Optical fiber protection device

Abstract

This optical fiber protection device (10) comprises an optical fiber (11) having a polished surface (15) on a part of a side surface (16), a holding part (21) having a groove part (22) in which the optical fiber (11) is fixed, and a protection part (31) that is in contact with the polished surface (15) and has a refractive index lower than that of a cladding (13) of the optical fiber (11).

Description

Optical Fiber Protection Device

[0001] The present disclosure relates to an optical fiber protection device.

[0002] As one of the optical multiplexing and demultiplexing technologies that can demultiplex light from an existing optical fiber (hereinafter referred to as the existing optical fiber) already laid in an optical network without cutting the existing optical fiber, or multiplex light into the existing optical fiber, a method for manufacturing an optical fiber coupler using the side polishing method has been studied (see, for example, Non-Patent Documents 1 and 2).

[0003] This method for manufacturing an optical fiber coupler is mainly manufactured by the following steps. (1) Fix the existing optical fiber in the groove of the holding member having the groove into which the existing fiber fits, and partially polish the side surface of the existing optical fiber from several micrometers from the core or to the core, including the coating and cladding. (2) Partially polish the side surface of the optical fiber (hereinafter referred to as the branching fiber) previously embedded in the holding member from several micrometers from the core or to the core, including the coating and cladding. (3) Apply a refractive index matching agent between the polished surfaces of the existing optical fiber and the branching fiber with the side surfaces polished, align the polished surfaces, relatively move these optical fibers in the direction of the polished surface, and fix them at a position where a desired branching ratio is obtained. The cores are optically coupled by evanescent coupling through the polished surface, and thus, the optical fiber coupler is completed.

[0004] Uematsu et al., "Fundamental study on optical branching using the side polishing method," IEICE Technical Report, vol. 119, no. 223, OFT2019-36, pp. 23-26, Oct. 2019. Uematsu et al., "Study on in-service optical branching using optical fiber side polishing," IEICE Technical Report, vol. 121, no. 332, OFT2021-61, pp. 32-35, Jan. 2022.

[0005] When the use of the optical fiber coupler is completed, the cores of the two side-polished fibers are separated from each other, and the polished surfaces are separated. As a result, the evanescent coupling disappears, and the function as an optical fiber coupler stops.

[0006] However, in the areas where the polished surface is formed, the coating and cladding of the optical fiber are partially removed, reducing its strength. Therefore, if the two polished surfaces are separated and left exposed to the outside air, the durability and operational reliability of the optical fiber will decrease. Furthermore, the separated polished surfaces will continue to be in contact with air or residual refractive index composite material. Consequently, evanescent waves that leak slightly from the core are reflected and scattered by the irregularities of the polished surface, resulting in optical loss.

[0007] This disclosure is made in view of the circumstances described above and aims to provide an optical fiber protection device that can suppress the increase in optical loss due to side-polished fibers when the optical fiber coupler ceases to function.

[0008] An optical fiber protection device according to one aspect of the present disclosure comprises an optical fiber having a polished surface on a part of its side surface, a holding portion having a groove for fixing the optical fiber, and a protective portion that contacts the polished surface and has a refractive index less than or equal to that of the cladding of the optical fiber.

[0009] According to this disclosure, it is possible to provide an optical fiber protection device that can suppress the increase in optical loss due to side-polished fibers when the optical fiber coupler ceases to function.

