WO2024038648A1

WO2024038648A1 - Optical connector and method for manufacturing optical connector

Info

Publication number: WO2024038648A1
Application number: PCT/JP2023/017542
Authority: WO
Inventors: 裕幸山岸; 顕人西村
Original assignee: 株式会社フジクラ
Priority date: 2022-08-19
Filing date: 2023-05-10
Publication date: 2024-02-22

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 optical connector manufacturing method

The present invention relates to an optical connector and a method of manufacturing the optical connector.
This application claims priority to Japanese Patent Application No. 2022-130948 filed in Japan on August 19, 2022, and the contents thereof are incorporated herein.

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

Japanese Patent Application Publication No. 2013-125195

The adhesive filled in the insertion hole of the ferrule may shrink when it hardens. When the adhesive contracts, the position of the optical fiber inside the insertion hole may shift, which may lead to an increase in connection loss of the optical connector.

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 capable of suppressing misalignment of an optical fiber inside a ferrule, or a method of manufacturing such an optical connector.

In order to solve the above problems, an optical connector according to aspect 1 of the present invention includes: a ferrule having an insertion hole; a plurality of optical fibers inserted into the insertion hole; an adhesive that fixes the plurality of optical fibers to the ferrule in a state in which the plurality of optical fibers and the expansion member are inserted into the insertion hole, the adhesive being heated The adhesive is a curable resin, and the expansion member expands at a temperature lower than the curing temperature of the adhesive.

A second aspect of the present invention is the optical connector according to the first aspect, in which the expansion member may have a coefficient of linear expansion larger than that of the optical fiber at the curing temperature of the adhesive.

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

Aspect 4 of the present invention is an optical connector according to any one of aspects 1 to 3, in which the water absorption rate of the expansion member may be lower than the water absorption rate of the ferrule.

A fifth aspect of the present invention is the optical connector according to any one of aspects 1 to 4, in which the plurality of optical fibers may be arranged inside the insertion hole so as to surround the expansion member.

A sixth aspect of the present invention is the optical connector according to any one of aspects 1 to 5, in which the expansion member may contact all of the plurality of optical fibers inside the insertion hole.

A seventh aspect of the present invention is the optical connector according to any one of aspects 1 to 6, wherein the insertion hole has a curved portion and a straight portion in a cross section perpendicular to the central axis of the insertion hole. Good too.

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

A ninth aspect of the present invention is that an expansion member is inserted into an insertion hole of a ferrule together with a plurality of optical fibers, an adhesive is injected into the insertion hole, and the expansion member is heated and expanded. The method of manufacturing an optical connector includes fixing the plurality of optical fibers to the ferrule by pressing the plurality of optical fibers against the inner surface of the insertion hole and curing the adhesive.

A tenth aspect of the present invention is the method for manufacturing the optical connector according to aspect nine, in which the expansion member may be removed from the insertion hole after the plurality of optical fibers are fixed to the ferrule with the adhesive. .

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, or a method for manufacturing such an optical connector.

FIG. 1 is a perspective view of an optical connector according to the present embodiment. 2 is a perspective view of a plurality of optical fibers extracted from the optical connector shown in FIG. 1. FIG. FIG. 2 is a cross-sectional view taken along line III-III in FIG. 1; FIG. 3 is a cross-sectional view of the vicinity of the insertion hole, illustrating the method of manufacturing the optical connector according to the present embodiment. FIG. 3 is a cross-sectional view of the vicinity of the insertion hole, illustrating the method of manufacturing the optical connector according to the present embodiment. FIG. 3 is a cross-sectional view of the vicinity of the insertion hole, illustrating the method of manufacturing the optical connector according to the present embodiment. FIG. 7 is a cross-sectional view of the vicinity of an insertion hole of an optical connector according to a modification. FIG. 7 is a cross-sectional view of the vicinity of an insertion hole of an optical connector according to a modification. FIG. 7 is a cross-sectional view of the vicinity of an insertion hole of an optical connector according to a modification. FIG. 7 is a cross-sectional view of a method for manufacturing an optical connector according to a modification.

