Method for manufacturing an optical fiber and optical fiber

Abstract

To provide a method for manufacturing an optical fiber that enables prevention of occurrence of a crack in a protection resin for covering a removed portion of a covering layer and an exposed portion of a glass fiber in an optical fiber, and quality thereof to be stabilized without scratching the glass fiber.SOLUTION: A method for manufacturing an optical fiber includes: a removing step of partly removing a covering layer of an optical fiber; a connecting step of fusion-splicing an end face of an exposed glass fiber; and a re-covering step of re-covering a removed portion of the covering layer and an exposed portion of the glass fiber with a covering protection resin. The removing step is a step of irradiating the covering layer with a laser beam to remove the covering layer.SELECTED DRAWING: Figure 2C

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an optical fiber and an optical fiber. This application claims priority based on Japanese Application No. 2018-010607 filed on January 25, 2018, and incorporates all the descriptions described in the above Japanese application.

Background Art

[0002] Optical fibers are manufactured, for example, as long optical fibers extending for several tens of kilometers like undersea cables, according to requests from users. Such long optical fibers are usually formed by fusion-splicing a plurality of optical fibers. In this case, it is required that no peeling or cracking occurs at the interface between the protective resin for protecting the connection part and the original coating resin. As technologies that satisfy such requirements, for example, the technologies disclosed in Patent Documents 1 and 2 are known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] The method for manufacturing an optical fiber according to the present disclosure is a method for manufacturing an optical fiber in which the coating layers at the connecting ends of a pair of optical fibers are processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portions of the glass fibers is protected by a protective resin. The method includes a step of partially removing the coating layers of the pair of optical fibers to be connected to expose the glass fibers, a step of fusion-connecting the end faces of the pair of exposed glass fibers, and a step of recoating the removed portions of the coating layers and the protective resin covering the exposed portions of the glass fibers. The exposing step is a step of irradiating the coating layer with a laser beam to process the end of the coating layer into a tapered shape with a smaller diameter toward the exposed portion of the glass fiber to remove the coating layer, and a step of irradiating the optical fiber with the laser beam while disposing a mask for allowing only a predetermined region of the laser beam to pass between the optical fiber and the light source of the laser beam.

[0005] Further, an optical fiber according to the present disclosure is an optical fiber in which the coating layers at the connecting ends of a pair of optical fibers are processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portions of the glass fibers is protected by a protective resin, wherein the Young's modulus of the surface of the coating layer processed into the tapered shape is In the longitudinal direction of the optical fiber greater than the Young's modulus of the portion of the coating layer at the same radial position.

Brief Description of the Drawings

[0006]

Figure 1

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Figure 8

[0007] [Problems to be Solved by the Present Disclosure] The influence of side pressure during bobbin winding is a factor in the increase in optical fiber loss. To reduce the loss, it is necessary to use a two-layer coating layer for the optical fiber and a resin with a low Young's modulus (soft) for the primary layer on the center side. In a submarine cable using an optical fiber having such a two-layer coating layer, cracks may occur in the protective resin at the connection part.

[0008] FIG. 7 is a diagram showing the configuration of a connection portion of a conventional optical fiber having a two-layer coating layer. This connection portion is formed by connecting optical fibers 10 each provided with a glass fiber 11 and a two-layer coating layer composed of a primary layer 12 on the center side and a secondary layer 13 on the outer peripheral side around the glass fiber. The ends of the respective optical fibers 10 have the coating layer removed, and the exposed glass fibers 11 are fusion-connected at the fusion connection portion 14. The coating layer is removed in a tapered shape so as to have a smaller diameter toward the fusion connection portion 14, and a case is shown where only the secondary layer 13 is removed in a tapered shape and the primary layer 12 is not removed in a tapered shape. A protective resin 15 is molded and recoated so as to cover the entire fusion connection portion 14 and the removed portion of the coating layer.

