Optical connector and method for producing optical connector

Abstract

An optical connector (1A) comprises a ferrule (10) having a connection end surface (10a) and a fiber hole (11) that is open in the connection end surface (10a), a plurality of optical fibers (20) inserted into the fiber hole (11), an adhesive (30) that fixes the plurality of optical fibers (20) in the ferrule (10), and a stress relaxation material (50) having a Young's modulus smaller than that of the adhesive (30). Each of the plurality of optical fibers (20) has a small-diameter part (21a) that is inserted into the fiber hole (11), a large-diameter part (21b) that has a larger diameter than the small-diameter part (21a), and a tapered part (21c) that is positioned between the small-diameter part (21a) and the large-diameter part (21b) and has a diameter that changes along the longitudinal direction of the optical fiber (20), and the stress relaxation material (50) covers at least a portion of the small-diameter part (21c).

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. 2023-131668, filed on August 10, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses an optical connector having a structure in which multiple optical fibers are inserted into one fiber hole of a ferrule. In such an optical connector, the optical fiber may be etched to partially thin the cladding. By thinning the cladding, the pitch between the cores of the multiple optical fibers can be reduced. The pitch between the cores matches the pitch between the cores of the connection target (e.g., a multicore fiber).

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

[0004] In optical fibers with thinner cladding, the rigidity of the optical fiber decreases, and the light confinement effect of the cladding also decreases. This makes the optical fiber more susceptible to bending due to external forces, and light is more likely to leak when bent. In addition, the inside of the ferrule is filled with an adhesive to secure the optical fiber to the ferrule. The volume of the adhesive changes when it hardens. This change in volume of the adhesive can cause stress to act on the thin part of the cladding. This stress causes the optical fiber to bend, leading to light leakage and increased connection loss, which is an issue.

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an optical connector that can suppress an increase in connection loss and a method for manufacturing the optical connector.

[0006] In order to solve the above problem, an optical connector according to aspect 1 of the present invention comprises a ferrule having a connection end face and a fiber hole opening at the connection end face, a plurality of optical fibers inserted into the fiber hole, an adhesive for fixing the plurality of optical fibers to the ferrule, and a stress relaxation material having a smaller Young's modulus than the adhesive, wherein each of the plurality of optical fibers has a small diameter portion inserted into the fiber hole, a large diameter portion having a diameter larger than the small diameter portion, and a tapered portion located between the small diameter portion and the large diameter portion and having a diameter that changes along the longitudinal direction of the optical fiber, and the stress relaxation material covers at least a portion of the small diameter portion.

[0007] Aspect 2 of the present invention is an optical connector according to aspect 1, wherein the fiber hole has a positioning portion that opens to the connection end face and a guide portion that is located closer to the base end than the positioning portion and has a larger inner diameter than the positioning portion, and the stress relaxation material may cover the portion of the small diameter portion that is located inside the guide portion.

[0008] A third aspect of the present invention is the optical connector according to the first or second aspect, wherein the stress relaxation material may cover the tapered portion.

[0009] A fourth aspect of the present invention is the optical connector according to any one of the first to third aspects, wherein the stress relaxation material may integrally cover the small diameter portions of the plurality of optical fibers.

[0010] A method for manufacturing an optical connector according to aspect 5 of the present invention includes preparing a plurality of optical fibers each having a small diameter portion, a tapered portion, and a large diameter portion, bundling the plurality of optical fibers together and applying a resin that serves as a stress relief material to at least a portion of the small diameter portion, hardening the resin while the plurality of optical fibers are bundled together to form the stress relief material, and while the plurality of optical fibers are bundled together, inserting the small diameter portions into fiber holes of a ferrule all at once, and fixing the plurality of optical fibers to the ferrule with an adhesive having a larger Young's modulus than the stress relief material.

[0011] According to the above aspects of the present invention, an increase in connection loss in an optical connector can be suppressed.

[0012] Fig. 2 is a perspective view of the optical connector according to the present embodiment. Fig. 3 is a cross-sectional view taken along the line II-II in Fig. 1. Fig. 4 is an enlarged view of Fig. 2. Fig. 5 is a perspective view of the optical connector shown in Fig. 1, with a plurality of optical fibers extracted. Fig. 6 is an enlarged view of Fig. 2. Fig. 7 is a cross-sectional view of an optical connector according to a modified example.