Hereinafter, the optical connector of this embodiment will be explained based on 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 need to include the positioning pins 40.

The ferrule 10 has a connecting end surface 10a, a rear end surface 10b, an insertion hole 11, an injection hole 12, and two positioning holes 13. The connection end surface 10a is a surface that is abutted against another connector or the like when the optical connector 1 is connected to the other connector or the like. The insertion hole 11 and the two positioning holes 13 are open to the connection end surface 10a. An introduction hole (not shown) communicating with the insertion hole 11 is opened in the rear end surface 10b, and a plurality of 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.

(direction definition)
In this specification, a direction parallel to the central axis O of the insertion hole 11 is referred to as a Z direction, an axial direction Z, or a longitudinal direction Z. One direction perpendicular to the longitudinal direction Z is referred to as a first direction X. The first direction X is also the direction in which the two positioning holes 13 are arranged. A direction perpendicular to both the longitudinal direction Z and the first direction X is referred to as a second direction Y. The direction from the rear end surface 10b of the ferrule 10 toward the connection end surface 10a along the longitudinal direction Z is referred to as the +Z direction, the front, or the tip side. The direction opposite to the +Z direction is referred to as the -Z direction, rearward, or proximal side. The direction perpendicular to the central axis O when viewed from the longitudinal direction Z is referred to as the radial direction. Along the radial direction, the direction approaching the center axis O is called the radially inner side, and the direction away from the center axis O is called the radially outer side. The direction of rotation around the central axis O when viewed from the longitudinal direction Z is referred to as the circumferential direction. A cross section perpendicular to the longitudinal direction Z is called a cross section. That is, the cross section is a cross section extending along the first direction X and the second direction Y.

In the connection end surface 10a, the insertion hole 11 is arranged so as to be sandwiched between two positioning holes 13. The injection hole 12 is open in one end surface of the ferrule 10 facing in 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, the adhesive 30 is injected into the ferrule 10 through the injection hole 12. The injected adhesive 30 also enters the inside of the insertion hole 11 .

FIG. 2 is an extracted diagram of the plurality of 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 made of, for example, quartz glass. The covering 22 partially covers the bare fiber 21 and has the role of protecting the bare fiber 21. The covering 22 is made of 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 insertion hole 11 of the ferrule 10.

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

FIG. 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 cladding 21d. The cladding 21d is arranged to surround the core 21c. The refractive index of the cladding 21d is lower than that of the core 21c. Therefore, the optical fiber 20 can confine light inside the core 21c.

As shown in FIG. 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 come into contact with both the curved portion 11a and the straight portion 11b. The remaining two bare fibers 21 contact the curved portion 11a but do not contact the straight portion 11b. With this configuration, the bare fiber 21 and the insertion hole 60 are in contact with each other at six locations. The positions of these four bare fibers 21 are determined by being pressed against the inner surface of the insertion hole 11 by an expansion member 50, which will be described later.

The adhesive 30 has the function of fixing the plurality of optical fibers 20 to the ferrule 10. As the material of the adhesive 30, for example, thermosetting resin can be used. More specifically, the material of the adhesive 30 may be epoxy resin.

When manufacturing the optical connector 1, the insertion hole 11 is filled with liquid adhesive 30 through the injection hole 12 with the bare fiber 21 inserted into the insertion hole 11. Then, the adhesive 30 is cured. Here, the adhesive 30 may shrink during curing. When the adhesive 30 contracts, a force directed inward in the radial direction may be applied to the bare fibers 21 . The position of the bare fiber 21 is determined by contacting the inner surface of the insertion hole 11. Therefore, if the bare fiber 21 separates from the inner surface of the insertion hole 11 due to the shrinkage of the adhesive 30, the bare fiber 21 will be displaced from the predetermined position. If the bare fiber 21 is misaligned inside the insertion hole 11, the connection loss of the optical connector 1 will increase.

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 rapidly decreases from 30°C to 50°C, and when the temperature exceeds 50°C, the viscosity of the epoxy resin becomes equal to or lower than that of water. When the viscosity of the adhesive 30 decreases in this way, the bare fiber 21 easily moves inside the insertion hole 11 and becomes easily separated from the inner surface of the insertion hole 11.

