Optical connector and method for manufacturing optical connector

Abstract

This optical connector comprises: a ferrule having an insertion through-hole (11); a plurality of optical fibers inserted into the insertion through-hole; an expansion member (50) inserted into the insertion through-hole together with the plurality of optical fibers; and an adhesive (30) which fixes the plurality of optical fibers to the ferrule while the plurality of optical fibers and the expansion member are inserted through the insertion through-hole, wherein the adhesive is a thermosetting resin and the expansion member expands at a lower temperature than the curing temperature of the adhesive.

Description

Optical connector and method for manufacturing the same

[0001] The present invention relates to an optical connector and a method for manufacturing the optical connector. This application claims priority to Japanese Patent Application No. 2022-130948, filed on August 19, 2022, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a structure in which multiple optical fibers are inserted into an insertion hole of a ferrule. The insertion hole is filled with an adhesive for fixing the multiple optical fibers to the ferrule. With an optical connector having such a structure, for example, multiple optical fibers can be connected to a single multi-core fiber.

[0003] Japanese Patent Application Publication No. 2013-125195

[0004] The adhesive filled in the insertion hole of the ferrule may shrink as it hardens, which can cause the optical fiber to shift position inside the insertion hole, potentially increasing the connection loss of the optical connector.

[0005] The present invention has been made in consideration of the above circumstances, and has as its object to provide an optical connector that can suppress misalignment of an optical fiber inside a ferrule, and a method for manufacturing such an optical connector.

[0006] In order to solve the above problem, the optical connector of aspect 1 of the present invention comprises a ferrule having an insertion hole, a plurality of optical fibers inserted into the insertion hole, an expansion member inserted into the insertion hole together with the plurality of optical fibers, and an adhesive that fixes the plurality of optical fibers to the ferrule while the plurality of optical fibers and the expansion member are inserted into the insertion hole, wherein the adhesive is a thermosetting resin and the expansion member expands at a temperature lower than the hardening temperature of the adhesive.

[0007] A second aspect of the present invention is the optical connector according to the first aspect, wherein the expansion member may have a linear expansion coefficient greater than that of the optical fiber at a curing temperature of the adhesive.

[0008] A third aspect of the present invention is the optical connector according to the first or second aspect, wherein the expansion member may have a glass transition temperature lower than the glass transition temperature of the adhesive.

[0009] A fourth aspect of the present invention is the optical connector according to any one of the first to third aspects, wherein the expansion member may have a water absorption rate lower than that of the ferrule.

[0010] Aspect 5 of the present invention is an optical connector according to any one of aspects 1 to 4, wherein the plurality of optical fibers may be arranged inside the insertion hole so as to surround the expansion member.

[0011] A sixth aspect of the present invention is the optical connector according to any one of the first to fifth aspects, wherein the expansion member may contact all of the plurality of optical fibers inside the insertion hole.

[0012] A seventh aspect of the present invention is an optical connector according to any one of the first to sixth aspects, wherein the insertion hole may have a curved portion and a straight portion in a cross section perpendicular to the central axis of the insertion hole.

[0013] Aspect 8 of the present invention is the optical connector according to any one of aspects 1 to 7, wherein a release layer may be provided on a surface of the expansion member.

[0014] Aspect 9 of the present invention is a method for manufacturing an optical connector, which includes inserting an expansion member together with multiple optical fibers into a through-hole of a ferrule, injecting adhesive into the through-hole, heating and expanding the expansion member, thereby pressing the multiple optical fibers against the inner surface of the through-hole with the expansion member, and hardening the adhesive to fix the multiple optical fibers to the ferrule.

[0015] A tenth aspect of the present invention is a method for manufacturing an optical connector according to the ninth aspect, wherein the expansion member may be removed from the insertion hole after the plurality of optical fibers are fixed to the ferrule by the adhesive.

[0016] According to the above aspects of the present invention, it is possible to provide an optical connector capable of suppressing misalignment of an optical fiber inside a ferrule, and a method for manufacturing such an optical connector.

[0017] FIG. 2 is a perspective view of an optical connector according to the present embodiment. FIG. 3 is a perspective view of the optical connector shown in FIG. 1 with a plurality of optical fibers extracted. FIG. 4 is a cross-sectional view taken along the III-III arrow in FIG. 1. FIG. 5 is a diagram explaining a method for manufacturing an optical connector according to the present embodiment, showing a cross-sectional view of the vicinity of the insertion hole. FIG. 6 is a diagram explaining a method for manufacturing an optical connector according to the present embodiment, showing a cross-sectional view of the vicinity of the insertion hole. FIG. 7 is a diagram explaining a method for manufacturing an optical connector according to the present embodiment, showing a cross-sectional view of the vicinity of the insertion hole. FIG. 8 is a cross-sectional view of the vicinity of the insertion hole of an optical connector according to a modified example. FIG. 9 is a cross-sectional view of the vicinity of the insertion hole of an optical connector according to a modified example. FIG. 10 is a cross-sectional view of the vicinity of the insertion hole of an optical connector according to a modified example.

