaking out from the butted surfaces of the ferrules 14 and 24.

[0034] 9 and 10, a case will be described in which, in the optical connection structure 1 having the above-described configuration, a part of the optical fiber 22 is pulled inward (rearward) in the second optical connector 20 due to the influence of heat, etc. In Fig. 9 and Fig. 10, one optical fiber 22A is pulled inward, and the tip surface 22c of the optical fiber 22A is approximately flush with or slightly above the surface 28a of the wiring adhesive 28.

[0035] In the optical connection structure 1 according to this embodiment, even if some of the optical fibers 22A are pulled inward in this way, the refractive index matching agent 40 injected into the space S will enter between the tip surface 22c of the pulled-in optical fiber 22A and the corresponding core 12a of the MCF 12 due to capillary action or the like. Therefore, optical communication between the core 22a of the optical fiber 22A and the core 12a of the MCF 12 can continue in the same state as it was initially. Note that if the refractive index matching agent 40 is oil-like, the refractive index matching agent 40 will move more quickly to the required location.

[0036] Next, a holding structure for maintaining the ferrule 14 and the ferrule 24 in the butted state in the optical connection structure 1 configured as described above will be described with reference to Figs. 11 to 13. Fig. 11 is a perspective view showing a structure for fixing the optical connection structure 1. Fig. 12 is a perspective view showing another structure for fixing the optical connection structure 1. Fig. 13 is a perspective view showing yet another structure for fixing the optical connection structure 1. In the optical connection structure 1, this holding structure maintains a state in which the refractive index matching agent 40 described above does not leak from the butted surfaces of the ferrule 14 and the ferrule 24.

[0037] 11 includes a spring member 50 (pressing member) that presses the flange 16 of the first optical connector 10 inward along arrow A1, and a spring member 52 (pressing member) that presses the flange 26 of the second optical connector 20 inward along arrow A2. Note that FIG. 11 does not illustrate the retaining structure on the base end side of each spring member 50, 52. In this configuration 100, the spring members 50, 52 press against each other, thereby sealing the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24. In this configuration, the ferrules 14 and 24 may be adhesively fixed to each other within the split sleeve 30 so that the end faces 14b and 24b are kept in close contact with each other. Alternatively, the ferrules 14 and 24 may be adhesively fixed to the split sleeve 30 so that the end faces 14b and 24b are kept in close contact with each other. As a result, in the configuration 100, the refractive index matching material 40 injected into the space S is maintained in a sealed state.

[0038] 12, a plate spring member 60 (pressing member) is provided that presses the flange 16 of the first optical connector 10 and the flange 26 of the second optical connector 20 inward. The plate spring member 60 has a support portion 62 that engages with the flange 16 and a support portion 64 that engages with the flange 26. In this configuration 101, the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24 are sealed by the pressure of the plate spring member 60. In this configuration, similar to the above, the ferrule 14 and the ferrule 24 may be adhesively fixed so that the end face 14b and the end face 24b are maintained in close contact with each other. As described above, in the configuration 101, the refractive index matching material 40 injected into the space S is maintained sealed therein.

[0039] In a configuration 102 shown in FIG. 13, the configuration 101 shown in FIG. 11 may be further packaged with a sealing resin or the like to provide a sealing portion 70. This configuration 102 makes it possible to more reliably maintain the refractive index matching material 40 injected into the space S sealed therein. The configuration 102 may further include a boot 72 that covers the flange 16 and the MCF 12, and a boot 74 that covers the flange 26 and the optical fiber 22. This makes it possible to prevent or protect the MCF 12 and the optical fiber 22 from moving in the longitudinal direction. Note that the configuration 101 shown in FIG. 12 may be packaged with a sealing resin or the like as shown in FIG. 13.

[0040] Next, a method for fabricating the optical connection structure 1 described above will be described. First, prepare the MCF 12, ferrule 14, flange 16, multiple optical fibers 22, ferrule 24, flange 26, connection adhesive 28, split sleeve 30, and refractive index matching material 40. The MCF 12 has cores 12a arranged in a predetermined manner (for example, a square arrangement with four cores), and a fiber with a cladding diameter of 125 μm and a core pitch of 40 μm is prepared. The ferrules 14 and 24 are, for example, LC ferrules.

[0041] 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 after the fitting, the end surface 14b of the ferrule 14 may be polished by PC (physical contact) so that the tip surface 12c of the MCF 12 is aligned with the end surface 14b of the ferrule 14. When PC polishing is performed, the radius of curvature of the diameter of the ferrule is, for example, 1 mm or more and 50 mm or less. In this way, the first optical connector 10 is prepared.

