Optical fiber, tape fiber, and method for manufacturing optical fiber

Abstract

To provide an optical fiber that has directionality relative to a rotation direction and allows the optical fiber to be aligned with high precision.SOLUTION: An optical fiber includes: a fiber including at least one core and a clad covering the core, and extending in a longitudinal direction; a primary resin layer covering an outer periphery of the fiber; and a secondary resin layer covering an outer periphery of the primary resin layer. The fiber has directionality relative to a rotation direction with the longitudinal direction as an axis. The primary resin layer includes, in the longitudinal direction, a plurality of first regions having a first Young's modulus, and a plurality of second regions having a second Young's modulus higher than the first Young's modulus.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to optical fibers, ribbon fibers, and methods for manufacturing optical fibers.

Background Art

[0002] Patent Document 1 discloses various multi-core fibers having a predetermined directivity with respect to the rotational direction. Here, "having directivity" means that the cross-sectional structure (for example, the positions of the cores of the multi-core fiber) changes during one rotation.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The optical fiber described in Patent Document 1 is configured as a fiber having directivity with respect to the rotational direction. In such an optical fiber, during optical connection, centering in the rotational direction is required to align each core with the counterpart core. Also, in the winding process of the optical fiber, adjustment of the rotational direction is required when winding while aligning the rotational directions. Alternatively, when manufacturing a tape fiber in which a plurality of optical fibers are arranged, adjustment of the rotational direction is required to align the arrangements of the cores of the plurality of optical fibers. On the other hand, in an optical fiber, a primary resin layer or a secondary resin layer is provided to further cover the outer periphery of the cladding in order to improve the side pressure resistance characteristics. The primary resin layer is a coating layer that directly covers the cladding of the optical fiber and is made of a material that is softer (has a lower Young's modulus) than the outer secondary resin layer (see, for example, Patent Document 2). When these coating layers are provided on a multi-core fiber, centering in the rotational direction is performed while holding the coating layer outside the cladding. However, since the primary resin layer is soft and has a weak holding force, the primary resin layer may be twisted with respect to the cladding, and it may be difficult to accurately perform centering in the rotational direction.

[0005] An object of the present disclosure is to provide an optical fiber capable of accurately performing centering of an optical fiber having directivity with respect to the rotational direction, a tape fiber including a plurality of such fibers, and a method for manufacturing the optical fiber.

Means for Solving the Problems

[0006] An optical fiber according to an embodiment of the present disclosure includes at least one core and a cladding covering the core, a fiber extending in the longitudinal direction, a primary resin layer covering the outer periphery of the fiber, and a secondary resin layer covering the outer periphery of the primary resin layer. The fiber is a fiber having directivity with respect to the rotational direction about the longitudinal direction as an axis. The primary resin layer includes a plurality of first regions having a first Young's modulus and a plurality of second regions having a second Young's modulus higher than the first Young's modulus in the longitudinal direction.

Effects of the Invention

[0007] According to the present disclosure, the alignment of an optical fiber having directionality with respect to the rotation direction can be accurately performed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. [1] An optical fiber according to an embodiment includes at least one core and a cladding that covers the core, a fiber extending in the longitudinal direction, a primary resin layer that covers the outer periphery of the fiber, and a secondary resin layer that covers the outer periphery of the primary resin layer. The fiber is a fiber having directionality with respect to the rotation direction about the longitudinal direction as an axis. The primary resin layer includes a plurality of first regions having a first Young's modulus and a plurality of second regions having a second Young's modulus higher than the first Young's modulus in the longitudinal direction.

[0010] In this optical fiber, a second region with an increased Young's modulus is provided in the primary resin layer that coats the outer periphery of the fiber. In this case, in the second region with the increased Young's modulus, the primary resin layer becomes hard, and the holding force of the primary resin layer with respect to the fiber including the cladding is improved. Therefore, when performing rotational centering of the optical fiber by holding the portion corresponding to the second region with the increased Young's modulus, centering of the optical fiber having directionality with respect to the rotational direction can be accurately performed. Also, in the winding process of the optical fiber and the tape manufacturing process, when the secondary resin layer is rotated to adjust the rotational direction, since the holding force of the entire optical fiber is improved by the plurality of second regions, the adjustment can be accurately performed. Furthermore, in a tape fiber manufactured using such an optical fiber having such a configuration, since the rotational direction is maintained in the vicinity of the second region, multi-core batch connection that does not require rotational centering can be performed. Note that the "optical fiber having directionality with respect to the rotational direction" as used herein includes at least a multi-core fiber (also referred to as "MCF") in which a plurality of cores are arranged in one cladding, but is not limited thereto, and also includes a polarization-maintaining fiber (also referred to as "PMF"), a hole-assisted fiber (also referred to as "HAF"), and a hole-core fiber (also referred to as "HCF") that require centering in the rotational direction.