[0009] As described above, in the connection portion of the conventional optical fiber, the coatings at the ends of the short fibers are removed and fusion-connected, and the connection portion is recoated with the protective resin 15. Here, if the Young's modulus of the primary layer 12 of the optical fiber 10 is low, the amount of deformation of the primary layer 12 at the coating-removed end becomes large when screening (strength test) is performed. For this reason, the stress becomes maximum at the boundary between the primary layer 12 and the secondary layer 13 and the contact point of the protective resin 15, and the protective resin 15 may be strained and a crack X may occur.

[0010] As a measure to prevent the occurrence of the crack X in the protective resin, in order to disperse the stress at the boundary between the primary layer 12 and the secondary layer 13 and the contact point of the protective resin 15, for example, as shown in FIG. 8, it is desirable to form the coating-removed end at the connection end of the primary layer 12 and the secondary layer 13 into a tapered shape T. That is, it is desirable that the boundary between the primary layer 12 and the secondary layer 13 after the coating layer is removed is formed into a tapered shape T at a predetermined angle. However, for example, it requires skill to cut the coating layer of a thin optical fiber with a razor to form a tapered shape as shown in FIG. 8. In particular, when the primary layer 12 is made of a soft resin, it has been difficult to cut the primary layer 12 well. Also, when cutting the coating layer with a rotary tool such as a router, the soft primary layer 12 adheres to the grindstone, and it has been difficult to cut it into a desired shape. Thus, when removing the coating layer using a conventional tool, there has been a problem that variations in shape occur due to differences in skill, and the quality of the manufactured cable is not constant. Furthermore, there has been a risk of damaging the glass fiber by the tool.

[0011] The present disclosure has been made in view of these circumstances, and an object thereof is to provide a method for manufacturing an optical fiber with stable quality and an optical fiber that prevent cracks from occurring in a protective resin that covers a removed portion of a coating layer and an exposed portion of a glass fiber without damaging the glass fiber.

[0012] [Effects of the Present Disclosure] According to the present disclosure, it is possible to prevent cracks from occurring in the protective resin that covers the removed portion of the coating layer and the exposed portion of the glass fiber, and it is possible to obtain an optical fiber with stable quality without damaging the glass fiber.

[0013] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described. (1) The method for manufacturing an optical fiber according to an embodiment of the present disclosure is a method for manufacturing an optical fiber in which the coating layer at the connecting ends of a pair of optical fibers is processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portion of the glass fiber is protected by a protective resin. The method includes a step of partially removing the coating layers of the pair of optical fibers to be connected to expose the glass fibers, a step of fusion-connecting the end faces of the pair of exposed glass fibers, and a step of recoating the removed portion of the coating layer and the protective resin covering the exposed portion of the glass fiber. The exposing step is a step of irradiating the coating layer with a laser beam to process the end of the coating layer into a tapered shape with a smaller diameter toward the exposed portion of the glass fiber to remove the coating layer, and a step of irradiating the optical fiber with the laser beam while disposing a mask for passing only a predetermined region of the laser beam between the optical fiber and the light source of the laser beam. According to this embodiment, since the coating layer of the optical fiber is removed by laser processing, the glass fiber is not damaged non-contactly, and the processing variation can be reduced. In addition, the overlapping portion between the removed coating layer and the protective resin can be increased. Furthermore, when the coating layer has a two-layer structure, it is possible to prevent stress from concentrating at the boundary between the primary layer on the center side and the secondary layer on the outer peripheral side. And a specific method for removing the coating layer of the optical fiber in a tapered shape can be provided.

[0014] (2) The method for manufacturing an optical fiber according to an embodiment of the present disclosure is such that the exposing step is a step of irradiating only the coating layer with the laser beam while avoiding the glass fiber of the optical fiber. According to this embodiment, while preventing the glass fiber from being irradiated with the laser beam, a specific method for removing the coating layer of the optical fiber in a tapered shape can be provided.

