Optical connection structure and method for manufacturing optical fiber

Abstract

This optical connection structure may be in the form of a bare fiber adapter (20) comprising: a holding part (22) that holds an optical fiber (10) in which a magnetic body (31) is exposed on an end surface (10a); and a ferrule (23) that has at least one fiber hole (24) into which the optical fiber (10) inserted in the holding part (22) is inserted. The fiber hole (24) has a diameter whereby twisting of the optical fiber (10) along the circumferential direction of the optical fiber (10) is possible.

Description

Optical connection structure and method for manufacturing optical fiber

[0001] The present disclosure relates to optical connection structures and methods for making optical fibers.

[0002] Currently widely used single-core fibers have one core in the center of the cladding. On the other hand, multi-core fibers (MCFs) have multiple cores in the cladding. Multi-core fibers are expected to have a larger communication capacity than single-core fibers.

[0003] To align a single MCF, it is necessary to adjust the horizontal and vertical positions of the cross section of the MCF, and also to adjust the rotation angle around the center of the cross section of the MCF as the central axis (see Non-Patent Document 1). Also, a bare fiber adapter is a technology for easily connecting fibers (see Non-Patent Document 2). When connecting MCFs using a bare fiber adapter, a rotation suppression mechanism is required.

[0004] R. Nagase, K. Sakaime, K. Watanabe, and T. Saito, “MU-Type Multicore Fiber Connector”, Trans. IEICE, Vol. E96-C, No. 9, pp. 1173-1177, (2013). Sanwa Technologies Co., Ltd., “SANWA Press - Sanwa Electric Industry Development Case Study / Technical Information Media Bare Fiber Adapter Proposal”, [online], [Retrieved June 7, 2024], Internet <URL: https: / / case-study.snwd.co.jp / media / 2017 / 11 / 27 / 65>

[0005] When splicing optical fibers such as the above-mentioned MCF and polarization-maintaining fiber (PMF), rotational alignment is generally required. In this case, alignment must be performed under observation of the end faces using a microscope, etc., which reduces the efficiency of the splicing work.

[0006] The present disclosure has been proposed in consideration of the above circumstances, and aims to provide an optical connection structure and an optical fiber manufacturing method that can improve the efficiency of optical fiber connection work that requires rotational alignment.

[0007] A method for manufacturing an optical fiber according to a first aspect of the present disclosure comprises attaching a first filler material containing a magnetic substance to a first end face of an optical fiber having a cladding, at least one core provided in the cladding, and at least one air hole provided in the cladding and extending parallel to the core, sealing the periphery of the first end face with a first material having heat shrinkability, and injecting the first filler material into the air hole by heating the first material.

[0008] An optical connection structure according to a second aspect of the present disclosure comprises a holding portion that holds an optical fiber having a magnetic material exposed at its end surface, and a ferrule having at least one fiber hole into which the optical fiber is inserted via the holding portion, the fiber hole having a diameter that allows twisting of the optical fiber along the circumferential direction of the optical fiber.

[0009] An optical connection structure according to a third aspect of the present disclosure comprises a base portion having at least one groove portion in which a pair of optical fibers having a magnetic material exposed at their end surfaces are placed, a lid portion facing the base portion via the pair of optical fibers placed in the groove portion, and a biasing member that biases the base portion and the lid portion toward each other, wherein one of the base portion and the lid portion has a magnetic material provided at a position where the pair of optical fibers are butted together.

[0010] According to the present disclosure, it is possible to provide an optical connection structure and an optical fiber manufacturing method that can improve the efficiency of the connection work of optical fibers that require rotational alignment.

[0011] FIG. 1 is a diagram illustrating an optical fiber and its rotational alignment according to each embodiment of the present disclosure. FIG. 2 is a flowchart of a method for manufacturing an optical fiber according to the present embodiment. FIG. 3A is a diagram illustrating a state in which the end face of the optical fiber is wrapped with a material. FIG. 3B is a diagram illustrating a state in which the material shown in FIG. 3A is heated. FIG. 4 is a diagram illustrating another example of a method for injecting a filler material. FIG. 5 is a diagram illustrating the injection of a filler material into holes opening at the other end face. FIG. 6 is a perspective view of a bare fiber adapter, which is an example of an optical connection structure according to the first embodiment. FIG. 7A is a cross-sectional view showing an example of a fiber hole shape according to the present embodiment. FIG. 7B is a cross-sectional view showing an example of a fiber hole shape according to the present embodiment. FIG. 8 is a perspective view showing a pair of bare fiber adapters butted together. FIG. 9 is a diagram illustrating an example in which a magnetic material is embedded in a ferrule. FIG. 10 is a perspective view of an MT connector, which is an example of an optical connection structure according to a second embodiment of the present disclosure. FIG. 11A is a cross-sectional view of the MT connector. FIG. 11B is a cross-sectional view of the MT connector after a curing material has been injected. FIG. 12A is a cross-sectional view of an MT connector according to a first modification of the second embodiment. FIG. 12B is a cross-sectional view of an MT connector according to a second modified example of the second embodiment. FIG. 12C is a cross-sectional view taken along line A-A in FIG. 12B. FIG. 12D is a cross-sectional view of an MT connector according to a third modified example of the second embodiment. FIG. 12E is a cross-sectional view of an MT connector according to a fourth modified example of the second embodiment. FIG. 13 is a cross-sectional view of a mechanical splice member, which is an example of an optical connection structure according to a third embodiment of the present disclosure. FIG. 14A is a perspective view of the mechanical splice member before clamping an optical fiber. FIG. 14B is a perspective view of the mechanical splice member after clamping an optical fiber. FIG. 15A is a cross-sectional view of a mechanical splice member according to a first modified example of the third embodiment. FIG. 15B is a cross-sectional view of a mechanical splice member according to a second modified example of the third embodiment.

