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

Abstract

Provided are an optical fiber, a ribbon optical fiber, and a method for manufacturing an optical fiber, whereby it is possible to align an optical fiber having directivity with respect to the rotational direction with high precision. An optical fiber is provided with: a fiber which includes at least one core and a cladding covering the core, and which extends 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 fibers are directional with respect to a rotation direction about 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, the second Young's modulus being higher than the first Young's modulus.

Description

Technical Field

[0001] The present disclosure relates to an optical fiber, a ribbon optical fiber, and a method for manufacturing an optical fiber. Background Art

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

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-155308

[0006] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2023-035025 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] The optical fiber described in Patent Document 1 is configured as a fiber having directionality with respect to the rotation direction. For such an optical fiber, when performing an optical connection, in order to align each core with the counterpart core, alignment of the rotation direction is required. In addition, in the winding process of the optical fiber, when winding while aligning the rotation directions, adjustment of the rotation direction is required. Or, when manufacturing a ribbon optical fiber in which a plurality of optical fibers are arranged, in order to align the configurations of the cores of the plurality of optical fibers, adjustment of the rotation direction is required. On the other hand, in an optical fiber, in order to improve the side pressure resistance characteristics, a primary resin layer and a secondary resin layer are provided so as to further cover the outer periphery of the cladding. 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 (for example, refer to Patent Document 2). When these coating layers are provided on a multi-core optical fiber, alignment of the rotation direction is performed while maintaining the coating layer on the outer side of the cladding. However, since the primary resin layer is soft and the holding force is weak, the primary resin layer sometimes twists with respect to the cladding, and it is sometimes difficult to perform alignment of the rotation direction with high precision.

[0009] An object of the present disclosure is to provide an optical fiber capable of performing alignment of an optical fiber having directionality with respect to the rotation direction with high precision, a ribbon optical fiber including a plurality of such optical fibers, and a method for manufacturing the optical fiber.

[0010] Technical Solution for Solving the Technical Problem

[0011] An optical fiber according to an embodiment of the present disclosure includes: a fiber including at least one core and a cladding covering the core and extending in a length 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 is a fiber having a directionality with respect to a rotation direction about the length direction as an axis. The primary resin layer includes, in the length direction, a plurality of first regions having a first Young's modulus and a plurality of second regions having a second Young's modulus, and the second Young's modulus is higher than the first Young's modulus.

[0012] Advantageous Effects of the Invention

[0013] According to the present disclosure, alignment of an optical fiber having directionality with respect to a rotation direction can be performed with high precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a cross-sectional view showing an optical fiber according to an embodiment.

[0015] Figure 2 is a top view showing the optical fiber and the primary resin layer shown along the length direction Figure 1 in FIG.

[0016] Figure 3 Part (a) of FIG. is a view showing a cross-section of a region (first region) where the Young's modulus of the primary resin layer is low, Figure 3 and part (b) of FIG. is a view showing a cross-section of a region (second region) where the Young's modulus of the primary resin layer is high.

[0017] Figure 4 is a top view showing a ribbon optical fiber obtained by gathering the multi-core optical fibers shown in Figure 1 FIG. into a ribbon shape.

[0018] Figure 5 is a cross-sectional view when the ribbon optical fiber shown in Figure 4 FIG. is cut in a region (second region) where the Young's modulus is high.

[0019] Figure 6 is a cross-sectional view showing a modified example in which a region (second region) where the Young's modulus of the primary resin layer is high is changed in the circumferential direction in the optical fiber shown in Figure 1 FIG. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] [Description of Embodiments of the Present Disclosure]

[0021] First, the contents of the embodiments of the present disclosure will be listed and described.

[0022] [1]An optical fiber according to an embodiment includes: a fiber including at least one core and a cladding 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 is a fiber having a directionality with respect to a rotation direction about 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, and the second Young's modulus is higher than the first Young's modulus.