[0011] [2] In the optical fiber of [1] above, the first Young's modulus may be 0.1 MPa or more and 5 MPa or less at 23°C, and the second Young's modulus may be 10 MPa or more and 500 MPa or less at 23°C. In this case, in the first region having the first Young's modulus, sufficient lateral pressure resistance characteristics can be imparted to the optical fiber, and in the second region having the second Young's modulus, the primary resin layer can be made harder and the holding force can be improved more reliably. Therefore, according to this optical fiber, rotational centering of the optical fiber can be performed more accurately.

[0012] [3] In the optical fiber of [1] or [2] above, the plurality of second regions may be provided periodically along the longitudinal direction. In this case, since the portions (second regions) where the twist of the primary resin layer is less likely to occur with respect to the fiber (clad) are formed periodically along the longitudinal direction, it becomes difficult for the core and the clad in the entire optical fiber to twist. Further, since operations such as optical connection are to be carried out in the second regions, the periodic provision of the second regions makes it possible to reduce the surplus length portion (the portion that does not correspond to the second region) when the optical fiber is cut at a predetermined location to perform operations such as optical connection.

[0013] [4] In any of the optical fibers of [1] to [3] above, the width along the longitudinal direction of the plurality of second regions may be 0.1 mm or more and 5 mm or less, and the pitch between the plurality of second regions may be 20 mm or more and 300 mm or less. By the width of each second region being 0.1 mm or more, the holding force of the primary resin layer with respect to the fiber (clad) can be surely ensured. On the other hand, by suppressing the width of each second region to 5 mm or less, it is possible to prevent the lateral pressure resistance characteristics due to the primary resin layer from being reduced in the entire optical fiber. Further, by the pitch between the second regions being 20 mm or more, when a temperature change occurs in the optical fiber and it expands and contracts, the difference in linear expansion between the fiber made of glass and the coating made of resin can be sufficiently absorbed in the first region with a low Young's modulus. Therefore, an increase in transmission loss due to microbending can be suppressed. On the other hand, by the pitch between the second regions being 300 mm or less, when performing an optical connection such as fusion splicing or connector connection and cutting and rotationally aligning the optical fiber, it becomes easier for an operator to cut the fiber with reference to the second region, and the working efficiency can be improved. Also, the length of the fiber can be finely determined in pitch units, the difference with respect to the required length can be made small, and the surplus length portion can be reduced. Here, the pitch between the second regions means the shortest distance between adjacent second regions in the longitudinal direction.

[0014] [5] In any of the optical fibers of [1] to [4] above, the primary material constituting the primary resin layer may include an acrylic resin containing a radical polymerization initiator. In this case, a function as a coating for maintaining good transmission characteristics of the optical fiber can be obtained, and even when manufacturing at a high drawing speed, for example, 2000 m / min or more, the second region can be cured quickly and the Young's modulus can be increased.

[0015] [6] In the optical fiber of [5] above, the radical polymerization initiator may include a photo-polymerization initiator and a thermal polymerization initiator. In this case, the overall curing of the primary resin layer can be performed by heat, and the formation of the second region where the Young's modulus is increased in the primary resin layer can be performed by photo-curing, and the two processes (curing mechanisms) can be separated. Thereby, even if there are changes over time in the optical fiber, it is possible to suppress the further curing of the first region with a low Young's modulus, and maintain the initial Young's modulus over a long period. Therefore, according to this optical fiber, even when a second region for accurately performing rotational alignment is provided, it is possible to maintain good side pressure resistance characteristics of the optical fiber.

