Coated optical fiber ribbon and method for manufacturing coated optical fiber ribbon

Abstract

A coated optical fiber ribbon (1) comprises: a plurality of multicore fibers (10) each having a plurality of cores (11) and a cladding (12) that covers the plurality of cores (11); and a covering member (50) that at least partially covers the plurality of multicore fibers (10). In at least one multicore fiber (10) among the plurality of multicore fibers (10), the plurality of cores (11) are eight or more cores and are disposed so as to be line-symmetric with respect to a reference line passing through the fiber center in a cross section of the at least one multicore fiber (10). The distance between a pair of adjustment cores (11a) located on the reference line and farthest from each other among the plurality of cores (11) is larger than a maximum radius that is the distance between the fiber center and the outermost core (11b) farthest from the fiber center.

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. 2023-120859, filed on July 25, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Documents 1 and 2 disclose a ribbon core wire including a plurality of multi-core fibers and a manufacturing method thereof. Patent Document 3 discloses a method for aligning a multi-core fiber. In the alignment method described in Patent Document 3, illumination light is irradiated onto the side surface of the multi-core fiber, and displacement of the shadow of the core is detected with an imaging device, thereby detecting twist of the multi-core fiber, and the twist is eliminated using a twist-eliminating pulley.

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

[0004] An optical fiber ribbon according to an embodiment of the present disclosure includes a plurality of multi-core fibers, each having a plurality of cores and a cladding covering the plurality of cores, and a coating member at least partially coating the plurality of multi-core fibers. In at least one of the plurality of multi-core fibers, the plurality of cores is eight or more, and is arranged so as to be symmetrical with respect to a reference line passing through the center of the fiber in a cross section of the at least one multi-core fiber. The distance between a pair of adjustment cores that are located on the reference line and are farthest from each other is greater than the maximum radius, which is the distance between the fiber center and the outermost core that is farthest from the fiber center.

[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 for aligning cores in a 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 a rotation angle. Fig. 6 is a schematic diagram for explaining the inter-core distance dc and the core movement amount in a multicore fiber. Part (a) of Fig. 7 shows a typical core arrangement in a 12-core multicore fiber, and parts (b) and (c) show a core arrangement in which the inter-core distance in the 12-core multicore fiber is increased. Part (a) of Fig. 8 shows a typical core arrangement in a 16-core multicore fiber, and parts (b), (c), (d), and (e) show core arrangements in which the inter-core distance in the 16-core multicore fiber is increased and the cores are positioned in a rotationally asymmetric position. Parts (a) and (b) of Fig. 9 show modified core arrangements in which the inter-core distance is increased in a 12-core multi-core fiber, and parts (c) and (d) of Fig. 9 show modified core arrangements in which the inter-core distance is increased in a 16-core multi-core fiber. Part (a) of Fig. 10 shows a general core arrangement in an 8-core multi-core fiber, and part (b) of Fig. 10 shows a core arrangement in which the inter-core distance is increased in an 8-core multi-core fiber and the cores are positioned in rotationally asymmetric positions.

[0006] [Problem to be Solved by the Present Disclosure] When manufacturing the ribbon core wires described in Patent Documents 1 and 2, the rotation direction of each multi-core fiber may be adjusted around the fiber center. In this case, as described in Patent Document 3, for example, illumination light is irradiated onto the side surface of the multi-core fiber, and the rotation adjustment is performed by detecting whether the core arrangement in the fiber is appropriate based on the symmetry and asymmetry of the transmitted light containing the core images (see, for example, parts (a) to (c) of FIG. 4). However, as the number of cores arranged in one multi-core fiber increases beyond seven, for example to 12 or 16, the distance between the aligned cores (hereinafter referred to as "adjustment cores") used as the basis for the above-mentioned adjustment becomes shorter. The value of the asymmetry of the transmitted light is proportional to the product of the distance between such adjustment cores and the rotation angle during adjustment. Therefore, as the distance between the adjustment cores becomes shorter, it becomes difficult to adjust the asymmetry, and the detection accuracy of the core positions in each multi-core fiber decreases. Therefore, a method capable of accurately detecting core positions in a ribbon core wire including multiple multi-core fibers is desired. There may be more than two adjusting cores, but in that case, the pair of adjusting cores with the greatest distance between them, i.e., the pair located on the outermost sides, will be most effective in adjusting asymmetry.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to accurately detect the core positions 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 plurality of multi-core fibers, each having a plurality of cores and a cladding covering the plurality of cores, and a coating member that at least partially coats the plurality of multi-core fibers. In at least one multi-core fiber among the plurality of multi-core fibers, the plurality of cores are eight or more cores, and are arranged to be line-symmetrical with respect to a reference line passing through the center of the fiber in a cross section of the at least one multi-core fiber. Among the plurality of cores, the distance between a pair of adjustment cores that are located on the reference line and are farthest from each other is greater than the maximum radius, which is the distance between the fiber center and the outermost core that is farthest from the fiber center.