[0018] The optical connector of this embodiment will be described below with reference to the drawings. As shown in Fig. 1, the optical connector 1 includes a ferrule 10, a plurality of optical fibers 20, an adhesive 30, and two positioning pins 40. Note that the optical connector 1 does not necessarily have to include the positioning pins 40.

[0019] The ferrule 10 has a connection end face 10a, a rear end face 10b, an insertion hole 11, an injection hole 12, and two positioning holes 13. The connection end face 10a is the surface that is butted against another connector or the like when the optical connector 1 is connected to that other connector or the like. The insertion hole 11 and the two positioning holes 13 open to the connection end face 10a. An introduction hole (not shown) that communicates with the insertion hole 11 opens to the rear end face 10b, and multiple optical fibers 20 are introduced into the ferrule 10 through the introduction hole. A positioning pin 40 is inserted into each of the two positioning holes 13.

[0020] (Direction Definition) In this specification, the direction parallel to the central axis O of the insertion hole 11 is referred to as the Z direction, axial direction Z, or longitudinal direction Z. A direction perpendicular to the longitudinal direction Z is referred to as the first direction X. The first direction X is also the direction in which the two positioning holes 13 are aligned. A direction perpendicular to both the longitudinal direction Z and the first direction X is referred to as the second direction Y. The direction from the rear end face 10b of the ferrule 10 toward the connecting end face 10a along the longitudinal direction Z is referred to as the +Z direction, forward, or tip side. The direction opposite to the +Z direction is referred to as the -Z direction, rear, or base end side. A direction perpendicular to the central axis O as viewed from the longitudinal direction Z is referred to as the radial direction. A direction approaching the central axis O along the radial direction is referred to as the radially inward direction, and a direction away from the central axis O is referred to as the radially outward direction. A direction going around the central axis O as viewed from the longitudinal direction Z is referred to as a circumferential direction. A cross section perpendicular to the longitudinal direction Z is referred to as a transverse cross section. In other words, a transverse cross section is a cross section extending along the first direction X and the second direction Y.

[0021] In the connection end face 10a, the insertion hole 11 is arranged so as to be sandwiched between two positioning holes 13. The injection hole 12 opens to one end face of the ferrule 10 facing the second direction Y. The injection hole 12 communicates with the internal space of the ferrule 10 and the insertion hole 11. When the optical connector 1 is assembled, an adhesive 30 is injected into the ferrule 10 through the injection hole 12. The injected adhesive 30 also enters the interior of the insertion hole 11.

[0022] 2 is a diagram of the optical fibers 20 shown in FIG. 1 . As shown in FIG. 2 , the optical connector 1 of this embodiment has four optical fibers 20. However, the number of optical fibers 20 may be changed. Each optical fiber 20 has a bare fiber 21 and a coating 22. The bare fiber 21 is formed of, for example, quartz glass. The coating 22 partially covers the bare fiber 21 and serves to protect the bare fiber 21. The coating 22 is formed of, for example, a resin. For example, the material of the coating 22 may be a UV-curable resin. At the front end of each optical fiber 20, the coating 22 is not provided, and the bare fiber 21 is exposed. The exposed bare fiber 21 is inserted into the insertion hole 11 of the ferrule 10.

[0023] The bare fiber 21 has a small diameter portion 21 a and a large diameter portion 21 b. The outer diameter of the small diameter portion 21 a is smaller than the outer diameter of the large diameter portion 21 b. The small diameter portion 21 a can be formed by thinning the end of the bare fiber 21, which has a constant outer diameter (the same outer diameter as the large diameter portion 21 b) in the longitudinal direction Z, for example, by etching. In this embodiment, the small diameter portion 21 a is inserted into the insertion hole 11 of the ferrule 10.

[0024] 3 is a cross-sectional view of the vicinity of the insertion hole 11. As shown in FIG. 3, the bare fiber 21 has a core 21c and a clad 21d. The clad 21d is disposed so as to surround the core 21c. The refractive index of the clad 21d is lower than the refractive index of the core 21c. Therefore, the optical fiber 20 can confine light within the core 21c.

