Optical fiber holding jig and optical fiber holding method

Abstract

An optical fiber holding jig (30) comprises a holding part (31) for holding an optical fiber. The holding part (31) includes a body (32) including a flat surface (32a) in which a groove part (34) for accommodating a part of the optical fiber is formed, and a pair of flange parts (33, 33) provided on both sides of the body (32) and positioned at a position lower than the flat surface (32a) in the height direction of the body (32) and orthogonal to the flat surface (32a).

Description

Optical fiber holding jig and optical fiber holding method

[0001] The present disclosure relates to an optical fiber holding jig and an optical fiber holding method.

[0002] With the development of IoT (Internet of Things), an increase in sensors installed in optical communication networks is expected. However, installing a large number of sensors in an optical communication network and providing communication functionality to those sensors requires, for example, connection to the optical fiber that makes up the optical communication network. In the past, when constructing an optical communication network, the number of optical fibers was determined by predicting the demand for sensors or devices to be connected to the optical fiber. However, there are many installation candidates for sensors related to IoT devices, and there are a wide variety of types. This makes it difficult to predict the demand for the number of sensors, and it also makes it difficult to predict the number of optical fibers that need to be laid.

[0003] One solution to this problem is to utilize optical fiber that is already installed at the location where the IoT device will be newly installed. Specifically, the side of the optical fiber is polished, and a branching optical fiber is connected to create an optical branch point (see Non-Patent Document 1). By creating such a branch point, it is possible to connect IoT devices to the optical communication network without cutting or installing additional optical fiber in the trunk line.

[0004] Takutake Uematsu, "Study on in-service optical branching using optical fiber side polishing," IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, OFT2021-61 (2022-01), pp. 32-35 (2022)

[0005] When polishing the side surface of an optical fiber, an optical fiber holding jig is used. A groove is formed on the surface of the holding jig to accommodate a portion of the optical fiber. With the optical fiber held in this groove, polishing is performed on the side surface of the optical fiber. At this time, the optical fiber is held in the holding jig by a fixing agent such as adhesive or ultraviolet-curing resin. However, because the amount of fixing agent used is not fixed, the polishing conditions for the optical fiber, such as the thickness and shape of the hardened fixing agent, are not determined, and it is not possible to maintain a constant polishing time or quality of the polished state.

[0006] The present disclosure has been made in view of the above circumstances, and aims to provide an optical fiber holding jig and an optical fiber holding method that are capable of suppressing changes in the polishing conditions for an optical fiber.

[0007] An optical fiber holding jig according to a first aspect of the present disclosure includes a holding portion for holding an optical fiber, the holding portion including a main body including a plane on which a groove portion for accommodating a portion of the optical fiber is formed, and a pair of flange portions provided on both sides of the main body and positioned lower than the plane in a height direction of the main body perpendicular to the plane.

[0008] An optical fiber holding method according to a second aspect of the present disclosure is a method using the optical fiber holding jig according to the first aspect, and includes applying a fixing agent over the entire surface of the surface in an amount that allows some of the fixing agent to flow out of the surface while the optical fiber is placed in the groove portion, and hardening the fixing agent.

[0009] According to the present disclosure, it is possible to provide an optical fiber holding jig and an optical fiber holding method that are capable of suppressing changes in polishing conditions for an optical fiber.

[0010] FIG. 1 is a cross-sectional view of an example of an optical branching unit. FIG. 2A is a perspective view of an optical fiber holding jig according to this embodiment. FIG. 2B is a front view of the optical fiber holding jig as viewed from the Z direction. FIG. 3A is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3B is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3C is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3D is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3E is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3F is a diagram showing one step of a method for fabricating an optical branching unit. FIG. 3G is a diagram showing one step of a method for fabricating an optical branching unit.