[0009] In the optical fiber ribbon described above in [1], the distance between a pair of adjustment cores that are located on the reference line and are farthest from each other among the multiple cores is greater than the maximum radius, which is the distance between the fiber center and the outermost core among the multiple cores that is farthest from the fiber center in the radial direction. In this case, in a multi-core fiber having eight or more cores, it is easy to adjust the asymmetry even if the number of cores is large, and the detection accuracy of the core positions in the multi-core fiber can be improved. Therefore, with this optical fiber ribbon, it is possible to accurately detect the core positions in a ribbon fiber including multiple multi-core fibers.

[0010] [2] In the optical fiber ribbon according to [1], at least one of the pair of adjustment cores may be arranged on a circumference centered on the fiber center and on which the outermost core is arranged. In this case, the distance between the pair of adjustment cores can be made longer, making it easier to adjust the asymmetry even when the number of cores is large. Therefore, with this optical fiber ribbon, the core positions can be detected with even greater accuracy.

[0011] [3] In the optical fiber ribbon according to [1] or [2] above, in at least one multicore fiber, the multiple cores may be arranged so as to be rotationally asymmetric when rotated around the fiber center by an angle of 360 / n degrees (n is any integer equal to or greater than 2). In this case, since the cores are arranged rotationally asymmetric, the rotation direction for core alignment can be easily determined and the alignment can be performed.

[0012] [4] In the optical fiber ribbon according to any one of the above [1] to [3], the number of cores may be 12. In this case, in a 12-core multi-core fiber, even if the number of cores is large, it becomes easy to adjust the asymmetry, and it is possible to improve the detection accuracy of the core positions in the multi-core fiber.

[0013] [5] In the optical fiber ribbon according to any one of the above [1] to [3], the number of cores may be 16. In this case, in a 16-core multi-core fiber, even if the number of cores is large, it becomes easy to adjust the asymmetry, and it is possible to improve the detection accuracy of the core positions in the multi-core fiber.

[0014] [6] A manufacturing method of an optical fiber ribbon according to one embodiment includes the steps of: preparing a plurality of multi-core fibers, each having a plurality of cores and a cladding covering the plurality of cores; coating each of the plurality of multi-core fibers with resin while arranging the plurality of multi-core fibers in parallel to one another; and irradiating light onto a light irradiation surface of a coating resin portion covering at least one multi-core fiber among the plurality of multi-core fibers, and aligning the arrangement of the plurality of cores in the at least one multi-core fiber based on the result of the light irradiation. In the at least one multi-core fiber, the plurality of cores are eight or more cores, and are arranged so as to be line-symmetrical with respect to a reference line passing through the fiber center in a cross section of the at least one multi-core fiber. The distance between a pair of adjustment cores that are located on the reference line and are farthest from each other among the plurality of cores is greater than a maximum radius, which is the distance between the fiber center and the outermost core farthest from the fiber center. In this manufacturing method, in the step of aligning the core arrangement, at least one multi-core fiber is arranged so that the reference line of at least one multi-core fiber intersects with the light irradiation surface, and light is irradiated onto the light irradiation surface in the coating resin portion, and the multiple cores of at least one multi-core fiber are aligned using an image that has passed through a pair of adjustment cores.

