Optical fiber ribbon and method for manufacturing optical fiber ribbon

Abstract

This optical fiber ribbon (1) is provided with: a first multicore fiber (10) having a plurality of first cores (11); a second multicore fiber (20) disposed in parallel with the first multicore fiber (10); and a coating member (50). The coating member (50) has a first coating portion (51) that coats the first multicore fiber (10), and a second coating portion (52) that coats the second multicore fiber (20). A first light irradiation surface (51a) having a width longer than the diameter of each of the first cores (10) is provided in at least one region in which either a virtual line passing through at least two or more first cores (11) among the plurality of first cores (11), or a virtual line passing through the center of the first multicore fiber (10), intersects with the outer periphery of the first coating portion (51). The first light irradiation surface (51a) includes a flat surface or a curved surface having a radius of curvature of 0.5 mm or greater.

Description

Optical fiber ribbon and method for manufacturing the same

[0001] This disclosure relates to an optical fiber ribbon and a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2023-120735, filed on July 25, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 discloses a ribbon fiber having a plurality of multi-core fibers and capable of separating each fiber, and a manufacturing method thereof. Patent Document 2 discloses a method for aligning a multi-core fiber. In the alignment method described in Patent Document 2, illumination light is irradiated to the side of the multi-core fiber and displacement of the shadow of the core is detected with an imaging device. This detects twist in the multi-core fiber, and the twist is eliminated using a twist-eliminating pulley. Patent Document 3 discloses a ribbon fiber of a different type from the ribbon fiber of Patent Document 1.

[0003] JP 2017-173514 A JP 2014-133673 A International Publication No. 2016 / 047658

[0004] An optical fiber ribbon according to an embodiment of the present disclosure includes: a first multicore fiber having a plurality of first cores and a first cladding covering the plurality of first cores; a second multicore fiber having a plurality of second cores and a second cladding covering the plurality of second cores and arranged in parallel to the first multicore fiber; and a coating member at least partially covering the first multicore fiber and the second multicore fiber. The coating member has a first coating portion covering the first multicore fiber and a second coating portion covering the second multicore fiber. A first light irradiation surface having a width greater than the diameter of the first cores is provided in at least one region where a virtual line passing through at least two or more of the plurality of first cores or a virtual line passing through the center of the first multicore fiber intersects with the outer periphery of the first coating portion. The first light irradiation surface includes a curved surface or a flat surface having a curvature radius of 0.5 mm or greater.

[0005] FIG. 1 is a cross-sectional view showing an optical fiber ribbon according to an embodiment. FIG. 2 is a diagram showing a manufacturing method of the optical fiber ribbon shown in FIG. 1. FIG. 3 is a diagram for explaining a method of core alignment by light irradiation in a general multicore fiber. Parts (a), (b), and (c) of FIG. 4 are diagrams showing measurement results of symmetry in the core alignment shown in FIG. 3. FIG. 5 is a diagram showing an example of the relationship between asymmetry and rotation angle. Part (a) of FIG. 6 is an example showing the transmission state of light irradiated when there is no uneven distribution of coating resin in the ribbon, and part (b) of FIG. 6 is an example showing the transmission state of light irradiated when there is uneven distribution of coating resin in the ribbon. Part (a) of FIG. 7 is a diagram showing the measurement results of symmetry in the core alignment shown in part (a) of FIG. 6, and part (b) of FIG. 7 is a diagram showing the measurement results of symmetry in the core alignment shown in part (b) of FIG. 6. Parts (a), (b), and (c) of Fig. 8 are examples showing the light transmission state when the coating resin of the ribbon fiber is unevenly distributed and the light is transmitted to a general multi-core fiber, a multi-core fiber whose light irradiation surface is a curved surface with a large radius of curvature, and a multi-core fiber whose light irradiation surface is flat. Fig. 9 is a diagram showing the relationship between the asymmetry in the multi-core fiber and the radius of curvature of the light irradiation surface when the radius of curvature of the light irradiation surface is changed. Fig. 10 is a graph showing the measurement results of symmetry when light is irradiated to a multi-core fiber having the structure shown in part (c) of Fig. 8. Parts (a), (b), and (c) of Fig. 11 are examples showing the light transmission state when the coating resin of the ribbon fiber is unevenly distributed and the light is transmitted to a general multi-core fiber, a multi-core fiber having a light irradiation surface on one side, and a multi-core fiber having light irradiation surfaces on both sides. Fig. 12 is a diagram showing the relationship between the asymmetry in the multi-core fiber shown in parts (a) to (c) of Fig. 11 and the radius of curvature of the light irradiation surface. Parts (a), (b), and (c) of Fig. 13 are diagrams showing an example of the positional relationship between the installation position of the light irradiation surface and each core. Parts (a), (b), and (c) of Fig. 14 are diagrams showing another example of the positional relationship between the installation position of the light irradiation surface and each core. Fig. 15 is a cross-sectional view showing a first modified example of an optical fiber ribbon. Fig. 16 is a cross-sectional view showing a second modified example of an optical fiber ribbon.

[0006] [Problem to be Solved by the Present Disclosure] When manufacturing the separable ribbon fiber described in Patent Document 1, various resins covering the cladding of each multicore fiber may be unevenly distributed (so-called uneven thickness portions may be formed). Such resins may be, for example, primary or secondary resin layers covering the cladding, or a resin layer that collectively coats the fibers. When the resin is unevenly distributed in this manner, even if the cores in each fiber are uniformly arranged, the uneven distribution of resin may affect core alignment, for example, by light irradiation, and may result in poor alignment. For example, when illumination light is irradiated onto a fiber with uniform core arrangement (each core aligned in one direction) as shown in part (a) of FIG. 6, if there is no uneven distribution of resin, the light transmitted through the fiber will be represented by a symmetrical brightness graph (see part (a) of FIG. 7). On the other hand, as shown in part (b) of FIG. 6, if there is uneven distribution of resin, even if the cores are uniformly arranged, the light transmitted through the fiber will be represented by an asymmetrical brightness graph (see part (b) of FIG. 7). In this case, although the cores are actually aligned, they are detected as not being aligned due to uneven distribution of resin.

[0007] Effect of the Present Disclosure According to the present disclosure, core alignment can be reliably performed in a ribbon optical fiber including a plurality of multi-core fibers.