[0025] As shown in Figure 3, the insertion hole 11 of this embodiment has a curved portion 11a and a straight portion 11b when viewed from the longitudinal direction Z. The curved portion 11a has an arc shape. That is, the insertion hole 11 is D-shaped. Of the four bare fibers 21, two bare fibers 21 abut both the curved portion 11a and the straight portion 11b. The remaining two bare fibers 21 abut the curved portion 11a but not the straight portion 11b. With this configuration, the bare fibers 21 and the insertion hole 60 contact each other at six locations. The four bare fibers 21 are positioned by being pressed against the inner surface of the insertion hole 11 by an expansion member 50, which will be described later.

[0026] The adhesive 30 has a function of fixing the plurality of optical fibers 20 to the ferrule 10. The material of the adhesive 30 may be, for example, a thermosetting resin. More specifically, the material of the adhesive 30 may be an epoxy resin.

[0027] During manufacturing of the optical connector 1, the bare fiber 21 is inserted into the insertion hole 11, and the liquid adhesive 30 is filled into the insertion hole 11 through the injection hole 12. The adhesive 30 is then hardened. Here, the adhesive 30 may shrink as it hardens. If the adhesive 30 shrinks, a radially inward force may act on the bare fiber 21. The position of the bare fiber 21 is determined by its contact with the inner surface of the insertion hole 11. Therefore, if the bare fiber 21 moves away from the inner surface of the insertion hole 11 as the adhesive 30 shrinks, the bare fiber 21 will shift from its predetermined position. If the position of the bare fiber 21 inside the insertion hole 11 shifts, the connection loss of the optical connector 1 will increase.

[0028] In particular, when an epoxy resin is used as the adhesive 30, heating is performed to harden the adhesive 30. The viscosity of the epoxy resin drops sharply between 30°C and 50°C, and above 50°C, the viscosity of the epoxy resin becomes equal to or lower than that of water. When the viscosity of the adhesive 30 drops in this way, the bare fiber 21 moves easily inside the insertion hole 11, and is more likely to separate from the inner surface of the insertion hole 11.

[0029] Therefore, as shown in Fig. 3, the optical connector 1 of this embodiment has an expansion member 50 for pressing the bare fiber 21 against the inner surface of the insertion hole 11. The expansion member 50 is a linear member extending in the longitudinal direction Z. The expansion member 50 is inserted into the insertion hole 11 together with the plurality of bare fibers 21. Inside the insertion hole 11, the expansion member 50 contacts each bare fiber 21 (small diameter portion 21a). Each bare fiber 21 is arranged to surround the expansion member 50. Although the expansion member 50 is not shown in Fig. 1, the expansion member 50 may extend rearward from the ferrule 10 together with the plurality of optical fibers 20.

[0030] The expansion member 50 is configured to press the bare fiber 21 against the inner surface of the insertion hole 11. The expansion member 50 of this embodiment has a main body 51 and a release layer 52. The main body 51 is linear, and the release layer 52 is provided on the surface of the main body 51. The release layer 52 has the function of preventing the main body 51 from adhering to the adhesive 30. The presence of the release layer 52 makes it easier to remove the expansion member 50 from the optical connector 1, as will be described later. The release layer 52 may be formed, for example, by performing a surface treatment on the main body 51. The release layer 52 may be, for example, a fluorine-based coating agent. Note that the expansion member 50 does not necessarily have to have the release layer 52.

[0031] An example of a method for manufacturing the optical connector 1 will now be described.

[0032] First, a preparation step is performed. In this step, the ferrule 10, the plurality of optical fibers 20, the adhesive 30, the expansion member 50, and the like are prepared. In this step, the coating 22 at the tip of the optical fiber 20 is removed to expose the bare fiber 21. If necessary, the exposed bare fiber 21 is subjected to an etching process or the like to form the small diameter portion 21a. Also, if necessary, the main body 51 of the expansion member 50 is subjected to a surface treatment to form a peel layer 52.

[0033] Next, an insertion process is performed. In the insertion process, the bare fibers 21 of the multiple optical fibers 20 and the expansion member 50 are inserted into the insertion holes 11 of the ferrule 10. In the insertion process, the expansion member 50 may be used as an introduction tool for introducing the bare fibers 21 into the insertion holes 11. Specifically, the expansion member 50 is first inserted into the insertion holes 11, and the optical fibers 20 are temporarily fixed to a portion of the expansion member 50 located behind the ferrule 10. In this state, the expansion member 50 is pulled forward from the ferrule 10, or the expansion member 50 is pushed into the ferrule 10 from behind, thereby introducing the bare fibers 21 together with the expansion member 50 into the insertion holes 11.