[0010] Figure 1 is a diagram of an optical fiber protection device according to an embodiment of the present disclosure, where Figure 1(a) is a cross-sectional view taken along line A-A in Figure 1(b), and Figure 1(b) is a cross-sectional view taken along line B-B in Figure 1(a). Figure 2 is a diagram of an optical fiber protection device according to a first modification of an embodiment of the present disclosure, where Figure 2(a) is a cross-sectional view taken along line A-A in Figure 2(b), and Figure 2(b) is a cross-sectional view taken along line B-B in Figure 2(a). Figure 3 is a diagram of an optical fiber protection device according to a second modification of an embodiment of the present disclosure, where Figure 3(a) is a cross-sectional view taken along line A-A in Figure 3(b), and Figure 3(b) is a cross-sectional view taken along line B-B in Figure 3(a). Figure 4 is a diagram of an optical fiber protection device according to a third modification of an embodiment of the present disclosure, where Figure 4(a) is a cross-sectional view taken along line A-A in Figure 4(b), and Figure 4(b) is a cross-sectional view taken along line B-B in Figure 4(a). Figure 5 is a diagram of an optical fiber protection device according to a fourth modified embodiment of the present disclosure, where Figure 5(a) is a cross-sectional view showing the first state and Figure 5(b) is a cross-sectional view showing the second state. It is a cross-sectional view showing the two polished surfaces and their surroundings in the initial state.

[0011] The optical fiber protection device according to the embodiment of this disclosure will be described below. In each figure, common parts are denoted by the same reference numerals, and redundant explanations will be omitted. For the sake of convenience, mutually orthogonal X, Y, and Z directions are defined. The Z direction is the direction in which the optical fiber extends, and the X and Y directions are the width and height directions of the optical fiber protection device, respectively. For the sake of convenience, the optical fiber protection device 10 according to this embodiment will be referred to as protection device 10 below.

[0012] Figure 1 is a diagram of an optical fiber protection device 10 according to an embodiment of the present disclosure, where Figure 1(a) is a cross-sectional view taken along line A-A in Figure 1(b), and Figure 1(b) is a cross-sectional view taken along line B-B in Figure 1(a). As shown in Figure 1(a), the protection device 10 comprises an optical fiber 11, a holding portion 21 for holding the optical fiber 11, and a protection portion 31 for protecting the polished surface of the optical fiber 11. The optical fiber 11 is a single-mode optical fiber or a multimode optical fiber and comprises a core 12, a cladding 13, and a covering 14.

[0013] The optical fiber 11 has a polished surface 15 on a part of its side surface 16. The polished surface 15 is formed by partial polishing of the side surface 16. As shown in Figure 1(b), the optical fiber 11 is fixed in the groove 22 of the holding part 21, for example, using adhesive 23.

[0014] The holding portion 21 has, for example, a rectangular parallelepiped shape extending in the Z direction. The holding portion 21 has a plane 21a facing the protective portion 31. The plane 21a functions as a mounting surface for the protective portion 31. A groove (first groove) 22 is formed in the plane 21a. As shown in Figure 1(a), when viewed from the Z direction, the groove 22 has, for example, a V-shaped cross-section. The holding portion 21 is formed of, for example, optically transparent glass.

[0015] The groove 22 is curved with a predetermined radius of curvature. Therefore, the optical fiber 11 fixed in the groove 22 is also curved with a radius of curvature corresponding to the radius of curvature of the groove 22. However, when the optical fiber 11 is fixed in the groove 22 before polishing, the optical fiber 11 is exposed from the groove 22 at the shallowest part of the groove 22. In this state, by polishing the side surface 16, the side surface 16 is polished to a desired depth that reaches the cladding 13 or core 12. As a result, a polished surface 15 is formed that is on the same plane as the plane 21a.

[0016] The protective portion 31 is placed on the flat surface 21a of the holding portion 21, contacts the polishing surface 15, and covers the polishing surface 15. The protective portion 31 is, for example, a plate-shaped member having a predetermined thickness in the Y direction, and is formed of resin or glass. The resin may be a photocurable resin such as an ultraviolet curing resin. The protective portion 31 is fixed to the holding portion 21 by means of, for example, an adhesive or an ultraviolet curing resin, so as not to move relative to the holding portion 21.

[0017] The protective portion 31 has a refractive index less than or equal to that of the cladding 13. However, the closer the refractive index of the protective portion 31 is to that of the cladding 13, the more reflection and scattering due to irregularities on the polished surface 15 can be reduced, thereby reducing light loss.