[0008] [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 ribbon according to one embodiment includes: a first multicore fiber having a plurality of first cores and a first cladding covering the plurality of first cores; a second multicore fiber having a plurality of second cores and a second cladding covering the plurality of second cores and arranged in parallel to the first multicore fiber; and a coating member at least partially covering the first multicore fiber and the second multicore fiber. The coating member has a first coating portion covering the first multicore fiber and a second coating portion covering the second multicore fiber. A first light irradiation surface having a width greater than the diameter of the first cores is provided in at least one region where a virtual line passing through at least two or more of the plurality of first cores or a virtual line passing through the center of the first multicore fiber intersects with the outer periphery of the first coating portion. The first light irradiation surface includes a curved surface or a flat surface having a curvature radius of 0.5 mm or more.

[0009] In this optical fiber ribbon, a first light irradiation surface having a width greater than the diameter of the first cores is provided in at least one region where a virtual line passing through at least two or more of the multiple first cores or a virtual line passing through the center of the first multicore fiber intersects with the outer periphery of the first coating portion. This first light irradiation surface includes a curved surface or a flat surface having a radius of curvature of 0.5 mm or more. In this case, simulation results by the inventors have shown that even if the resin coating the cladding in the optical fiber ribbon has some uneven distribution (uneven thickness), by irradiating illumination light from the light irradiation surface with the above structure, the transmitted light will be symmetrical if the first cores are aligned. Therefore, this optical fiber ribbon can provide a ribbon in which the multiple first cores are reliably aligned.

[0010] [2] In the optical fiber ribbon according to [1] above, a second light irradiation surface having a width greater than the diameter of the second cores may be provided in at least one region where an imaginary line passing through at least two or more of the plurality of second cores or an imaginary line passing through the center of the second multicore fiber intersects with the outer periphery of the second coating portion. This second light irradiation surface may include a curved surface or a flat surface having a curvature radius of 0.5 mm or more. In this case, the ribbon can be one in which the alignment of the plurality of second cores is reliably performed in addition to the alignment of the plurality of first cores.

[0011] [3] In the optical fiber ribbon according to [2] above, the normal direction of the first light irradiation surface at the intersection of the first light irradiation surface and the virtual line may be the same as the normal direction of the second light irradiation surface at the intersection of the second light irradiation surface and the virtual line. In this case, illumination light for aligning the cores in the first multicore fiber and the second multicore fiber can be irradiated from the same direction. This makes it possible to provide an optical fiber ribbon that can easily align a ribbon including multiple multicore fibers. Note that the term "same direction" here does not only mean that the normal direction of the first light irradiation surface and the normal direction of the second light irradiation surface are exactly the same, but also means that there can be a slight deviation, for example, a deviation of about ±1°, between the normal direction of the first light irradiation surface and the normal direction of the second light irradiation surface.

[0012] [4] In the optical fiber ribbon according to [3] above, the axis of the imaginary line and the normal direction of the first light irradiation surface may be oriented in the same direction. Note that the term "same direction" here does not only mean that they are in the exact same direction, but also means that there may be a slight deviation, for example, a deviation of about ±1°, between the axis of the imaginary line and the normal direction of the first light irradiation surface.

[0013] [5] In the optical fiber ribbon according to any one of [1] to [4] above, the arrangement of the plurality of first cores may be line-symmetric with respect to a virtual line passing through the center of the first multicore fiber, at least in a range corresponding to the first light irradiation surface. By being line-symmetric at least in a range corresponding to the first light irradiation surface, it is possible to make the light transmitted through the optical fiber into a symmetric brightness graph.

[0014] [6] In the optical fiber ribbon according to any one of [1] to [5] above, the arrangement of the plurality of first cores may be line-symmetric with respect to a virtual line passing through the center of the first multicore fiber. By being line-symmetric, it is possible to make the light transmitted through the optical fiber have a symmetric brightness graph.

[0015] [7] In the optical fiber ribbon according to any one of [1] to [6] above, the width of the first light irradiation surface may be 20 μm or more longer than the diameter of the first core. In an optical fiber ribbon, the resin, which is a constituent element, may be unevenly distributed. However, for example, if the core center is shifted by about 10 μm from the predetermined position (no change in thickness ratio of 70%), this is acceptable as a product. Therefore, even in a ribbon with such uneven resin distribution, by providing a first light irradiation surface with the above-mentioned width, the influence of the uneven distribution can be reduced, and the ribbon can be made with reliable alignment of the first core.

[0016] [8] In the optical fiber ribbon according to any one of [1] to [7] above, the virtual line may pass through at least three or more first cores. In this case, the alignment light passes through more cores, thereby improving alignment accuracy and enabling a ribbon ribbon including a plurality of multi-core fibers to be more reliably aligned. The three or more first cores referred to here may include a marker core that has a higher refractive index than the cladding portion, like a normal first core, but does not have a trench or the like formed around the outer periphery of the cladding.

[0017] [9] In the optical fiber ribbon according to any one of [1] to [8] above, the first light irradiation surface may be provided in each of two opposing regions where the imaginary line intersects on the outer periphery of the first coating portion. In this case, even if the resin coating the clad is unevenly distributed to some extent, the transmitted light becomes more symmetrical, so that it is possible to provide a ribbon including a plurality of multi-core fibers that can be easily aligned.

[0018]

[10] The optical fiber ribbon according to any one of [1] to [9] above may further include a third multicore fiber having a plurality of third cores and a third cladding covering the plurality of third cores, and a fourth multicore fiber having a plurality of fourth cores and a fourth cladding covering the plurality of fourth cores. In this optical fiber ribbon, the first multicore fiber, the second multicore fiber, the third multicore fiber, and the fourth multicore fiber may be arranged in parallel in this order, and the coating member may cover the third multicore fiber and the fourth multicore fiber as well as the first multicore fiber and the second multicore fiber. The coating member may further include a third coating portion that coats the third multicore fiber and a fourth coating portion that coats the fourth multicore fiber. A recess may be provided in at least one of between the first coating portion and the second coating portion, between the second coating portion and the third coating portion, and between the third coating portion and the fourth coating portion. A third light irradiation surface having a width greater than the diameter of the third cores may be provided in a region where a virtual line passing through at least two or more of the multiple third cores or a virtual line passing through the center of the third multicore fiber intersects with the outer periphery of the third coating portion, and this third light irradiation surface may include a curved surface or a flat surface having a radius of curvature of 0.5 mm or more. Furthermore, a fourth light irradiation surface having a width greater than the diameter of the fourth cores may be provided in a region where a virtual line passing through at least two or more of the multiple fourth cores or a virtual line passing through the center of the fourth multicore fiber intersects with the outer periphery of the fourth coating portion, and this fourth light irradiation surface may include a curved surface or a flat surface having a radius of curvature of 0.5 mm or more. In this case, even when the number of fibers in the optical fiber ribbon increases to four, alignment can be easily performed. Furthermore, in this optical fiber ribbon, a recess is provided in at least one of the spaces between the first coated portion and the second coated portion, between the second coated portion and the third coated portion, and between the third coated portion and the fourth coated portion, so that each fiber can be easily separated.