[0015] In the manufacturing method of an optical fiber ribbon according to the above [6], in a multi-core fiber to which light is irradiated when aligning the cores, the multiple cores are eight or more cores, and are arranged so as to be linearly symmetrical with respect to a reference line passing through the center of the fiber in the cross section of the multi-core fiber. Furthermore, the distance between a pair of adjustment cores that are located on the reference line and are farthest from each other among the multiple cores is greater than the maximum radius, which is the distance between the fiber center and the outermost core among the multiple cores that is farthest from the fiber center in the radial direction. In this case, in a multi-core fiber with eight or more cores (e.g., 8, 12, or 16 cores), it is easy to adjust the asymmetry even if the number of cores is large, and the detection accuracy of the core positions in the multi-core fiber can be improved. Therefore, with this optical fiber ribbon, it is possible to accurately detect the core positions in a ribbon fiber including multiple multi-core fibers.

[0016] [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.

[0017] 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 also 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-core ribbon, and recesses 55, 56, and 57 are provided between each fiber to enable individual fiber separation. The optical fiber ribbon 1 does not necessarily have to be provided with the recesses 55 to 57.

[0018] The multi-core fiber 10 has a plurality of cores 11, a cladding 12 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 multi-core fiber 10, for example, 12 cores 11 are arranged in line symmetry, with eight cores 11 evenly spaced on the outer periphery and four cores 11 evenly spaced on the inner periphery. The line serving as a reference for line symmetry here is an observation axis used when inspecting the core arrangement by rotating the multi-core fiber when fabricating the optical fiber ribbon 1, and is, for example, a line that intersects orthogonally with (intersects with) the light irradiation surface 51 a of the coating member 50 and passes through the fiber center of the multi-core fiber 10. Such a reference line extends, for example, along the third direction D3. 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 cores 11 is 12 in the example shown in Fig. 1, but is not limited to this and may be 8 or 16 (see Figs. 8 and 10). The core arrangement in each multi-core fiber will be described in detail later.

[0019] The core 11 is made of pure silica (SiO ２ The 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.

[0020] 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.

[0021] 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.

[0022] The multi-core fiber 20, like the multi-core fiber 10, has a plurality of cores 21, a clad 22 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 multi-core fiber 30, like the multi-core fiber 10, has a plurality of cores 31, a clad 32 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 multi-core fiber 40, like the multi-core fiber 10, has a plurality of cores 41, a clad 42 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. The cores, clads, primary resin layers, and secondary resin layers of the multi-core fibers 20 to 40 have the same structures as the cores 11, clad 12, primary resin layer 13, and secondary resin layer 14 of the multi-core fiber 10, respectively, and therefore detailed description thereof will be omitted. The number of cores in each of the multicore fibers 20 to 40 may be 12 cores, or 8 or 16 cores.

[0023] 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-curing resin such as an epoxy acrylate, a urethane acrylate, or a polyester acrylate, from the viewpoint of preventing damage to the optical fiber and making it easy to separate. The coating member 50 has a coating portion 51 that covers the multi-core fiber 10, a coating portion 52 that covers the multi-core fiber 20, a coating portion 53 that covers the multi-core fiber 30, and a coating portion 54 that covers the multi-core fiber 40. The coating portions 51 to 54 are in contact with the outer circumferential surfaces of the corresponding multi-core fibers (the outer circumferential surfaces of the secondary resin layers, and the outer circumferential surfaces of the colored inks, if any), and coat the entirety of each multi-core fiber.

[0024] The 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 coated portion 52, the coated portion 53, and the 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.