[0034] 4A is a cross-sectional view showing the state inside the insertion hole 11 after the insertion step has been performed. As shown in FIG. 4A , during the insertion step, a gap G may exist between the inner surface of the insertion hole 11 and the bare fiber 21, or between the bare fiber 21 and the expansion member 50. Providing such a gap allows the bare fiber 21 to be smoothly inserted into the insertion hole 11. The outer diameter of the bare fiber 21 (outer diameter of the small diameter portion 21 a), the outer diameter of the expansion member 50, or the shape of the insertion hole 11 may be set so that the gap G is generated during the insertion step.

[0035] Next, an injection step is performed. In the injection step, the adhesive 30 in a fluid state is injected into the ferrule 10 through the injection hole 12. At this time, the adhesive 30 also enters the insertion hole 11. The adhesive 30 may be actively forced into the insertion hole 11 by sucking the insertion hole 11, which opens on the connection end face 10a, with a vacuum or the like. Alternatively, the adhesive 30 may be forced into the insertion hole 11 by capillary force or the like generated in the insertion hole 11.

[0036] Next, the expansion process is performed. In the expansion process, the expansion member 50 is heated to a first temperature and expanded, thereby pressing the bare fiber 21 against the inner surface of the insertion hole 11. The first temperature is lower than the curing temperature of the adhesive. The "curing temperature" refers to the temperature at which the adhesive 30 sufficiently hardens when the adhesive 30 is a thermosetting resin. For example, when the adhesive 30 is an epoxy resin, the curing temperature of the adhesive 30 (epoxy resin) is approximately 100°C. Therefore, the first temperature in this case is a temperature lower than 100°C (e.g., approximately 50°C). As a result of the expansion process, the bare fiber 21 is pressed against the inner surface of the insertion hole 11, as shown in FIG. 4B , eliminating the gap G. This positions the bare fiber 21. Note that the viscosity of epoxy resin is extremely low at around 50°C, so setting the first temperature to approximately 50°C facilitates movement of the bare fiber 21 during the expansion process. In other words, the movement of the bare fiber 21 is prevented from being hindered by the viscosity of the adhesive 30.

[0037] 4B, the two bare fibers 21 located at the top of the drawing (hereinafter sometimes referred to as "first bare fibers") are positioned by abutting against both the curved portion 11 a and the straight portion 11 b, and the two bare fibers 21 located at the bottom of the drawing (hereinafter sometimes referred to as "second bare fibers") are positioned by abutting against both the first bare fibers and the curved portion 11 a.

[0038] Next, a curing step is performed. In the curing step, the adhesive 30 is cured to fix the bare fiber 21 to the ferrule 10. For example, if the adhesive 30 is a thermosetting resin such as an epoxy resin, the adhesive 30 is heated to a second temperature that is equal to or higher than the curing temperature. Note that if the adhesive 30 is not a thermosetting resin, the adhesive 30 may be cured by a method other than heating. For example, if the adhesive 30 is a UV-curable resin, the curing step may be performed by irradiating the adhesive 30 with UV light.

[0039] If the adhesive 30 is a thermosetting resin, the expansion step and the curing step can be performed consecutively. For example, in the expansion step, the optical connector 1 is heated from room temperature to a first temperature, and in the curing step, the optical connector 1 is heated from the first temperature to a second temperature. These heating steps can be performed in the same chamber. If heating is performed in the curing step, the optical connector 1 is then cooled. If necessary, the connection end surface 10a may be polished to remove the bare fiber 21, the adhesive 30, and the portions of the expansion member 50 that protrude from the insertion hole 11.

[0040] Next, a removal process may be performed. As described above, the expansion member 50 contracts when cooled after heating. This creates a gap between the adhesive 30 and the expansion member 50. In the removal process, the expansion member 50 is removed from the insertion hole 11. Specifically, the expansion member 50 is pulled forward or backward relative to the ferrule 10. If a release layer 52 is provided on the expansion member 50, the release layer 52 easily peels off from the adhesive 30, making the removal process easier. FIG. 4C is a cross-sectional view showing the state of the insertion hole 11 after the removal process. When the removal process is performed, a cavity H is formed in the area where the expansion member 50 was located.