[0013] An optical connector according to this embodiment will now be described with reference to the drawings. As shown in Fig. 1, the optical connector 1A includes a ferrule 10, a plurality of optical fibers 20, two positioning pins 40, and a boot 60. Note that the optical connector 1A does not necessarily have to include the positioning pins 40 and the boot 60.

[0014] The ferrule 10 has a connection end face 10a, a rear end face 10b, a fiber hole 11, an injection hole 12, two positioning holes 13, and an introduction hole 14 (see FIG. 2). The connection end face 10a is the surface that is abutted against another connector or the like when the optical connector 1A is connected to another connector or the like. The fiber hole 11 and the two positioning holes 13 open in the connection end face 10a. As shown in FIG. 2, the introduction hole 14 opens in the rear end face 10b and communicates with the fiber hole 11.

[0015] A plurality of optical fibers 20 are introduced into a single fiber hole 11 through introduction holes 14. As shown in Fig. 1, a positioning pin 40 is inserted into each of the two positioning holes 13. The illustrated optical connector 1A is a male type and has the positioning pin 40. However, the optical connector 1A may be a female type and not have the positioning pin 40.

[0016] The ferrule 10 is made of a material such as resin, ceramic, etc. Examples of resin include epoxy, PPS, PEEK, and PEI. Examples of ceramic include zirconia.

[0017] (Direction Definition) In this specification, the direction parallel to the central axis O of the fiber hole 11 is referred to as the Z direction, axial direction Z, or longitudinal direction Z. The direction from the rear end face 10b of the ferrule 10 toward the connection 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. In this embodiment, 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. The direction perpendicular to both the longitudinal direction Z and the first direction X is referred to as the second direction Y.

[0018] In the connection end face 10a, the fiber 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 fiber hole 11. When the optical connector 1A is assembled, an adhesive 30 is injected into the optical connector 1A through the injection hole 12. The injected adhesive 30 also enters the fiber hole 11. To cause the adhesive 30 to enter the fiber hole 11, suction may be performed from the connection end face 10a side. Alternatively, the adhesive 30 may enter the fiber hole 11 by capillary force.

[0019] 3 is an enlarged view of the fiber hole 11 and its surroundings in FIG. 2. The fiber hole 11 has a guide portion 11a and a positioning portion 11b. The guide portion 11a is located closer to the base end (-Z side) than the positioning portion 11b. The inner diameter of the guide portion 11a is larger than the inner diameter of the positioning portion 11b. The guide portion 11a functions as a guide to facilitate entry of the bare fiber 21 into the positioning portion 11b. The guide portion 11a may be omitted. The positioning portion 11b functions to define the position of the bare fiber 21. By determining the position of each bare fiber 21 inside the positioning portion 11b, optical connection between the optical connector 1A and another optical connector is achieved.

[0020] The optical connector to which the optical connector 1A is connected may have a so-called multi-core fiber. A multi-core fiber is an optical fiber in which multiple cores are provided inside one cladding. To correspond to the optical connector 1A of this embodiment, the multi-core fiber may have four cores. Alternatively, the optical connector to which the optical connector 1A is connected may have the same structure as the optical connector 1A, except for the presence or absence of a positioning pin 40.

[0021] Fig. 4 is a diagram of the optical fibers 20 shown in Fig. 1. As shown in Fig. 4, the optical connector 1A 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 made of, for example, silica glass. The bare fiber 21 has a core and a cladding (not shown).

[0022] The coating 22 partially covers the bare fiber 21 and serves to protect the bare fiber 21. The coating 22 is made of a resin or the like. 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 fiber hole 11 of the ferrule 10.

[0023] The bare fiber 21 has a small diameter portion 21a, a large diameter portion 21b, and a tapered portion 21c. The outer diameter of the small diameter portion 21a is smaller than the outer diameter of the large diameter portion 21b. The small diameter portion 21a is located at the tip of the bare fiber 21. The tapered portion 21c is located between the small diameter portion 21a and the large diameter portion 21b. The outer diameter of the tapered portion 21c decreases toward the front. The small diameter portion 21a and the tapered portion 21c 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 21b) in the longitudinal direction Z, by, for example, etching. In this embodiment, the four small diameter portions 21a of the four optical fibers 20 are inserted into one fiber hole 11 of the ferrule 10. Note that the bare fiber 21 does not necessarily have to have the tapered portion 21c. That is, the bare fiber 21 may have a shape in which the small diameter portion 21a and the large diameter portion 21b are connected in a step shape.