[0025] Furthermore, planar light irradiation surfaces 51a, 52a, 53a, and 54a are formed on the coated portion 51, the coated portion 52, the coated portion 53, and the coated portion 54, respectively. The light irradiation surfaces 51a to 54a may not be planar but may be curved. The light irradiation surface 51a is provided in a region where a reference line (center line) passing through the fiber center and two or more cores 11 intersects with the outer periphery of the coated portion 51. In other words, the light irradiation surface 51a is provided on one side of the third direction D3 (upward in the figure) with respect to the core 11. Like the light irradiation surface 51a, the light irradiation surfaces 52a to 54a are provided in regions where a reference line (center line) passing through each fiber center and two or more cores 21, 31, and 41 intersects with the outer periphery of the coated portion 52, the coated portion 53, and the coated portion 54, respectively.

[0026] 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, multicore fibers 10, 20, 30, and 40 are prepared. Each of the multicore fibers 10 to 40 is wound around a corresponding supply roll 15, 25, 35, and 45, with each fiber being pulled out from each roll.

[0027] The multi-core fibers 10, 20, 30, and 40 drawn out from the 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 to 40 aligned in the die 61. Thereafter, the applied resin is irradiated with ultraviolet light (not shown), and the ribbon resin is cured.

[0028] Once the coating member 50 is formed, as shown in FIGS. 2 and 3 , 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 brightness data, which is the shadow of the light transmitted through the optical fiber ribbon 1, is received by a light receiving device 63. The light receiving device 63 is, for example, a camera. In FIG. 3 , for ease of explanation, the number of cores along the reference line is reduced to three. The light received by the light receiving device 63 can be expressed as brightness data shown, for example, in parts (a) to (c) of FIG. 4 . The brightness data shown in parts (a) to (c) of FIG. 4 is a graph of brightness data corresponding to the multicore fiber when rotationally adjusted, and the protruding portion in the center corresponds to the three cores shown in FIG. 3 . In part (b) of FIG. 4 , this central portion protrudes neatly with symmetry, indicating that the multiple cores on the reference line are aligned. 4, the symmetry of the central portion is broken and asymmetrical, indicating that the multiple cores on the reference line are not aligned (shifted). By detecting whether such a graph of brightness data has symmetry, it is possible to determine whether the core arrangements in each of the multi-core fibers 10 to 40 are aligned. Details of such core arrangements that improve the detection accuracy of core arrangements will be described later.

[0029] 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.

[0030] In the manufacturing method according to the present embodiment, such illumination light is irradiated onto the inside of the multi-core fiber from light irradiation surfaces 51 a, 52 a, 53 a, and 54 a provided corresponding to each of the multi-core fibers 10, 20, 30, and 40, and alignment is performed by rotating the multi-core fiber until each of the transmitted lights has a symmetrical shape (for example, the shape of (b) in Fig. 4). The relationship with the core arrangement when performing fiber alignment will be described below.

[0031] First, with reference to FIGS. 3 to 5 , a method for irradiating the side surface of a multi-core fiber with illumination light to acquire brightness data and then performing core alignment of a multi-core fiber by utilizing the symmetry of the brightness data will be described. FIG. 3 is a diagram for explaining core alignment of a 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 , the multi-core fiber includes multiple cores 11, a cladding 12 covering the cores 11, a primary resin layer 13, and a secondary resin layer 14. Here, for ease of explanation, three cores 11 are shown, but the same applies when more cores 11 are included. Illumination light L is irradiated onto the side surface of such a multi-core fiber 10, and the transmitted light is received by a camera, which is a light receiving device, for observation. Graphs of the brightness data received by such a camera are, for example, as shown in parts (a) to (c) of FIG. 4. Then, the multi-core fiber 10 is slightly rotated in the plus (+) or minus (-) direction shown in Figure 3 to align the brightness data graph so that it has symmetry as shown in part (b) of Figure 4.

[0032] FIG. 5 shows a graph representing the symmetry of such brightness data in relation to the rotation angle. The graph in FIG. 5 shows the relationship between the asymmetry and the rotation angle when the maximum distance dc between the cores to be aligned (see FIG. 6) is changed. dc1 is a graph when the inter-core distance dc is 40 μm, and dc2 is a graph when the inter-core distance dc is 80 μm. As is clear from these graphs, it is clear that the wider the inter-core distance dc2, the greater the asymmetry can be adjusted and the easier it is to adjust the core position as the rotation angle increases. FIG. 6 explains the core movement amount and inter-core distance dc when a multi-core fiber is rotated.