[0012] Hereinafter, several embodiments of the present disclosure will be described. Note that common parts in each drawing are assigned the same reference numerals, and redundant description will be omitted. Furthermore, the optical fiber according to this embodiment is an optical fiber that requires rotational alignment, such as a multicore fiber or a polarization-maintaining fiber. Below, a multicore fiber will be described as an example. For convenience of explanation, the multicore fiber will be simply referred to as the optical fiber. Furthermore, the X direction, Y direction, and Z direction, which are orthogonal to each other, will be defined. The Z direction is the extension direction of the optical fiber and the fiber hole (described later). Furthermore, the circumferential direction will be defined as the circumferential direction centered on the central axis of the optical fiber.

[0013] First Embodiment Fig. 1 is a diagram for explaining an optical fiber (multicore fiber) 10 and its rotational alignment according to each embodiment of the present disclosure. The left diagram in Fig. 1 shows the optical fiber 10 in a state ST0 before a magnetic material (first magnetic material) 31 is injected into the air holes 13. As shown in this figure, the optical fiber 10, which is a multicore fiber, includes a cladding 11, at least one core 12 provided in the cladding 11, and at least one air hole 13 provided in the cladding 11. The air holes 13 extend parallel to the cores 12.

[0014] An optical fiber having holes 13 can be produced, for example, by bundling rod-shaped members that will become the core 12 and cladding 11 and a tubular member (a so-called capillary) that has the same refractive index as the cladding 11 in a desired arrangement, and then heating and drawing the resulting fiber.

[0015] The central diagram in Fig. 1 shows the optical fiber 10 in state ST1. The optical fiber 10 in state ST1 includes a core 12, a cladding 11, and a magnetic material 31 injected into the holes 13. One or more cores 12 are arranged at positions other than the center on the end face 10a of the optical fiber 10. Fig. 1 illustrates an example in which cores 12 are arranged at the vertices of a square. Therefore, the number of cores in this case is four.

[0016] The air holes 13 are arranged at positions eccentric to the central axis of the cladding 11 (the central axis of the outer periphery of the optical fiber 10). The number of air holes 13 into which the magnetic material 31 is injected is not limited to one, and may be multiple. However, the positions of the air holes 13 (magnetic material 31) are set at positions where, when the optical fiber 10 and the optical fiber to be connected are butted together, the relative positions between the cores and the relative positions between the air holes both match.

[0017] 1 shows state ST2 of the optical fiber 10. State ST2 is a state in which an external magnetic field acts on the optical fiber 10 in state ST1, causing it to rotate in the circumferential direction CD and become aligned. Application of the external magnetic field causes a magnetic force to act on the magnetic body 31, attracting it in a specific direction, thereby adjusting the rotational position of the core 12 relative to the central axis of the cladding 11.

[0018] Next, a method for manufacturing the optical fiber 10 will be described. Fig. 2 is a flowchart of the method for manufacturing the optical fiber 10. Fig. 3A is a diagram showing the state in which the end face 10a of the optical fiber 10 is wrapped with a material. Fig. 3B is a diagram showing the state when the material 34 shown in Fig. 3A is heated. Note that the optical fiber 10 in state ST0, i.e., the optical fiber 10 before the magnetic material 31 is filled into the holes 13, is assumed to have been manufactured in advance using a well-known method.

[0019] First, a filler (first filler) 30 containing a magnetic substance 31 is attached to the end face (first end face) 10a of the optical fiber 10 (step S1). The magnetic substance 31 is a ferromagnetic material such as iron, cobalt, or nickel. To ensure fluidity, the filler 30 also contains a curable material that hardens when heated or exposed to ultraviolet light, such as epoxy resin, ultraviolet-curable resin, or acrylic resin.