[0011] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Furthermore, in the description of the drawings, identical parts are given the same reference numerals, and description thereof will be omitted. An optical fiber holding jig 30 (see FIG. 2A ) according to this embodiment holds an optical fiber in order to polish a portion of the side surface of the optical fiber, and is used in the optical fiber holding method according to this embodiment. Hereinafter, for convenience of description, the optical fiber holding jig 30 according to this embodiment will be referred to as jig 30.

[0012] For ease of explanation, the X, Y, and Z directions are defined as being orthogonal to each other. The X direction is the width direction of the jig 30. The Y direction is the height direction of the jig 30, which is the vertical direction. The Z direction is the depth direction of the jig 30.

[0013] First, an optical branching unit (optical multiplexing / demultiplexing coupler) 1 according to this embodiment will be described. Fig. 1 is a cross-sectional view of an example of the optical branching unit 1. The optical branching unit 1 branches light propagating through one optical fiber into two optical fibers, or combines light propagating through two optical fibers into one optical fiber. As shown in Fig. 1, the optical branching unit 1 includes an optical fiber 10 and an optical fiber 20. The optical fiber 10 and the optical fiber 20 are single-mode optical fibers or multi-mode optical fibers.

[0014] The optical fiber 10 includes a core 11, a cladding 12, and a coating 13. The optical fiber 20 includes a core 21, a cladding 22, and a coating 23. One of the optical fiber 10 and the optical fiber 20 may be, for example, a so-called active optical fiber that has already been laid in a network. The other of the optical fiber 10 and the optical fiber 20 may be, for example, a so-called branch fiber that is newly connected to the optical fiber 10 as an additional path in an optical communication network.

[0015] The optical fiber 10 has a polished surface 14 on a side surface 15. The polished surface 14 is formed by polishing the side surface 15. During this polishing, the optical fiber 10 is held by a jig 30, which will be described later.

[0016] The optical fiber 10 extends in the Z direction while being bent at a radius of curvature R at least in a portion including the polished surface 14. The polished surface 14 is formed by polishing the side surface 15 of the optical fiber 10 that is placed in a state where it is bent at the radius of curvature R. Therefore, when the optical fiber 10 is bent at the radius of curvature R, the polished surface 14 forms an elliptical plane that extends in the longitudinal direction of the optical fiber 10.

[0017] Similar to the optical fiber 10, the optical fiber 20 has a polished surface 24 on a side surface 25. The polished surface 24 is formed by polishing the side surface 25. This polishing process can also be performed using, for example, a jig 30, which will be described later.

[0018] A refractive index matching material (not shown) is interposed between the polished surface 14 and the polished surface 24. The refractive index matching material may be a viscous liquid or a deformable solid. The refractive index of the refractive index matching material is smaller than the refractive indexes of the cladding 12 and the cladding 22. This suppresses an increase in insertion loss.

[0019] The polished surfaces 14 and 24 are in contact with each other via the refractive index matching agent (not shown) described above. Therefore, the cores 11 and 21 are positioned with a predetermined gap between them. By making this gap sufficiently small, evanescent coupling between them is achieved. In other words, the cores 11 and 21 are optically coupled, enabling the multiplexing or demultiplexing of light, which is the function of the optical branching unit 1.

[0020] Next, the configuration of the jig 30 used when creating the above-mentioned optical branching unit 1 will be described. Fig. 2A is a perspective view of the jig 30. Fig. 2B is a front view of the jig 30 as viewed from the Z direction. As shown in Fig. 2A, the jig 30 includes a holding portion 31 that holds the optical fiber. The holding portion 31 is formed of an optically transparent material such as glass or resin. However, if a substance such as an adhesive that does not require ultraviolet irradiation is assumed as the fixing agent 40, the holding portion 31 does not need to be optically transparent.