[0016] [7] In any of the optical fibers of [1] to [6] above, marking may be provided in a region corresponding to a plurality of second regions on the outer sheath of the optical fiber. In this case, when performing rotational alignment of the optical fiber, the operator can surely recognize the portion to be gripped. Therefore, the rotational alignment of the optical fiber can be performed more surely.

[0017] [8]The fiber tape according to one embodiment includes a plurality of optical fibers, each of which is one of the optical fibers [1] to [7] above, and the positions of the plurality of second regions in the longitudinal direction in the plurality of optical fibers are aligned. According to such a fiber tape, when optically connecting to another fiber tape, it is possible to easily perform rotational alignment. Further, if the rotational directions of the respective optical fibers are aligned during the manufacture of the tape fiber, by performing optical connection at the position of the second region or a position in the vicinity thereof, it is possible to perform multi-core batch connection with the rotational directions aligned.

[0018] [9]A method for manufacturing an optical fiber according to one embodiment includes a step of drawing a fiber including at least one core and a cladding covering the core, a step of forming a primary resin layer covering the outer periphery of the fiber, and a step of forming a secondary resin layer covering the outer periphery of the primary resin layer. In the step of forming the primary resin layer, at least one of photocuring and thermocuring is partially performed on the primary resin layer in the longitudinal direction to form portions having different degrees of curing in the longitudinal direction. By such a method, it is possible to produce an optical fiber capable of accurately performing rotational alignment by a simple means.

[0019]

[10] In the method for manufacturing an optical fiber of [9] above, in the step of forming the primary resin layer, ultraviolet light may be periodically irradiated to partially cure the primary resin layer. In this case, it is possible to simply execute periodically providing regions having a high Young's modulus.

[0020] [Details of Embodiments of the Present Disclosure] Specific examples of the optical fiber, tape fiber, and method for manufacturing an optical fiber according to embodiments of the present disclosure will be described below with reference to the drawings. In the following description, the same reference numerals will be used for the same elements or elements having the same function, and redundant descriptions will be omitted. It should be noted that the present invention is not limited to these examples, and is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0021] Referring to FIG. 1, an example of an optical fiber according to an embodiment will be described. FIG. 1 is a cross-sectional view showing an optical fiber according to an embodiment. As shown in FIG. 1, the optical fiber 1 is, for example, a multi-core fiber, and includes a glass fiber 4 (fiber) including a plurality of cores 2 and a cladding 3 covering the plurality of cores 2, a primary resin layer 5 covering the outer periphery of the glass fiber 4, and a secondary resin layer 6 covering the outer periphery of the primary resin layer 5. In the optical fiber 1, the core arrangement is such that the position of the core changes by rotating in any direction, and the fiber configuration has directivity with respect to the rotation direction. Note that the optical fiber 1 is not limited to an MCF, and may be a PMF, HAF, or HCF that requires alignment in the rotation direction.

[0022] The core 2 is composed of pure silica (SiO2) glass, or silica glass containing germanium dioxide or fluorine element. The cladding 3 has a refractive index lower than that of the core 2. The cladding 3 is composed of, for example, pure silica glass, or silica glass to which a fluorine element is added. Note that a trench having a refractive index lower than that of the cladding 3 may be provided between each core 2 and the cladding 3. The glass fiber 4 is composed of the plurality of cores 2 and the cladding 3.

[0023] The primary resin layer 5 covers the outer periphery of the cladding 3 of the glass fiber 4. More specifically, the primary resin layer 5 is in contact with the outer peripheral surface of the cladding 3 and covers the entire cladding 3. The secondary resin layer 6 further covers the outer periphery of the primary resin layer 5. More specifically, the secondary resin layer 6 is in contact with the outer peripheral surface of the primary resin layer 5 and covers the entire primary resin layer 5.