[0020] 3A, the periphery of the end surface 10a is then covered with a heat-shrinkable material (first material) 34 (step S2), and sealed by forming a crimped portion 34a (step S3). The material 34 is made of a material that shrinks significantly when heated, such as polyolefin, fluoropolymer, or thermoplastic elastomer. The crimped portion 34a can be formed by momentarily heating the material 34 using a tool such as an ultrasonic welder.

[0021] In step S3, the interior region surrounded by the material 34 is sealed. Note that air may or may not remain in this interior region. In the latter case, the material 34 covers the filler 30 while contacting it.

[0022] Next, the magnetic substance 31 in the filler 30 is magnetized (step S4). In step S4, the magnetic field is oriented so that the magnetic poles generated between the opposing end faces of the optical fibers form a pair of south and north poles. To magnetize the magnetic substance 31, for example, a capacitor-type magnetizing device capable of generating a relatively strong magnetic field is used. In this case, the end face 10a of the optical fiber 10 covered with the material 34 is placed inside the coil of the magnetizing device, and the magnetic substance 31 is magnetized by the magnetic field generated inside the coil.

[0023] Next, the material 34 is heated to inject the filler 30 into the voids 13 (step S5). The material 34 shrinks when heated using a known heating device 38, directly pressing against the filler 30. Furthermore, if air remains between the material 34 and the filler 30, the air pressure increased by heating presses against the filler 30. Meanwhile, the voids 13 open at the end face (second end face) 10b opposite the end face 10a, and their internal spaces communicate with the outside of the optical fiber 10. Therefore, the pressure inside the material 34 becomes greater than the pressure outside the optical fiber 10 (i.e., atmospheric pressure). As shown in FIG. 3B , a force acts on the filler 30 attached to the end face 10a to flow into the voids 13. As a result, the filler 30 flows into the voids 13. The material 34 is heated at a temperature below the Curie temperature of the magnetic substance 31.

[0024] Next, the filler 30 is hardened and fixed in the hole 13 of the optical fiber 10 (step S6). Then, the end of the optical fiber 10 is cut off so as to leave the filler 30, and excess filler 30 is removed (step S7). As a result, the magnetic material 31 remains in the hole 13 with the magnetic material 31 exposed at the end face 10a. Note that the above-mentioned step S4 may be performed after step S5.

[0025] FIG. 4 illustrates another example of a method for injecting the filler material 30. As shown in FIG. 4, the end face 10b may be cooled while the material 34 on the end face 10a side is heated. Specifically, the periphery of the end face 10b is covered with the same material (second material) 35 as the material 34 and crimped. That is, the periphery of the end face 10b is sealed with the material 35. Then, while the material 34 is being heated, the material 35 is cooled. The material 34 on the end face 10a side is heated and contracts, and the air in the material 35 on the end face 10b side is cooled and contracted by a cooling device 39 having a known configuration. Therefore, for example, the air pressure in the material 34 on the end face 10a side increases, and the air pressure in the material 34 on the end face 10b side decreases. This increases the pressure difference, facilitating the flow of the filler material 30 into the pores 13.

[0026] From the viewpoint of the increase in the pressure difference described above, it is also possible to seal the periphery of the end face 10a with the material 34, and then connect the end face 10b to a suction pump to suck the air from the pores 13 while heating the material 34. By sucking the air from the pores 13, the pressure in the pores decreases, and the flow of the filler 30 into the pores 13 can be promoted.

[0027] 5 is a diagram illustrating the injection of filler material 30 into holes 13 opening in end face 10b. In optical fiber 10 shown in FIG. 5, holes 13 opening in end face (first end face) 10a are sealed with filler material 30. When injecting filler material 30 into the other end face (second end face) 10b of this optical fiber 10, the above-described process of injecting filler material 30 into end face 10a sides of holes 13 is performed on end face 10b.

[0028] That is, the filler material 30 is attached to the end face 10b, and the periphery of the end face 10b is covered with a material (third material) 36 having the same composition as the material 34 encasing the end face 10a. The material 36 is then crimped to form a crimped portion 36a to seal the periphery of the end face 10b, and the material 36 is heated. This causes the filler material 30 to flow into the voids 13 opening in the end face 10b. At this time, the region (portion) 14 between the end faces 10a and 10b of the optical fiber 10 may be cooled with a cooling device 39. Cooling the region 14 causes the air in the voids 13 to contract, facilitating the flow of the filler material 30 attached to the end face 10b into the voids 13.

[0029] Next, an optical connection structure according to this embodiment will be described. As described below, the optical connection structure according to this embodiment includes a holding part that holds an optical fiber having a magnetic material exposed on its end face, and a ferrule having at least one fiber hole into which the optical fiber is inserted via the holding part. The fiber hole has a diameter that allows twisting of the optical fiber along the circumferential direction of the optical fiber.