[0021] The holding part 31 includes a main body 32. The main body 32 has a flat surface (upper surface) 32a on which the fixing agent 40 is applied. The flat surface 32a is parallel to the X-Z plane, in other words, perpendicular to the Y direction. A groove 34 that accommodates a portion of the optical fiber 10 is formed in the flat surface 32a. The main body 32 may have any shape as long as it has the flat surface 32a and the groove 34 and can suppress deformation during polishing of the optical fiber 10 (20). For example, the main body 32 is formed as a substantially rectangular body having flat surfaces facing the X, Y, and Z directions.

[0022] The flat surface 32a forms a corner 32c with the side surface 32b of the holding portion 31. In other words, the flat surface 32a and the side surface 32b are not smoothly (continuously) connected to each other. However, this definition does not exclude curved surfaces or chamfered corners that are unavoidably formed due to manufacturing or structural reasons. When the fixing agent 40 is applied (dropped) to the flat surface 32a, the flow of the fixing agent 40 is temporarily restricted by the corner 32c. This allows a certain amount of the fixing agent 40 to remain on the flat surface 32a.

[0023] The area of ​​the flat surface 32a has a value set according to the amount of fixing agent 40 remaining on the flat surface 32a. Due to the viscosity, surface tension, and the presence of the corners 32c of the fixing agent 40, a certain amount of fixing agent 40 remains on the flat surface 32a. This amount is approximately proportional to the area of ​​the flat surface 32a. In other words, by setting the area of ​​the flat surface 32a to a predetermined value, an amount of fixing agent 40 corresponding to that value can be left on the flat surface 32a. In other words, by adjusting the area of ​​the flat surface 32a, the amount of fixing agent 40 remaining on the flat surface 32a can be controlled.

[0024] As described above, the flat surface 32a has a groove 34. The groove 34 has a V-shaped cross section that narrows toward the bottom surface 31b and extends in the Z direction. The depth of the groove 34 along the Y direction is such that the cladding 12 is polished and optical coupling between the core 11 and the core of another optical fiber is obtained.

[0025] The extending direction of the groove 34 may be curved with a predetermined radius of curvature corresponding to the radius of curvature R (see FIG. 1) of the optical fiber 10 (20). In this case, the groove 34 is formed so that the depth from the plane 32 a is shallowest near the center of the plane 32 a in the Z direction.

[0026] The holding portion 31 includes a pair of flanges 33, 33. The pair of flanges 33, 33 are provided on both sides of the main body 32 in the X direction. Each flange 33 extends a predetermined length from a side surface 32b of the main body 32 toward one side or the other in the X direction. The length of each flange 33 in the Z direction is equal to the length of the main body 32 in the same direction.

[0027] Each flange 33 shares the bottom surface 31b of the holding portion 31 with the main body 32. In other words, the bottom surfaces of each flange 33 and the main body 32 are located on the same plane formed by the bottom surface 31b. Using the bottom surface 31b as a reference, the height (thickness) of each flange 33 along the Y direction is lower than the height of the main body 32. That is, in the Y direction, each flange 33 is located lower than the flat surface 32a, and the holding portion 31 has a convex cross-sectional shape when viewed from the Z direction (see FIG. 2B). Therefore, the upper surface 33a of each flange 33 is located lower than the flat surface 32a, forming a step between the upper surface 33a and the flat surface 32a via the side surface 32b. The upper surface 33a receives the fixing agent 40 that flows from the flat surface 32a to the side surface 32b (see FIG. 3C).

[0028] The jig 30 may further include a pressing member 38. The pressing member 38 is formed of an optically transparent material such as glass or resin, and includes a flat pressing surface 38a. However, if the fixing agent 40 is a substance such as an adhesive that does not require ultraviolet irradiation, the pressing member 38 does not need to be optically transparent. The pressing member 38 presses the fixing agent 40 on the flat surface 32a toward the flat surface 32a via the pressing surface 38a, causing excess fixing agent 40 to flow out from the flat surface 32a.