[0024] The primary material that constitutes the primary resin layer 5 contains an acrylic resin containing a radical polymerization initiator. This primary material can be formed from an ultraviolet curable resin composition containing a photopolymerizable compound, a photopolymerization initiator, and a silane coupling agent. As the photopolymerizable compound, for example, urethane (meth)acrylate or epoxy (meth)acrylate can be used. Further, the primary material further contains a thermopolymerizable compound and a thermopolymerization initiator. As the thermopolymerizable compound, for example, urethane (meth)acrylate or epoxy (meth)acrylate can be used. As the thermopolymerization initiator, for example, azo compounds such as 2,2'-azobisbutyronitrile (AIBN) or peroxides such as benzoyl peroxide (BPO) can be used. The primary resin layer 5 made of the above-described materials is formed to have a predetermined hardness by curing with light (for example, ultraviolet light) or heat. Note that the primary material that constitutes the primary resin layer 5 according to the present embodiment contains different types of polymerization initiators.

[0025] Such a primary resin layer 5 has a lower elastic modulus (Young's modulus) than the secondary resin layer 6 and is formed softer than the secondary resin layer 6. For example, the Young's modulus of the primary resin layer 5 at 23°C is 0.1 MPa or more and 5 MPa or less. Thereby, side pressure resistance characteristics are imparted to the optical fiber 1, and it is suppressed that the transmission loss in the optical fiber 1 increases even when side pressure is applied. Note that the primary resin layer 5 according to the present embodiment is formed such that the Young's modulus is different in the longitudinal direction of the optical fiber 1. Details will be described later.

[0026] The secondary material constituting the secondary resin layer 6 can be formed from a resin composition containing urethane (meth) acrylate, monomer, and a photopolymerization initiator. By curing such a material, the secondary resin layer 6 is formed. The secondary resin layer 6 has a higher elasticity (Young's modulus) than the primary resin layer 7, and the secondary resin layer 6 is harder than the primary resin layer 5. For example, the Young's modulus of the secondary resin layer 6 at 23°C is 1200 MPa or more and 2800 MPa or less. The thickness of each of the primary resin layer 5 and the secondary resin layer 6 is, for example, 5 μm or more and 50 μm or less.

[0027] Next, with reference to FIGS. 2 and 3, in the optical fiber 1 according to the present embodiment, an aspect in which the Young's modulus of the primary resin layer 5 varies in the longitudinal direction will be described. FIG. 2 is a plan view showing the optical fiber 1 and the primary resin layer 5 shown in FIG. 1 along the longitudinal direction. The (a) part of FIG. 3 is a cross-sectional view showing a region (first region) where the Young's modulus of the primary resin layer 5 is low, and the (b) part of FIG. 3 is a cross-sectional view showing a region (second region) where the Young's modulus of the primary resin layer is high.

[0028] As shown in FIG. 2, the primary resin layer 5 is configured to include a plurality of first regions 5a (see (a) of FIG. 3) having a first Young's modulus and a plurality of second regions 5b (see (b) of FIG. 3) having a second Young's modulus higher than the first Young's modulus of the first regions 5a in the longitudinal direction. The second region 5b is, for example, a portion where the Young's modulus is increased compared to the first region 5a by further curing the region corresponding to the second region 5b with heat or light after the entire primary resin layer 5 is formed to have the first Young's modulus. The first region 5a is formed, for example, so as to extend over the entire circumferential direction as shown in the (b) part of FIG. 3. Due to such a high Young's modulus portion (second region 5b), the primary resin layer 5 covering the cladding 3 becomes partially hard, improving the holding force and enabling the operator to perform rotational centering with high accuracy.

[0029] In the primary resin layer 5, the first Young's modulus of the first region 5a is, for example, 0.1 MPa or more and 5 MPa or less at 23°C. On the other hand, the second Young's modulus of the second region 5b is, for example, 10 MPa or more and 500 MPa or less at 23°C. That is, the second Young's modulus of the second region 5b is significantly higher than the first Young's modulus of the first region 5a. However, the Young's modulus of both the first region 5a and the second region 5b of the primary resin layer 5 is lower than the Young's modulus of the secondary resin layer 6. Further, in the primary resin layer 5, as shown in FIG. 2, each of the plurality of second regions 5b is provided periodically along the longitudinal direction. However, the plurality of second regions 5b may be provided irregularly instead of periodically.

