Ferrule

Abstract

Provided is a ferrule having a structure in which external stress is less likely to act on an adhesively fixed optical fiber. A ferrule (1) is characterized by having formed therein an insertion hole (11) through which an optical fiber is inserted and a recess (12) communicating with the insertion hole (11) via an opening (13) formed in a bottom surface, wherein the opening (13) is a slit-shaped opening having a width direction in a direction perpendicular to the central axis of the insertion hole (11), the width of the opening (13) being smaller than the diameter of the insertion hole (11).

Description

Ferrule

[0001] The present invention relates to a ferrule through which an optical fiber is inserted.

[0002] Multi-Core Fiber (hereinafter also referred to as MCF) is widely used for increasing the capacity of optical communication networks. While Single Mode Fiber (hereinafter also referred to as SMF) has a single core, MCF has a plurality of cores. Therefore, MCF can transmit more information simultaneously than SMF.

[0003] Fan-In / Fan-Out (hereinafter also referred to as FIFO) devices are widely used for connecting a single MCF to a plurality of SMFs. As shown for example in Fig. 7, the FIFO device is constituted by an SMF-side ferrule 2 into which ends of a plurality of SMFs are drawn, and an MCF-side ferrule 3 into which an end of a single MCF is drawn. When such a FIFO device is used, the core of each SMF and each core of the MCF can be optically coupled by mechanically coupling the SMF-side ferrule 2 and the MCF-side ferrule 3. As a document disclosing such a FIFO device, for example, Patent Document 1 is known.

[0004] Republished WO2013-172322, Japanese Unexamined Patent Application Publication No. 2005-41134

[0005] A conventional SMF-side ferrule 2 is provided with an insertion hole 21 for inserting an SMF therethrough. Further, the conventional SMF-side ferrule 2 is provided with a recess 22 communicating with the insertion hole 21. When molding the SMF-side ferrule 2, the recess 22 is used as a space for arranging another core (which may be a part of a mother die) that is in surface contact with a core pin, which is a core for forming the insertion hole 21, in order to maintain an appropriate extending direction of the core pin (see Patent Document 2). Further, when fixing the SMF inserted into the insertion hole 21 to the SMF-side ferrule 2, the recess 22 is used as an injection port for injecting an adhesive into the insertion hole 21.

[0006] In the section where the recess 22 is formed, the shape of the cross-section of the insertion hole 21 (the cross-section perpendicular to the central axis of the insertion hole 21) is semicircular, and the adhesive fills the recess 22 not only inside the insertion hole 21 but also so that the SMF is immersed in the adhesive. As a result, in the section where the recess 22 is formed, particularly near the boundary between the section where the recess 22 is formed and the section where the recess 22 is not formed, anisotropy occurs in the amount of adhesive surrounding the SMF, and consequently, anisotropy occurs in the curing shrinkage of the adhesive surrounding the SMF. Therefore, external stress that causes excessive loss acts on the SMF that is bonded and fixed to the SMF-side ferrule. Such problems can occur not only in the SMF-side ferrule but also in ferrules in general where a recess communicating with the insertion hole is formed.

[0007] One aspect of the present invention has been made in view of the above-mentioned problems, and one of its objectives is to realize a ferrule with a structure that makes it difficult for external stress to act on an adhesively fixed optical fiber.

[0008] A ferrule according to one aspect of the present invention is characterized in that it has a through hole for inserting an optical fiber and a recess that communicates with the through hole through an opening formed on its bottom surface, the opening is a slit-shaped opening whose width is perpendicular to the central axis of the through hole, and the width of the opening is smaller than the diameter of the through hole.

[0009] According to one aspect of the present invention, a ferrule with a structure that makes it difficult for external stress to act on an adhesively fixed optical fiber can be realized.