[0029] The pressing member 38 is, for example, a plate-like member having a rectangular shape when viewed in the Y direction and a predetermined thickness in the Y direction. In this case, as shown in FIG. 2B , the pressing member 38 has a width W3 in the direction spanning the groove portion 34 (i.e., the X direction). This width W3 is equal to or greater than the width W1 of the flat surface 32a (main body 32) in the X direction and is less than the width W2 of the pair of flange portions 33, 33 (holding portion 31) along the same direction. For example, as shown in FIG. 2B , the width W3 of the pressing member 38 may be equal to the width W1 of the flat surface 32a.

[0030] The depth D3 of the pressing member 38 along the Z direction is equal to or slightly longer than the depth D1 of the flat surface 32a (main body 32, holding portion 31) along the same direction. Note that the pressing member 38 may have an additional structure (e.g., a knob, a screw hole, etc.) for operating the pressing member 38.

[0031] The pressing surface 38a of the pressing member 38 is formed as a flat surface facing the flat surface 32a. The pressing surface 38a makes contact with the fixing agent 40 applied to the flat surface 32a, thereby flattening the surface of the hardening fixing agent 40.

[0032] Next, a method for fabricating the optical branching unit 1 will be described. For ease of explanation, an example will be described in which, as a step in the method for fabricating the optical branching unit 1, the side surface of the optical fiber 10 is polished, and the optical fiber 20, which has been polished in advance, is connected to the optical fiber 10. Furthermore, the holding portion 31 of the jig 30 that holds the optical fiber 10 will be referred to as holding portion 31A, and the holding portion 31 of the jig 30 that holds the optical fiber 20 will be referred to as holding portion 31B.

[0033] 3A to 3G are diagrams showing steps in a method for fabricating the optical branching unit 1. Fabrication of the optical branching unit 1 can be mainly divided into polishing steps S10 to S14 of the optical fiber 10 and the subsequent aligning steps S20 to S23 of the optical fiber 10 and the optical fiber 20.

[0034] First, as shown in FIG. 3A, the optical fiber 10 is placed in the groove 34 of the holder 31A (step S10). The holder 31A is attached to and held on a predetermined stand (not shown). Next, as shown in FIG. 3B, the fixing agent 40 is applied (dripped) onto the entire surface of the flat surface 32a (step S11). Specifically, with the optical fiber 10 placed in the groove 34, an amount of the fixing agent 40 that allows some of it to flow out of the flat surface 32a is applied (dripped) over the entire surface of the flat surface 32a. At this time, the fixing agent 40 flows on the flat surface 32a and penetrates into the groove 34. The optical fiber 10 is completely buried in the fixing agent 40.

[0035] Next, as shown in FIG. 3C , the pressing member 38 is placed on the flat surface 32a with the pressing surface 38a facing the flat surface 32a, and the pressing member 38 is pressed toward the flat surface 32a (step S12). This causes excess fixing agent 40 to flow out from the flat surface 32a. The fixing agent 40 that has flowed out from the flat surface 32a flows along the side surface 32b of the main body 32 and accumulates on the upper surface 33a of the flange portion 33. Furthermore, since the pressing member 38 presses the optical fiber 10 immersed in the fixing agent 40 into the groove portion 34, the optical fiber 10 can be reliably positioned and fixed within the groove portion 34. Note that, in order to ensure that the fixing agent 40 remains on the flat surface 32a without excess or deficiency, it is desirable to maintain the pressing surface 38a parallel to the flat surface 32a while the pressing member 38 is being pressed. Furthermore, if the viscosity of the fixing agent 40 allows the fixing agent 40 to be spread over the entire area of ​​the flat surface 32a and an appropriate thickness of the fixing agent 40 is obtained, the pressing by the pressing member 38 may be omitted.