[0019]

[11] In the optical fiber ribbon according to

[10] above, the normal direction of the first light irradiation surface at the intersection of the first light irradiation surface and the virtual line, the normal direction of the second light irradiation surface at the intersection of the second light irradiation surface and the virtual line, the normal direction of the third light irradiation surface at the intersection of the third light irradiation surface and the virtual line, and the normal direction of the fourth light irradiation surface at the intersection of the fourth light irradiation surface and the virtual line may all face the same direction. In this case, illumination light for aligning each core in the first multicore fiber, the second multicore fiber, the third multicore fiber, and the fourth multicore fiber can be irradiated from the same direction. Therefore, it is possible to provide an optical fiber ribbon that can easily align a ribbon including a plurality of multicore fibers. Note that the term "same direction" here does not only mean that the normal directions are completely the same, but also means that there can be a slight deviation, for example, a deviation of about ±1°, between the normal directions.

[0020]

[12] A manufacturing method of an optical fiber ribbon according to one embodiment includes the steps of: preparing a first multicore fiber having a plurality of first cores and a first cladding covering the plurality of first cores, preparing a second multicore fiber having a plurality of second cores and a second cladding covering the plurality of second cores, coating the first multicore fiber and the second multicore fiber with resin while arranging the first multicore fiber and the second multicore fiber in parallel, and irradiating light onto a light irradiation surface in a coating resin portion that coats the first multicore fiber, and aligning the plurality of first cores in the first multicore fiber based on the result of the light irradiation. In this manufacturing method, the light irradiation surface is a surface provided in a region where an imaginary line passing through at least two or more of the plurality of first cores or an imaginary line passing through the center of the first multicore fiber intersects with the outer periphery of the coating resin portion, and this light irradiation surface includes a curved surface or a flat surface having a width greater than the diameter of the first cores and a radius of curvature of 0.5 mm or more.

[0021] This method for manufacturing an optical fiber ribbon includes the steps of irradiating light onto a light irradiation surface in a coating resin portion that coats the first multicore fiber and aligning multiple first cores in the first multicore fiber based on the results of the light irradiation. The light irradiation surface is a surface provided in a region where an imaginary line passing through at least two or more of the multiple first cores or an imaginary line passing through the center of the first multicore fiber intersects with the outer periphery of the coating resin portion, and the light irradiation surface has a width greater than the diameter of the first cores and includes a curved or flat surface with a radius of curvature of 0.5 mm or more. Simulation results by the inventors have shown that even if the resin coating the cladding in an optical fiber ribbon has uneven distribution (uneven thickness), providing such a light irradiation surface makes the transmitted light symmetrical when the first cores are aligned. Therefore, this method for manufacturing an optical fiber ribbon can provide a ribbon in which multiple first cores are reliably aligned.

[0022] [Details of the embodiments of the present disclosure] Specific examples of optical fiber ribbons and methods for manufacturing optical fiber ribbons according to embodiments of the present disclosure will be described below with reference to the drawings. In the following description, the same elements or elements having the same functions will be designated by the same reference numerals, and duplicated explanations will be omitted. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0023] An example of an optical fiber ribbon according to an embodiment will be described with reference to FIG. 1 . FIG. 1 is a cross-sectional view showing an optical fiber ribbon according to an embodiment. As shown in FIG. 1 , the optical fiber ribbon 1 includes a plurality of multicore fibers 10, 20, 30, and 40, and a coating member 50. The multicore fibers 10 to 40 extend along a first direction D1. The multicore fibers 10 to 40 are arranged in parallel along a second direction D2, and are entirely covered by a coating member 50. The optical fiber ribbon 1 is, for example, a four-fiber ribbon, and recesses 55, 56, and 57 are provided between each fiber to enable individual fiber separation. Note that in this four-fiber ribbon, the recess 56 may be provided but the recesses 55 and 57 may not be provided, and the ribbon may be formed from two pairs of fibers (see the modified example in FIG. 16 ).

[0024] The multicore fiber 10 (first multicore fiber) has a plurality of cores 11 (a plurality of first cores), a cladding 12 (first cladding) covering the plurality of cores 11, a primary resin layer 13 covering the cladding 12, and a secondary resin layer 14 covering the primary resin layer 13. In the multicore fiber 10, for example, 12 cores 11 are arranged in an order of 2, 4, 4, and 2, line-symmetrically with respect to an imaginary line passing through the center of the multicore fiber 10. Note that it is sufficient that the 12 cores 11 are arranged line-symmetrically with respect to an imaginary line passing through the center of the multicore fiber 10, in ranges corresponding to each of light irradiation surfaces 51 a to 54 a described below. The diameter of the cores 11 may be, for example, 5 μm to 15 μm. The diameter of the cladding 12 may be, for example, 120 μm to 130 μm, or 170 μm to 190 μm. The number of fibers in the core 11 is 12 in the example shown in FIG. 1, but is not limited to this and may be 16 (see FIG. 14) or another number of fibers.

[0025] The core 11 is made of pure silica (SiO ２The cladding 12 is made of a material in which germanium dioxide or fluorine is added to silica glass. The cladding 12 has a refractive index lower than that of the core 11. The cladding 12 is made of, for example, pure silica glass or a material in which fluorine is added to silica glass. A trench having a refractive index lower than that of the cladding 12 may be provided between each core 11 and the cladding 12.

[0026] The primary resin layer 13 coats the outer periphery of the clad 12. More specifically, the primary resin layer 13 is in contact with the outer periphery of the clad 12 and coats the entire clad 12. The secondary resin layer 14 further coats the outer periphery of the primary resin layer 13. More specifically, the secondary resin layer 14 is in contact with the outer periphery of the primary resin layer 13 and coats the entire primary resin layer 13.

[0027] The primary resin layer 13 can be formed by curing an ultraviolet-curable resin composition containing a photopolymerizable compound, a photopolymerization initiator, and a silane coupling agent. Examples of the photopolymerizable compound include urethane (meth)acrylate and epoxy (meth)acrylate. The secondary resin layer 14 can be formed by curing a resin composition containing urethane (meth)acrylate, a monomer, and a photopolymerization initiator. The secondary resin layer 14 has higher elasticity than the primary resin layer 13 and is harder than the primary resin layer 13. The thickness of each of the primary resin layer 13 and the secondary resin layer 14 is, for example, 5 μm or more and 50 μm or less.