Therefore, the optical connector 1 of this embodiment includes an expansion member 50 for pressing the bare fiber 21 against the inner surface of the insertion hole 11, as shown in FIG. 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 along with the plurality of bare fibers 21 . Inside the insertion hole 11, the expansion member 50 is in contact with each bare fiber 21 (small diameter portion 21a). Each bare fiber 21 is arranged so as 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.

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 includes a main body portion 51 and a release layer 52. The main body 51 has a linear shape, and the release layer 52 is provided on the surface of the main body 51 . The release layer 52 has a function of preventing the main body portion 51 from being fixed to the adhesive 30. The presence of the peeling layer 52 facilitates the operation of removing the expansion member 50 from the optical connector 1, as will be described later. The release layer 52 may be formed, for example, by subjecting the main body portion 51 to a surface treatment. The release layer 52 may be, for example, a fluorine-based coating agent. Note that the inflatable member 50 does not need to have the release layer 52.

Hereinafter, an example of a method for manufacturing the optical connector 1 will be described.

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

Next, the insertion process is performed. In the insertion step, the bare fibers 21 of the plurality of optical fibers 20 and the expansion member 50 are inserted into the insertion hole 11 of the ferrule 10. In the insertion step, the expansion member 50 may be used as an introduction jig for introducing the bare fiber 21 into the insertion hole 11. Specifically, the expansion member 50 is first inserted into the insertion hole 11, and the optical fiber 20 is temporarily fixed to a portion of the expansion member 50 located behind the ferrule 10. In this state, the bare fiber 21 is introduced into the insertion hole 11 together with the expansion member 50 by pulling the expansion member 50 forward from the ferrule 10 or by pushing the expansion member 50 into the ferrule 10 from behind.

FIG. 4A is a cross-sectional view showing the state inside the insertion hole 11 after performing the insertion process. As shown in FIG. 4A, at the stage of the insertion process, there may be a gap G 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. By providing such a gap, the bare fiber 21 can be smoothly inserted into the insertion hole 11.
The outer diameter of the bare fiber 21 (the outer diameter of the small diameter portion 21a), the outer diameter of the expansion member 50, the shape of the insertion hole 11, etc. may be set so that a gap G is generated during the insertion process.

Next, an injection process is performed. In the injection step, fluid adhesive 30 is injected into ferrule 10 through injection hole 12 . At this time, the adhesive 30 also enters into the insertion hole 11. The adhesive 30 may be actively introduced into the insertion hole 11 by suctioning the insertion hole 11 opened on the connection end surface 10a with a vacuum or the like. Alternatively, the adhesive 30 may be introduced into the insertion hole 11 by capillary force or the like generated within the insertion hole 11 .

Next, an expansion step is performed. In the expansion step, the bare fiber 21 is pressed against the inner surface of the insertion hole 11 by heating the expansion member 50 to a first temperature and expanding the expansion member 50 . The first temperature is a temperature lower than the curing temperature of the adhesive. The "curing temperature" is the temperature at which the adhesive 30 is sufficiently cured 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 about 100°C.
Therefore, the first temperature in this case is a temperature lower than 100°C (for example, about 50°C). By the expansion process, the bare fiber 21 is pressed against the inner surface of the insertion hole 11, as shown in FIG. 4B, and the gap G disappears. Thereby, the bare fiber 21 is positioned. Note that, since the viscosity of the epoxy resin becomes extremely small near 50°C, if the first temperature is about 50°C, the movement of the bare fiber 21 during the expansion process becomes easy. In other words, the movement of the bare fibers 21 can be prevented from being inhibited by the viscosity of the adhesive 30.

In the example shown in FIG. 4B, the two bare fibers 21 (hereinafter sometimes referred to as "first bare fibers") located above in the drawing are abutted against both the curved part 11a and the straight part 11b, The position is determined. Furthermore, the two bare fibers 21 (hereinafter sometimes referred to as "second bare fibers") located at the lower side in the drawing are abutted against both the first bare fiber and the curved portion 11a, and their positions are determined.