[0036] Next, as shown in FIG. 3D , the fixing agent 40 is hardened (step S13). In this example, the fixing agent 40 is an ultraviolet-curing resin. Therefore, ultraviolet rays 41 are irradiated onto the fixing agent 40. The ultraviolet rays 41 reach the groove 34 and harden the fixing agent 40 in the groove 34. As the fixing agent 40 hardens, the optical fiber 10 is fixed within the groove 34, and the optical fiber 10 and the holding portion 31A are integrated. In other words, the optical fiber 10 is held by the jig 30. The fixing agent 40 may be, for example, an adhesive. In this case, the ultraviolet irradiation described above is omitted.

[0037] While the fixing agent 40 hardens, it is pressed by the pressing surface 38a. Therefore, the hardened fixing agent 40 has a flat surface that is approximately parallel to the flat surface 32a. As in step S12, it is desirable to maintain the pressing surface 38a parallel to the flat surface 32a in step S13 as well. This makes it possible to prevent uneven consumption of the fixing agent 40 in the next step, polishing.

[0038] Next, as shown in Fig. 3E, polishing is started from above the fixing agent 40 using a polishing sheet 42 to remove excess fixing agent 40, coating 13, and cladding 12 (step S14). This polishes a portion of the side surface 15 of the optical fiber 10. Polishing is continued until the polishing surface 14 (see Fig. 3F) reaches the vicinity of the core 11.

[0039] Next, as shown in Figure 3G, the optical fiber 20 held by the holder 31B is prepared, and alignment steps S20 to S23 are performed. The side of the optical fiber 20 has been polished in advance, exposing the polished surface 24. This polished surface 24 is placed on the polished surface 14 of the optical fiber 10 (step S21). The refractive index matching agent (not shown) described above is interposed between the polished surface 24 and the polished surface 14.

[0040] Then, one of the optical fibers 10 and 20 is aligned with the other to bring the core 11 and the core 21 closer to each other (step S22). This alignment is performed by measuring the intensity of light propagating through the optical fiber 10 or the optical fiber 20, or by observation with a microscope. For example, when communication light is propagating through the core 11, gradually bringing the core 11 and the core 21 closer to each other increases the optical coupling rate, and a portion of the communication light propagating through the core 11 begins to propagate through the core 21.

[0041] The branching ratio of light depends on the distance between the cores 11 and 21 and the wavelength of the communication light. Therefore, when the intensity of the communication light propagating through the core 21 reaches an intensity corresponding to the desired branching ratio, the relative positions of the optical fibers 10 and 20 are fixed (step S23). In this way, the optical branching unit 1 (see FIG. 1) is constructed.

[0042] According to this embodiment, when polishing the side surface, an appropriate amount of fixing agent is applied to the holding portion of the jig, and the fixing agent can be hardened while controlling the thickness and flatness, thereby suppressing changes in the polishing conditions for the optical fiber.

[0043] As described above, the holding portion 31 of the jig 30 according to this embodiment includes a main body 32 and a pair of flanges 33. The main body 32 includes a flat surface 32a on which a groove 34 is formed. Meanwhile, the pair of flanges 33 are provided on both sides of the main body 32 and are positioned lower than the flat surface 32a in the height direction (Y direction) of the main body 32, which is perpendicular to the flat surface 32a. In other words, this embodiment employs a holding portion 31 with a convex cross-sectional shape, with the flat surface 32a at its top (upper portion). This allows excess fixing agent 40 to flow downward, and a certain amount of fixing agent 40 to remain on the flat surface 32a. Therefore, compared to a case where the holding portion is configured as a rectangular parallelepiped of the same size, the area of ​​the flat surface for retaining the fixing agent 40 is reduced, thereby reducing the amount of fixing agent 40 required and the time required for polishing.

[0044] Furthermore, since the main body 32 is supported on a stand or the like via the flange 33, it is possible to suppress deflection of the main body 32 during polishing, which is caused by the thinness of the main body 32, compared to when the flange 33 is not provided, and it is possible to suppress deterioration in the processing accuracy of the polishing surface 14, such as flatness. Furthermore, it is also possible to improve the operability of the holding part 31.