[0042] Furthermore, the optical fibers 22 are inserted into the inner hole of the flange 26 and the inner hole 24a of the ferrule 24 together, and the tip portions 22d of the optical fibers 22 are arranged in the inner hole 24a of the ferrule 24. The optical fibers 22 are either thinned so that the tip portions 22d correspond to the MCF 12, or drawn to have such a diameter (for example, an optical fiber with a cladding diameter of 40 μm at the tip). Such optical fibers 22 are arranged in the ferrule 24, for example, two-dimensionally, to correspond to the arrangement of the MCF. At this time, the claddings 22b of the optical fibers 22 are arranged so that they are in contact with each other and also with the inner hole 24a of the ferrule 24. Then, a bonding adhesive 28 is injected into the gap between the inner hole 24a of the ferrule 24 and the optical fibers 22. At this time, the bonding adhesive 28 is injected sufficiently to cover the tip surfaces 22c of the optical fibers 22 and the end face 24b of the ferrule 24. The bonding adhesive 28 is then thermally cured, for example, by heating. This fixes the multiple optical fibers 22 to the ferrule 24. Then, the end face 24b of the ferrule 24 is PC polished together with the tip face 22c of the optical fiber 22 so that the tip face 22c of the optical fiber 22 is flush with the end face 24b of the ferrule 24. By PC polishing, the adhesive on the tip face 22c and the end face 24b is removed, exposing the tip face 22c and the end face 24b. When PC polishing is performed, the radius of curvature of the diameter of the ferrule 24 is, for example, 1 mm or more and 50 mm or less, as described above. This prepares the initial form of the second optical connector 20.

[0043] Next, once the PC polishing is complete, the second optical connector 20 in its initial state is subjected to an additional heat treatment. This additional heat treatment may be performed at a temperature higher than that used to harden the bonding adhesive 28, and may be performed for a longer period of time. This additional heat treatment promotes contraction of the bonding adhesive 28, causing the surface 28a of the bonding adhesive 28 to retract further into the inner bore 24a than the end face 24b of the ferrule 24, for example, by a maximum of 0.5 μm to 5 μm or 3 μm. This causes the surface 28a of the bonding adhesive 28 to retract further into the inner bore 24a than the end face 24b of the ferrule 24, thereby preparing a second optical connector having a space S on the tip side.

[0044] Next, a refractive index matching agent 40 is applied to the end face 24b of the ferrule 24, including the space S of the second optical connector 20. Then, the first optical connector 10 and the second optical connector 20 are connected within the split sleeve 30 so that the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24 are abutted against each other.

[0045] Next, one of the fibers is rotated and aligned within the split sleeve 30 so that each core 12a of the MCF 12 and each corresponding core 22a of the plurality of optical fibers 22 are optically coupled.

[0046] Next, after the alignment of the fibers 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 by a pressing member as shown in Figures 11 to 13. At this time, the ferrules 14 and 24 may be pressed against each other by friction with the split sleeve 30 without using a pressing member, or the ferrules 14 and 24 may be bonded and fixed with an adhesive. In this way, the optical connection structure 1 or the configuration 100, the configuration 101, and the configuration 102 can be obtained.

[0047] As described above, in the optical connection structure 1 according to this embodiment, the surface 28a of the connection adhesive 28 filled in the ferrule 24 holding the multiple optical fibers 22 is configured to be recessed further into the inner hole 24a than the end face 24b of the ferrule 24. A refractive index matching agent 40 is sealed in the space S sealed by the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24. With this configuration, even if a portion of the optical fiber 22 is recessed due to thermal influence or the like on the optical connection structure 1, the refractive index matching agent 40 moves into the gap and fills the gap. Therefore, with the optical connection structure 1, even if there is thermal influence or the like, the return loss and insertion loss between the MCF 12 and the recessed optical fiber 22 are not degraded, and deterioration of the optical characteristics over time can be suppressed.

[0048] Furthermore, in this embodiment, the maximum amount of retraction along the longitudinal direction A from the end face 24b of the ferrule 24 to the surface 28a of the wire connection adhesive 28 may be 0.1 μm or more and 5 μm or less. With this configuration, the space S in which the refractive index matching material 40 is sealed is extremely small, so even if some of the multiple optical fibers 22 are retracted due to thermal influence, the refractive index matching material 40 quickly moves into the gap by capillary action and fills the gap. Therefore, with the optical connection structure 1, it is possible to easily prevent deterioration in the return loss and insertion loss between the MCF 12 and the retracted optical fibers 22, and it is possible to easily suppress deterioration of the optical characteristics over time.