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

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

Next, a removal step may be performed. As described above, the expansion member 50 that has been cooled after being heated contracts. This creates a gap between the adhesive 30 and the expansion member 50. In the removal step, 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. When the expansible member 50 is provided with the release layer 52, the release layer 52 is easily peeled off from the adhesive 30, so that the removal process can be performed more smoothly. 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 portion where the expansion member 50 was present.

Since 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. Further, by performing the removal step, for example, the following advantages can be obtained. As a first advantage, it is possible to prevent the expansion member 50 from protruding forward from the connection end surface 10a and inhibiting physical contact between the optical connector 1 and other connectors. As a second advantage, when the expansion member 50 has water absorption properties, it is possible to suppress deterioration of the adhesive 30 due to moisture contained in the expansion member 50. As a third advantage, the weight of the optical connector 1 can be reduced. As a fourth advantage, the formed cavity H can be used for other purposes. For example, in the inspection after manufacturing the optical connector 1, a light source for illumination may be inserted into the cavity H. As a fifth advantage, when the adhesive 30 expands due to a temperature change after manufacturing the optical connector 1, the volume of the expanded adhesive 30 can be released into the cavity H. Thereby, the expansion of the adhesive 30 can be suppressed from acting to move the bare fibers 21.

When the removal process is performed, the cavity H is formed so as to penetrate the adhesive 30 in the longitudinal direction Z. Moreover, in the example of FIG. 4C, the plurality of bare fibers 21 are arranged so as to face the cavity H and surround the cavity H.
Note that it is not essential to perform the removal step. That is, the optical connector 1 may or may not include the expansion member 50 in the state after manufacture.

In order to perform the above function, the expansion member 50 is configured to expand at a temperature lower than the curing temperature of the adhesive 30. As the material of the main body portion 51 of the expansion member 50, for example, resin, metal, etc. can be adopted. More specifically, the material of the main body portion 51 may be oxetane resin or copper. The linear expansion coefficient of the oxetane resin can be changed depending on the formulation, but is, for example, about 90×10 ^-6 /K at 0 to 50°C, and about 170×10 ^-6 /K at 50 to 100°C. The coefficient of linear expansion of copper is approximately constant between 0 and 100° C., and is approximately 16.8×10 ⁻⁶ /K. When metal is used as the main body part 51, the electric charge on the surface of the bare fiber 21 is released through the main body part 51 during the insertion process, and the effect of suppressing the lifting of the bare fiber 21 due to charging can be obtained.

The glass transition temperature of the main body portion 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 increases rapidly when the glass transition temperature is exceeded. By increasing the linear expansion coefficient of the main body portion 51, the expansion speed of the expansion member 50 increases, and the bare fiber 21 can be quickly pressed against the inner surface of the insertion hole 11. Thereby, the bare fiber 21 can be positioned at an early stage. Note that once the adhesive 30 begins to harden, movement of the bare fiber 21 within the insertion hole 11 is inhibited, so it is preferable to position the bare fiber 21 early.

The water absorption rate of the expansion member 50 is preferably lower than that of the ferrule 10. Since the water absorption rate of the expansion member 50 is low, deterioration of the adhesive 30 due to moisture contained in the expansion member 50 can be suppressed. Note that, since the volume occupied by the release layer 52 in the inflatable member 50 is very small, the water absorption rate of the inflatable member 50 is substantially the same as the water absorption rate of the main body portion 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 the linear expansion coefficient, glass transition temperature, and water absorption rate of the main body portion 51. The material of the ferrule 10 is, for example, PPS+GF (polyphenylene sulfide containing 30% to 70% glass fiber). The material of the main body portion 51 of the expansion member 50 is, for example, oxetane resin, and the water absorption rate in this case is lower than that of PPS+GF.

As described above, the optical connector 1 of the present embodiment includes a ferrule 10 having an insertion hole 11, a plurality of optical fibers 20 inserted into the insertion hole 11, and a plurality of optical fibers 20 inserted into the insertion hole 11 together with the plurality of optical fibers 20. and an adhesive 30 for fixing the plurality of optical fibers 20 to the ferrule 10 in a state where the plurality of optical fibers 20 and the expansion member 50 are 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 curing temperature of the adhesive 30. With such a configuration, the optical fiber 20 can be pressed against the inner surface of the insertion hole 11 by the expansion member 50. Therefore, it becomes possible to suppress the positional shift of the optical fiber 20 inside the insertion hole 11.