[0024] The small diameter portion 21 a and the tapered portion 21 c can be formed by etching the bare fiber 21. For example, if the bare fiber 21 is made of quartz glass, hydrofluoric acid or buffered hydrofluoric acid (BHF) may be used as the etching solution. However, the material of the bare fiber 21 and the method for forming the small diameter portion 21 a and the tapered portion 21 c are not limited to those described above.

[0025] As shown in FIG. 2 , adhesive 30 is disposed around the small diameter portion 21 a. The adhesive 30 functions to fix the bare fiber 21 to the ferrule 10. The volume of the adhesive 30 changes when it hardens. For example, when the adhesive 30 is hardened by heating, the adhesive 30 thermally expands and then contracts as it cools. The volume of the adhesive 30 can also change when it is hardened by a chemical reaction. The adhesive 30 is filled inside the ferrule 10. Therefore, when the volume of the adhesive 30 changes, stress acts on the bare fiber 21.

[0026] Here, the thickness of the cladding is small in the small diameter portion 21a. When the cladding thickness is small, the light inside the bare fiber 21 is easily affected by external forces that the bare fiber 21 receives. More specifically, the small diameter portion 21a is thin and has low rigidity, so it is easily bent by external forces. This bending can cause light leakage. The cladding also has the function of confining light within the core. When the cladding thickness is small, the light confinement function is weakened, making light more likely to leak. Light leakage leads to increased connection loss between the optical connector 1A and other optical connectors. In other words, a bare fiber 21 having a small diameter portion 21a has the problem that connection loss is easily caused by volumetric changes in the adhesive 30.

[0027] Therefore, in the optical connector 1A of this embodiment, as shown in Fig. 5, a stress relief material 50 is provided around the small diameter portion 21a. The stress relief material 50 is also provided around the tapered portion 21c. The stress relief material 50 has the function of alleviating the stress acting on the bare fiber 21 due to volumetric changes in the adhesive 30. To fulfill this function, the stress relief material 50 is made of a material with a smaller Young's modulus than the adhesive 30. Note that the stress relief material 50 and the guide portion 11a are not shown in Fig. 2.

[0028] It is preferable that the stress relief material 50 not be provided in the portion of the small diameter portion 21a that is located in the positioning portion 11b (see FIG. 3) of the fiber hole 11. It is preferable that the stress relief material 50 be provided in the portion of the small diameter portion 21a that is located in the guide portion 11a of the fiber hole 11. The reason for this is as follows. Because the positioning portion 11b has the function of determining the position of the small diameter portion 21a, the gap between the positioning portion 11b and the small diameter portion 21a is very small. By not providing the stress relief material 50 inside the positioning portion 11b, it is possible to ensure ease of insertion of the small diameter portion 21a into the positioning portion 11b. In addition, the volume of the adhesive 30 filled inside the positioning portion 11b is small. Therefore, inside the positioning portion 11b, the effect of volumetric changes of the adhesive 30 on the small diameter portion 21a is small. Note that the stress relief material 50 is not provided on the tip side of the small diameter portion 21a that is located inside the guide portion 11a.

[0029] The gap between the guide portion 11a and the small diameter portion 21a is larger than the gap between the positioning portion 11b and the small diameter portion 21a. Therefore, even if a stress relief material 50 is provided inside the guide portion 11a, the small diameter portion 21a can be easily inserted into the guide portion 11a. For example, it is possible to determine the inner diameter of the guide portion 11a according to the thickness of the stress relief material 50. Furthermore, the volume of the adhesive 30 filled inside the guide portion 11a is larger than the volume of the adhesive 30 filled inside the positioning portion 11b. Therefore, the stress relief function of the stress relief material 50 can be effectively exerted inside the positioning portion 11b.

[0030] The Young's modulus of the adhesive 30 is, for example, 500 to 2000 MPa at room temperature. The Young's modulus of the stress relief material 50 is, for example, 0.4 to 1.5 MPa at room temperature. The Young's modulus of the stress relief material 50 is preferably 1 / 10 or less of the Young's modulus of the adhesive 30. A thermosetting resin or a UV-curable resin may be used as the adhesive 30. The adhesive 30 may be an epoxy-based, acrylic-based, or urethane-based resin. A thermosetting resin or a UV-curable resin may be used as the stress relief material 50. The stress relief material 50 may be an epoxy-based, acrylic-based, urethane-based, or silicone-based resin.