[0028] The multicore fiber 20 (second multicore fiber), like the multicore fiber 10, has a plurality of cores 21 (a plurality of second cores), a clad 22 (second clad) covering the plurality of cores 21, a primary resin layer 23 covering the clad 22, and a secondary resin layer 24 covering the primary resin layer 23. The multicore fiber 30 (third multicore fiber), like the multicore fiber 10, has a plurality of cores 31 (a plurality of third cores), a clad 32 (third clad) covering the plurality of cores 31, a primary resin layer 33 covering the clad 32, and a secondary resin layer 34 covering the primary resin layer 33. The multicore fiber 40 (fourth multicore fiber), like the multicore fiber 10, has a plurality of cores 41 (a plurality of fourth cores), a clad 42 (fourth clad) covering the plurality of cores 41, a primary resin layer 43 covering the clad 42, and a secondary resin layer 44 covering the primary resin layer 43. Each core, clad, primary resin layer and secondary resin layer of each multi-core fiber 20, 30, 40 has the same structure as each core 11, clad 12, primary resin layer 13 and secondary resin layer 14 of the multi-core fiber 10, and therefore detailed description thereof will be omitted.

[0029] The coating member 50 is formed from a ribbon resin. For example, the ribbon resin may contain a thermosetting resin such as a silicone resin, an epoxy resin, or a urethane resin, or an ultraviolet-curable resin such as an epoxy acrylate, a urethane acrylate, or a polyester acrylate, from the viewpoint of preventing damage to the optical fiber and facilitating separation. The coating member 50 has a first coating portion 51 covering the multicore fiber 10, a second coating portion 52 covering the multicore fiber 20, a third coating portion 53 covering the multicore fiber 30, and a fourth coating portion 54 covering the multicore fiber 40. Each of the coating portions 51 to 54 is in contact with the outer circumferential surface of the corresponding multicore fiber (the outer circumferential surface of each secondary resin layer, and the outer circumferential surface of the colored ink layer, if any), and coats the entirety of each multicore fiber. However, it is sufficient for the coating member 50 to coat each multicore fiber to an extent that the user does not unintentionally separate them, and the coating member 50 may have a structure that partially coats the corresponding multicore fiber without entirely covering it.

[0030] The first coated portion 51 has a shape that generally corresponds to the outer circumferential shape of the coated multi-core fiber 10, for example, a substantially circular cross-sectional shape. Similarly, the second coated portion 52, the third coated portion 53, and the fourth coated portion 54 have shapes that generally correspond to the outer circumferential shapes of the coated multi-core fibers 20, 30, and 40, respectively, and have a substantially circular cross-sectional shape, for example.

[0031] As will be described in detail later, the first covered portion 51, the second covered portion 52, the third covered portion 53, and the fourth covered portion 54 each have a light irradiation surface 51a, 52a, 53a, 54a formed from a flat surface. The light irradiation surfaces 51a to 54a may not be flat, but may be curved surfaces with a curvature radius of 0.5 mm or more (see, for example, part (b) in FIG. 8). When the light irradiation surfaces 51a to 54a are curved, the curvature radius may be larger than the radius of the curved surface of the portions of each covered portion 51 to 54 other than the light irradiation surfaces 51a to 54a. When the light irradiation surfaces 51a to 54a are flat, the curvature radius may be considered to be infinite.

[0032] The light irradiation surface 51a is provided in a region where a virtual line passing through two or more cores 11a or two or more cores 11b, or a virtual line (center line) passing through the center of the multi-core fiber 10, intersects with the outer periphery of the first coating portion 51. In other words, the light irradiation surface 51a is provided on one side (upward in the figure) in the third direction D3 with respect to the core 11. Like the light irradiation surface 51a, the light irradiation surfaces 52a, 53a, and 54a are provided in regions where a virtual line passing through two or more cores 21, 31, and 41, or a virtual line (center line) passing through the centers of the multi-core fibers 20, 30, and 40, intersect with the outer peripheries of the second coating portion 52, the third coating portion 53, and the fourth coating portion 54, respectively.

[0033] The width of such light irradiation surfaces 51a, 52a, 53a, 54a along the second direction D2 is longer than the diameter of the cores 11, 21, 31, 41 of each multicore fiber 10, 20, 30, 40. The width of the light irradiation surfaces 51a, 52a, 53a, 54a along the second direction D2 may be equal to or greater than the sum of the diameter of the cores 11, 21, 31, 41 of each multicore fiber 10, 20, 30, 40 and 20 μm. Furthermore, the width of the light irradiation surfaces 51a, 52a, 53a, 54a along the second direction D2 may be longer than the center distance (core pitch) between two cores 11 (e.g., core 11a and core 11b), 21, 31, 41 located at the center of each multicore fiber 10, 20, 30, 40 and adjacent to each other in the second direction.

[0034] Furthermore, the light irradiation surfaces 51 a, 52 a, 53 a, and 54 a are formed to face the same direction (upward in the third direction D3). In other words, the light irradiation surfaces 51 a to 54 a are formed so that the normal direction of the light irradiation surface 51 a at the intersection of the light irradiation surface 51 a and the virtual line in the multi-core fiber 10, the normal direction of the light irradiation surface 52 a at the intersection of the light irradiation surface 52 a and the virtual line in the multi-core fiber 20, the normal direction of the light irradiation surface 53 a at the intersection of the light irradiation surface 53 a and the virtual line in the multi-core fiber 30, and the normal direction of the light irradiation surface 54 a at the intersection of the light irradiation surface 54 a and the virtual line in the multi-core fiber 40 all face the same direction. Here, the term "same direction" not only refers to the case where the normal directions are completely the same direction, but also allows for a slight deviation, for example, a deviation of about ±1°, between the normal directions. Any one of the light irradiation surfaces 51 a to 54 a may be formed to face in a direction different from the other light irradiation surfaces. In the example shown in Fig. 1, one light irradiation surface 51 a to 54 a is provided on each of the covered portions 51 to 54, but two or more light irradiation surfaces may be provided. In this case, for example, two light irradiation surfaces 51 a may be provided on the covered portions 51 facing each other in the third direction D3 (see, for example, Fig. 15).