[0023] In this optical fiber, second regions having an increased Young's modulus are provided in the primary resin layer covering the outer periphery of the fiber. In this case, in the second regions where the Young's modulus is increased, the primary resin layer becomes harder, and the holding force of the primary resin layer on the fiber including the cladding is increased. Therefore, when aligning the optical fiber with respect to the rotation direction by holding a portion corresponding to the second region where the Young's modulus is increased, alignment of the optical fiber having a directionality with respect to the rotation direction can be performed with high precision. Further, in a winding process and a ribbon manufacturing process of the optical fiber, when the rotation direction is adjusted by rotating the secondary resin layer, since the holding force of the entire optical fiber is increased by the plurality of second regions, this adjustment can be performed with high precision. Furthermore, in a ribbon optical fiber manufactured using such an optical fiber, since the rotation direction is maintained near the second region, multi-core parallel connection without rotational alignment can be performed. It should be noted that the "optical fiber having a directionality with respect to the rotation direction" mentioned herein includes at least a multi-core optical fiber (also denoted as "MCF") in which a plurality of cores are arranged in one cladding, but is not limited thereto, and also includes a polarization-maintaining optical fiber (also denoted as "PMF"), a hole-assisted optical fiber (also denoted as "HAF"), and a hollow-core optical fiber (also denoted as "HCF") that require alignment of the rotation direction.

[0024] [2]In the optical fiber of [1] above, it may be that 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. In this case, while sufficient side pressure resistance characteristics can be imparted to the optical fiber in the first regions having the first Young's modulus, the primary resin layer can be made harder and the holding force can be increased more reliably in the second regions having the second Young's modulus. Therefore, according to this optical fiber, rotational alignment of the optical fiber can be performed with higher precision.

[0025] [3]In the optical fiber of [1] or [2] above, multiple second regions may also be periodically arranged along the length direction. In this case, since portions (second regions) that are less likely to cause torsion of the primary resin layer with respect to the fiber (cladding) are periodically formed along the length direction, torsion of the core and cladding is less likely to occur in the entire optical fiber. In addition, since operations such as optical connection are performed in the second regions, by periodically arranging the second regions, the surplus length portion (portion not equivalent to the second region) when cutting the optical fiber at a specified position and performing operations such as optical connection can be reduced.

[0026] [4]In the optical fiber of any one of [1] to [3] above, the width of the multiple second regions along the length direction may also be 0.1 mm or more and 5 mm or less, and the spacing between the multiple second regions may also be 20 mm or more and 300 mm or less. By making the width of each second region 0.1 mm or more, the holding force of the primary resin layer on the fiber (cladding) can be reliably ensured. On the other hand, by suppressing the width of each second region to 5 mm or less, the lateral pressure resistance characteristics brought about by the primary resin layer can be prevented from degrading in the entire optical fiber. In addition, by making the spacing between the second regions 20 mm or more, when the optical fiber expands and contracts due to temperature changes, the difference in linear expansion between the fiber made of glass and the coating made of resin can be sufficiently absorbed by the first region with a low Young's modulus. Therefore, an increase in transmission loss caused by microbending can be suppressed. On the other hand, by making the spacing between the second regions 300 mm or less, when cutting the optical fiber and performing rotational alignment in the case of optical connection such as fusion splicing or connector connection, it is easy for the operator to cut the fiber with the second region as a reference, and the operation efficiency can be improved. In addition, the length of the fiber can be determined in detail in units of the spacing, and the difference from the required length can be reduced to decrease the surplus length portion. It should be noted that the spacing between the second regions mentioned here means the shortest distance between adjacent second regions in the length direction.

[0027] [5]In the optical fiber of any one of [1] to [4] above, the primary material constituting the primary resin layer may also contain an acrylic resin containing a radical polymerization initiator. In this case, the function of the coating that can well maintain the transmission characteristics of the optical fiber can be obtained, and even when manufactured at a high drawing speed of, for example, 2000 m / minute or more, the second region can be quickly cured to increase the Young's modulus.

[0028] [6]In the optical fiber of [5] above, the radical polymerization initiator may also include a photopolymerization initiator and a thermal polymerization initiator. In this case, the curing of the entire primary resin layer is carried out using heat, and the formation of the second region where the Young's modulus is increased in the primary resin layer is carried out by curing using light, enabling the separation of the two processes (curing mechanisms). Thus, even if there are changes over time with respect to the optical fiber, it is possible to suppress the further curing of the first region in a state where the Young's modulus is low, and the initial Young's modulus can be maintained for a long time. Therefore, according to this optical fiber, even when a second region for highly precisely performing rotational alignment is provided, the side pressure resistance characteristics of the optical fiber can be maintained well.

[0029] [7]In the optical fiber of any one of [1] to [6] above, it is also possible to make a mark in a region corresponding to the plurality of second regions in the outer skin of the optical fiber. In this case, when performing rotational alignment of the optical fiber, the operator can reliably identify the portion to be gripped. Therefore, the rotational alignment of the optical fiber can be carried out more reliably.