[0033] Here, an arrangement of multiple cores including a pair of adjustment cores to be irradiated with light will be described with reference to Fig. 7 . In the following description, the multi-core fiber 10 will be used as an example, but the same applies to the multi-core fibers 20, 30, and 40. Part (a) of Fig. 7 shows a typical core arrangement in a 12-core multi-core fiber, and parts (b) and (c) show core arrangements in which the inter-core distance in a 12-core multi-core fiber is increased. The black circles shown in parts (a) to (c) of Fig. 7 indicate cores in the multi-core fiber.

[0034] 7A, 12 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber. Furthermore, in this multicore fiber, the number of adjustment cores 11a arranged on the observation axis G is two, and the distance dc between a pair of adjustment cores 11a is smaller than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.58, while the inter-core distance dc is 1.41. In this case, since the distance dc between the adjustment cores 11a is shorter than the maximum radius r, it is not necessarily easy to eliminate the asymmetry.

[0035] 7B , similarly, 12 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G (reference line) that is orthogonal to the light irradiation surface 51 a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11 a arranged on the observation axis G is four, and a pair of the adjustment cores 11 a are arranged at positions on the outer periphery S. According to the multicore fiber 10 having such a core arrangement, the distance dc between the pair of adjustment cores 11 a located on the outermost sides is larger than the maximum radius r, which is the distance between the fiber center C and the outermost core 11 b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.71, while the inter-core distance dc is 3.41. In this case, since the distance dc between the adjustment cores 11 a is longer than the maximum radius r, it is easy to eliminate asymmetry and accurate alignment can be performed.

[0036] 7(c), 12 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11a arranged on the observation axis G is two, and of the pair of adjustment cores 11a, one is arranged on the outer periphery S and the other is arranged inside the outer periphery S. However, in the multicore fiber 10 having this core arrangement, the distance dc between the pair of adjustment cores 11a is larger than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.53, while the inter-core distance dc is 1.73. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, it is easy to eliminate the asymmetry and the alignment can be performed with high accuracy. Also, in the example shown in part (c) of Figure 7, the multiple cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined.

[0037] Next, another example of an arrangement of multiple cores including a pair of adjustment cores to be irradiated with light will be described with reference to Fig. 8 . In the following description, the multi-core fiber 10 will be used as an example, but the same applies to the multi-core fibers 20, 30, and 40. Part (a) of Fig. 8 shows a typical core arrangement in a 16-core multi-core fiber, and parts (b), (c), (d), and (e) show core arrangements in which the inter-core distance in a 16-core multi-core fiber is increased. The black circles shown in parts (a) to (e) of Fig. 8 indicate cores in the multi-core fiber.

[0038] In part (a) of Figure 8, 16 cores 11 are arranged so as to be axisymmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber. On the other hand, in this multicore fiber 10, the number of adjustment cores 11a arranged on the observation axis G is four, and the distance dc between the pair of adjustment cores 11a located on the outermost sides is greater than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 2.12, while the inter-core distance dc is 4.24, making it easy to eliminate asymmetry. However, in this example, the cores 11 are arranged so as to be rotationally symmetric. In this case, it may not be easy to determine the rotation direction for alignment.

[0039] In the example shown in part (b) of FIG. 8 , similarly, 16 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to the observation axis G, which is orthogonal to the light irradiation surface 51 a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11 a arranged on the observation axis G is four, and among them, a pair of adjustment cores 11 a located on the outer periphery S is left arranged, while one of the other cores 11 c arranged on the observation axis G is moved radially outward (upward in the figure) on the observation axis G from the arrangement structure shown in part (a) of FIG. 8 . With this arrangement, in the example shown in part (b) of FIG. 8 , the cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined. In this example, for example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.93, while the inter-core distance dc is 3.86. This makes it easy to eliminate asymmetry and enable accurate alignment.