[0010] This is a longitudinal cross-sectional view showing the configuration of a ferrule according to one embodiment of the present invention. This is a perspective cross-sectional view showing a cross-section of the ferrule shown in Figure 1. (a) is a cross-sectional view showing a cross-section of the ferrule shown in Figure 1. (b) is a cross-sectional view showing a cross-section of a conventional ferrule. This is a cross-sectional view showing a longitudinal section of a ferrule according to a first modified example. This is a cross-sectional view showing a cross-section of a ferrule according to a second modified example. This is a cross-sectional view showing a cross-section of a ferrule according to a third modified example. This is a perspective view showing the configuration of a conventional FIFO device.

[0011] (Ferrule Configuration) The configuration of the ferrule 1 according to one embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing the longitudinal section of the ferrule 1 (a section parallel to the central axis of the insertion hole 11), and Figure 2 is a perspective cross-sectional view showing the transverse section of the ferrule 1 (a section perpendicular to the central axis of the insertion hole 11). Here, the section shown in Figure 2 is the AA' section shown in Figure 1.

[0012] Ferrule 1 is a resin structure used as the SMF-side ferrule of the FIFO device.

[0013] The ferrule 1 is composed of a front end portion 1a, an intermediate portion 1b, and a rear end portion 1c. The front end portion 1a is a rectangular parallelepiped-shaped portion having a front end surface 1p. The rear end portion 1c is a rectangular parallelepiped-shaped portion having a rear end surface 1q. The width and height of the front end portion 1a are greater than the width and height of the rear end portion 1c, respectively. The intermediate portion 1b is a rectangular parallelepiped-shaped portion located between the front end portion 1a and the rear end portion 1c. The width and height of the intermediate portion 1b are greater than the width and height of the front end portion 1a, respectively.

[0014] The front end 1a, middle section 1b, and rear end 1c of the ferrule 1 have through holes 11 extending from the rear end surface 1q to the front end surface 1p. The through holes 11 are for inserting multiple SMFs. Each SMF is inserted into the through hole 11 from the rear end surface 1q side so that its tip surface is flush with the front end surface 1p. The cross-sectional shape of the through hole 11 is circular, except for the section where the recess 12 described later is not formed. The diameter of the through hole 11 decreases in stages as it moves away from the rear end surface 1q.

[0015] Furthermore, a recess 12 is formed on the upper surface of the front end portion 1a of the ferrule 1. When forming the ferrule 1, the recess 12 is used as a space for positioning a core (which may be part of the master mold) that makes line contact with the core pin, which is the core for providing the insertion hole 11, in order to properly maintain the extension direction of the core pin. The cross-sectional shape of the recess 12 is rectangular. The recess 12 communicates with the aforementioned insertion hole 11 through the opening 13.

[0016] The opening 13 is a slit-shaped opening formed on the bottom surface of the recess 12, with its width direction perpendicular to the central axis of the through hole 11. The width W of the opening 13 is smaller than the diameter D of the through hole 11 in the section where the recess 12 is formed. Therefore, the cross-sectional shape of the through hole 11 in the section where the recess 12 is formed is the same as the larger of the two arc-shaped regions obtained by dividing the circular region with a chord shorter than its diameter (hereinafter also simply referred to as "arc-shaped").

[0017] Furthermore, a pair of positioning holes 14a and 14b are formed in the front end portion 1a of the ferrule 1, extending from the front end surface 1p to the rear end surface 1q. The positioning holes 14a and 14b are holes for inserting positioning pins provided in the MCF-side ferrule. The positioning holes 14a and 14b are located on either side of the insertion hole 11, and do not communicate with the insertion hole 11 or the recess 12.

[0018] (Effect of the ferrule) The effect of ferrule 1 will be explained with reference to Figure 3. In Figure 3, (a) is a cross-sectional view showing the cross-section of ferrule 1, and (b) is a cross-sectional view showing the cross-section of a conventional ferrule (SMF side ferrule) 2.