[0041] Because the adhesive 30 has already hardened, the bare fiber 21 remains in contact with the inner surface of the insertion hole 11 even after the removal process. In other words, the bare fiber 21 remains positioned. Furthermore, performing the removal process provides the following advantages, for example: First, the expansion member 50 can be prevented from protruding forward from the connection end face 10a, preventing physical contact between the optical connector 1 and other connectors. Second, if the expansion member 50 is water-absorbent, the adhesive 30 can be prevented from being deteriorated by moisture contained in the expansion member 50. Third, the optical connector 1 can be made lighter. Fourth, the formed cavity H can be reused for other purposes. For example, a light source for illumination may be inserted into the cavity H during post-manufacture inspection of the optical connector 1. Fifth, if the adhesive 30 expands due to a temperature change after manufacture of the optical connector 1, the volume of the expanded adhesive 30 can be released into the cavity H. This prevents the expansion of the adhesive 30 from acting to move the bare fiber 21.

[0042] When the removal process is performed, the cavity H is formed so as to penetrate the adhesive 30 in the longitudinal direction Z. In the example of Fig. 4C, the plurality of bare fibers 21 face the cavity H and are arranged so as to surround the cavity H. Note that it is not essential to perform the removal process. In other words, the optical connector 1 may or may not include the expansion member 50 in the manufactured state.

[0043] In order to achieve the above function, the expansion member 50 is configured to expand at a temperature lower than the hardening temperature of the adhesive 30. The material of the main body 51 of the expansion member 50 can be, for example, a resin or a metal. More specifically, the material of the main body 51 may be oxetane resin or copper. The linear expansion coefficient of oxetane resin can be changed by the composition, but is, for example, about 90×10 at 0 to 50°C. -6 / K, and at 50 to 100°C it is about 170 × 10 -6 / K. The linear expansion coefficient of copper is approximately constant between 0 and 100°C, and is approximately 16.8 × 10 -6When a metal is used for the main body 51, the charge on the surface of the bare fiber 21 can be released through the main body 51 during the insertion process, thereby suppressing the bare fiber 21 from floating due to the charge.

[0044] The glass transition temperature of the main body 51 of the expansion member 50 is preferably lower than the glass transition temperature of the adhesive 30. For example, the glass transition temperature of epoxy resin is 90°C, and the glass transition temperature of oxetane resin is 50°C to 80°C. The linear expansion coefficient of oxetane resin rises rapidly above its glass transition temperature. As the linear expansion coefficient of the main body 51 increases, the expansion speed of the expansion member 50 increases, allowing the bare fiber 21 to be quickly pressed against the inner surface of the insertion hole 11. This allows the bare fiber 21 to be positioned early. Note that, once the adhesive 30 begins to harden, the movement of the bare fiber 21 within the insertion hole 11 is hindered, so it is preferable to position the bare fiber 21 early.

[0045] The water absorption rate of the expansion member 50 is preferably lower than that of the ferrule 10. The low water absorption rate of the expansion member 50 can prevent the adhesive 30 from being deteriorated by moisture contained in the expansion member 50. Since the release layer 52 occupies a very small volume in the expansion member 50, the water absorption rate of the expansion member 50 is substantially the same as that of the main body 51. The same applies to other physical properties of the expansion member 50. That is, in this embodiment, the linear expansion coefficient, glass transition temperature, and water absorption rate of the expansion member 50 are substantially the same as those of the main body 51. The ferrule 10 is made of, for example, PPS+GF (polyphenylene sulfide with 30% to 70% glass fiber added). The main body 51 of the expansion member 50 is made of, for example, oxetane resin, which has a lower water absorption rate than PPS+GF.

[0046] As described above, the optical connector 1 of this embodiment includes a ferrule 10 having an insertion hole 11, a plurality of optical fibers 20 inserted into the insertion hole 11, an expansion member 50 inserted into the insertion hole 11 together with the plurality of optical fibers 20, and an adhesive 30 that fixes the plurality of optical fibers 20 to the ferrule 10 with the plurality of optical fibers 20 and the expansion member 50 inserted into the insertion hole 11. The adhesive 30 is, for example, a thermosetting resin, and the expansion member 50 expands at a temperature lower than the hardening temperature of the adhesive 30. With this configuration, the expansion member 50 can press the optical fiber 20 against the inner surface of the insertion hole 11. Therefore, it is possible to suppress misalignment of the optical fiber 20 inside the insertion hole 11.

[0047] Furthermore, it is preferable that the expansion member 50 has a larger linear expansion coefficient than the optical fiber 20 at the curing temperature of the adhesive. This increases the expansion speed of the expansion member 50, making it possible to quickly determine the position of the optical fiber 20 in the insertion hole 11.