[0035] Next, a method for manufacturing the above-mentioned optical fiber ribbon 1 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing a method for manufacturing the optical fiber ribbon shown in Fig. 1. To manufacture the optical fiber ribbon 1, first, the multicore fibers 10, 20, 30, and 40 are prepared. The multicore fibers 10, 20, 30, and 40 are wound around corresponding supply rolls 15, 25, 35, and 45, respectively, with the respective fibers being pulled out from the respective rolls.

[0036] The multi-core fibers 10, 20, 30, and 40 drawn out from the respective supply rolls 15, 25, 35, and 45 in this manner are coated with resin in the die 61 while being arranged in parallel to one another along the second direction D2. This resin is a ribbon resin that forms the coating member 50, and contains a thermosetting resin such as a silicone resin, an epoxy resin, or a urethane resin, or an ultraviolet-curable resin such as an epoxy acrylate, a urethane acrylate, or a polyester acrylate. Such a resin is introduced into the die 61, and the ribbon resin is applied to cover the multi-core fibers 10, 20, 30, and 40 aligned in the die 61. Thereafter, the applied resin is irradiated with ultraviolet light (not shown), and the ribbon resin is cured. The molding holes located inside the die 61 and through which the multi-core fibers 10, 20, 30, and 40 pass have a cross-sectional shape that corresponds to the outer shape of the coating member 50 shown in FIG. 1 .

[0037] When the coating member 50 is formed, illumination light L is irradiated from a light irradiation device 62 onto light irradiation surfaces 51 a, 52 a, 53 a, and 54 a in the coating resin portions that coat the multicore fibers 10, 20, 30, and 40, and luminance data, which is the shadow of the light that has passed through the optical fiber ribbon 1, is received by a light receiving device 63. The light receiving device 63 is, for example, a camera. The light received by the light receiving device 63 can be expressed as luminance data shown, for example, in parts (a) to (c) of FIG. 4. The luminance data shown in parts (a) to (c) of FIG. 4 are graphs of luminance data corresponding to the multicore fibers. By detecting whether such luminance data graphs have symmetry, it is possible to determine whether the core arrangements in each of the multicore fibers 10, 20, 30, and 40 are aligned.

[0038] Then, based on the results of the light irradiation (graph of the brightness data), the multiple cores in each of the multicore fibers 10, 20, 30, and 40 are aligned. In this alignment, the brightness data from the light receiving device 63 is analyzed by the control device 64, and the angles of the supply rolls 15, 25, 35, and 45 are finely adjusted by a motor (not shown) or the like so that the brightness data has symmetry based on the analysis results. This adjusts the positions of the cores.

[0039] In the manufacturing method according to the present embodiment, the illumination light L is irradiated onto light irradiation surfaces 51 a, 52 a, 53 a, and 54 a provided corresponding to the multicore fibers 10, 20, 30, and 40. As described above, these light irradiation surfaces 51 a to 54 a are flat surfaces having a predetermined width or curved surfaces having a curvature radius of 0.5 mm or more, and therefore, even if there is uneven distribution of resin in each of the multicore fibers 10, 20, 30, and 40, the effect on the symmetry of the luminance data of light transmitted through the fiber is reduced. Below, it will be described how, even if there is uneven distribution of resin (uneven thickness portion), providing such light irradiation surfaces reduces the effect on core alignment.

[0040] First, with reference to FIGS. 3 and 4 , a general method for aligning the cores of a multi-core fiber by irradiating the side surface of the multi-core fiber with illumination light to obtain brightness data and utilizing the symmetry of the brightness data will be described. FIG. 3 is a diagram for explaining core alignment by light irradiation in a general multi-core fiber. Parts (a), (b), and (c) of FIG. 4 are diagrams showing measurement results of the symmetry in the core alignment shown in FIG. 3 , and respectively show cases where the alignment angles are −1°, ±0°, and +1°. As shown in FIG. 3 , a general multi-core fiber 110 includes multiple cores 111, a cladding 112, a primary resin layer 113, and a secondary resin layer 114. Here, for ease of explanation, three cores 111 are shown, but the same applies when more cores 111 are included. Illumination light L is irradiated from the side of such a multi-core fiber 110, and transmitted light is received by a camera, which is a light receiving device, for observation. Graphs of brightness data received by such a camera are, for example, as shown in parts (a) to (c) of Fig. 4. Then, the multicore fiber 110 is aligned by slightly rotating it in the plus (+) or minus (-) direction shown in Fig. 3 so that the graph of such brightness data has symmetry as shown in part (b) of Fig. 4.

[0041] Such symmetry of the luminance data can also be shown, for example, as an asymmetry graph as shown in FIG. 5. The graph in FIG. 5 displays the value obtained by integrating the square of the difference between the normal signal of the luminance data and the signal obtained by flipping the luminance data horizontally. If the luminance data is completely symmetric, the value is 0, and the value increases as the asymmetry increases. It has been empirically found that when such an asymmetry value is, for example, 0.2 or less, the core arrangement in the multicore fiber is uniform and appropriate. However, as shown in part (b) of FIG. 6, there may be uneven distribution of the resin outside the cladding 112. Part (a) of FIG. 6 shows a case where there is no uneven distribution of the resin. When there is no uneven distribution of the resin as shown in part (a) of FIG. 6, and when the core arrangement is uniform as shown in part (a) of FIG. 7, symmetrical luminance data can be obtained. On the other hand, when there is uneven distribution of the resin as shown in part (b) of FIG. 6, even though the cores 111 themselves are uniform, the symmetry of the luminance data is lost, resulting in asymmetric luminance data, as shown in part (b) of FIG. 7. In this case, if the determination is made based on the brightness data alone, it may be determined that the cores 111 of the multicore fiber 110A are not aligned.

[0042] Parts (a), (b), and (c) of Fig. 8 show examples of the light transmission state when the light irradiation surface is changed to a curved surface with a large radius of curvature or a flat surface when there is uneven distribution of the coating resin of the ribbon fiber. Part (a) of Fig. 8 shows the general multi-core fiber 110A described above, and parts (b) and (c) of Fig. 8 show multi-core fibers provided with a light irradiation surface corresponding to the present embodiment described above. Parts (a), (b), and (c) of Fig. 8 all have the same core arrangement. Fig. 9 is a diagram showing the relationship between asymmetry and the radius of curvature of the light irradiation surface in each of the aspects shown in parts (a) to (c) of Fig. 8. In the structure shown in part (a) of Fig. 8, as described above, uneven distribution of resin causes the transmitted illumination light to become distorted (asymmetric), but simulations have shown that when a curved light irradiation surface 51A with a curvature radius of 0.5 mm or more is provided on the optical fiber ribbon 1A as shown in part (b) of Fig. 8, the illumination light maintains symmetry. Similarly, simulations have shown that when a flat light irradiation surface 51B with an infinite curvature radius is provided on the optical fiber ribbon 1B as shown in part (c) of Fig. 8, the illumination light maintains symmetry.