Furthermore, it is preferable that the expansion member 50 has a larger coefficient of linear expansion than the optical fiber 20 at the curing temperature of the adhesive. This makes it possible to increase the expansion speed of the expansion member 50 and quickly determine the position of the optical fiber 20 within the insertion hole 11.

Further, the glass transition temperature of the expansion member 50 is preferably lower than that of the adhesive 30. Since the glass transition temperature of the expansion member 50 is low, the linear expansion coefficient of the expansion member 50 increases steeply due to heating. This makes it possible to increase the expansion speed of the expansion member 50 and quickly determine the position of the optical fiber 20 within the insertion hole 11.

Further, it is preferable that the water absorption rate of the expansion member 50 is smaller than that of the ferrule 10.
Since the water absorption rate of the expansion member 50 is small, deterioration of the adhesive 30 can be suppressed.

Furthermore, it is preferable that the plurality of optical fibers 20 be arranged inside the insertion hole 11 so as to surround the expansion member 50. Furthermore, it is preferable that the expansion member 50 contacts all of the plurality of optical fibers 20 inside the insertion hole 11 . According to this arrangement, when the expansion member 50 expands, a radially outward pressing force acts on each optical fiber 20. Therefore, each optical fiber 20 can be pressed against the inner surface of the insertion hole 11 more reliably.

Further, it is preferable that the insertion hole 11 has a curved portion 11a and a straight portion 11b in a cross section perpendicular to the central axis O. In this case, by abutting at least a portion of the optical fiber 20 against both the curved portion 11a and the straight portion 11b, the position of the optical fiber 20 can be determined more accurately.

Additionally, a release layer 52 may be provided on the surface of the inflatable member 50. In this case, when the adhesive 30 hardens, the expansion member 50 can be prevented from sticking to the adhesive 30 and the optical fiber 20. Therefore, even if the expansion member 50 contracts after the adhesive 30 hardens, the optical fiber 20 can be prevented from moving due to this contraction. Furthermore, it becomes easy to pull out the expansion member 50 from the ferrule 10.

Furthermore, the method for manufacturing the optical connector 1 according to the present embodiment includes inserting the expansion member 50 together with the plurality of optical fibers 20 into the insertion hole 11 of the ferrule 10, injecting the adhesive 30 into the insertion hole 11, and inserting the expansion member 50 into the insertion hole 11 of the ferrule 10. By heating and expanding, the plurality of optical fibers 20 are pressed against the inner surface of the insertion hole 11 by the expansion member 50, and the plurality of optical fibers 20 are fixed to the ferrule 10 by curing the adhesive 30. According to such a manufacturing method, it is possible to suppress misalignment of the optical fiber 20 inside the insertion hole 11.

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

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 for fixing the plurality of optical fibers 20 inside the insertion hole 11. In addition, a cavity H extending in the longitudinal direction Z of the insertion hole 11 may be formed in the adhesive 30.

Note that the technical scope of the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.

For example, in the embodiment, the bare fiber 21 has a small diameter portion 21a and a large diameter portion 21b, and the small diameter portion 21a 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. That is, the tip of the bare fiber 21 may be inserted into the insertion hole 11 as it is without reducing its diameter by etching or the like.

Further, in the embodiment, a plurality of bare fibers 21 are arranged to surround the expansion member 50, and one expansion member 50 is in contact with all the bare fibers 21. However, as long as the expansion member 50 can press the bare fiber 21 against the inner surface of the insertion hole 11, the arrangement of the bare fiber 21 and the expansion member 50 may be changed. For example, as shown in FIG. 5, two expansion members 50 may be arranged within the insertion hole 11. More specifically, the two expansion members 50 may be arranged apart in the radial direction and may be in contact with the inner surface of the insertion hole 11, respectively.
Then, one expansion member 50 may be in contact with two bare fibers 21, and the remaining expansion member 50 may be in contact with the remaining two bare fibers 21. Even with such an arrangement, each bare fiber 21 can be pressed against the inner surface of the insertion hole 11.