[0015] (3) The method for manufacturing an optical fiber according to an embodiment of the present disclosure is, in the manufacturing method of (1) or (2) above, a step of irradiating the optical fiber with the laser light in a state where a mask that allows only the laser light to pass through a predetermined region is disposed between the optical fiber and the light source of the laser light, and a step of rotating the optical fiber about the axis of the optical fiber to change the irradiation position of the laser light on the optical fiber, and repeating these steps. According to the present embodiment, a specific method for removing the coating layer of the optical fiber in a tapered shape can be provided.

[0016] (4) An optical fiber according to an embodiment of the present disclosure is an optical fiber in which the coating layers at the ends on the connecting side of a pair of optical fibers are processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portion of the glass fiber is protected by a protective resin, and the Young's modulus of the surface of the coating layer processed into the tapered shape is In the longitudinal direction of the optical fiber greater than the Young's modulus of the portion at the same radial position of the coating layer. According to the present embodiment, it is possible to prevent the occurrence of cracks in the protective resin that covers the removed portion of the coating layer and the exposed portion of the glass fiber.

[0017] (5) The optical fiber according to an embodiment of the present disclosure is an optical fiber in which the tapered shape is a regular pyramid shape symmetric with respect to the axis of the optical fiber.

[0018] [Details of Embodiments of the Present Disclosure] A method for manufacturing an optical fiber and specific examples of the optical fiber according to the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited to the following examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, as long as combinations of a plurality of embodiments are possible, the present invention includes combinations of any embodiments. In the following description, components denoted by the same reference numerals in different drawings are assumed to be the same, and the description thereof may be omitted.

[0019] FIG. 1 is a diagram for explaining the configuration of a connection portion of an optical fiber manufactured according to the present disclosure. The optical fiber manufactured according to the present disclosure is formed by fusion-connecting a plurality of short optical fibers 10. In the fusion connection of the optical fibers, the coating layer of the optical fiber 10 at the end portions of a pair of optical fibers 10 to be connected to each other is removed, and the glass fiber 11 is exposed. The end faces of the glass fibers 11 exposed by removing the coating layer are abutted against each other, and the butted end faces are connected as a fusion connection portion 14 by arc discharge or the like.

[0020] Since the fusion connection portion 14 and the bare glass fiber 11 in its vicinity are easily damaged and are in a mechanically weak state, they are recoated with a protective resin 15. As the protective resin 15, an ultraviolet curable resin of the same type as the coating layer is used. The coating of the protective resin 15 can be formed by injecting the resin using a predetermined molding die. In the present embodiment, the coating layer of the optical fiber 10 has a double structure of a primary layer 12 on the center side and a secondary layer 13 on the outer peripheral side. In the primary layer 12 on the center side, a resin having a low Young's modulus of 0.5 MPa or less is used in order to make the optical fiber 10 less susceptible to the influence of side pressure during bobbin winding or cabling, which is a factor increasing the loss of the optical fiber 10. In the secondary layer 13 on the outer peripheral side, a resin having a higher Young's modulus than that of the primary layer 12 is used. Further, the magnitude of the Young's modulus of the protective resin 15 is larger than that of the resin of the primary layer 12 and smaller than that of the resin of the secondary layer 13.

[0021] In the present embodiment, when coating the coating layer at the end portion of the optical fiber 10, it has a tapered shape T in which the coating diameter is reduced toward the end portion side. Then, the protective resin 15 is molded so as to cover the portion of the coating layer having the tapered shape. With this configuration, the end face at the time of coating the coating layer is covered and does not become exposed. Further, since the coating of the coating layer has the tapered shape T, the overlapping portion 16 covered by the protective resin 15 at the time of coating can be thickened, the adhesive area at this portion can be increased, and the adhesive force with the protective resin 15 can be enhanced. Further, the stress at the boundary between the primary layer 12 and the secondary layer 13 and the contact point of the protective resin 15 can be dispersed.

[0022] The manufacturing method of the optical fiber shown in FIG. 1 includes a removing step of partially removing the coating layers of two optical fibers 10 so that the coating edges become tapered to expose the glass fibers, a connecting step of fusion-connecting the end faces of the exposed glass fibers 11, and a recoating step of recoating the removed portions of the coating layers and the exposed portions of the glass fibers 11 with a protective resin 15. Hereinafter, the removing step of the coating layer of the optical fiber will be described.

