Optical fiber ribbon and method for manufacturing optical fiber ribbon

Abstract

This optical fiber ribbon (1) comprises: a first flat strand (10) having a plurality of glass fibers (23); and a second flat strand (10) having a plurality of glass fibers (23). Each glass fiber (23) has directionality with respect to the rotation direction. In the first flat strand (10), both first and second glass fibers (23) are disposed such that the difference between a first reference angle in the rotation direction of the first glass fiber (23) and a second reference angle in the rotation direction of the second glass fiber (23) is equal to or less than a fixed value. In the second flat strand (10), both third and fourth glass fibers (23) are disposed such that the difference between a third reference angle in the rotation direction of the third glass fiber (23) and a fourth reference angle in the rotation direction of the fourth glass fiber (23) is equal to or less than a fixed value. The first flat strand (10) and the second flat strand (10) are disposed in parallel and are coupled to each other by a coupling resin (15).

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 Application No. 2024-097491, filed on June 17, 2024, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Documents 1 to 4 disclose optical fiber ribbons each having two or more glass fibers.

[0003] JP 2017-173514 A U.S. Patent Application Publication No. 2016 / 0223774 JP 1-216305 A Japanese Utility Model Application Laid-Open Publication No. 63-128502 A

[0004] An optical fiber ribbon according to an embodiment of the present disclosure includes a first flat strand and a second flat strand. The first flat strand includes at least a first glass fiber including at least one first core and a first cladding covering the first core and extending in the longitudinal direction, and a second glass fiber including at least one second core and a second cladding covering the second core and extending in the longitudinal direction. The second flat strand includes at least a third glass fiber including at least one third core and a third cladding covering the third core and extending in the longitudinal direction, and a fourth glass fiber including at least one fourth core and a fourth cladding covering the fourth core and extending in the longitudinal direction. The first, second, third, and fourth glass fibers have directionality relative to a rotational direction about their respective longitudinal axes. In the first flat wire, the first glass fiber and the second glass fiber are arranged in parallel and connected to each other so that the difference between the first reference angle in the rotation direction of the first glass fiber and the second reference angle in the rotation direction of the second glass fiber is equal to or less than a certain value. In the second flat wire, the third glass fiber and the fourth glass fiber are arranged in parallel and connected to each other so that the difference between the third reference angle in the rotation direction of the third glass fiber and the fourth reference angle in the rotation direction of the fourth glass fiber is equal to or less than a certain value. In this optical fiber ribbon, the first flat wire and the second flat wire are further arranged in parallel and connected to each other over their entire length or intermittently with a connecting resin.

[0005] FIG. 1 is a cross-sectional view of an optical fiber ribbon according to the first embodiment. FIG. 2 is a cross-sectional view of a flat wire forming the optical fiber ribbon shown in FIG. 1. FIG. 3 is a schematic diagram showing a method of producing the flat wire shown in FIG. 2. FIG. 4A is a cross-sectional view at position A in the production method shown in FIG. 3. FIG. 4B is a cross-sectional view at position B in the production method shown in FIG. 3. FIG. 4C is a cross-sectional view at position C in the production method shown in FIG. 3. FIG. 5A is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon according to the first embodiment. FIG. 5B is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon according to the first embodiment. FIG. 5C is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon according to the first embodiment. FIG. 6A is a cross-sectional view showing another modified flat wire forming the optical fiber ribbon according to the first embodiment. FIG. 6B is a cross-sectional view showing another modified flat wire forming the optical fiber ribbon according to the first embodiment. FIG. 7 is a cross-sectional view of an optical fiber ribbon according to the second embodiment. FIG. 8A is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon shown in FIG. 7. 8B is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon shown in FIG. 7 . FIG. 8C is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon shown in FIG. 7 . FIG. 9A is a cross-sectional view showing another modified flat wire forming the optical fiber ribbon shown in FIG. 7 . FIG. 9B is a cross-sectional view showing another modified flat wire forming the optical fiber ribbon shown in FIG. 7 . FIG. 9C is a cross-sectional view showing another modified flat wire forming the optical fiber ribbon shown in FIG. 7 . FIG. 10A is a cross-sectional view of a flat wire forming the optical fiber ribbon according to the third embodiment. FIG. 10B is a cross-sectional view showing a modified flat wire shown in FIG. 10A . FIG. 10C is a cross-sectional view showing a modified flat wire shown in FIG. 10A . FIG. 11 is a schematic view showing a method of producing a bunch-type flat wire forming the optical fiber ribbon according to the fourth embodiment. FIG. 12A is a cross-sectional view at position A in the production method shown in FIG. 11 . FIG. 12B is a cross-sectional view at position B in the production method shown in FIG. 11 . FIG. 13A is a cross-sectional view showing a modified example of a flat wire forming an optical fiber ribbon according to the fourth embodiment.FIG. 13B is a cross-sectional view showing a modified flat wire forming the optical fiber ribbon according to the fourth embodiment. FIG. 14 is a cross-sectional view of the optical fiber ribbon according to the fifth embodiment. FIG. 15A is a cross-sectional view showing an example of a three-fiber flat wire. FIG. 15B is a cross-sectional view showing an example of a four-fiber flat wire. FIG. 16A is a cross-sectional view of the optical fiber ribbon according to the sixth embodiment. FIG. 16B is a cross-sectional view showing a modified example of the optical fiber ribbon shown in FIG. 16A. FIG. 17A shows a flat wire forming the optical fiber ribbon shown in FIGS. 16A and 16B. FIG. 17B is a cross-sectional view showing a modified example of the flat wire shown in FIG. 17A. FIG. 18A is a cross-sectional view of the optical fiber ribbon according to the seventh embodiment. FIG. 18B is a cross-sectional view showing a modified example of the optical fiber ribbon shown in FIG. 18A. FIG. 19 is a cross-sectional view of a flat wire forming the optical fiber ribbon according to the eighth embodiment.