Furthermore, 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 have the entire curved portion 11a. That is, the insertion hole 11 may have a circular shape.

Further, in the embodiment, the insertion hole 11 has a D shape, but the insertion hole 60 may have a rectangular shape as shown in FIG. 6. The insertion hole 60 of this modification has four straight portions 61a to 61d and a corner portion 62 when viewed from the longitudinal direction Z.
Here, when 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 equation (1).
Rh<r…(1)
According to the above equation (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 straight portions among the straight portions 61a to 61d. Therefore, the four bare fibers 21 come into contact with the insertion hole 60 at eight locations.
Further, 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 can be calculated using the following equations (2) and (3). Fulfill.
L>4r…(2)
Pc<L-2r…(3)
The positions of these four bare fibers 21 are determined by being pressed against the inner surface of the insertion hole 60 by the above-described expansion member 50.

In this modification, since the insertion hole 60 has a rectangular shape, by pressing the bare fiber 21 against the inner surface of the insertion hole 60, which has a simple configuration, the optical fiber 20 inside the insertion hole 60 can be It becomes possible to suppress positional deviation.
Further, since 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 straight portions 61a to 61d. Thereby, the four bare fibers 21 can be easily inserted into the insertion hole 60.

Further, in the embodiment, the insertion hole 11 was D-shaped, but as shown in FIG. 7, the insertion hole 70 is composed of four curved parts 71a to 71d when viewed from the longitudinal direction Z. It's okay.
When the radius of curvature 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 equation (4).
Rh1>r…(4)
From the above equation (4), the radius of curvature Rh1 of the curved portions 71a to 71d is larger than the radius r of the bare fibers 21A to 21D. Therefore, the outer peripheral surface of each of the four bare fibers 21A to 21D contacts each of the curved portions 71a to 71d at one point. With this configuration, the four bare fibers 21A to 21D come into contact with the insertion hole 70 at four locations.
The positions of these four bare fibers 21 are determined by being pressed against the inner surface of the insertion hole 70 by the above-mentioned expansion member 50.

Also, let P1 and P2 be the respective contact points of the two

bare fibers

21A and 21C and the

curved parts

71a and 71c, which are arranged diagonally, and let W be the distance between the contact point P1 and the contact point P2. , when the design value of the distance between the cores 21c of adjacent bare fibers 21 is Pc, the shape of the insertion hole 70 satisfies the following equations (5) to (7).
Rh1>W/2...(5)
W>2r+2r√2…(6)
Pc√2<W-2r…(7)

In this modification, there are four contact points between the bare fibers 21A to 21D and the insertion hole 70. Therefore, the number of contact points can be reduced compared to the insertion hole 11 of the embodiment described above. This makes it possible to further suppress misalignment of the optical fiber 20 inside the insertion hole 70.
Further, by satisfying the above formulas (5) to (7), some gaps are formed between the bare fiber 21 and the curved portions 71a to 71d. This makes it possible to easily insert the four bare fibers 21A to 21D into the insertion hole 70.

Moreover, the manufacturing method of the optical connector 1 of the said embodiment may have a suppression process.
Specifically, the suppressing step is a step of suppressing the expansion member 50 from protruding from the tip surface 21e of the bare fiber 21, as shown in FIG. For example, a pin 80 is used as a jig for holding down 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 that extends toward the proximal end of the pin 80. The tip of the tapered portion 81 of the pin 80 has a planar shape.
Here, assuming that the outer diameter of the tip 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 formula (8), the outer diameter D1 of the tip end surface 80a of the pin 80 is smaller than the outer diameter of the expansion member 50. This allows the tip end surface 80a of the pin 80 to contact only the expansion member 50.

Further, the material of the pin 80 is not particularly limited, but a material with lower hardness than quartz glass may be used. For example, the material of the pin 80 is aluminum or plastic.
Further, 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 about 1.0 to 3.5 μm.