[0043] FIG. 9 shows a table plotting asymmetry when the curvature of the curved surface forming the light irradiation surface 51A is changed. As is clear from FIG. 9, it has been found that by setting the radius of curvature to 0.5 mm or more, the asymmetry value in the transmitted light when the illumination light L is irradiated onto the multicore fiber can be set to the above-mentioned specified value of 0.2 or less. Furthermore, FIG. 10 shows brightness data when the light irradiation surface 51B is formed from a flat surface, as shown in part (c) of FIG. 8. As is clear from FIG. 10, it has been found that by using a flat light irradiation surface 51B, a graph with good symmetry can be obtained even if the resin is unevenly distributed, as long as the cores are aligned.

[0044] Next, with reference to FIG. 11 , an example comparing cases where the light irradiation surface 51B is provided on one side and on both sides will be described. Part (a) of FIG. 11 shows the transmission state when illumination light is irradiated onto a general multi-core fiber 110A in the case where there is uneven resin distribution. Part (b) of FIG. 11 shows the transmission state when illumination light is irradiated onto a multi-core fiber (optical fiber ribbon 1C) having a light irradiation surface 51B provided on one side in the case where there is uneven resin distribution. Part (c) of FIG. 11 shows the transmission state when illumination light is irradiated onto a multi-core fiber having a light irradiation surface 51B provided on both sides in the case where there is uneven resin distribution. In parts (a), (b), and (c) of FIG. 11 , the core arrangement is aligned. As shown in parts (b) and (c) of FIG. 11 , it is clear that when there is uneven resin distribution, by providing a flat light irradiation surface 51B on either one side or both sides, the transmitted light becomes symmetrical. Figure 12 plots the asymmetry values ​​for the multicore fiber shown in parts (a), (b), and (c) of Figure 11. As is clear from Figure 12, by providing the light irradiation surface 51B on one or both surfaces, the asymmetry value is significantly smaller than the reference value of 0.2. Furthermore, when the light irradiation surface 51B is provided on both surfaces, the asymmetry value is even lower than when the light irradiation surface 51B is provided on only one surface. In other words, it can be seen that providing both light irradiation surfaces 51B allows for more reliable core alignment. However, since the asymmetry value is sufficiently small even when the light irradiation surface 51B is provided on only one surface, it is clear that core alignment can be reliably performed even when the light irradiation surface 51B is provided on only one surface.

[0045] As explained above, by providing a light irradiation surface having a width greater than the diameter of the core in the region where a virtual line passing through at least two or more cores or a virtual line (center line) passing through the center of the multi-core fiber intersects with the outer periphery of the coating portion, and by including a curved surface or a flat surface with a curvature radius of 0.5 mm or more, it can be seen that core alignment can be performed without problems even if there is uneven distribution of resin around the cladding.

[0046] Next, examples of the positional relationship between each light irradiation surface and the cores of the multi-core fiber in the optical fiber ribbon according to this embodiment will be described with reference to FIGS. 13 and 14 . FIG. 13 describes an example of an optical fiber ribbon 201 including a multi-core fiber 210. Although FIG. 13 shows only one multi-core fiber 210, the optical fiber ribbon 201 includes a plurality of multi-core fibers 210. The multi-core fiber shown in FIG. 13 has 12 cores 211. Furthermore, parts (a) and (b) of FIG. 14 describe an example of an optical fiber ribbon 301 including a multi-core fiber 310. Part (c) of FIG. 14 describes an example of an optical fiber ribbon 401 including a multi-core fiber 410. Although FIG. 14 shows only one multi-core fiber 310, 410, the optical fiber ribbons 301, 401 include a plurality of multi-core fibers 310, 410. The multi-core fiber 310 shown in parts (a) and (b) of Fig. 14 is provided with 16 cores 311. The multi-core fiber 410 shown in part (c) of Fig. 14 is provided with 12 cores 411 and one core marker 411b.

[0047] Returning to FIG. 13 , the explanation will be continued. In the example shown in part (a) of FIG. 13 , a flat light irradiation surface 251a is formed in the region where an imaginary line A1 passing through four cores 211 in a row shifted to the right from the center intersects with the outer periphery of the covering portion 251. The axis of the imaginary line A1 faces in the same direction as the normal to the light irradiation surface 251a. The width of this light irradiation surface 251a is 20 μm or more longer than the diameter of the core 211. The light irradiation surface 251a may not be flat, but may be a curved surface with a large radius of curvature of 0.5 mm or more. The same applies to the following examples. The structure of this example makes it easy to select and align cores that are the target of core alignment.

[0048] In the example shown in part (b) of Figure 13, a flat light irradiation surface 251a is formed in a region where a virtual line A2 (center line) passing between four cores 211a in a row shifted leftward from the center and four cores 211b in a row shifted rightward from the center intersects with the outer periphery of the coating portion 251. In this case, the virtual line A2 passes through the center of the multicore fiber 210. The axis of the virtual line A2 faces in the same direction as the normal direction of the light irradiation surface 251a. The width of this light irradiation surface 251a is 20 µm or more longer than the diameter of the cores 211 (cores 211a, 211b). According to the structure of this example, although the signal of the brightness data through which the irradiation light passes is weakened, it is easier to obtain symmetry.

[0049] In the example shown in part (c) of Figure 13, the multi-core fiber 210 shown in part (a) of Figure 13 is rotated 45 degrees. In this example, a flat light irradiation surface 251a is formed in the region where a virtual line A3 passing through two cores 211c on a center line passing through the center of the fiber intersects with the outer periphery of the coating portion 251. The axis of the virtual line A3 is oriented in the same direction as the normal to the light irradiation surface 251a. The width of this light irradiation surface 251a is 20 µm or more longer than the diameter of the core 211 (core 211c). The structure of this example allows for selective alignment of cores to be aligned, and also improves the symmetry of the luminance data of transmitted illumination light.

[0050] In the example shown in part (a) of FIG. 14 , a flat light irradiation surface 351a is formed in the region where a virtual line B1 (center line) passing through the four cores 311a on the center line passing through the center of the multicore fiber 310 intersects with the outer periphery of the coating portion 351. The axis of the virtual line B1 faces the same direction as the normal to the light irradiation surface 351a. The width of this light irradiation surface 351a is 20 μm or more longer than the diameter of the core 311 (core 311a). The light irradiation surface 351a may not be flat, but may be a curved surface with a large radius of curvature of 0.5 mm or more. The same applies to the following examples. According to the structure of this example, it is possible to select and align the cores to be targeted for core alignment, and to improve the symmetry of the luminance data of the transmitted illumination light.