[0023] (Example 1 of the removing step) FIGS. 2A to 2C are diagrams for explaining an example of the removing step of the coating layer of the optical fiber. First, as shown in FIG. 2A, the coating layer at the end of the optical fiber 10 is cut at the position C-C, and the coating layer on the end side is pulled out and removed to expose the glass fiber 11 on the end side. The exposed glass fiber 11 is cut so that the distance from the coating layer becomes a predetermined length to form an end face for fusion connection. Note that the formation of the end face for fusion connection may be performed after the formation of the tapered surface of the coating layer described later.

[0024] Next, as shown in FIG. 2B, triangular laser light B is irradiated onto the coating layer of the optical fiber 10 to process the end of the coating layer into a tapered shape. Specifically, triangular laser light B with an apex angle α of approximately 30° and a height of approximately 500 μm is scanned radially from the upper surface side of the optical fiber 10. Here, as the laser light, it is preferable to use a laser with a wavelength of 250 nm or less. When the energy density of the laser light exceeds 1000 mJ / cm 2 Hereinafter, it is preferable to use a laser with a wavelength of 250 nm or less. When the energy density of the laser light exceeds 1000 mJ / cm 2 When the glass fiber is irradiated with laser light exceeding this value, the glass fiber may be damaged and the optical characteristics and strength may be affected. Further, when the glass fiber is irradiated with ultraviolet light having a wavelength shorter than 170 nm, the ultraviolet light is absorbed by the glass fiber and defects are generated, affecting the optical characteristics and strength. Therefore, it is preferable to use laser light with a wavelength of 170 nm or more. The triangular shape can be obtained by disposing a mask having a triangular opening between the light source of the laser light and the optical fiber. Note that the diameter of the optical fiber 10 is approximately 250 μm.

[0025] As shown in FIG. 2B, as the laser light scanning step, with the base of the triangular laser light substantially coinciding with the end of the coating layer of the optical fiber 10 and the apex positioned on the side opposite to the end face of the optical fiber, the laser light is scanned a predetermined number of times in the radial direction indicated by the arrow S from the upper surface side of the optical fiber 10 to sublime the coating layer. On the laser light irradiation surface of the optical fiber 10, since the irradiation amount of the laser light is large at the triangular base portion, a large amount of resin removed by sublimation is present, and since the irradiation amount of the laser light is small at the apex portion, the amount of resin removed by sublimation is small. Thereby, the coating layer on the upper surface side of the optical fiber 10 is removed in a substantially tapered shape.

[0026] Next, as shown in FIG. 2C, as the position changing step, the optical fiber 10 is rotated by a predetermined angle as indicated by the arrow R to change the position of the laser light irradiation surface of the optical fiber 10. Then, again, the triangular laser light B is scanned from the upper surface side of the optical fiber 10 to remove the coating layer on the upper surface side of the optical fiber 10 in a tapered shape. By repeating the laser light scanning step and the position changing step a predetermined number of times, the end of the coating layer of the optical fiber 10 can be removed so as to have a polygonal pyramid shape. And by adjusting the rotation angle of the optical fiber 10, and the energy density and the number of scans of the laser light, the end of the coating layer can be made into a regular polygonal pyramid shape symmetric with respect to the axis of the optical fiber.

[0027] As a specific laser light, an excimer laser with a short wavelength using a mixed gas of KrF with a wavelength of 248 nm or ArF with a wavelength of 193 nm can be used below. When using a laser light with a long wavelength, since the resin of the coating layer melts or burns, the coating layer cannot be removed in a good shape. Also, 1000 mJ / cm 2 Hereinafter, an excimer laser with a short wavelength using a mixed gas of KrF with a wavelength of 248 nm or ArF with a wavelength of 193 nm can be used. When using a laser light with a long wavelength, since the resin of the coating layer melts or burns, the coating layer cannot be removed in a good shape. Also, 1000 mJ / cm 2When using a larger laser beam, when the laser beam irradiates the glass fiber, the optical damage to the glass fiber increases. Further, by performing taper processing by laser irradiation, in the tapered surface portion, the curing of the resin progresses more after post-curing than before irradiation, and the Young's modulus of the surface of the coating layer processed into a tapered shape is larger than that of the portion at the same radial position of the coating layer away from the surface.