[0019] As shown in Figure 3(b), in a conventional ferrule 2, the width W of the opening 23 interposed between the insertion hole 21 and the recess 22 is the same as the diameter D of the insertion hole 21, and the cross-sectional shape of the insertion hole 21 is semicircular. The adhesive 25 for fixing the SMF to the ferrule 2 is filled into the insertion hole 21 from the recess 22. In this case, in order to immerse the SMF in the adhesive 25, it is insufficient to fill the inside of the insertion hole 21 with the adhesive 25, and it is necessary to fill at least the bottom of the recess 22 with the adhesive 25 as well. Normally, the recess 22 is filled with adhesive 25. Therefore, anisotropy occurs in the amount (thickness) of adhesive 25 covering the SMF, and as a result, anisotropy occurs in the curing shrinkage amount of the adhesive 25 covering the SMF. For this reason, in the section where the recess 22 is formed, in particular near the boundary between the section where the recess 22 is formed and the section where the recess 22 is not formed, external stress that causes excessive loss acts on the SMF bonded to the ferrule 2.

[0020] On the other hand, as shown in Figure 3(a), in the ferrule 1, the width W of the opening 13 interposed between the insertion hole 11 and the recess 12 is smaller than the diameter D of the insertion hole 11, and the cross-sectional shape of the insertion hole 11 is arc-shaped. The adhesive 15 for fixing the SMF to the ferrule 1 is filled into the insertion hole 11 from the front end surface 1p. In this case, in order to immerse the SMF in the adhesive 15, it is sufficient to fill the inside of the insertion hole 11 with the adhesive 15, and it is not necessary to fill the bottom of the recess 12 with the adhesive 15. Therefore, anisotropy is unlikely to occur in the amount (thickness) of the adhesive 15 covering the SMF, and as a result, anisotropy is unlikely to occur in the curing shrinkage amount of the adhesive 15 covering the SMF. For this reason, external stress that causes excessive loss is unlikely to act on the SMF bonded to the ferrule 1 in the section where the recess 12 is formed, in particular near the boundary between the section where the recess 12 is formed and the section where the recess 12 is not formed.

[0021] Furthermore, the fact that an opening 13 is provided that communicates with the insertion hole 11 is the same as in the conventional ferrule 2. Therefore, in order to properly maintain the extension direction of the core pin, which is the core for providing the insertion hole 11, it is possible to arrange a core (which may be part of the matrix) that makes line contact with the core pin. For this reason, as in the conventional ferrule 2, it is possible to prevent the insertion hole 11 from being oblique to the outer shape of the ferrule 1.

[0022] The width W of the opening 13 is preferably as small as possible while ensuring line contact between the core pin and the core during the molding of the ferrule 1. However, the width W of the opening 13 in the ferrule 1 after molding will be wider than the width W of the opening 13 in the ferrule 1 at the time of molding due to the curing shrinkage of the resin material of the ferrule 1. Therefore, the width W of the opening 13 must be determined taking into consideration the type of resin material of the ferrule 1 and the molding conditions for molding the ferrule 1. As an example, the width W of the opening 13 is preferably 1 / 2 or less of the diameter D of the insertion hole 11, and more preferably 1 / 3 or less of the diameter D of the insertion hole 11. If the width W of the opening 13 is 1 / 2 or less of the diameter D of the insertion hole 11, external stress will be less likely to act on the SMF compared to a conventional ferrule 2, and if the width W of the opening 13 is 1 / 3 or less of the diameter D of the insertion hole 11, external stress will be even less likely to act on the SMF.

[0023] (First Modified Example of Ferrule) The first modified example of ferrule 1 (hereinafter also referred to as "ferrule 1A") will be described with reference to Figure 4. Figure 4 is a cross-sectional view showing the longitudinal section of ferrule 1A. The differences between ferrule 1A and ferrule 1 are as follows.

[0024] The first difference lies in the position of the recess 12. In ferrule 1, the recess 12 is formed on the rear end surface 1q side of the front end 1a, rather than on the center of the front end 1a, whereas in ferrule 1A, the recess 12 is formed on the front end surface 1p side of the front end 1a, rather than on the center of the front end 1a. This allows for more precise adjustment of the core pin's extension direction when forming ferrule 1A.