[0030] 6 is a perspective view of a bare fiber adapter 20, which is an example of an optical connection structure according to this embodiment. The bare fiber adapter 20 includes a housing 21, a holding portion 22 that holds the optical fiber 10, and a ferrule 23 having a fiber hole 24 into which the optical fiber 10 is inserted via the holding portion 22. The holding portion 22 holds the optical fiber 10 by biasing or clamping using a spring or the like. The ferrule 23 protrudes from the housing 21 by a predetermined length.

[0031] 6 shows a state in which the optical fiber 10 inserted into the fiber hole 24 is temporarily held by the holding portion 22. At this time, as shown in the enlarged view in FIG. 6, the optical fiber 10 protrudes slightly from the fiber hole 24. The portion of the optical fiber 10 in the bare fiber adapter 20 that is not held by the holding portion 22 is not fixed with an adhesive or the like, and can rotate freely in the circumferential direction of the optical fiber 10. Therefore, the optical fiber 10 positioned in the fiber hole 24 is also not fixed to the inner surface of the fiber hole 24.

[0032] 7A and 7B are cross-sectional views showing examples of the shape of the fiber hole 24 according to this embodiment. As described above, the optical fiber 10 is allowed to rotate in the circumferential direction within the fiber hole 24 of the ferrule 23. That is, the fiber hole 24 has a diameter D that allows twisting of the optical fiber 10 along the circumferential direction of the optical fiber 10. For example, as shown in FIG. 7A , the diameter D is constant up to the end face 23 a of the ferrule 23.

[0033] 7B , the fiber hole 24 may be formed in a flared shape from a position midway within the ferrule 23 to the end face 23a of the ferrule 23. In this case, friction between the optical fiber 10 and the inner surface of the fiber hole 24 is reduced, and restrictions on twisting of the optical fiber 10 within the fiber hole 24 due to this friction are alleviated. Note that the portion of the fiber hole 24 closer to the holding portion 22 has a constant diameter, which limits excessive bending and displacement of the central axis of the optical fiber 10 when the optical fiber 10 is twisted.

[0034] 8 is a perspective view showing a pair of bare fiber adapters 20, 20 butted against each other. Each bare fiber adapter 20 temporarily holds the optical fiber 10 inserted into the fiber hole 24 with the holding portion 22. As described above, the end face 10a of the optical fiber 10 inserted into the fiber hole 24 slightly protrudes from the fiber hole 24.

[0035] A sleeve member (not shown) is used to connect the optical fibers 10 together. The sleeve member is a hollow, tubular member having a through hole into which the ferrule 23 is inserted. The cross-sectional shape of the through hole parallel to the XY plane is complementary to the cross-sectional shape of the ferrule 23 parallel to the same plane. In other words, the inner diameter of the hole in the sleeve member into which the ferrule 23 is inserted is equal to the diameter of the ferrule 23. The ferrules 23, 23 of the bare fiber adapters 20, 20 are inserted from both ends of the sleeve member, with their end faces 23 a, 23 a facing and butting against each other within the sleeve member.

[0036] The magnetic bodies 31, 31 of the optical fibers 10, 10 are already magnetized and have opposite polarities at the end faces 10a, 10a of the optical fibers 10, 10. In this case, one of the magnetic bodies 31, 31 at the end faces 10a, 10a is an S pole and the other is an N pole.

[0037] Furthermore, each optical fiber 10 is held in the bare fiber adapter 20 so as to be twistable in the circumferential direction. However, when the opposing optical fibers 10, 10 are separated from each other, the mutual attractive force of the magnetic bodies 31, 31 is relatively small. Therefore, no twisting occurs in the optical fibers 10, 10, and the rotational states (phase states) of the optical fibers 10, 10 are not aligned. In other words, the positions of the core 12 and magnetic body 31 on one end face 10a and the core 12 and magnetic body 31 on the other end face 10a are misaligned.

[0038] As the opposing optical fibers 10, 10 are brought closer together from the above state, the mutual attractive force of the magnetic bodies 31, 31 increases, causing the optical fibers 10, 10 to twist in the circumferential direction. This twisting reduces the relative distance between the magnetic body 31 on one end face 10a and the magnetic body 31 on the other end face 10a. When the end faces 10a, 10a of the optical fibers 10, 10 are in contact with each other, their respective rotational states (phase states) are aligned, and the positions of the cores 12 and magnetic bodies 31 match. In other words, rotational alignment is complete.

[0039] The outer periphery of the ferrule 23 is surrounded by the housing 21, and a protrusion provided on the housing 21 is used to fix the sleeve member to the housing 21. This maintains the connection state of the pair of bare fiber adapters 20, 20, completing the optical connection. In this way, the alignment of the optical fibers 10 is completed by the contact between the magnetic bodies 31, 31 using magnetic force. This eliminates the need for precise alignment work under observation of the end faces using a microscope or the like, improving the efficiency of the optical fiber connection work.