[0049] In this embodiment, the refractive index matching agent 40 is sealed in a space S defined by the end face 12c of the MCF 12, the inner hole 24a, the surface 28a of the bonding adhesive 28, and the exposed end portions 22e of the optical fibers 22, including the end faces 22c. With this configuration, even if some of the optical fibers 22 are pulled in due to thermal influence on the optical connection structure 1, the refractive index matching agent 40 disposed near the gap quickly moves to fill the gap. Therefore, the optical connection structure 1 can easily prevent deterioration in the return loss and insertion loss between the MCF 12 and the pulled optical fibers 22, and easily suppress deterioration of the optical characteristics over time. A portion of the refractive index matching agent 40 is located between the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24.

[0050] In this embodiment, the refractive index matching material 40 may have a refractive index that is within 3% of the refractive index of the core 12 a or the core 22 a. This configuration can more reliably prevent deterioration in the return loss and insertion loss between the MCF 12 and the inserted optical fiber 22, and more reliably suppress deterioration of the optical characteristics over time.

[0051] Furthermore, in this embodiment, the arrangement of the multiple cores 12a in the planar direction along the tip surface 12c of the MCF 12 may match the arrangement of the cores 22a in the planar direction along the tip surface 22c of the optical fiber 22. This configuration can further optimize the optical connection between the MCF 12 and the multiple optical fibers 22. Note that the cores 12a of the MCF 12 and the cores 22a of the multiple optical fibers 22 may all be arranged to correspond to each other, or some may not.

[0052] In this embodiment, the ferrules 14 and 24 may be pressed against each other by the spring members 50, 51 or the leaf spring member 60 so that the end faces 14b and 24b are sealed. This simple configuration makes it possible to more reliably maintain the state in which the refractive index matching material 40 is sealed in the space S defined by the end faces 14b and 24b of the ferrules 14 and 24.

[0053] In this embodiment, the ferrules 14 and 24 may be adhesively fixed so that the end faces 14b and 24b are kept in close contact with each other. This simple configuration makes it possible to keep the refractive index matching material 40 sealed in the space S defined by the end faces 14b and 24b.

[0054] In this embodiment, the optical connection structure 1 further includes a split sleeve 30 that holds the ferrules 14 and 24 from the outside so as to align the optical axes of the cores 12a and 22a. The ferrules 14 and 24 and the split sleeve 30 may be adhesively fixed to each other so that the end faces 14b and 24b are kept in close contact with each other. This simple configuration makes it possible to keep the refractive index matching material 40 sealed in the space S defined by the end faces 14b and 24b of the ferrules 14 and 24.

[0055] In this embodiment, the end face 14b of the ferrule 14 and the end face 24b of the ferrule 24 may have at least a portion that is spherical with a radius of curvature of 1 mm or more and 50 mm or less. With this configuration, when the ferrule 14 and the ferrule 24 are butted together, the tips of the ferrules are likely to come into close contact with each other, which facilitates direct connection, for example, PC (Physical Contact) connection, between the tip face 12c of the MCF 12 and the tip faces 22c of the multiple optical fibers 22.

[0056] Furthermore, the method for fabricating an optical connection structure according to this embodiment includes the steps of inserting the tip portions 22d of the plurality of optical fibers 22 into the inner hole 24a of the ferrule 24 and fixing the plurality of optical fibers 22 to the ferrule 24 with a bonding adhesive 28, polishing the end face of the ferrule 24 to which the plurality of optical fibers 22 are fixed, and, after the polishing step, performing an additional heat treatment on the member including the bonding adhesive 28. In this method for fabricating an optical connection structure, the additional heat treatment causes the surface 28a of the bonding adhesive 28 to be recessed further into the inner hole 24a than the end face 24b of the ferrule 24. This fabrication method makes it possible to easily form a space S between the MCF 12 and the plurality of optical fibers 22, into which the refractive index matching agent 40 to be injected is to be placed.