[0030] The width W along the longitudinal direction of the second region 5b may be, for example, 0.1 mm or more and 5 mm or less. More preferably, the width W may be 0.5 mm or more and 2 mm or less. Also, the pitch P between the second regions 5b may be 20 mm or more and 300 mm or less. More preferably, the pitch P may be 50 mm or more and 150 mm or less. By setting the pitch P of the second region 5b to 20 mm or more, the difference in linear expansion between the glass (core 2 and cladding 3) due to the expansion and contraction of the coating (primary resin layer 5 and secondary resin layer 6) during temperature change is absorbed by the gentle bend in the low Young's modulus portion (first region 5a) between the pitches. Therefore, an increase in transmission loss due to microbending can be reduced. On the other hand, by setting the pitch P of the second region 5b to 300 mm or less, when performing an optical connection such as a fusion connection or a connector connection at a location of the second region 5b where the fiber rotation is aligned, the length of the optical fiber 1 can be finely determined in pitch units, and the difference from the necessary and sufficient length is small, so that the excess length can be reduced. In addition, markings may be provided in the regions corresponding to each of the second regions 5b in the outer coating of the optical fiber 1 (for example, the secondary resin layer 6 or the colored ink layer). In this case, since it becomes easier for the operator to discriminate the second region 5b, various operations become easier to perform.

[0031] In order to manufacture the optical fiber 1 such that the Young's modulus of the primary resin layer 5 varies in the longitudinal direction as described above, first, a glass fiber 4 including a core 2 and a clad 3 covering the core 2 is drawn from a base material. Then, a primary resin layer 5 is formed so as to cover the outer periphery of the drawn glass fiber 4, and a secondary resin layer 6 is formed so as to cover the outer periphery of the primary resin layer 5. The primary resin layer 5 and the secondary resin layer 6 may be formed in sequence or simultaneously. When forming the primary resin layer, at least one of photocuring and thermosetting is partially performed on the primary resin layer 5 to form the second region 5b described above. More preferably, ultraviolet light (LED or laser) or infrared light (laser or flash lamp) is periodically irradiated to further partially cure the primary resin layer 5 so that a plurality of second regions 5b are provided in the first region 5a. Such irradiation may be pulsed irradiation, and light in the range from visible light with a long wavelength having a low material absorption coefficient to infrared light may be used. In this case, damage to the coating material can be reduced.

[0032] Also, by not irradiating heat or light only to the region corresponding to the second region 5b, the Young's modulus of the second region 5b may be made higher than that of the first region 5a. Further, in parallel with the light irradiation, marking may be performed using inkjet so that the second region 2b can be discriminated from the outside. Conversely, when irradiated with a laser, the ink portion may be removed with the laser to perform marking so that the second region 2b can be discriminated. Then, through this removal portion (as a mask), ultraviolet light may be irradiated to the primary resin layer 5 to perform the above-described curing to form the second region 5b having a high Young's modulus. Alternatively, the wavelength and irradiation conditions of the laser and the material of the coating layer may be selected, and the coating layer may be colored by the laser irradiated for curing to perform marking. In this case, since the laser irradiation location and the marking location are the same, the position can be discriminated more accurately.

[0033] As described above, in the optical fiber 1 according to the present embodiment, the primary resin layer 5 that coats the outer periphery of the cladding 3 of the glass fiber 4 is provided with a second region 5b having a higher Young's modulus than the first region 5a. In the second region 5b where the Young's modulus is increased in this way, the primary resin layer 5 becomes hard, and the holding force of the primary resin layer 5 with respect to the glass fiber 4 including the cladding 3 is improved. Therefore, when the optical fiber 1 is rotationally centered by holding the portion corresponding to the second region 5b with an increased Young's modulus, the centering of the optical fiber 1 having directionality with respect to the rotation direction can be accurately performed.

[0034] Next, the configuration of a tape fiber provided with a plurality of the above-described optical fibers 1 will be described with reference to FIGS. 4 and 5. FIG. 4 is a plan view showing a tape fiber in which the optical fibers shown in FIG. 1 are bundled in a tape shape. FIG. 5 is a view showing a cross section of the tape fiber shown in FIG. 4. As shown in FIGS. 4 and 5, the tape fiber 10 has a plurality of optical fibers 1 (four optical fibers 1 in the example of the figure). The plurality of optical fibers 1 are connected to each other by a coating resin 11 and are formed in a tape shape. In the tape fiber 10, the second regions 5b in which the Young's modulus is increased in each of the above-described primary resin layers 5 are configured to be aligned with each other in the longitudinal direction.