[0040] FIG. 9 shows an example in which a magnetic body 32 is embedded in the ferrule 23. For ease of explanation, the core 12 is not shown. As shown in FIG. 9 , the ferrule 23 may include a magnetic body (second magnetic body) 32 disposed around the fiber hole 24. The magnetic body 32 is pre-magnetized to set a magnetic field in a desired direction. Since the magnetic force weakens in inverse proportion to the square of the distance between the magnetic bodies, arranging the magnetic body 32 near the fiber hole 24 can shorten the distance between the magnetic body 32 in the ferrule 23 and the magnetic body 31 in the optical fiber 10, thereby strengthening the magnetic force of the magnetic body 31 for rotational alignment. The magnetic field generated at the end faces 10 a, 10 a by the magnetic bodies 31, 31 is not limited to that shown in FIG. 9 , as long as the magnetic bodies 31, 31 generate a force that attracts each other. For example, the magnetic bodies 31, 31 may be magnetized by the magnetic bodies 32, 32 so that a south pole appears on one of the end faces 10a, 10a and a north pole appears on the other end face 10a, 10a.

[0041] 9 shows a pair of ferrules 23, 23 facing each other and a pair of optical fibers 10, 10 being optically connected. In each ferrule 23, the magnetic body 31 in the optical fiber 10 is magnetically attracted to the magnetic body 32 in the ferrule 23, causing the optical fiber 10 to rotate in the circumferential direction. In other words, the optical fiber 10 is rotationally aligned.

[0042] By setting the magnetization direction of the magnetic bodies 31, 32 in one of the pair of ferrules 23, 23 to be opposite to that of the magnetic bodies 31, 32 in the other, when the pair of ferrules 23, 23 are butted together, a magnetic bonding force of the magnetic bodies 31, 31 is generated between the end faces 10 a, 10 a. As a result, the optical fibers 10, 10 are further rotationally aligned, and their respective rotational states (phase states) coincide, achieving optical connection.

[0043] Since the magnetization direction of the magnetic body 32 and the location where it is embedded in the ferrule 23 are set in advance, the magnetic body 31 of the optical fiber 10 is attracted to the vicinity of the magnetic body 32, causing the optical fiber 10 to rotate (twist). Therefore, by aligning the positions of the magnetic body 31 of each ferrule 23 as viewed from the Z direction, it becomes easier to obtain the magnetic coupling between the end faces 10 a, 10 a described above, and it becomes easier to obtain a match in the rotational state (phase state).

[0044] Second Embodiment Fig. 10 is a perspective view of an MT connector 40, which is an example of an optical connection structure according to a second embodiment of the present disclosure. Fig. 11A is a cross-sectional view of the MT connector 40 perpendicular to the X direction. Like the bare fiber adapter 20, the MT connector 40 also holds the above-described optical fiber 10 and performs optical connection between cores by connecting with another MT connector. Note that the optical connection structure according to the second embodiment is not limited to MT connectors, but can also be applied to other multi-core connectors (multi-core connector plugs).

[0045] The MT connector 40 includes a ferrule 41, which includes a plurality of fiber holes 42 aligned in the X direction, guide grooves 43 that guide the optical fibers 10 into the fiber holes 42, a window 44, and a cavity (first cavity) 45. In this embodiment, the optical fibers 10 are held in the ferrule 41 by being filled with adhesive. That is, the ferrule 41 of this embodiment also serves as the holding portion 22 described above.

[0046] The plurality of fiber holes 42 extend along the Z direction within the ferrule 41 and open to an end face (front face) 41 a of the ferrule 41. The plurality of fiber holes 42 are aligned in the X direction and open. Like the fiber holes 24 of the first embodiment, each fiber hole 42 has a diameter that allows twisting of the optical fiber 10 along the circumferential direction.

[0047] In addition, guide holes 46 are formed on both sides of the plurality of fiber holes 42 aligned in the X direction on the end surface 41a. Guide pins (not shown) are inserted into the guide holes 46 when connecting to another MT connector.

[0048] The guide groove portion 43 is located between an introduction port 47 for the optical fiber 10 and the fiber hole 42. The introduction port 47 opens to the back surface 41c of the ferrule 41. The guide groove portion 43 has a groove with a V-shaped cross section that extends in the Z direction. The number of these grooves is equal to the number of fiber holes 42. The guide groove portion 43 supports the optical fiber 10 and guides the optical fiber 10 to the corresponding fiber hole 42. Note that the cross-sectional shape of the groove is not limited to a V-shape, and may be any shape that can support the fiber, such as a semicircular shape.