[0028] (Example 2 of the removal process) Figures 3A to 3C are diagrams for explaining another example of the removal process of the coating layer of the optical fiber. In the present embodiment, as shown in Figure 3A, the coating layer at the end of the optical fiber 10 is cut at the position C-C, and the coating layer on the end side is pulled out and removed, thereby exposing the glass fiber 11 on the end side. This is the same as the point explained in Figure 2A.

[0029] Next, as shown in Figure 3B, for example, when viewed from the upper surface side, the rectangular laser beam B or the triangular laser beam and the optical fiber 10 are positioned so that the laser beam B obliquely hits only the coating layer at the end of the optical fiber 10, avoiding the glass fiber. Then, as shown in Figure 3C, the laser beam B is irradiated while rotating the optical fiber 10. As a result, the resin of the coating layer in the portion irradiated with the laser beam B is sublimated and removed, and the shape of the end of the coating layer becomes a conical taper shape. Here, regarding the type and energy density of the laser beam, the same laser beam as in Example 1 of the removal process described in Figures 2B and 2C can be used.

[0030] (Example 3 of the removal process) Figures 4A to 4C are diagrams for explaining still another example of the removal process of the coating layer of the optical fiber. In the present embodiment, as shown in Figure 4A, the coating layer at the end of the optical fiber 10 is cut at the position C-C, and the coating layer on the end side is pulled out and removed, thereby exposing the glass fiber 11 on the end side. This is the same as the point explained in Figure 2A.

[0031] Next, as shown in FIG. 4B, while rotating the optical fiber 10, the bottom side of the triangular laser beam B is made to substantially coincide with the end of the coating layer of the optical fiber 10, and with the apex positioned on the side opposite to the end face of the optical fiber, the laser beam B is irradiated from the upper surface side. The shape, type, and energy density of the light beam are the same as those of the laser beam B in Example 1 of the removal process shown in FIGS. 2B and 2C. On the laser beam irradiation surface of the optical fiber 10, since the irradiation amount of the laser beam is large at the triangular bottom side portion, a large amount of resin removed by sublimation is present, and since the irradiation amount of the laser beam is small at the apex portion, the amount of resin removed by sublimation is reduced. While rotating the optical fiber 10, the laser beam B is irradiated, so that the end of the coating layer of the optical fiber 10 is removed in a substantially conical taper shape as shown in FIG. 4C.

[0032] (Example 4 of the removal process) FIGS. 5A to 5C are diagrams for explaining still another example of the removal process of the coating layer of the optical fiber. In the present embodiment, as shown in FIG. 5A, the coating layer at the end of the optical fiber 10 is cut at the location C-C, and the coating layer on the end side is pulled out and removed, thereby exposing the glass fiber 11 on the end side. This is the same as the point explained in FIG. 2A.

[0033] This embodiment is similar to Example 2 of the removal process explained in FIGS. 3A to 3C. The rectangular laser beam B is irradiated onto the optical fiber 10 while avoiding the glass fiber so that the laser beam B hits obliquely only the coating layer at the end of the optical fiber 10, for example, as seen from the upper surface side. That is, the mask shape of the laser beam is set so that the shape of the laser beam B at the portion hitting the coating layer of the optical fiber 10 becomes the uneven shape B1 as shown in FIG. 5B. As a result, due to the rotation of the optical fiber 10, as shown in FIG. 5C, the coating layer processed into the taper shape T' at the end of the optical fiber 10 has unevenness extending on the circumference formed thereon. Therefore, when the protective resin is recoated after the glass fiber 11 is fusion-connected, the adhesion area between the coating layer and the protective resin increases, so that the strength of the fusion-connected optical fiber can be increased.