[0048] Furthermore, it is preferable that the glass transition temperature of the expansion member 50 is lower than the glass transition temperature of the adhesive 30. The low glass transition temperature of the expansion member 50 causes a steep increase in the linear expansion coefficient of the expansion member 50 when heated. This increases the expansion speed of the expansion member 50, making it possible to quickly determine the position of the optical fiber 20 in the insertion hole 11.

[0049] Furthermore, the water absorption rate of the expansion member 50 is preferably lower than the water absorption rate of the ferrule 10. When the water absorption rate of the expansion member 50 is low, deterioration of the adhesive 30 can be suppressed.

[0050] Furthermore, it is preferable that the plurality of optical fibers 20 are arranged so as to surround the expansion member 50 inside the insertion hole 11. Furthermore, it is preferable that the expansion member 50 contacts all of the plurality of optical fibers 20 inside the insertion hole 11. With this arrangement, when the expansion member 50 expands, a pressing force toward the outside in the radial direction acts on each optical fiber 20. Therefore, it is possible to more reliably press each optical fiber 20 against the inner surface of the insertion hole 11.

[0051] Furthermore, it is preferable that the insertion hole 11 has a curved portion 11 a and a straight portion 11 b in a cross section perpendicular to the central axis O. In this case, by abutting at least a part of the optical fiber 20 against both the curved portion 11 a and the straight portion 11 b, the position of the optical fiber 20 can be determined with higher accuracy.

[0052] A release layer 52 may also be provided on the surface of the expansion member 50. In this case, the expansion member 50 can be prevented from adhering to the adhesive 30 and the optical fiber 20 when the adhesive 30 hardens. Therefore, even if the expansion member 50 shrinks after the adhesive 30 hardens, the optical fiber 20 can be prevented from moving due to this shrinkage. Furthermore, the expansion member 50 can be easily pulled out of the ferrule 10.

[0053] Furthermore, the manufacturing method of the optical connector 1 of this embodiment involves inserting the expansion member 50 together with the plurality of optical fibers 20 into the insertion hole 11 of the ferrule 10, injecting adhesive 30 into the insertion hole 11, heating and expanding the expansion member 50, thereby pressing the plurality of optical fibers 20 against the inner surface of the insertion hole 11 with the expansion member 50, and hardening the adhesive 30 to fix the plurality of optical fibers 20 to the ferrule 10. This manufacturing method makes it possible to suppress misalignment of the optical fibers 20 inside the insertion hole 11.

[0054] Furthermore, after the plurality of optical fibers 20 are fixed to the ferrule 10 by the adhesive 30, the expansion member 50 may be removed from the insertion hole 11. In this case, the formation of the cavity H in the adhesive 30 can provide various advantages.

[0055] The optical connector 1 also includes a ferrule 10 having an insertion hole 11, a plurality of optical fibers 20 inserted into the insertion hole 11, and an adhesive 30 that fixes the plurality of optical fibers 20 inside the insertion hole 11, and the adhesive 30 may have a cavity H formed therein that extends in the longitudinal direction Z of the insertion hole 11.

[0056] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0057] For example, in the above embodiment, the bare fiber 21 has a small diameter portion 21 a and a large diameter portion 21 b, and the small diameter portion 21 a is inserted into the insertion hole 11 of the ferrule 10. However, the outer diameter of the bare fiber 21 may be constant in the longitudinal direction Z. In other words, the tip of the bare fiber 21 may be inserted into the insertion hole 11 as is without being thinned by etching or the like.

[0058] In the above embodiment, the bare fibers 21 are arranged to surround the expansion member 50, with one expansion member 50 contacting all of the bare fibers 21. However, as long as the expansion member 50 can press the bare fibers 21 against the inner surface of the insertion hole 11, the arrangement of the bare fibers 21 and the expansion member 50 may be changed. For example, as shown in FIG. 5 , two expansion members 50 may be arranged in the insertion hole 11. More specifically, the two expansion members 50 may be arranged radially apart and each contact the inner surface of the insertion hole 11. Furthermore, one expansion member 50 may contact two bare fibers 21, and the remaining expansion member 50 may contact the remaining two bare fibers 21. Even with this arrangement, it is possible to press each bare fiber 21 against the inner surface of the insertion hole 11.

[0059] The shape of the insertion hole 11 can be changed. For example, the insertion hole 11 may not have the straight portion 11b and may be entirely curved portion 11a. That is, the insertion hole 11 may be circular.