[0040] Similarly, in the example shown in part (c) of FIG. 8 , 16 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51 a and passes through the fiber center C of the multicore fiber 10. On the other hand, in this multicore fiber 10, the number of adjustment cores 11 a arranged on the observation axis G is two, and while a pair of adjustment cores 11 a remains arranged on the outer periphery S, the four cores 11 d located on the inner side are arranged above the multicore fiber. With this arrangement, in the example shown in part (c) of FIG. 8 , the cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined. In this example, for example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.93, while the inter-core distance dc is 3.86. This makes it easy to eliminate asymmetry and enable accurate alignment.

[0041] Similarly, in the example shown in part (d) of FIG. 8 , 16 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11a arranged on the observation axis G is two, and the first adjustment core of the pair of adjustment cores 11a is arranged on the outer periphery S, the second adjustment core is arranged within the outer periphery S, and the five cores 11e (including the second adjustment core 11a) located on the inside are arranged to form a pentagonal shape. With this arrangement, in the example shown in part (d) of FIG. 8 , the cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined. In this example, for example, when the minimum distance between cores (core pitch) is 1, the maximum radius r1 is 1.81, while the inter-core distance dc is 2.71. This makes it easy to eliminate asymmetry and enable accurate alignment.

[0042] Similarly, in the example shown in part (e) of FIG. 8 , 16 cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11a arranged on the observation axis G is four, and among them, a pair of adjustment cores 11a located on the outer periphery S is arranged, and two more cores 11f are arranged on the observation axis G, and the five inner cores 11e (one core 11f is shared) are arranged to form a pentagonal shape. With this arrangement, in the example shown in part (e) of FIG. 8 , the cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined. In this example, for example, when the minimum distance between cores is 1, the maximum radius r1 is 2.00, while the inter-core distance dc is 4.00. This makes it easy to eliminate asymmetry and achieve accurate alignment.

[0043] Next, another example of an arrangement of multiple cores including a pair of adjustment cores to be irradiated with light will be described with reference to Fig. 9. In the following description, the multi-core fiber 10 will be used as an example, but the same applies to the multi-core fibers 20, 30, and 40. Parts (a) and (b) of Fig. 9 show modified core arrangements in which the inter-core distance in a 12-core multi-core fiber is increased, and parts (c) and (d) of Fig. 9 show modified core arrangements in which the inter-core distance in a 16-core multi-core fiber is increased.

[0044] In the example shown in part (a) of FIG. 9 , the number of adjustment cores 11a arranged on the observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10 is four. Of the pair of adjustment cores 11a located at the outermost positions, the first adjustment core is arranged at the outer periphery S, and the second adjustment core is positioned slightly inside the outer periphery S. The cores 11 are arranged such that some of the cores arranged in a square are shifted. According to the multicore fiber 10 having such a core arrangement, the distance dc between the pair of adjustment cores 11a is larger than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.80, while the inter-core distance dc is 3.30. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, it is easy to eliminate asymmetry and accurate alignment can be performed. 9A, the cores 11 are arranged so as to be rotationally asymmetric, which makes it easy to determine the rotation direction for alignment.

[0045] In the example shown in part (b) of FIG. 9 , the number of adjustment cores 11a arranged on the observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10 is four, and both of the pair of adjustment cores 11a located on the outermost sides are arranged at the outer periphery S. The cores 11 are arranged by thinning out some of the cores arranged in a square. According to the multicore fiber 10 having such a core arrangement, the distance dc between the pair of adjustment cores 11a is larger than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 2.00, while the inter-core distance dc is 4.00. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, it is easy to eliminate asymmetry and accurate alignment can be performed. 9B, the cores 11 are arranged so as to be rotationally asymmetric, which makes it easy to determine the rotation direction for alignment.