[0049] The window 44 opens in the upper surface (surface) 41b of the ferrule 41 and extends in the Y direction from the upper surface 41b to the guide groove 43. A hardening material 8 is poured into the window 44 to fix the optical fiber 10 in the guide groove 43. The window 44 communicates with both the introduction port 47 and the fiber hole 42.

[0050] The cavity 45 is provided between the fiber holes 42 and the guide grooves 43 in the Z direction and communicates with the window 44. The cavity 45 is, for example, a groove extending in the Z direction and recessed in the Y direction from an imaginary plane including the plurality of fiber holes 42 and the guide grooves 43. Therefore, with the window 44 open upward, the cavity 45 is located below the optical fibers 10 inserted into the fiber holes 42 and the guide grooves 43.

[0051] When the MT connector 40 is mated with another MT connector having a similar configuration, the magnetic body 31 of the optical fiber 10 is attracted to the magnetic body of the optical fiber of the other MT connector as the optical fibers 10 of the two MT connectors approach each other. This causes the optical fiber 10 to rotate and be aligned in the fiber hole 42. Therefore, as with the first embodiment, precise alignment work under observation of the end face using a microscope or the like is not required, improving the efficiency of the optical fiber connection work.

[0052] As described above, the optical fiber 10 is held in the ferrule 41 by the curing material 8 injected from the window portion 44 curing inside the ferrule 41. Specifically, the optical fiber 10 is held in place by the curing material 8 flowing into the guide groove portion 43 in which the optical fiber 10 is placed and curing. The guide groove portion 43 is located close to the fiber hole 42 in order to guide the optical fiber 10 to the fiber hole 42. Therefore, there is a concern that the uncured curing material 8 that has flowed into the guide groove portion 43 will flow into the fiber hole 42 and fix the optical fiber 10 in the fiber hole 42.

[0053] Therefore, in this embodiment, a hollow portion 45 is provided. For example, as shown in Fig. 11B, even if the hardening material 8 flows out from the guide groove portion 43 into the fiber hole 42, the hollow portion 45 receives the hardening material 8 and prevents it from flowing into the fiber hole 42. This allows the optical fiber 10 to be held while maintaining a rotatable state of the optical fiber 10 within the fiber hole 42, and prevents the hardening material 8 from interfering with rotational alignment.

[0054] Furthermore, by adjusting the distance between the cavity 45 and the fiber hole 42, the length of the optical fiber 10 from the cavity 45 to the end face 41a of the ferrule 41 can be adjusted. This portion of the optical fiber 10 is not fixed to any surrounding members. On the other hand, the maximum twist angle of the optical fiber 10 that is not fixed to the surrounding members is proportional to its length. Therefore, by adjusting the position of the cavity 45, the range of twist angles that allows rotational alignment can be widened.

[0055] 12A is a cross-sectional view of an MT connector 40 according to a first modified example of the second embodiment. As shown in FIG. 12A , the ferrule 41 according to the first modified example may further include a cavity (second cavity) 48. The cavity 48 is provided on the opposite side of the guide groove 43 from the cavity 45. In other words, the cavity 48 is located between the introduction port 47 and the guide groove 43 in the Z direction. The cavity 48 also communicates with the window 44.

[0056] The cavity 48 is a recess recessed in the Y direction from an imaginary plane including the introduction port 47 and the guide groove 43. For example, the cavity 48 has an inclined surface 48a extending such that the distance from the imaginary plane increases as the cavity 48 approaches the introduction port 47 from the guide groove 43. The cavity 48 allows the portion of the optical fiber 10 from the guide groove 43 to the end face 41a to be securely fixed to the ferrule 41 by the curing material 8, while keeping the portion of the optical fiber 10 from the guide groove 43 to the end face 41a unfixed by the curing material 8. Furthermore, for example, the appropriate volume of the curing material 8 can be calculated in advance from the dimensional design values ​​of the cavity 48. This prevents the curing material 8 from overflowing from the window 44 toward the end face 41a due to excessive injection.

[0057] 12B is a cross-sectional view of an MT connector 40 according to a second modification of the second embodiment. As shown in FIG. 12B , a ferrule 41 according to the second modification may include a communication passage 49 provided on the opposite side of the guide groove 43 from the window 44. The communication passage 49 provides communication between the cavity 45 and the cavity 48. The communication passage 49 may open to, for example, an inclined surface 48 a of the cavity 48.

[0058] 12C is a cross-sectional view taken along line A-A in FIG. 12B. The communication path 49 is at least one hole spaced apart in the X direction and extending in the Z direction. By forming the communication path 49, the hardening material 8 that has flowed into the cavity 45 flows out into the cavity 48 via the communication path 49. Therefore, the mechanical strength of the ferrule 41 can be maintained while preventing the hardening material 8 from flowing into the fiber hole 42.