[0034] (Example 5 of the removal process) FIG. 6 is a diagram for explaining still another example of the process of removing the coating layer of the optical fiber. In the present embodiment, as in Examples 1 to 4 of the removing process, the coating layer at the end of the optical fiber 10 is cut at the C-C position, and the coating layer on the end side is pulled out and removed, so that there is no need for a process of exposing the glass fiber 11 on the end side. In the present embodiment, the coating layer near the end of the optical fiber 10 entirely covered with the coating layer is partially removed by any one of the methods of Examples 1 to 4 of the above removing process. As a result, the coating layer at the C-C position shown in FIG. 6 is removed, and at this position, the glass fiber 11 is exposed. Further, a tapered shape T is formed in the coating layer at the position A2 on the opposite end side from the C-C position of the optical fiber 10.

[0035] Then, by pulling out the coating layer at the position A1 remaining on the end side of the optical fiber 10 from the position A2 on the opposite end side, an exposed portion of the glass fiber 11 to be fusion-connected can be obtained. In this way, since it is not necessary to form an exposed portion of the glass fiber in advance on one end side of the optical fiber, the process can be simplified. Further, in the process of removing the coating layer, since there is no exposed portion of the glass fiber 11 except for the portion of the coating layer to be removed, the handling of the optical fiber 10 can be facilitated, and the glass fiber 11 can be prevented from being irradiated with laser light.

[0036] As described above, the embodiments of the present disclosure have been described. However, in the method for manufacturing an optical fiber of the present disclosure, the coating layer of the optical fiber 10 is not limited to having a two-layer structure, and the present disclosure is also applicable to those composed of one layer or three or more resin layers.

Description of Reference Numerals

[0037] 10... optical fiber, 11... glass fiber, 12... primary layer, 13... secondary layer, 14... fusion connection portion, 15... protective resin, 16... overlapping portion.

Claims

1. A method for manufacturing an optical fiber, wherein the coating layers at the connecting ends of a pair of optical fibers are processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portions of the glass fibers is protected by a protective resin, comprising a step of partially removing the coating layers of the pair of optical fibers to be connected to expose the glass fibers, a step of fusion-connecting the end faces of the pair of exposed glass fibers, and a step of recoating the protective resin covering the removed portion of the coating layer and the exposed portion of the glass fiber, wherein the exposing step is a step of irradiating the coating layer with a laser beam to process the end of the coating layer into a tapered shape with a smaller diameter toward the exposed portion of the glass fiber to remove the coating layer, and a step of irradiating the optical fiber with the laser beam while disposing a mask for allowing the laser beam to pass through only a predetermined region between the optical fiber and the light source of the laser beam.

2. The method for manufacturing an optical fiber according to claim 1, wherein the exposing step is a step of irradiating the laser beam only on the coating layer while avoiding the glass fiber of the optical fiber.

3. The method for manufacturing an optical fiber according to claim 1 or claim 2, wherein the exposing step is a step of irradiating the optical fiber with the laser beam while disposing a mask for allowing the laser beam to pass through only a predetermined region between the optical fiber and the light source of the laser beam, and a step of repeatedly rotating the optical fiber about the axis of the optical fiber to change the irradiation position of the laser beam on the optical fiber.

4. An optical fiber, wherein the coating layers at the connecting ends of a pair of optical fibers are processed into a tapered shape, the end faces of the exposed glass fibers are fusion-connected, and the periphery of the exposed portions of the glass fibers is protected by a protective resin, An optical fiber in which the Young's modulus of the surface of the coating layer processed into the tapered shape is greater than the Young's modulus of the portion at the same radial position of the coating layer in the longitudinal direction of the optical fiber.

5. The optical fiber according to claim 4, wherein the tapered shape is a regular pyramid shape symmetric with respect to the axis of the optical fiber.

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