[0051] In the example shown in part (b) of Figure 14, similar to the example shown in part (a) of Figure 14, a flat light irradiation surface 351a is formed in a region where a virtual line B2 passing through four cores 311a on a center line passing through the center of the multicore fiber 310 intersects with the outer periphery of the coating portion 351. The axis of the virtual line B2 faces the same direction as the normal to the light irradiation surface 351a. However, in this example, the pitch between the cores 311a on the center line and the outer cores 311b is larger than the other core pitches. The rest of the structure is similar to the example shown in part (a) of Figure 14. According to the structure of this example, the distance between the cores 311a to be aligned and the non-aligned cores 311b, etc., is increased, thereby reducing core overlap during rotation during alignment and enabling accurate alignment.

[0052] In the example shown in part (c) of FIG. 14 , a core marker 411b is further provided in addition to the multi-core fiber 210 shown in part (c) of FIG. 13 . A flat light irradiation surface 451a is formed in the region where a virtual line B3 (center line) passing through two cores 411a and the core marker 411b on a center line passing through the center of the fiber intersects with the outer periphery of the coating portion 451. The axis of the virtual line B3 faces the same direction as the normal to the light irradiation surface 451a. The width of this light irradiation surface 451a is 20 μm or more longer than the diameters of the cores 411a and the core marker 411b. According to the structure of this example, similar to the example shown in part (c) of FIG. 13 , it is possible to select and align the cores to be aligned, and it is also possible to improve the symmetry of the luminance data of the transmitted illumination light. Furthermore, the addition of a marker can improve detection sensitivity. The above core arrangement is merely an example, and other arrangements may be used.

[0053] As described above, in the optical fiber ribbon 1 according to the present embodiment, light irradiation surfaces 51 a, 52 a, 53 a, and 54 a having a width greater than the diameter of the cores are provided in regions where an imaginary line passing through at least two of the multiple cores 11, 21, 31, and 41 or an imaginary line (e.g., a center line) passing through the center of each multi-core fiber intersects with the outer periphery of the coating portions 51, 52, 53, and 54. These light irradiation surfaces 51 a to 54 a are curved or flat surfaces with a radius of curvature of 0.5 mm or greater. In this case, according to the simulation results (e.g., FIGS. 8 and 9 ) by the inventors, even if the resin coating the cladding in the optical fiber ribbon has a certain degree of uneven distribution (uneven thickness), by irradiating illumination light from the light irradiation surfaces with the above structure, the transmitted light can be symmetrical if the cores are aligned. Therefore, the optical fiber ribbon 1 can provide a ribbon in which the multiple cores 11, 21, 31, and 41 are reliably aligned.

[0054] Furthermore, in this optical fiber ribbon 1, recesses 55, 56, and 57 are provided between the coating portions, which allows the individual fibers to be easily separated. That is, the optical fiber ribbon 1 can be used as a single-fiber separable ribbon.

[0055] In the optical fiber ribbon 1 according to this embodiment, the light irradiation surfaces 51 a, 52 a, 53 a, and 54 a face the same direction. Therefore, the illumination light L for aligning each core in each of the multi-core fibers 10, 20, 30, and 40 can be irradiated from the same direction. Therefore, it is possible to provide an optical fiber ribbon that allows easy alignment of a ribbon including a plurality of multi-core fibers.

[0056] In the optical fiber ribbon 1 according to this embodiment, the width of each of the light irradiation surfaces 51a, 52a, 53a, and 54a is 20 μm or more longer than the diameter of each of the cores 11, 21, 31, and 41. In the optical fiber ribbon 1, the resin, which is a constituent element, may be unevenly distributed. However, for example, if the core center is shifted by about 10 μm from the predetermined position (no change in thickness rate of 70%), this is acceptable as a product. Therefore, even in a ribbon with such uneven resin distribution, by providing the light irradiation surfaces 51a to 54a with the above-mentioned widths, the influence of the uneven distribution can be reduced, and a ribbon with reliable core alignment can be obtained.

[0057] In the optical fiber ribbon according to this embodiment, the imaginary line defining the positions of the light irradiation surfaces 51 a, 52 a, 53 a, and 54 a may pass through at least three or more cores. In this case, the ribbon including a plurality of multi-core fibers can be more reliably aligned.

[0058] In the optical fiber ribbon 1 according to this embodiment, all of the light irradiation surfaces 51 a, 52 a, 53 a, and 54 a may be flat, which makes it possible to easily improve the accuracy of forming each light irradiation surface.

[0059] Although the optical fiber ribbon 1 and its manufacturing method according to the present disclosure have been described in detail above, the present invention is not limited to the above embodiment and can be applied to various embodiments and modified examples. For example, in the above description, the light irradiation surfaces 51 a, 52 a, 53 a, and 54 a are provided on one side of each of the multi-core fibers 10, 20, 30, and 40. However, as shown in Fig. 15, an optical fiber ribbon 1D may be provided with the light irradiation surfaces 51 a to 54 a on both sides of each of the multi-core fibers 10, 20, 30, and 40. In this case, each of the light irradiation surfaces 51 a to 54 a may be a flat surface or a curved surface having a curvature radius of 0.5 mm or more.

[0060] In the above description, an optical fiber ribbon including four (or two pairs) multi-core fibers has been described, but the present disclosure is not limited to this. That is, it will be clear to those skilled in the art that the present disclosure can be applied to any optical fiber ribbon including two or more multi-core fibers. For example, as shown in FIG. 16 , an optical fiber ribbon 1E may be provided with 12 (or six pairs) multi-core fibers 10, 20, 30, 40 (optical fibers), which is more than four (or two pairs). In this case, too, light irradiation surfaces 51 a to 54 a are provided in the regions where the imaginary lines of each optical fiber intersect with the outer periphery of the coating portion, and similarly to the above, a ribbon can be provided in which the alignment of the multiple cores in each optical fiber is reliably performed.