[0030] [8]The ribbon optical fiber according to an embodiment includes a plurality of optical fibers, and the plurality of optical fibers are respectively the optical fibers of any one of [1] to [7] above, and the positions of the plurality of second regions in the plurality of optical fibers are the same in the length direction. According to such a ribbon optical fiber, when performing optical connection with other ribbon optical fibers, rotational alignment can be easily carried out. In addition, if the rotational directions of the respective optical fibers are the same when manufacturing the ribbon optical fiber, by performing optical connection at the position of the second region or a position near it, multi-core parallel connection with the same rotational direction can be carried out.

[0031] [9]The method for manufacturing an optical fiber according to an embodiment includes: a step of drawing out 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 thermal curing is locally performed on the primary resin layer in the length direction to form portions with different degrees of curing in the length direction. According to such a method, an optical fiber capable of highly precisely performing rotational alignment can be manufactured in a simple manner.

[0032]

[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 locally cure the primary resin layer. In this case, the periodic setting of a region with a high Young's modulus can be carried out in a simple manner.

[0033] [Details of the embodiments of the present disclosure]

[0034] A specific example of an optical fiber, a ribbon optical fiber, and a method for manufacturing an optical fiber according to an embodiment of the present disclosure will be described below with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same elements or elements having the same function, and repeated descriptions are omitted. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0035] Referring to Figure 1 , an example of an optical fiber according to an embodiment will be described. Figure 1 is a cross-sectional view showing an optical fiber according to an embodiment. As Figure 1 shown, the optical fiber 1 is, for example, a multi-core optical 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 is configured to have a directionality with respect to the rotation direction. It should be noted that the optical fiber 1 is not limited to MCF, and may also be PMF, HAF, and HCF that require alignment of the rotation direction.

[0036] The core 2 is made of pure silica (SiO2) glass or a material containing germanium oxide or fluorine element in silica glass. The cladding 3 has a refractive index lower than that of the core 2. The cladding 3 is made of, for example, pure silica glass or a material in which fluorine element is added to silica glass. It should be noted 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 a plurality of cores 2 and the cladding 3.

[0037] 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.

[0038] The primary material constituting 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. In addition, the primary material further contains a thermopolymerizable compound and a thermal polymerization initiator. As the thermopolymerizable compound, for example, urethane (meth)acrylate or epoxy (meth)acrylate can be used. As the thermal polymerization initiator, for example, azo compounds such as 2,2'-azobisisobutyronitrile (AIBN), peroxides such as benzoyl peroxide (BPO), etc. can be used. The primary resin layer 5 composed of the above materials is formed into a specified hardness by curing using light (e.g., ultraviolet light) or heat. It should be noted that different types of polymerization initiators are included in the primary material constituting the primary resin layer 5 of the present embodiment.

[0039] Such a primary resin layer 5 has a lower elastic modulus (Young's modulus) than the secondary resin layer 6 and is formed to be 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, the optical fiber 1 is imparted with side pressure resistance characteristics, and even when side pressure is applied, an increase in transmission loss in the optical fiber 1 will be suppressed. It should be noted that the primary resin layer 5 of 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 below.

[0040] The secondary material constituting the secondary resin layer 6 can be formed from a resin composition containing urethane (meth)acrylate, a 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 elastic modulus (Young's modulus) than the primary resin layer 5, 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. It should be noted that 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.

[0041] Next, with reference to Figure 2 and Figure 3 , a scheme in which the Young's modulus of the primary resin layer 5 in the optical fiber 1 of the present embodiment is different in the longitudinal direction will be described. Figure 2 is a top view showing the optical fiber 1 and the primary resin layer 5 shown in Figure 1 along the longitudinal direction. Figure 3 Part (a) of Figure 3 is a diagram showing a cross-section of a region (first region) where the Young's modulus of the primary resin layer 5 is low, and

[0042] As Figure 2 shown, the primary resin layer 5 is configured to include, in the longitudinal direction, a plurality of first regions 5a having a first Young's modulus (see Figure 3 (a) of FIG. 1) and a plurality of second regions 5b having a second Young's modulus higher than the first Young's modulus of the first regions 5a (see Figure 3 (b) of FIG. 1). The second regions 5b are, for example, portions where the Young's modulus is higher than that of the first regions 5a by curing the regions corresponding to the second regions 5b further with heat or light after the entire primary resin layer 5 is formed with the first Young's modulus. For example, as Figure 3 (b) of FIG. 1 shows, the second regions 5b are formed to extend in the entire circumferential direction. Through such portions with a high Young's modulus (second regions 5b), the primary resin layer 5 that coats the cladding 3 is locally hardened to improve the holding force, and the rotational alignment can be performed with high precision by an operator.