[0046] In the example shown in part (c) of FIG. 9 , the number of adjustment cores 11a arranged on the observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10 is four, and both of the pair of outermost adjustment cores 11a are arranged at the outer periphery S. According to the multicore fiber 10 with such a core arrangement, the distance dc between the pair of adjustment cores 11a is greater than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 2.12, while the inter-core distance dc is 4.24. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, asymmetry can be easily eliminated, and alignment can be performed accurately. Furthermore, in the example shown in part (c) of FIG. 9 , the multiple cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined.

[0047] In the example shown in part (d) of Fig. 9 , the number of adjustment cores 11a arranged on the observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10 is four, and of the pair of adjustment cores 11a located on the outermost sides, a first adjustment core is arranged at a position on the outer periphery S, and a second adjustment core is positioned slightly inside the outer periphery S. According to the multicore fiber 10 with such a core arrangement, the distance dc between the pair of adjustment cores 11a is larger than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 2.06, while the inter-core distance dc is 3.56. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, it is easy to eliminate asymmetry and accurate alignment can be performed. 9(d), the cores 11 are arranged so as to be rotationally asymmetric, which makes it easy to determine the rotation direction for alignment.

[0048] Next, with reference to Fig. 10 , yet another example of an arrangement of multiple cores including a pair of adjustment cores to be irradiated with light will be described. In the following description, the multi-core fiber 10 will be used as an example, but the same applies to the multi-core fibers 20, 30, and 40. Part (a) of Fig. 10 shows a typical core arrangement in an eight-core multi-core fiber, and part (b) of Fig. 10 shows a core arrangement in an eight-core multi-core fiber in which the inter-core distance is increased and the cores are positioned in rotationally asymmetric positions.

[0049] 10 (a), eight cores 11 are arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber. Furthermore, in this multicore fiber, the number of adjustment cores 11a arranged on the observation axis G is two, and the distance dc between a pair of adjustment cores 11a is the same as the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.15, while the inter-core distance dc is 1.15. In this case, since the distance dc between the adjustment cores 11a is the same as the maximum radius r, it is not necessarily easy to eliminate the asymmetry.

[0050] 10 (b) , eight cores 11 are similarly arranged so as to be line-symmetric (bilaterally symmetric) with respect to an observation axis G (reference line) that is orthogonal to the light irradiation surface 51a and passes through the fiber center C of the multicore fiber 10. Meanwhile, in this multicore fiber 10, the number of adjustment cores 11a arranged on the observation axis G is two, with the first adjustment core 11a being arranged at a position on the outer periphery S and the second adjustment core 11a being moved in a direction away from the center C (downward in the figure). According to the multicore fiber 10 arranged in this manner, the distance dc between the pair of adjustment cores 11a is greater than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b of the multiple cores 11 that is the farthest from the fiber center C in the radial direction. Specifically, in this example, when the minimum distance between cores (core pitch) is 1, the maximum radius r is 1.15, while the inter-core distance dc is 1.33. In this case, since the distance dc between the adjustment cores 11a is longer than the maximum radius r, it is easy to eliminate the asymmetry and the alignment can be performed with high accuracy. Also, in this example, the cores 11 are arranged so as to be rotationally asymmetric. In this case, the rotation direction for alignment can be easily determined.

[0051] As described above, according to the optical fiber ribbon 1 of this embodiment, the distance dc between the pair of adjustment cores 11a that are located on the observation axis G, which is a reference line, and that are farthest from each other among the multiple cores 11 is greater than the maximum radius r, which is the distance between the fiber center C and the outermost core 11b, among the multiple cores 11, that is farthest from the fiber center C in the radial direction. In this case, it becomes easier to adjust asymmetry in multiple multi-core fibers even if the number of cores is large, and it is possible to improve the detection accuracy of core positions in the multi-core fiber. Therefore, according to this optical fiber ribbon, it is possible to accurately detect core positions in a ribbon core including multiple multi-core fibers.