[0018] The protective portion 31 has a thickness greater than or equal to the distance from the core 12 to the outer circumference of the cladding 13. For example, if the optical fiber 11 is a single-mode fiber, the protective portion 31 has a thickness of 60 μm or more. Having such a thickness in the protective portion 31 reduces optical loss due to evanescent wave leakage in the protective portion 31. In other words, it can suppress the increase in optical loss due to side-polished fibers when the optical fiber coupler stops functioning. Furthermore, by using a protective portion 31 with a relatively high optical transmittance for the wavelength band of light propagating through the optical fiber 11, optical loss can be further reduced.

[0019] The protective portion 31 may be a film or sheet having the thickness described above. By using a protective portion 31 made of film or sheet, the protective portion 31 can be easily removed from the optical fiber 11 when the optical fiber 11 is used again as an optical fiber coupler, thereby reducing the burden of manufacturing the optical fiber coupler.

[0020] Figure 2 is a diagram of a protective device 10 according to a first modified example of an embodiment of the present disclosure, where Figure 2(a) is a cross-sectional view taken along line A-A in Figure 2(b), and Figure 2(b) is a cross-sectional view taken along line B-B in Figure 2(a). In this example, the high refractive index portion 32 is placed on the protective portion 31 described above. In other words, the high refractive index portion 32 is provided at a position where the protective portion 31 is interposed between it and the polished surface 15, thereby protecting the high refractive index portion 32. Consequently, the durability of the protective portion 31 is improved.

[0021] The high refractive index section 32 is, for example, a plate-shaped member having a predetermined thickness in the Y direction, and is formed of resin, glass, or the like. The refractive index of the high refractive index section 32 is higher than that of the protective section 31. This allows light propagating through the protective section 31 to be diverted to the high refractive index section 32, thereby suppressing multi-path interference. Multi-path interference is a phenomenon in which light that has traveled from the core 12 to the protective section 31 travels back to the core 12 and mixes with light propagating only within the core 12, causing interference. Multi-path interference adversely affects communication quality.

[0022] Figure 3 is a diagram of an optical fiber protection device according to a second modified embodiment of the present disclosure, where Figure 3(a) is a cross-sectional view taken along line A-A in Figure 3(b), and Figure 3(b) is a cross-sectional view taken along line B-B in Figure 3(a). In this example, a low refractive index portion 33 is provided between the polished surface 15 and the protection portion 31.

[0023] The low refractive index portion 33 is a component formed from a liquid such as silicone oil or an elastic material such as silicone resin. However, the low refractive index portion 33 is not limited to these. The refractive index of the low refractive index portion 33 is lower than the refractive index of the cladding 13. Furthermore, it is desirable that the thickness of the low refractive index portion 33 is greater than or equal to the distance from the core 12 to the outer circumference of the cladding 13 (for example, 60 μm as described above). By having a refractive index of the low refractive index portion 33 lower than the refractive index of the cladding 13, optical loss due to evanescent wave leakage can be reduced. Furthermore, by using a low refractive index portion 33 that has a relatively high optical transmittance for the wavelength band of light propagating through the optical fiber 11, optical loss can be further reduced.

[0024] Furthermore, even if the holding portion 21, the protective portion 31, or both expand or contract due to temperature changes in the external environment, the low refractive index portion 33 can reduce stress on the optical fiber 11. Therefore, it is possible to suppress increased optical loss and a decrease in reliability due to breakage of the optical fiber 11.

[0025] Figure 4 is a diagram of an optical fiber protection device according to a third modified embodiment of the present disclosure, where Figure 4(a) is a cross-sectional view taken along line A-A in Figure 4(b), and Figure 4(b) is a cross-sectional view taken along line B-B in Figure 4(a). In this example, a recess 34 is provided in the protection portion 31, and a low refractive index portion 33 is housed in the recess 34.

[0026] The recess 34 is formed in the protective portion 31 at a position facing the polishing surface 15. Therefore, the low refractive index portion 33 within the recess 34 contacts the polishing surface 15 and covers it. The cross-sectional shape of the recess 34 is not limited to the triangle shown in Figure 4; it may be a rectangle or other shape such as a semicircle. On the other hand, the protective portion 31 is placed on the plane 21a of the holding portion 21 and reinforces the holding portion 21.