[0006] The optical fiber ribbon described in Patent Document 1 describes a multicore fiber in which multiple cores (e.g., seven cores) are provided in each glass fiber. Such multicore fibers and polarization-maintaining fibers have directionality in the rotation direction around the longitudinal direction as the central axis. With such glass fibers, core position alignment is required when fusion splicing or optical connector connection is performed, and therefore rotational alignment is necessary. Therefore, when tape-forming the optical fibers, it is necessary to tape the optical fibers while adjusting the angle of the core position in the rotation direction of each glass fiber, and the alignment work when tape-forming is time-consuming. Furthermore, the angle adjustment of the core position may not be appropriate, resulting in an optical fiber ribbon with insufficient adjustment precision.

[0007] The present disclosure aims to provide an optical fiber ribbon and a method for manufacturing an optical fiber ribbon that can improve alignment accuracy when tape-forming multiple glass fibers, each of which has directionality relative to a rotational direction around its longitudinal axis.

[0008] According to the present disclosure, it is possible to improve the alignment accuracy when forming a ribbon from a plurality of glass fibers, each of which has directionality relative to the direction of rotation about its central axis in the longitudinal direction.

[0009] First, the details of the embodiments of the present disclosure will be listed and described. [1] An optical fiber ribbon according to one embodiment includes a first flat wire and a second flat wire. The first flat wire includes at least a first glass fiber including at least one first core and a first cladding covering the first core and extending in the longitudinal direction, and a second glass fiber including at least one second core and a second cladding covering the second core and extending in the longitudinal direction. The second flat wire includes at least a third glass fiber including at least one third core and a third cladding covering the third core and extending in the longitudinal direction, and a fourth glass fiber including at least one fourth core and a fourth cladding covering the fourth core and extending in the longitudinal direction. The first glass fiber, the second glass fiber, the third glass fiber, and the fourth glass fiber have directionality relative to a rotational direction about their respective longitudinal axes. In the first flat wire, the first glass fiber and the second glass fiber are arranged in parallel and connected to each other so that the difference between the first reference angle in the rotation direction of the first glass fiber and the second reference angle in the rotation direction of the second glass fiber is equal to or less than a certain value. In the second flat wire, the third glass fiber and the fourth glass fiber are arranged in parallel and connected to each other so that the difference between the third reference angle in the rotation direction of the third glass fiber and the fourth reference angle in the rotation direction of the fourth glass fiber is equal to or less than a certain value. In this optical fiber ribbon, the first flat wire and the second flat wire are further arranged in parallel and connected to each other over their entire length or intermittently with a connecting resin.

[0010] In the optical fiber ribbon according to the above [1], the first flat wire and the second flat wire are arranged and connected to each other so that the difference in the reference angle between the glass fibers in the rotation direction is a certain value or less. The first flat wire and the second flat wire, whose difference in the reference angle is kept to a certain value or less, are further arranged in parallel and connected to each other over their entire length or intermittently with a connecting resin. In this case, since the flat wires whose difference in the reference angle between the glass fibers in the rotation direction is kept to a certain value or less are connected to each other, the alignment accuracy can be improved when a plurality of glass fibers, each of which has directionality in the rotation direction around the longitudinal axis, are assembled into a ribbon. In other words, an optical fiber ribbon with high alignment accuracy can be provided.