[0025] The second difference is the length of the recess 12 (the size of the recess 12 in the direction parallel to the insertion hole 11). That is, the length of the recess 12 in ferrule 1A is shorter than the length of the recess 12 in ferrule 1. The recess 12 is used to maintain the extension direction of the core pin when forming ferrule 1A, but it is not used to inject the adhesive 15. Therefore, shortening the length of the recess 12 in ferrule 1A does not cause any particular problems.

[0026] (Second Modification of Ferrule) The second modification of ferrule 1 (hereinafter also referred to as "ferrule 1B") will be explained with reference to Figure 5. Figure 5 is a cross-sectional view showing the cross-section of ferrule 1B. The differences between ferrule 1B and ferrule 1 are as follows.

[0027] In other words, in ferrule 1, the cross-sectional shape of the recess 12 is rectangular and the draft angle on the side of the recess 12 is weak, whereas in ferrule 1B, the cross-sectional shape of the recess 12 is trapezoidal and the draft angle on the side of the recess 12 is strong. This makes it easier to remove the core that supports the core pin from the molded ferrule 1B after molding ferrule 1B. The cross-sectional shape of the recess 12 may be a trapezoid itself, or it may be a shape that can be approximated by a trapezoid. For example, a trapezoid with one or both of the two corners on the insertion hole 11 side rounded, or a shape that is slightly modified from a trapezoid.

[0028] (Third Modification of Ferrule) The third modification of ferrule 1 (hereinafter also referred to as "ferrule 1C") will be explained with reference to Figure 6. Figure 6 is a cross-sectional view showing the cross-section of ferrule 1C. The differences between ferrule 1C and ferrule 1 are as follows.

[0029] In other words, while ferrule 1 has a single through hole 11, ferrule 1C has multiple (three in the illustrated example) through holes 111 to 113. That is, in addition to the through hole 112, other through holes 111 and 113 are formed. The other through holes 111 and 113 are arranged so that their central axes are parallel to the central axis of the through hole 112, and the multiple through holes 111 to 113 are aligned perpendicular to the central axis of the through hole 111. The cross-sectional shape of the other through holes 111 and 113 is the same as the cross-sectional shape of the through hole 112, and the cross-sectional area of ​​the other through holes 111 and 113 is the same as the cross-sectional area of ​​the through hole 112. As a result, by inserting one bundle of SMF into each of the multiple through holes 111 to 113, multiple bundles (three in the illustrated example) of SMF can be inserted into ferrule 1C.

[0030] The multiple insertion holes 111 to 113 may be configured to merge with each other inside the ferrule 1C, or they may be configured to penetrate the ferrule 1C without merging with each other. The former configuration is suitable when connecting multiple bundles of SMF to one MCF, and the latter configuration is suitable when connecting multiple bundles of SMF to multiple MCFs.

[0031] (Further Modifications of the Ferrule) In this embodiment, ferrule 1 used as the SMF-side ferrule of a FIFO device has been described, but the present invention is not limited thereto. For example, the present invention can also be applied to the MCF-side ferrule of a FIFO device. Furthermore, the present invention can be applied to ferrules in general that are attached to the ends of optical fibers or optical fiber bundles. The optical fiber to which the ferrule according to the present invention is attached may be an SMF, an MCF, or another type of optical fiber. Also, the optical fiber bundle to which the ferrule according to the present invention is attached may be a bundle of multiple SMFs, a bundle of multiple MCFs, or a bundle of multiple other optical fibers.

[0032] (Summary) The ferrule according to Embodiment 1 is characterized by having a through hole for inserting an optical fiber and a recess that communicates with the through hole through an opening formed on the bottom surface, wherein the opening is a slit-shaped opening whose width direction is perpendicular to the central axis of the through hole, and the width of the opening is smaller than the diameter of the through hole.

[0033] According to the above configuration, it is possible to realize a ferrule in which external stress that causes excessive loss is less likely to act on the adhesively fixed optical fiber.

[0034] The ferrule according to embodiment 2 is characterized in that, in the ferrule according to embodiment 1, the width of the opening is 1 / 3 or less of the diameter of the insertion hole.