In the suppression step, the pin 80 is placed on the distal end surface 50a of the expansion member 50 before the expansion step. Thereafter, the expansion member 50 is heated and expanded. At this time, by holding down the expansion member 50 expanding in the +Z direction with the pin 80, the expansion member 50 expands in the circumferential direction.
Next, in the removal step, when the expansion member 50 is cooled, the pin 80 is removed. As a result, the distal end surface 50a of the inflatable member 50 is depressed, and a mark of the distal end surface 80a of the tapered portion 81 remains on the distal end surface 50a of the inflatable member 50.

According to this manufacturing method, by suppressing the expansion member 50, it becomes easier to expand the expansion member 50 in the circumferential direction, so that the bare fiber 21 can be pressed against the inner surface of the insertion hole 11 more efficiently.
Further, since the pin 80 is in contact with the bare fiber 21, the pin 80 can assist in positioning. Furthermore, since the pin 80 is in contact with the bare fiber 21, it is possible to suppress the expansion member 50 from protruding beyond the tip end surface 21e of the bare fiber 21.
The material of the pin 80 is made of a material with lower hardness than quartz glass, so that even if the pin 80 and the bare fiber 21 come into contact, the expansion member 50 can protrude without damaging the bare fiber 21. It becomes possible to suppress this.

In this modification, the expansion member 50 is pushed in the -Z direction from the position of the tip surface 21e of the bare fiber 21 by the pin 80, but the invention is not limited to this. You can also push it in.
Note that if the pin 80 does not need to assist in positioning, the pin 80 does not need to have a portion that satisfies the above formula (9). In this configuration, the jig does not come into contact with the bare fiber 21. Therefore, it is possible to suppress the expansion member 50 from protruding while suppressing the possibility of damaging the tip end surface 21e of the polished bare fiber 21.
Further, the jig may have a constant outer diameter as a whole, or may have a configuration having only a tapered portion where the outer diameter widens toward the proximal end. In the case of this configuration, the jig only needs to satisfy at least the above equation (8) among the above equations (8) and (9).
Further, although the tip of the tapered portion 81 of the pin 80 is made into a planar shape, it may be curved.

In addition, the components in the embodiments described above can be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the embodiments and modifications described above may be combined as appropriate.

10...

Ferrule

11, 60, 70... Insertion hole 11a... Curved part 11b... Straight part 12... Injection hole 20... Optical fiber 30... Adhesive 50... Expansion member 52... Peeling layer O... Center axis Z... Longitudinal direction

Claims

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;
an adhesive that fixes the plurality of optical fibers to the ferrule in a state where the plurality of 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 curing temperature of the adhesive.
The optical connector according to claim 1, wherein the expansion member has a coefficient of linear expansion larger than that of the optical fiber at the curing temperature of the adhesive.
The optical connector according to claim 1 or 2, wherein the expansion member has a glass transition temperature lower than that of the adhesive.
The optical connector according to any one of claims 1 to 3, wherein the expansion member has a water absorption rate smaller than that of the ferrule.
The optical connector according to any one of claims 1 to 4, wherein the plurality of optical fibers are arranged inside the insertion hole so as to surround the expansion member.
The optical connector according to any one of claims 1 to 5, wherein the expansion member contacts all of the plurality of optical fibers inside the insertion hole.
The optical connector according to any one of claims 1 to 6, wherein the insertion hole has a curved portion and a straight portion in a cross section perpendicular to the central axis of the insertion hole.
The optical connector according to any one of claims 1 to 7, wherein a release layer is provided on the surface of the expansion member.
Insert the expansion member along with multiple optical fibers into the insertion hole of the ferrule,
Inject adhesive into the insertion hole,
pressing the plurality of optical fibers against the inner surface of the insertion hole by the expansion member by heating and expanding the expansion member;
A method of manufacturing an optical connector, wherein the plurality of optical fibers are fixed to the ferrule by curing the adhesive.
The method for manufacturing an optical connector according to claim 9, wherein the expansion member is removed from the insertion hole after the plurality of optical fibers are fixed to the ferrule with the adhesive.