[0035] In the tape fiber 10, as in the above-described optical fiber 1, since the primary resin layer 5 is hardened and the holding force is improved in each second region 5b, when optically connecting to another fiber tape, rotational centering can be easily and accurately performed. Such a tape fiber 10 may be formed by bundling optical fibers 1 in which the second region 5b with a high Young's modulus is previously formed, or by bundling optical fibers 1 before the second region 5b is formed into a tape shape, and then forming the second regions 5b together (for example, by laser irradiation and curing together). In the case of the latter method, the positions of the second regions 5b in the longitudinal direction in each optical fiber 1 can be easily aligned.

[0036] As described above, the optical fiber 1, the tape fiber 10, and the manufacturing methods thereof according to the embodiments of the present disclosure have been described in detail. However, the present invention is not limited to the above embodiments and can be applied to various embodiments and modifications. For example, in the above description, in the second region 5b of the optical fiber 1, as shown in the (b) part of FIG. 3, the overall Young's modulus in the circumferential direction was increased, but it is not limited to this. That is, as shown in FIG. 6, in the second region 5b, the optical fiber is irradiated with the laser light L along the first direction (from above to below) and the second direction (from left to right), and a part of the primary resin layer 5 in the circumferential direction is cured to increase the Young's modulus higher than that of the first region 5a. In such an optical fiber 1A, the second region 5b is formed by being divided into a plurality of parts 5c (four parts in the example of FIG. 6) in the circumferential direction. Even with such a configuration, it is possible to improve the holding force of the cladding 3 by the primary resin layer 5 and perform rotational alignment with high accuracy.

Explanation of Signs

[0037] 1, 1A... Optical fiber 2... Core 3... Cladding 4... Glass fiber 5... Primary resin layer 5a... First region 5b... Second region 5c... Part 6... Secondary resin layer 10... Tape fiber 11... Coating resin L... Laser light P... Pitch W... Width

Claims

1. A fiber optic cable comprising at least one core and a cladding covering the core, the fiber extending longitudinally, a primary resin layer covering the outer periphery of the fiber, and a secondary resin layer covering the outer periphery of the primary resin layer, wherein the fiber is a fiber having a directionality with respect to the rotational direction about the longitudinal axis, and the primary resin layer includes, in the longitudinal direction, a plurality of first regions having a first Young's modulus and a plurality of second regions having a second Young's modulus higher than the first Young's modulus. Optical fiber.

2. The first Young's modulus is 0.1 MPa or more and 5 MPa or less at 23°C, and the second Young's modulus is 10 MPa or more and 500 MPa or less at 23°C. The optical fiber according to Claim 1.

3. The plurality of second regions are provided periodically along the longitudinal direction. The optical fiber according to Claim 1.

4. The width of the plurality of second regions along the longitudinal direction is 0.1 mm or more and 5 mm or less, and the pitch between the plurality of second regions is 20 mm or more and 300 mm or less. The optical fiber according to Claim 1.

5. The primary material constituting the primary resin layer includes an acrylic resin containing a radical polymerization initiator. The optical fiber according to Claim 1.

6. The radical polymerization initiator includes a photoinitiator and a thermal polymerization initiator. The optical fiber according to Claim 5.

7. Marking is applied to a region corresponding to the plurality of second regions in the outer jacket of the optical fiber. The optical fiber according to Claim 1.

8. A plurality of optical fibers, each being the optical fiber according to any one of Claims 1 to 7, wherein the positions of the plurality of second regions in the longitudinal direction in the plurality of optical fibers are aligned. Tape fiber.

9. A step of drawing a fiber including at least one core and a cladding covering the core, a step of forming a primary resin layer covering the outer periphery of the fiber, and a step of forming a secondary resin layer covering the outer periphery of the primary resin layer, wherein, in the step of forming the primary resin layer, at least one of photocuring and thermosetting is partially performed on the primary resin layer in the longitudinal direction to form portions having different degrees of curing in the longitudinal direction.

10. In the step of forming the primary resin layer, ultraviolet light is periodically irradiated to partially cure the primary resin layer. The method for manufacturing an optical fiber according to claim 9.

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