[0027] Similar to the second modified example, the low refractive index portion 33 in this example is also a liquid or elastic material with a lower refractive index than the cladding 13, such as silicone oil or silicone resin. As shown in Figure 4, the recess 34 is filled with the low refractive index portion 33.

[0028] In this example, even if the protective part 31, the holding part 21, or both expand or contract due to temperature changes in the external environment, the low refractive index part 33 can reduce stress on the optical fiber 11. Therefore, it is possible to suppress increased optical loss and a decrease in reliability due to breakage of the optical fiber 11.

[0029] Furthermore, by housing the low refractive index portion 33 in the recess 34, the entire low refractive index portion 33 is surrounded by the holding portion 21 and the protective portion 31. Therefore, even if the low refractive index portion 33 is a liquid, leakage of the low refractive index portion 33 can be prevented.

[0030] Figure 5 is a diagram of an optical fiber protection device according to a fourth modification of an embodiment of the present disclosure, where Figure 5(a) is a cross-sectional view showing the first state and Figure 5(b) is a cross-sectional view showing the second state. In the fourth modification, a groove (second groove) 35 for a branching side-polished optical fiber 41 (hereinafter referred to as optical fiber 41) is provided in the protection part 31 of the third modification, and the optical fiber 41 is fixed in the groove 35. The optical fiber 41 is the same type of optical fiber as the optical fiber 11. The optical fiber 41 is fixed in the groove 35 by adhesive 38 in a position where its polished surface 45 is in contact with the polished surface 15.

[0031] The groove 35 is provided adjacent to the recess 34 in the X direction. The shape of the groove 35 is the same as that of the groove 22. The holding portion 21 and the protective portion 31 are slidably provided so as to be relative to each other in the X direction (i.e., in a direction perpendicular to the extending direction of the optical fibers 11 and 41 in the plane 21a) so that the recess 34 and the groove 35 face each other.

[0032] For example, in the first state shown in Figure 5(a), the recess 34 faces the groove 22, and the low refractive index portion 33 contacts the polished surface 15, suppressing optical loss of the optical fiber 11. On the other hand, in the second state shown in Figure 5(b), the groove 35 faces the groove 22, and the optical fiber 41 optically couples with the optical fiber 11 via the polished surfaces 45 and 15. That is, in the second state, an optical fiber coupler is constructed. In this example, the first and second states can be switched by the relative movement of the holding portion 21 and the protective portion 31. In other words, according to this example, by moving the holding portion 21 and the protective portion 31 relative to each other in the X direction, the presence or absence of optical branching can be easily switched, making it possible to reuse the optical fiber coupler easily and quickly.

[0033] This disclosure is not limited to the embodiments described above, but includes all modifications within the meaning and scope of the claims as indicated by the claims.

[0034] 10 Optical fiber protection device (protection device) 11 Optical fiber 12 Core 13 Cladding 14 Coating 15 Polished surface 16 Side surface 21 Holding part 22 Groove (first groove) 21a Plane 23 Adhesive 31 Protection part 32 High refractive index part 33 Low refractive index part 34 Recess 35 Groove (second groove) 35 Groove 38 Adhesive 41 Optical fiber 45 Polished surface

Claims

1. An optical fiber protection device comprising: an optical fiber having a polished surface on a part of its side surface; a holding part having a groove for fixing the optical fiber; and a protective part that contacts the polished surface and has a refractive index less than or equal to that of the cladding of the optical fiber.

2. The optical fiber protection device according to claim 1, further comprising a high refractive index portion provided at a position where the protective portion is interposed between the polished surface and the protective portion, and having a refractive index higher than that of the protective portion.

3. The optical fiber protection device according to claim 1, further comprising a low refractive index portion provided between the polished surface and the protective portion, having a refractive index lower than or equal to that of the cladding.

4. The optical fiber protection device according to claim 3, wherein the protective portion includes a recess in which the low refractive index portion is housed.

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