[0035] According to the above configuration, it is possible to further reduce the likelihood of external stresses that cause excessive loss acting on the optical fiber bonded and fixed to the ferrule.

[0036] The ferrule according to embodiment 3 is characterized in that, in the ferrule according to embodiment 1 or embodiment 2, it is composed of a front end having a front end surface, a rear end having a rear end surface, and an intermediate portion located between the front end and the rear end, the optical fiber is inserted into the insertion hole from the rear end surface side such that its tip surface is flush with the front end surface, and the recess is formed in the front end.

[0037] With the above configuration, the extension direction of the core pin can be adjusted more precisely when forming the ferrule compared to when the recess is formed at the rear end or in the middle.

[0038] The ferrule according to embodiment 4 is characterized in that, in the ferrule according to embodiment 3, the recess is formed on the front end surface side of the center of the front end.

[0039] With the above configuration, the extension direction of the core pin can be adjusted more precisely when forming the ferrule compared to when the recess is formed on the rear end face side rather than the center of the front end.

[0040] The ferrule according to Embodiment 5 is characterized in that, in any of Embodiments 1 to 4, the shape of the cross-section of the recess is trapezoidal, or a shape that can be approximated by a trapezoid.

[0041] With the above configuration, it becomes easy to remove the core that supports the core pin from the molded ferrule after the ferrule has been formed.

[0042] The ferrule according to embodiment 6 is characterized in that, in a ferrule according to any of embodiments 1 to 5, there is further formed an additional insertion hole for inserting another optical fiber, the central axis of which is parallel to the central axis of the insertion hole, and the recess communicates with the insertion hole and the other insertion hole through the opening.

[0043] According to the above configuration, even when multiple bundles of SMF are connected, it is possible to further reduce the external stress that causes excessive loss to be applied to the optical fibers bonded and fixed to the ferrules.

[0044] The ferrule according to aspect 7 is the single-mode fiber (SMF) side ferrule that, together with the multi-core fiber (MCF) side ferrule, constitutes a fan-in / fan-out (FIFO) device in the ferrule according to any one of aspects 1 to 6.

[0045] According to the above configuration, it is possible to realize a FIFO device in which external stress that causes excess loss is less likely to act on the adhesively fixed SMF.

[0046] 1, 1A, 1B Ferrule 1a Front end portion 1b Intermediate portion 1c Rear end portion 1p Front end face 1q Rear end face 11 Insertion through hole 12 Recessed portion 13 Opening

Claims

1. A ferrule having a through-hole for inserting an optical fiber and a recess communicating with the through-hole through an opening formed on its bottom surface, wherein the opening is a slit-shaped opening whose width is perpendicular to the central axis of the through-hole, and the width of the opening is smaller than the diameter of the through-hole.

2. The ferrule according to claim 1, wherein the width of the opening is 1 / 3 or less of the diameter of the insertion hole.

3. A ferrule according to claim 1 or 2, comprising a front end having a front end surface, a rear end having a rear end surface, and an intermediate portion located between the front end and the rear end, wherein the optical fiber is inserted into the insertion hole from the rear end surface side such that its tip surface is flush with the front end surface, and the recess is formed at the front end.

4. The ferrule according to claim 3, wherein the recess is formed on the front end surface side of the center of the front end.

5. The ferrule according to any one of claims 1 to 4, wherein the cross-sectional shape of the recess is trapezoidal, or a shape that can be approximated by a trapezoid.

6. A ferrule according to any one of claims 1 to 5, further comprising another insertion hole for inserting another optical fiber, wherein the central axis of the other insertion hole is parallel to the central axis of the other insertion hole, and the recess communicates with the other insertion hole and the other insertion hole through the opening.

7. A ferrule according to any one of claims 1 to 6, which is an SMF (Single Mode Fiber) side ferrule that constitutes a FIFO (Fan-In / Fan-Out) device together with an MCF (Multi-Core Fiber) side ferrule.

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