[0059] 12D is a cross-sectional view of an MT connector 40 according to a third modification of the second embodiment. As shown in FIG. 12D, the cavity 48 may open to the back surface 41 c of the ferrule 41 where the inlet 47 is formed (i.e., in the Z direction). Instead, a plate portion 50 that temporarily closes the opening is positioned in the opening. Furthermore, when the hardening material 8 is injected into the window portion 44, a partition portion 51 is inserted into the window portion 44.

[0060] The edge of the partition 51 inserted into the window 44 contacts, for example, the boundary between the guide groove 43 and the cavity 48. The hardening material 8 is injected into a region 44a of the window 44 that communicates with the cavity 48. Therefore, the hardening material 8 is injected into the cavity 48, and can be prevented from flowing into the fiber holes 42.

[0061] Furthermore, with the lower surface 41d of the ferrule 41 as the reference, the length of the plate portion 50 in the Y direction is defined as L1, and the length to the fiber hole 42 is defined as L2. By making the length of L1 shorter than L2, the hardening material 8 flows into the plate portion 50 side due to gravity acting in the Y direction. Therefore, the hardening material 8 can be prevented from flowing into the fiber hole 42.

[0062] 12E is a cross-sectional view of the MT connector 40 according to the fourth modification of the second embodiment. As shown in FIG. 12E, the plate portion 50 may be formed with a plurality of holes 50a having a diameter that allows the optical fibers 10 to be inserted therethrough.

[0063] 13 is a cross-sectional view parallel to the XY plane of a mechanical splice member 60, which is an example of an optical connection structure according to a third embodiment of the present disclosure. Similar to the bare fiber adapter 20, the mechanical splice member 60 also holds the pair of optical fibers 10, 10 described above. Furthermore, the mechanical splice member 60 holds the pair of optical fibers 10, 10, thereby maintaining the optical connection between them.

[0064] 13, the mechanical splice member 60 includes a base portion 61, a lid portion 62, and a biasing member 63. The base portion 61 and the lid portion 62 are plate-shaped members made of a material such as ceramic that has a relatively small coefficient of thermal expansion and can be precisely machined.

[0065] A groove 64 is provided in the base portion 61. The cross-sectional shape of the groove 64 is, for example, a V-shape as shown in FIG. 13 . However, this cross-sectional shape may be other shapes such as a semicircular shape. As will be described later, a pair of optical fibers 10, 10 are placed in the groove 64. The lid portion 62 faces the base portion 61 via the pair of optical fibers placed in the groove 64.

[0066] The biasing member 63 is a so-called clip made of steel or the like. The biasing member 63 clamps the base portion 61 and the lid portion 62 and biases them toward each other. The optical fiber 10 is pressed against the groove portion 64, and its movement is restricted.

[0067] 13 , recesses 65 are formed in parts of the base portion 61 and the lid portion 62. When the optical fiber 10 is inserted into the groove portion 64, a wedge (not shown) is inserted into this recess 65 to widen the gap between the lid portion 62 and the base portion 61. After the optical fiber 10 is inserted, the wedge is removed from the recess 65, whereby the optical fiber 10 is sandwiched between the lid portion 62 and the base portion 61, and the optical fiber 10 is fixed between the lid portion 62 and the base portion 61.

[0068] Fig. 14A is a perspective view of the mechanical splice member 60 before clamping the optical fiber 10. Fig. 14B is a perspective view of the mechanical splice member 60 after clamping the optical fiber 10. Fig. 14A shows a state in which the gap between the cover portion 62 and the base portion 61 has been widened by inserting a wedge into the recess 65. For convenience, the biasing member 63, recess 65, and wedge are not shown.

[0069] First, a pair of optical fibers 10 are placed in the groove 64 in the state shown in FIG. 14A . Then, the end faces 10 a of the optical fibers 10 are brought close to each other, and rotational alignment is promoted by utilizing the magnetic coupling between the magnetic bodies 31 of the optical fibers 10. After the rotational alignment is completed and the rotational states (phase states) of the optical fibers 10 are aligned, the wedge is removed from the recess 65. As shown in FIG. 14B , the optical fibers 10 are sandwiched between the base 61 and the lid 62, maintaining the optically connected state. As in the first embodiment, the third embodiment also eliminates the need for precise alignment while observing the end faces using a microscope or the like, thereby improving the efficiency of the optical fiber connection process.

[0070] Fig. 15A is a cross-sectional view parallel to the XY plane of a mechanical splice member 60 according to a first modified example of this embodiment. Fig. 15B is a cross-sectional view parallel to the XY plane of a mechanical splice member 60 according to a second modified example of this embodiment. In the first embodiment, a magnetic body (third magnetic body) 33 is embedded near the fiber hole 24 in the ferrule 23 to promote alignment of the optical fiber 10. This modified example is similar to this. That is, one of the base portion 61 and the lid portion 62 has a magnetic body 33 provided at a position where the pair of optical fibers 10, 10 are butted against each other.