[0061] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C, 1D, 1E... Optical fiber ribbon 10... Multicore fiber (first multicore fiber) 11, 11a, 11b... Core (first core) 12... Clad (first clad) 13, 23, 33, 43... Primary resin layer 14, 24, 34, 44... Secondary resin layer 15, 25, 35, 45... Supply roll 20... Multicore fiber (second multicore fiber) 21... Core (second core) 22... Clad (second clad) 30... Multicore fiber (third multicore fiber) 31... Core (third core) 32... Clad (third clad) 40... Multicore fiber (fourth multicore fiber) 41... Core (fourth core) 42... Clad (fourth clad) 50... Coating member 51... First coating portion DESCRIPTION OF THE SYMBOLS 51a...Light irradiation surface (first light irradiation surface) 51A, 51B...Light irradiation surface 52...Second coated portion 52a...Light irradiation surface (second light irradiation surface) 53...Third coated portion 53a...Light irradiation surface (third light irradiation surface) 54...Fourth coated portion 54a...Light irradiation surface (fourth light irradiation surface) 55, 56, 57...Recess 61...Die 62...Light irradiation device 63...Light receiving device 64...Control device 110, 110A...Multi-core fiber 111...Core 112...Cladding 113...Primary resin layer 114...Second resin layer 201, 301, 401...Optical fiber ribbon 210, 310, 410...Multi-core fiber 211, 211a, 211b, 211c, 311, 311a, 311b, 411, 411a...core 251, 351, 451...coated portion 251a, 351a, 451a...light irradiation surface 411b...core marker A1, A2, A3, B1, B2, B3...virtual line L...illumination light

Claims

1. An optical fiber ribbon comprising: a first multi-core fiber having a plurality of first cores and a first clad covering the plurality of first cores; a second multi-core fiber having a plurality of second cores and a second clad covering the plurality of second cores, the second multi-core fiber being arranged in parallel to the first multi-core fiber; and a coating member covering at least partially the first multi-core fiber and the second multi-core fiber, wherein the coating member has a first coating portion covering the first multi-core fiber and a second coating portion covering the second multi-core fiber, and a first light irradiation surface having a width greater than a diameter of the first cores is provided in at least one region where a virtual line passing through at least two or more of the plurality of first cores or a virtual line passing through a center of the first multi-core fiber intersects with an outer periphery of the first coating portion, and the first light irradiation surface includes a curved surface or a flat surface having a radius of curvature of 0.5 mm or more.

2. The optical fiber ribbon according to claim 1, wherein a second light irradiation surface having a width greater than a diameter of the second core is provided in at least one region where a virtual line passing through at least two or more of the plurality of second cores or a virtual line passing through the center of the second multicore fiber intersects with an outer periphery of the second coating portion, and the second light irradiation surface includes a curved surface or a flat surface having a radius of curvature of 0.5 mm or more.

3. The optical fiber ribbon according to claim 2, wherein the normal direction of the first light irradiation surface at the intersection of the first light irradiation surface and the virtual line is oriented in the same direction as the normal direction of the second light irradiation surface at the intersection of the second light irradiation surface and the virtual line.

4. The optical fiber ribbon according to claim 3, wherein an axis of the virtual line and a normal direction of the first light irradiation surface are oriented in the same direction.

5. An optical fiber ribbon according to any one of claims 1 to 4, wherein the arrangement of the multiple first cores is linearly symmetrical with respect to a virtual line passing through the center of the first multicore fiber, at least in the range corresponding to the first light irradiation surface.

6. An optical fiber ribbon according to any one of claims 1 to 5, wherein the arrangement of the multiple first cores is linearly symmetrical with respect to a virtual line passing through the center of the first multicore fiber.

7. An optical fiber ribbon according to any one of claims 1 to 6, wherein the width of the first light irradiation surface is at least 20 µm longer than the diameter of the first core.

8. The optical fiber ribbon according to any one of claims 1 to 7, wherein the virtual line passes through at least three or more of the first cores.

9. An optical fiber ribbon according to any one of claims 1 to 8, wherein the first light irradiation surface is provided in each of two opposing regions where the virtual line intersects on the outer periphery of the first coated portion.

10. A third multi-core fiber having a plurality of third cores and a third clad covering the plurality of third cores, and a fourth multi-core fiber having a plurality of fourth cores and a fourth clad covering the plurality of fourth cores, wherein the first multi-core fiber, the second multi-core fiber, the third multi-core fiber, and the fourth multi-core fiber are arranged in parallel in this order, the coating member covers the third multi-core fiber and the fourth multi-core fiber as well as the first multi-core fiber and the second multi-core fiber, the coating member further has a third coating portion coating the third multi-core fiber and a fourth coating portion coating the fourth multi-core fiber, and a recess is provided at least one between the first coating portion and the second coating portion, between the second coating portion and the third coating portion, and between the third coating portion and the fourth coating portion, 3. The optical fiber ribbon according to claim 2, wherein a third light irradiation surface having a width greater than a diameter of the third core is provided in a region where a virtual line passing through at least two or more of the plurality of third cores or a virtual line passing through a center of the third multicore fiber intersects with an outer periphery of the third coated portion, and the third light irradiation surface includes a curved surface or a plane having a radius of curvature of 0.5 mm or more; and a fourth light irradiation surface having a width greater than a diameter of the fourth core is provided in a region where a virtual line passing through at least two or more of the plurality of fourth cores or a virtual line passing through the center of the fourth multicore fiber intersects with an outer periphery of the fourth coated portion, and the fourth light irradiation surface includes a curved surface or a plane having a radius of curvature of 0.5 mm or more.

11. The optical fiber ribbon core wire as described in claim 10, wherein a normal direction of the first light irradiation surface at an intersection of the first light irradiation surface and the virtual line, a normal direction of the second light irradiation surface at an intersection of the second light irradiation surface and the virtual line, a normal direction of the third light irradiation surface at an intersection of the third light irradiation surface and the virtual line, and a normal direction of the fourth light irradiation surface at an intersection of the fourth light irradiation surface and the virtual line all face in the same direction.

12. A method for manufacturing an optical fiber ribbon, comprising: a step of preparing a first multi-core fiber having a plurality of first cores and a first clad covering the plurality of first cores; a step of coating the first multi-core fiber and the second multi-core fiber with resin while arranging the first multi-core fiber and the second multi-core fiber in parallel; a step of irradiating light to a light irradiation surface in a coating resin part that coats the first multi-core fiber, and aligning the plurality of first cores in the first multi-core fiber based on a result of the light irradiation, wherein the light irradiation surface is a surface provided in a region where a virtual line passing through at least two or more of the plurality of first cores or a virtual line passing through a center of the first multi-core fiber intersects with the outer periphery of the coating resin part, and the light irradiation surface has a width greater than a diameter of the first cores, and includes a curved surface or a flat surface having a radius of curvature of 0.5 mm or more.

Images