[0057] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments and can be applied to various embodiments. [Explanation of symbols]

[0058] 1...Optical connection structure 10...First optical connector 12...Multicore fiber 12a...Core (1st core) 12b... Clad (first clad) 12c...Tip surface (tip surface of first fiber) 12d…Tip part 14...Ferrule (first ferrule) 14a...Inner hole (first inner hole) 14b...End face (first ferrule end face) 16...Flange 20...Second optical connector 22...Optical fiber (multiple optical fibers) 22a...Core (second core) 22b... Clad (second clad) 22c...Tip surface (tip surface of second fiber) 22d…Tip part 22e...Exposed tip part 24...Ferrule (second ferrule) 24a...Inner hole (second inner hole) 24b...End face (second ferrule end face) 26...Flange 28...Wire bonding adhesive 28a…Surface 30...Split sleeve 40...Refractive index matching material 50, 52...Spring members (pressure members) 60... Leaf spring member (pressure member) 62,64...Support part 70...Sealing part 72,74...Boots 100, 101, 102...Configuration 200,200A...optical fiber 200a...tip 201...Ferrule 201a...end face 202...Adhesive 210...Multicore fiber 211...Ferrule A...Longitudinal direction A1, A2...arrows S…Space T…area V...gap

Claims

1. a multicore fiber having a plurality of first cores extending in a longitudinal direction, a first cladding covering the plurality of first cores, and a first fiber tip surface including tips of the plurality of first cores and the first cladding; a first ferrule having a first inner hole that houses a tip portion of the multi-core fiber and a first ferrule end face at which the first fiber tip face is exposed on the inside, the first ferrule fixing the tip portion of the multi-core fiber in the first inner hole; a plurality of optical fibers optically connected to the multicore fiber, each of the optical fibers having a second core extending along the longitudinal direction, a second clad covering the second core, and a second fiber tip surface including tips of the second core and the second clad; a second ferrule having a second inner hole that houses the tip portions of the optical fibers and a second ferrule end face at which the second fiber tip faces of the optical fibers are exposed on the inside, the second ferrule fixing the tip portions of the optical fibers in the second inner hole with a bonding adhesive; Equipped with the bonding adhesive is filled in the second inner hole such that a surface facing the tip face of the first fiber is recessed further into the second inner hole than an end face of the second ferrule; A method for producing an optical connection structure, wherein a refractive index matching material is sealed in a space sealed by the first ferrule end face and the second ferrule end face, the method comprising the steps of: inserting the tip portions of the optical fibers into the second inner hole of the second ferrule, respectively, and fixing the optical fibers to the second ferrule with the bonding adhesive; polishing the second ferrule end surface of the second ferrule to which the plurality of optical fibers are fixed together with the second fiber tip surfaces; performing additional heat treatment on the member containing the bonding adhesive after the polishing step; Equipped with The method for producing an optical connection structure, wherein the additional heat treatment causes the surface of the bonding adhesive to recede into the second inner hole further than the second ferrule end face.

2. a maximum retraction amount from the end face of the second ferrule to the surface of the wire bonding adhesive along the longitudinal direction is 0.1 μm or more and 5 μm or less; A method for producing the optical connection structure according to claim 1 .

3. the refractive index matching agent is sealed in the space defined by the first fiber tip surface, the second inner hole, the surface into which the bonding adhesive is drawn, and the tip exposed portions including the second fiber tip surfaces of the plurality of optical fibers; A method for producing the optical connection structure according to claim 1 or 2.

4. the refractive index matching material has a refractive index that is shifted by 3% or less with respect to the refractive index of the second core; A method for producing the optical connection structure according to claim 1 .

5. an arrangement of the plurality of first cores in a planar direction along the tip surface of the first fiber coincides with an arrangement of the second cores in a planar direction along the tip surface of the second fiber; A method for producing the optical connection structure according to claim 1 .

6. the first ferrule and the second ferrule are pressed against each other by a pressing member so that an end face of the first ferrule and an end face of the second ferrule are sealed. A method for producing the optical connection structure according to claim 1 .

7. The first ferrule and the second ferrule are adhesively fixed to each other such that an end face of the first ferrule and an end face of the second ferrule are maintained in close contact with each other. A method for producing the optical connection structure according to claim 1 .

8. The optical connection structure further includes a sleeve that holds the first ferrule and the second ferrule from the outside so as to align each optical axis of the plurality of first cores with each optical axis of the second core, The first ferrule and the second ferrule are adhesively fixed to the sleeve so that an end face of the first ferrule and an end face of the second ferrule are maintained in close contact with each other. A method for producing the optical connection structure according to claim 1 .

9. The first ferrule end face and the second ferrule end face at least partially have a spherical shape with a radius of curvature of 1 mm or more and 50 mm or less. A method for producing the optical connection structure according to claim 1 .

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