[0031] However, the above-mentioned materials and Young's modulus values ​​are merely examples. If the Young's modulus of the stress relaxation material 50 is smaller than that of the adhesive 30, the effect of relaxing the stress acting on the small diameter portion 21a can be obtained.

[0032] Next, an example of a method for manufacturing the optical connector 1A will be described.

[0033] First, a plurality of optical fibers 20 each having a coating 22 are prepared. Next, the coating 22 is partially removed from each of the plurality of optical fibers 20 to expose the bare fiber 21. Next, the exposed portion of the bare fiber 21 is thinned by etching or the like. The time for immersion in the etching solution is varied depending on the longitudinal position of the bare fiber 21. This allows the small diameter portion 21a and the tapered portion 21c to have any desired outer diameter.

[0034] Next, stress relaxation material 50 is provided on at least a portion of small diameter portion 21a. Specifically, a liquid resin that will become stress relaxation material 50 is applied to the periphery of small diameter portion 21a. The applied resin is then cured. This forms stress relaxation material 50 that covers small diameter portion 21a. Here, stress relaxation material 50 is not provided on the tip of small diameter portion 21a (the portion that is inserted into positioning portion 11b). An example of a method for providing stress relaxation material 50 partially on small diameter portion 21a in this manner will be described.

[0035] For example, a resin that will become the stress relaxation material 50 may be applied to the small diameter portion 21a excluding the tip and then cured. Alternatively, the resin that will become the stress relaxation material 50 may be applied to the entire small diameter portion 21a, and the resin may be cured only in the portion of the small diameter portion 21a excluding the tip. For example, if the stress relaxation material 50 is a UV-curable resin, the tip of the small diameter portion 21a may be masked and the resin attached to the remaining portion may be cured. Then, by removing the uncured resin, it is possible to leave the tip of the small diameter portion 21a without the stress relaxation material 50 formed thereon.

[0036] The stress relief material 50 may also be provided in the tapered portion 21c using the same procedure as above. The stress relief material 50 may also be provided partially in the large diameter portion 21b. When forming the stress relief material 50, a plurality of bare fibers 21 may be processed collectively. When processing the bare fibers 21 collectively, the plurality of bare fibers 21 are bundled together as shown in FIG. 4 . Then, a resin that will become the stress relief material 50 may be applied collectively to the small diameter portions 21a of the bundled bare fibers 21, and then cured.

[0037] Next, the small diameter portions 21a of the bare fibers 21 provided with the stress relaxation material 50 are inserted into the fiber holes 11 of the ferrule 10. Next, a resin that will become the adhesive 30 is injected through the injection hole 12, and this resin is allowed to harden. As a result, the bare fibers 21 are fixed to the ferrule 10.

[0038] In the above manufacturing method, the stress relief material 50 is formed on the bare fibers 21 at once. Therefore, as shown in Fig. 6, the stress relief material 50 fills the spaces between the small diameter portions 21a. In this case, the stress relief material 50 also functions to bundle the small diameter portions 21a and increase their rigidity. This makes it easier to insert the small diameter portions 21a into the fiber holes 11.

[0039] However, the stress relaxation material 50 may be individually formed for each bare fiber 21. In this case, as shown in Fig. 5, there may be a portion between the small diameter portions 21a where no stress relaxation material 50 exists.

[0040] As described above, the optical connector 1A of this embodiment comprises a ferrule 10 having a connection end face 10a and a fiber hole 11 opening into the connection end face 10a, a plurality of optical fibers 20 inserted into the fiber hole 11, an adhesive 30 that fixes the plurality of optical fibers 20 to the ferrule 10, and a stress relaxation material 50 having a Young's modulus smaller than that of the adhesive 30, wherein each of the plurality of optical fibers 20 has a small diameter portion 21a inserted into the fiber hole 11, a large diameter portion 21b having a diameter larger than that of the small diameter portion 21a, and a tapered portion 21c located between the small diameter portion 21a and the large diameter portion 21b and having a diameter that changes along the longitudinal direction Z, and the stress relaxation material 50 covers at least a portion of the small diameter portion 21a.

[0041] With this configuration, when the volume of the adhesive 30 changes, the stress acting on the small diameter portion 21a is relieved by the stress relief material 50. Therefore, the optical connection loss caused by the stress can be reduced.