[0071] 15A shows an example in which the magnetic body 33 is provided in the base portion 61. The magnetic body 33 is embedded in the base portion 61, for example, along the inner surface of the groove portion 64. Specifically, the magnetic body 33 is provided near the position where the optical fiber 10 contacts the groove portion 64. However, the position of the magnetic body 33 is not limited to this position, and it may be embedded near the bottom of the groove portion 64, for example.

[0072] 15B shows an example in which the magnetic body 33 is provided on the lid portion 62. The magnetic body 33 is provided near the position where the optical fiber 10 contacts the lid portion 62. Note that whether the magnetic body 33 is provided on the base portion 61 or the lid portion 62, magnetic coupling with the magnetic body 31 of the optical fiber 10 is necessary. Therefore, the magnetic body 33 is provided in the base portion 61 or the lid portion 62 at a position corresponding to the position where the optical fibers 10 are butted against each other, in other words, at a position where magnetic coupling with the magnetic body 31 of the optical fiber 10 is possible.

[0073] As described above, the magnetic material 33 may be embedded in the base portion 61 or the lid portion 62, or may be exposed on the surface of the base portion 61 or the lid portion 62. In either case, the magnetic material 33 attracts the magnetic material 31 of the optical fiber 10, facilitating rotational alignment of the optical fiber 10.

[0074] The base portion 61 may be provided with a plurality of grooves 64. In this case, a plurality of pairs of optical fibers 10 can be held together. Furthermore, these optical fibers 10 have the above-mentioned magnetic body 31. Therefore, in this case as well, rotational alignment can be performed without precise observation of the end faces, improving the efficiency of the splicing work.

[0075] REFERENCE SIGNS LIST 10 Optical fiber (multi-core fiber) 10a End face (first end face) 10b End face (second end face) 12 Core 13 Hole 20 Bare fiber adapter 22 Holding portion 23 Ferrule 23a End face 24 Fiber hole 30 Filler (first filler) 31 Magnetic body (first magnetic body) 32 Magnetic body (second magnetic body) 33 Magnetic body (third magnetic body) 34 Material (first material) 35 Material (second material) 36 Material (third material) 40 MT connector 41 Ferrule 42 Fiber hole 43 Guide groove portion 44 Window portion 45 Cavity portion (first cavity portion) 48 Cavity portion (second cavity portion) 49 Communication path 60 Mechanical splice member 61 Base portion 62 Lid portion 63 Urging member 64 Groove portion

Claims

1. An optical connection structure comprising: a holding part that holds an optical fiber having a magnetic material exposed on its end face; and a ferrule having at least one fiber hole into which the optical fiber is inserted via the holding part, wherein the fiber hole has a diameter that allows twisting of the optical fiber along the circumferential direction of the optical fiber.

2. The optical connection structure according to claim 1, wherein the fiber hole is formed in a flared shape from a position midway within the ferrule to the end face of the ferrule where the optical fiber is exposed.

3. The optical connection structure according to claim 1, wherein the ferrule includes a magnetic material provided around the fiber hole.

4. An optical connection structure according to any one of claims 1 to 3, wherein the holding portion is provided in the ferrule, and the ferrule includes: a guide groove portion for guiding the optical fiber into the fiber hole; a window portion extending from the surface of the ferrule to the guide groove portion and into which adhesive is injected; and a first cavity portion provided between the fiber hole and the guide groove portion and communicating with the window portion.

5. The optical connection structure according to claim 4, wherein the ferrule includes a second cavity portion provided on the opposite side of the guide groove portion from the first cavity portion and communicating with the window portion.

6. The optical connection structure according to claim 5, wherein the ferrule is provided on the opposite side of the guide groove from the window portion and includes a communication passage that connects the first cavity and the second cavity.

7. An optical connection structure comprising: a base portion having at least one groove portion in which a pair of optical fibers having a magnetic material exposed at their end faces are placed; a lid portion facing the base portion via the pair of optical fibers placed in the groove portion; and a biasing member for biasing the base portion and the lid portion toward each other, wherein one of the base portion and the lid portion has a magnetic material provided at a position where the pair of optical fibers are butted together.

8. A method for manufacturing an optical fiber, comprising: attaching a first filler material containing a magnetic substance to a first end face of an optical fiber having a cladding, at least one core provided in the cladding, and at least one air hole provided in the cladding and extending parallel to the core; sealing the periphery of the first end face with a first material having heat shrinkability; injecting the first filler material into the air holes by heating the first material; and magnetizing the magnetic substance in the first filler material after or before heating the first material.

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