[0043] In the primary resin layer 5, the first Young's modulus of the first regions 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 regions 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 regions 5b is significantly higher than the first Young's modulus of the first regions 5a. However, the Young's moduli of both the first regions 5a and the second regions 5b of the primary resin layer 5 are lower than the Young's modulus of the secondary resin layer 6. Further, in the primary resin layer 5, as Figure 2 shown, the plurality of second regions 5b are respectively provided periodically in the longitudinal direction. However, the plurality of second regions 5b may be provided irregularly instead of periodically.

[0044] The width W of the second region 5b in the longitudinal direction 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. In addition, 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 regions 5b to 20 mm or more, the linear expansion difference between the (primary resin layer 5 and secondary resin layer 6) and the glass (core 2 and cladding 3) caused by the expansion and contraction of the coating when the temperature changes is absorbed by the gentle bending at the low Young's modulus portion (first region 5a) between the pitches. Therefore, an increase in transmission loss caused by microbending can be reduced. On the other hand, by setting the pitch P of the second regions 5b to 300 mm or less, when performing optical connections such as fusion splicing and connector connection at the portions of the second regions 5b where the fiber rotation is consistent, the length of the optical fiber 1 can be determined in detail in units of pitch, and the difference from the required sufficient length can be reduced to reduce the excess length. It should be noted that marks may be made in the regions corresponding to the second regions 5b in the outer skin (for example, the secondary resin layer 6 or the colored ink layer) of the optical fiber 1. In this case, it is easy for the operator to identify the second regions 5b, so various operations can be easily performed.

[0045] In order to manufacture the optical fiber 1 such that the Young's modulus of the primary resin layer 5 is different in the longitudinal direction as described above, first, a glass fiber 4 including a core 2 and a cladding 3 covering the core 2 is drawn from a base material. Then, a primary resin layer 5 is formed so as to coat the outer periphery of the drawn glass fiber 4, and a secondary resin layer 6 is formed so as to coat 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. In addition, when forming the primary resin layer, at least one of photocuring and thermocuring is locally performed on the primary resin layer 5 to form the above-mentioned second region 5b. More preferably, ultraviolet light (LED or laser) or infrared light (laser or flash lamp) may be periodically irradiated to locally further cure the primary resin layer 5 so as to provide a plurality of second regions 5b in the first region 5a. Such irradiation may be pulsed irradiation, or light in the range of visible light to infrared light with a low material absorption coefficient may be used. In this case, damage to the coating material can be reduced.

[0046] Alternatively, the Young's modulus of the second region 5b can be made higher than that of the first region 5a by irradiating heat or light only to the region corresponding to the second region 5b. Furthermore, marking can be performed using inkjet in parallel with the irradiation of light, enabling the second region 5b to be distinguishable from the outside. Conversely, marking can be performed by removing the ink portion with a laser when irradiating the laser, enabling the second region 5b to be distinguishable. In addition, ultraviolet light can be irradiated to the primary resin layer 5 through the removed portion (as a mask) to perform the above curing, forming the second region 5b with a high Young's modulus. Or, the wavelength of the laser, the irradiation conditions, and the material of the coating layer can be selected, and the coating layer can be made to develop color with the laser irradiated for curing to perform marking. In this case, since the laser irradiation site is the same as the marking site, the position can be distinguished more precisely.

[0047] In summary, in the optical fiber 1 according to the present embodiment, the second region 5b having a Young's modulus higher than that of the first region 5a is provided in the primary resin layer 5 on the outer periphery of the cladding 3 that coats the glass fiber 4. 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 for the glass fiber 4 including the cladding 3 is increased. Therefore, when performing rotational alignment of the optical fiber 1 while holding the portion corresponding to the second region 5b where the Young's modulus is increased, alignment of the optical fiber 1 having directionality with respect to the rotational direction can be performed with high precision.