[0052] Furthermore, in the optical fiber ribbon 1 according to this embodiment, the multiple cores 11 may be arranged so as to be rotationally asymmetric when rotated around the fiber center by an angle of 360 / n degrees (n is any integer equal to or greater than 2) (for example, 180 degrees, 120 degrees, 90 degrees, 72 degrees, 51.43 degrees). In this case, since the cores 11 are arranged rotationally asymmetric, the rotation direction for core alignment can be easily determined and alignment can be performed.

[0053] Although the optical fiber ribbon and its manufacturing method according to the present disclosure have been described in detail above, the present disclosure is not limited to the above-described embodiment and can be applied to various embodiments and modifications. For example, although the above description has been made on an optical fiber ribbon including four multi-core fibers, the present disclosure is not limited to this. In other words, the contents of the present disclosure may be applied to an optical fiber ribbon including two multi-core fibers.

[0054] DESCRIPTION OF SYMBOLS 1...Optical fiber ribbon 10...Multi-core fiber 11, 11c, 11d, 11e, 11f...Core 11a...Adjustment core 11b...Outermost core 12...Cladding 13, 23, 33, 43...Primary resin layer 14, 24, 34, 44...Secondary resin layer 15, 25, 35, 45...Supply roll 20, 30, 40...Multi-core fiber 21, 31, 41...Core 22, 32, 42...Cladding 50...Coating member 51, 52, 53, 54...Coating portion 51a, 52a, 53a, 54a...Light irradiation surface 55, 56, 57...Recess 61...Die 62...Light irradiation device 63...Light receiving device 64...Control device C...Fiber center G...Observation axis (reference line) S...Outer circumference dc...Distance r...Maximum radius

Claims

1. An optical fiber ribbon comprising: a plurality of multicore fibers, each having a plurality of cores and a cladding covering the plurality of cores; and a coating member that at least partially coats the plurality of multicore fibers, wherein in at least one of the plurality of multicore fibers, the plurality of cores is eight or more cores and is arranged to be linearly symmetrical with respect to a reference line passing through the center of the fiber in a cross section of the at least one multicore fiber, and wherein the distance between a pair of adjustment cores that are located on the reference line and are furthest from each other among the plurality of cores is greater than a maximum radius that is the distance between the fiber center and the outermost core that is furthest from the fiber center.

2. The optical fiber ribbon according to claim 1, wherein at least one of the pair of adjustment cores is arranged on a circumference centered on the fiber center and on which the outermost core is arranged.

3. The optical fiber ribbon according to claim 1 or 2, wherein in said at least one multicore fiber, said multiple cores are arranged so as to be rotationally asymmetric when rotated through an angle of 360 / n degrees (n is any integer equal to or greater than 2) around the fiber center.

4. The optical fiber ribbon according to any one of claims 1 to 3, wherein the plurality of cores is 12 cores.

5. The optical fiber ribbon according to any one of claims 1 to 3, wherein the plurality of cores is 16 cores.

6. A method for manufacturing a multi-core fiber, the method comprising the steps of: preparing a plurality of multi-core fibers, each having a plurality of cores and a cladding covering the plurality of cores; coating each of the plurality of multi-core fibers with resin while arranging the plurality of multi-core fibers in parallel to one another; irradiating light onto a light irradiation surface in a coating resin portion covering at least one of the plurality of multi-core fibers, and aligning the arrangement of the plurality of cores in the at least one multi-core fiber based on a result of the light irradiation; wherein, in the at least one multi-core fiber, the plurality of cores are eight or more cores and are arranged to be linearly symmetrical with respect to a reference line passing through the center of the fiber in a cross section of the at least one multi-core fiber; a distance between a pair of adjustment cores that are located on the reference line and are furthest from each other among the plurality of cores is greater than a maximum radius that is a distance between the center of the fiber and the outermost core that is furthest from the center of the fiber; A method for manufacturing an optical fiber ribbon, wherein in the step of aligning the arrangement of the cores, the at least one multi-core fiber is arranged so that the reference line of the at least one multi-core fiber intersects with the light irradiation surface, light is irradiated onto the light irradiation surface, and the multiple cores of the at least one multi-core fiber are aligned using an image transmitted through the pair of adjustment cores.

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