[0060] Furthermore, while the insertion hole 11 in the above embodiment is D-shaped, as shown in FIG. 6 , the insertion hole 60 may be rectangular. The insertion hole 60 of this modification has four straight portions 61a to 61d and a corner 62 when viewed from the longitudinal direction Z. Here, if the radius of curvature of the corner 62 is Rh and the radius of the bare fiber 21 is r, the shape of the insertion hole 60 satisfies the following formula (1): Rh<r (1) According to formula (1), the radius of curvature Rh of the corner 62 is smaller than the radius r of the bare fiber 21, so a gap is formed between the corner 62 and the bare fiber 21. With this configuration, the outer circumferential surface of each of the four bare fibers 21 contacts two of the straight portions 61a to 61d. Therefore, the four bare fibers 21 contact the insertion hole 60 at eight locations. Furthermore, if the length of one side of the insertion hole 60 is L and the design value of the distance between the cores 21c of adjacent bare fibers 21 is Pc, the shape of the insertion hole 60 satisfies the following equations (2) and (3): L>4r ... (2) Pc<L-2r ... (3) These four bare fibers 21 are pressed against the inner surface of the insertion hole 60 by the expansion member 50 described above, thereby determining their positions.

[0061] In this modification, because the insertion hole 60 is rectangular, by pressing the bare fiber 21 against the inner surface of the insertion hole 60, which has a simple configuration, it is possible to suppress misalignment of the optical fiber 20 inside the insertion hole 60, as in the above embodiment. Furthermore, because the shape of the insertion hole 60 satisfies the above formulas (2) and (3), some gaps are formed between the bare fiber 21 and the linear portions 61a to 61d. This makes it possible to easily insert four bare fibers 21 into the insertion hole 60.

[0062] Furthermore, while in the above embodiment the insertion hole 11 was D-shaped, as shown in FIG. 7 , the insertion hole 70 may be composed of four curved portions 71a to 71d when viewed from the longitudinal direction Z. If the curvature radius of the curved portions 71a to 71d is Rh1 and the radius of the bare fibers 21A to 21D is r, the shape of the insertion hole 70 satisfies the following formula (4): Rh1 > r (4) From formula (4), the curvature radius Rh1 of the curved portions 71a to 71d is greater than the radius r of the bare fibers 21A to 21D. Therefore, the outer circumferential surfaces of the four bare fibers 21A to 21D contact the curved portions 71a to 71d at one point. With this configuration, the four bare fibers 21A to 21D contact the insertion hole 70 at four locations. These four bare fibers 21 are pressed against the inner surface of the insertion hole 70 by the expansion member 50 described above, thereby determining their positions.

[0063] Furthermore, if the contact points between the two diagonally arranged bare fibers 21A, 21C and the curved portions 71a, 71c are P1 and P2, respectively, the distance between the contact points P1 and P2 is W, and the design value of the distance between the cores 21c of the adjacent bare fibers 21 is Pc, the shape of the insertion hole 70 satisfies the following formulas (5) to (7): Rh1>W / 2 (5), W>2r+2r√2 (6), Pc√2<W-2r (7).

[0064] In this modification, there are four contact points between the bare fibers 21A-21D and the insertion hole 70. This reduces the number of contact points compared to the insertion hole 11 of the previous embodiment. This makes it possible to further suppress misalignment of the optical fiber 20 inside the insertion hole 70. Furthermore, by satisfying the above formulas (5) to (7), a small gap is formed between the bare fiber 21 and the curved portions 71a-71d. This makes it possible to easily insert the four bare fibers 21A-21D into the insertion hole 70.

[0065] The manufacturing method of the optical connector 1 according to the embodiment may also include a suppression step. Specifically, as shown in FIG. 8 , the suppression step is a step of suppressing the expansion member 50 from protruding beyond the distal end surface 21e of the bare fiber 21. A pin 80, for example, is used as a jig for suppressing the expansion member 50. The pin 80 has a tapered portion 81 whose outer diameter gradually decreases toward the distal end surface 80a of the pin 80, and a straight portion 82 extending toward the base end of the pin 80. The distal end of the tapered portion 81 of the pin 80 has a flat shape. Here, if the outer diameter of the distal end surface 80a of the pin 80 is D1 and the outer diameter of the straight portion 82 of the pin 80 is D2, the shape of the pin 80 satisfies the following equations (8) and (9): D1<W-4r ... (8) D2>W-4r ... (9) By satisfying the above equation (8), the outer diameter D1 of the distal end surface 80a of the pin 80 is smaller than the outer diameter of the expansion member 50. This allows the tip surface 80 a of the pin 80 to come into contact only with the expansion member 50 .