[0048] Next, with reference to Figure 4 and Figure 5 the configuration of a ribbon optical fiber provided with a plurality of the above optical fibers 1 will be described. Figure 4 is a top view of a ribbon optical fiber showing the Figure 1 optical fibers shown converged into a ribbon. Figure 5 is a view showing the cross section of the Figure 4 ribbon optical fiber shown. As shown in Figure 4 and Figure 5 the ribbon optical fiber 10 has a plurality of optical fibers 1 (four optical fibers 1 in the examples of Figure 4 and Figure 5 ). The plurality of optical fibers 1 are connected to each other by a coating resin 11 and formed into a ribbon shape. In the ribbon optical fiber 10, the second regions 5b where the Young's modulus is increased in the respective primary resin layers 5 are made to coincide with each other in the length direction.

[0049] In the ribbon optical fiber 10, similarly to the above-described optical fiber 1, the primary resin layer 5 hardens in each second region 5b to improve the holding force. Therefore, when optically connecting to other ribbon optical fibers, rotational alignment can be easily and highly accurately performed. Regarding such a ribbon optical fiber 10, it can be formed by bundling optical fibers 1 having a second region 5b with a high Young's modulus formed in advance, or the optical fibers 1 before forming the second region 5b can be bundled into a bundle and formed into a ribbon shape, and then the second region 5b is uniformly formed (for example, uniformly cured by irradiating laser light). In the case of the latter method, it is possible to easily make the positions of the second regions 5b in the length direction of the respective optical fibers 1 coincide with each other.

[0050] In summary, the optical fiber 1, the ribbon optical fiber 10, and their manufacturing methods according to the embodiments of the present disclosure have been described in detail. However, the present invention is not limited to the above-described embodiments and can be applied to various embodiments and modification examples. For example, in the above description, regarding the second region 5b in the optical fiber 1, as shown in the (b) part of Figure 3 , it is configured to increase the Young's modulus in the entire circumferential direction, but is not limited thereto. That is, as shown in Figure 6 , in the second region 5b, laser light L may be irradiated onto the optical fiber in the first direction (from above to below) and the second direction (from left to right) to cure a part of the primary resin layer 5 in the circumferential direction to make 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 portions 5c in the circumferential direction (four portions in the example of Figure 6 ). Even with such a configuration, it is possible to increase the holding force of the primary resin layer 5 on the cladding 3 and perform rotational alignment with high accuracy.

[0051] Explanation of reference numerals

[0052] 1, 1A Optical fiber

[0053] 2 Core

[0054] 3 Cladding

[0055] 4 Glass fiber

[0056] 5 Primary resin layer

[0057] 5a First region

[0058] 5b Second region

[0059] 5c Portion

[0060] 6 Secondary resin layer

[0061] 10 Ribbon optical fiber

[0062] 11 Coating resin

[0063] L Laser

[0064] P pitch

[0065] W width.

Claims

1. An optical fiber comprising: a fiber including at least one core and a cladding covering the core and extending in a length 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, wherein the fiber is a fiber having a directionality with respect to a rotational direction about the length direction as an axis, the primary resin layer includes, in the length direction, a plurality of first regions having a first Young's modulus and a plurality of second regions having a second Young's modulus, and the second Young's modulus is higher than the first Young's modulus.

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

3. The optical fiber according to claim 1, wherein the plurality of second regions are provided periodically in the length direction.

4. The optical fiber according to claim 1, wherein a width of the plurality of second regions in the length direction is 0.1 mm or more and 5 mm or less, a pitch between the plurality of second regions is 20 mm or more and 300 mm or less.

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

6. The optical fiber according to claim 5, wherein the radical polymerization initiator includes a photoinitiator and a thermal polymerization initiator.

7. The optical fiber according to claim 1, wherein marks are made in a region of an outer skin of the optical fiber corresponding to the plurality of second regions.

8. A ribbon optical fiber comprising a plurality of optical fibers, the plurality of optical fibers being the optical fiber according to any one of claims 1 to 7 respectively, wherein positions of the plurality of second regions in the plurality of optical fibers in the length direction are identical.

9. A method for manufacturing an optical fiber, comprising: 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 an outer periphery of the fiber; and a step of forming a secondary resin layer covering an outer periphery of the primary resin layer, wherein, in the step of forming the primary resin layer, at least one of photocuring and thermal curing is locally performed on the primary resin layer in the length direction to form portions having different degrees of curing in the length direction.

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

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