[0042] The fiber hole 11 has a positioning portion 11b that opens to the connection end face 10a and a guide portion 11a that is located closer to the base end than the positioning portion 11b and has a larger inner diameter than the positioning portion 11b, and the stress relaxation material 50 covers the portion of the small diameter portion 21a that is located inside the guide portion 11a. This configuration makes it possible to easily insert the small diameter portion 21a into the fiber hole 11 while also achieving the stress relaxation function of the stress relaxation material 50.

[0043] The tapered portion 21c is also covered with the stress relaxation material 50. With this configuration, the connection loss caused by the volume change of the adhesive 30 can be reduced even in the tapered portion 21c.

[0044] The manufacturing method of the optical connector 1A of this embodiment includes preparing a plurality of optical fibers 20 each having a small diameter portion 21a, a tapered portion 21c, and a large diameter portion 21b, bundling the plurality of optical fibers 20 together, applying a resin that will become the stress relaxation material 50 to at least a portion of the small diameter portion 21a, hardening the resin while the plurality of optical fibers 20 are bundled together to form the stress relaxation material 50, and while the plurality of optical fibers 20 are bundled together, inserting the small diameter portions 21a all at once into the fiber holes 11 of the ferrule 10, and fixing the plurality of optical fibers 20 to the ferrule 10 with an adhesive 30 having a larger Young's modulus than the stress relaxation material 50.

[0045] According to this manufacturing method, the stress relaxation material 50 can be made to integrally cover the small diameter portions 21 a of the plurality of optical fibers 20. This increases the rigidity of the bundle of optical fibers 20. Therefore, the operation of inserting the small diameter portions 21 a into the fiber holes 11 becomes easier.

[0046] 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.

[0047] For example, in the above embodiment, it has been described that the Young's modulus of the stress relaxation material 50 is smaller than that of the adhesive 30. However, it is also possible to specify the stress relaxation function of the stress relaxation material 50 using an index other than Young's modulus. For example, the linear expansion coefficient of the stress relaxation material 50 may be smaller than that of the adhesive 30. More specifically, the linear expansion coefficient of the stress relaxation material 50 may be 1 / 10 or less of that of the adhesive 30.

[0048] Alternatively, the water absorption rate of the stress relief material 50 may be lower than the water absorption rate of the adhesive 30. More specifically, the water absorption rate of the stress relief material 50 may be half or less of the water absorption rate of the adhesive 30.

[0049] 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.

[0050] 1A... Optical connector 10... Ferrule 10a... Connection end face 11... Fiber hole 11a... Guide portion 11b... Positioning portion 20... Optical fiber 21a... Small diameter portion 21b... Large diameter portion 21c... Tapered portion 30... Adhesive 50... Stress relaxation material Z... Longitudinal direction

Claims

1. An optical connector comprising: a ferrule having a connection end face and a fiber hole opening to the connection end face; a plurality of optical fibers inserted into the fiber holes; an adhesive for fixing the plurality of optical fibers to the ferrule; and a stress relaxation material having a smaller Young's modulus than that of the adhesive, wherein each of the plurality of optical fibers has a small diameter section inserted into the fiber hole, a large diameter section having a diameter larger than that of the small diameter section, and a tapered section located between the small diameter section and the large diameter section and having a diameter that changes along the longitudinal direction of the optical fiber, and the stress relaxation material covers at least a portion of the small diameter section.

2. An optical connector as described in claim 1, wherein the fiber hole has a positioning portion that opens into the connection end face, and a guide portion that is located toward the base end from the positioning portion and has a larger inner diameter than the positioning portion, and the stress relaxation material covers the portion of the small diameter portion that is located inside the guide portion.

3. An optical connector according to claim 1 or 2, wherein the stress relaxation material covers the tapered portion.

4. An optical connector according to any one of claims 1 to 3, wherein the stress relaxation material integrally covers the small diameter portions of the plurality of optical fibers.

5. A method for manufacturing an optical connector, comprising: preparing a plurality of optical fibers having a small diameter portion, a tapered portion, and a large diameter portion; bundling the plurality of optical fibers together and applying a resin that serves as a stress relief material to at least a portion of the small diameter portion; hardening the resin while the plurality of optical fibers are together to form the stress relief material; bundling the plurality of optical fibers together and inserting the small diameter portions into fiber holes of a ferrule all at once; and fixing the plurality of optical fibers to the ferrule with an adhesive having a larger Young's modulus than the stress relief material.

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