[0066] The material of the pin 80 is not particularly limited, but may be a material with a lower hardness than quartz glass. For example, the material of the pin 80 is aluminum or plastic. The distance between the tip surface 21e of the bare fiber 21 and the tip surface 50a of the expansion member 50 in the longitudinal direction Z is approximately 1.0 to 3.5 μm.

[0067] In the suppression process, a pin 80 is placed on the tip surface 50a of the expansion member 50 before the expansion process. The expansion member 50 is then heated and expanded. At this time, the pin 80 holds down the expansion member 50, which expands in the +Z direction, causing the expansion member 50 to expand in the circumferential direction. Next, in the removal process, when the expansion member 50 has cooled, the pin 80 is removed. As a result, the tip surface 50a of the expansion member 50 is recessed, and a mark of the tip surface 80a of the tapered portion 81 remains on the tip surface 50a of the expansion member 50.

[0068] According to this manufacturing method, by holding down the expansion member 50, it becomes easier for the expansion member 50 to expand in the circumferential direction, and therefore the bare fiber 21 can be pressed more efficiently against the inner surface of the insertion hole 11. Also, because the pin 80 is in contact with the bare fiber 21, it is possible to assist positioning by the pin 80. Furthermore, because the pin 80 is in contact with the bare fiber 21, it is possible to prevent the expansion member 50 from protruding from the tip surface 21e of the bare fiber 21. By using a material for the pin 80 that is less hard than quartz glass, it is possible to prevent the expansion member 50 from protruding even if the pin 80 and the bare fiber 21 come into contact without damaging the bare fiber 21.

[0069] In this modification, the pin 80 is used to push the expansion member 50 in the −Z direction from the distal end surface 21e of the bare fiber 21. However, this is not limited to this. The expansion member 50 may also be pushed at the distal end surface 21e of the bare fiber 21. If positioning assistance by the pin 80 is not required, the pin 80 does not need to have a portion that satisfies the above formula (9). In this configuration, the jig does not contact the bare fiber 21. This reduces the possibility of damaging the polished distal end surface 21e of the bare fiber 21 while preventing the expansion member 50 from protruding. The jig may have a constant outer diameter overall, or may have only a tapered portion whose outer diameter widens toward the base end. In this configuration, the jig only needs to satisfy at least formula (8) of formulas (8) and (9). The distal end of the tapered portion 81 of the pin 80 is flat, but it may also be curved.

[0070] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate, without departing from the spirit of the present invention.

[0071] REFERENCE SIGNS LIST 10... ferrule 11, 60, 70... insertion hole 11a... curved portion 11b... straight portion 12... injection hole 20... optical fiber 30... adhesive 50... expansion member 52... peeling layer O... central axis Z... longitudinal direction

Claims

1. A ferrule having an insertion hole; A plurality of optical fibers inserted into the insertion holes; an expansion member inserted into the insertion hole together with the plurality of optical fibers; an adhesive that fixes the optical fibers to the ferrule in a state in which the optical fibers and the expansion member are inserted into the insertion hole; the adhesive is a thermosetting resin; The expansion member expands at a temperature lower than a hardening temperature of the adhesive.

2. The optical connector according to claim 1 , wherein the expansion member has a linear expansion coefficient larger than that of the optical fiber at a curing temperature of the adhesive.

3. 3. The optical connector according to claim 1, wherein the expansion member has a glass transition temperature lower than a glass transition temperature of the adhesive.

4. 3. The optical connector according to claim 1, wherein the expansion member has a water absorption rate lower than that of the ferrule.

5. 3. The optical connector according to claim 1, wherein the plurality of optical fibers are arranged inside the insertion hole so as to surround the expansion member.

6. The optical connector according to claim 5 , wherein the expansion member contacts all of the plurality of optical fibers inside the insertion hole.

7. 3. The optical connector according to claim 1, wherein the insertion hole has a curved portion and a straight portion in a cross section perpendicular to a central axis of the insertion hole.

8. 3. The optical connector according to claim 1, wherein a release layer is provided on a surface of the expansion member.

9. Inserting an expansion member together with the plurality of optical fibers into the insertion hole of the ferrule; Injecting an adhesive into the insertion hole; The expansion member is heated and expanded, so that the expansion member presses the plurality of optical fibers against an inner surface of the insertion hole; and fixing the optical fibers to the ferrule by hardening the adhesive.

10. The method for manufacturing an optical connector according to claim 9 , further comprising the step of: removing the expansion member from the insertion hole after the optical fibers are fixed to the ferrule by the adhesive.