[0045] As described above, when applying the fixing agent 40 to the flat surface 32a, the fixing agent 40 is dripped onto the flat surface 32a from above. At this time, although the fixing agent 40 spreads across the flat surface 32a, the viscosity of the fixing agent 40 may limit smooth flow, causing the thickness of the fixing agent 40 on the flat surface 32a to remain uneven. In this case, when polishing of the hardened fixing agent 40 begins with the abrasive sheet 42, the thickest portion of the fixing agent 40 is polished first. Therefore, the abrasive sheet 42 does not come into surface contact with the fixing agent 40, and polishing proceeds with the abrasive sheet 42 excessively tilted relative to the flat surface 32a.

[0046] Therefore, in this embodiment, the pressing member 38 presses the fixing agent 40, spreading the liquid fixing agent 40 along the flat surface 32a and maintaining a constant thickness of the fixing agent 40 on the flat surface 32a. Furthermore, the holding portion 31 has a convex cross-sectional shape, and the flat surface 32a is provided at its top (upper portion). This reduces the amount of excess fixing agent 40 remaining on the flat surface 32a, suppresses unnecessary deformation of the pressing surface 38a during pressing due to uneven distribution of the fixing agent 40 caused by viscosity, and prevents a decrease in processing accuracy during polishing.

[0047] The area of ​​the plane 32a is set according to the amount of fixing agent 40 remaining on the plane 32a. Therefore, the amount of fixing agent 40 to be poured onto the plane 32a can be set in advance.

[0048] Furthermore, even if the amount of fixing agent 40 is not set in advance, it is possible to confirm that an appropriate amount of fixing agent 40 has been applied to the flat surface 32a by using the pressing member 38 to check for leakage of the fixing agent 40 from between the pressing surface 38a and the flat surface 32a. In this case, it is not necessary to accurately measure the amount of fixing agent 40 in advance. Therefore, the burden on the worker who fabricates the optical branching unit 1 on site can be reduced.

[0049] REFERENCE SIGNS LIST 1 Optical branching section (optical multiplexing / demultiplexing coupler) 10 Optical fiber 20 Optical fiber 30 Optical fiber holding jig (jig) 31 Holding section 32 Main body 32a Flat surface (upper surface) 33 Flange section 34 Groove section 38 Pressing member 38a Pressing surface 40 Fixing agent

Claims

1. An optical fiber holding jig comprising: a holding part for holding an optical fiber, the holding part including: a main body including a flat surface on which a groove for accommodating a portion of the optical fiber is formed; and a pair of flanges provided on both sides of the main body and positioned lower than the flat surface in a height direction of the main body perpendicular to the flat surface.

2. The optical fiber holding jig according to claim 1, wherein the flat surface forms a corner between the flat surface and the side surface of the holding portion.

3. The optical fiber holding jig according to claim 2, wherein the area of ​​the flat surface has a value set according to the amount of fixing agent remaining on the flat surface.

4. An optical fiber holder according to any one of claims 1 to 3, further comprising a pressing member including a pressing surface formed in a flat shape.

5. The optical fiber holding jig according to claim 4, wherein the pressing member is a plate-like member having a predetermined thickness in a direction perpendicular to the pressing surface, and has a width equal to or greater than the width of the plane in a direction spanning the groove portion, but less than the width of the pair of flange portions.

6. A method for holding an optical fiber using an optical fiber holding jig according to any one of claims 1 to 3, comprising the steps of: applying a fixing agent over the entire surface of said plane in an amount that allows a portion of the fixing agent to flow out of said plane while said optical fiber is placed in said groove; and hardening said fixing agent.

7. The optical fiber holding method according to claim 6, wherein, before the fixing agent hardens, a pressing member including a pressing surface parallel to the flat surface is pressed toward the flat surface with the pressing surface facing the fixing agent.

Images