[0011] Although not limited thereto, the first flat wire and the second flat wire in the optical fiber ribbon according to the above [1] can be formed by drawing the glass fibers at the same time using the same drawing device, which facilitates making the reference angles of the glass fibers constituting the respective flat wires similar. Furthermore, when a flat wire including each glass fiber is formed in one go by such drawing, the flat wire can be formed before twisting occurs during winding after drawing, which also facilitates making the reference angles of the glass fibers similar. Furthermore, when a flat wire including each glass fiber is formed in one go by such drawing, the reference angles can be adjusted before the outer periphery of the glass fiber is coated with resin, which facilitates alignment, which also facilitates making the reference angles of the glass fibers similar. Note that, when each glass fiber is a multicore fiber (hereinafter also referred to as "MCF"), the "reference angles" refer to the arrangement angles of the cores in the rotation direction. However, this is not limited thereto. For example, when each glass fiber is a polarization-maintaining fiber, the reference angles refer to the angular positions of the polarization in the rotation direction.

[0012] [2] In the optical fiber ribbon according to [1], the first flat fiber may have a cross-sectional flat shape including a minor axis and a major axis, and a flat portion may be formed in a region where an imaginary line passing through the central axis of at least one of the first glass fiber and the second glass fiber and extending along the minor axis intersects with the outer periphery of the first flat fiber. In this case, the directionality of the first glass fiber and the second glass fiber in the rotational direction can be reliably detected from the flat portion using optical means. In this case, the alignment accuracy can be further improved when a plurality of glass fibers having directionality relative to the rotational direction are formed into a ribbon.

[0013] [3] In the optical fiber ribbon according to [1] or [2], the first flat strand may have a first coating covering the outer periphery of the first glass fiber and a second coating covering the outer periphery of the second glass fiber, and the first and second coatings may be formed so that their outer peripheries are in contact with each other or spaced apart from each other. In this case, the glass fiber is protected by being coated with each coating.

[0014] [4] In the optical fiber ribbon according to [3], the first flat strand may have a third coating covering the first coating, a fourth coating covering the second coating, and a connecting member covering at least a portion of the third coating and the fourth coating and connecting the third coating and the fourth coating. In this case, the glass fiber is further protected by being covered with each of the coatings further provided on the outside.

[0015] [5] In the optical fiber ribbon according to the above [3], the first flat wire may have a connecting member that covers at least a part of the first coating and the second coating and connects the first coating and the second coating. In this case, the first flat wire can be prevented from becoming thick.

[0016] [6] In the optical fiber ribbon according to any one of [1] to [5] above, the first flat strand may have a first outermost coating that coats the outer periphery of the first glass fiber and a second outermost coating that coats the outer periphery of the second glass fiber, and at least one of the first outermost coating and the second outermost coating may have a polygonal cross-sectional shape. In this case, the optical fiber ribbon can be one in which the orientation of the glass fibers in the same flat strand in the rotational direction is more uniform.

[0017] [7] In the optical fiber ribbon of [1] or [2] above, the first clad and the second clad may be solid-state bonded. In this case, a so-called bunched fiber can be obtained. In addition, an optical fiber ribbon without fluctuations in twist of the glass fiber can be obtained.

[0018] [8] In the optical fiber ribbon according to any one of [1] to [7] above, the first glass fiber may be a multicore fiber including a plurality of first cores, and the second glass fiber may be a multicore fiber including a plurality of second cores. Furthermore, the difference between the first arrangement angle of the plurality of first cores, which is the first reference angle, and the second arrangement angle of the plurality of second cores, which is the second reference angle, may be 5 degrees or less in the rotation direction based on the central axis. In this case, an optical fiber ribbon with high alignment accuracy can be provided. With a rotation accuracy of 5 degrees or less, the multicore fiber included in this optical fiber ribbon can be optically spliced ​​to another optical component (e.g., a mating multicore fiber) by making a slight alignment adjustment without causing a large splice loss. Furthermore, when the multicore fiber included in this optical fiber ribbon has a small number of cores and each core is arranged at the center of the glass fiber, with a rotation accuracy of 5 degrees or less, the splice loss is not so high even when the multicore fiber is spliced ​​to another optical component without alignment, and therefore the splice operation can be simplified.

[0019] [9] In the optical fiber ribbon according to [8] above, the difference between the first arrangement angle and the second arrangement angle may be 1 degree or less in the rotation direction based on the central axis. In this case, the difference in the reference angles between the glass fibers in the flat fiber is reduced, so that an optical fiber ribbon with even higher alignment accuracy can be provided. Therefore, an optical fiber ribbon with a rotation accuracy of 1 degree or less can easily manufacture multi-core fusion splices or multi-core connector connections when connecting ribbon core wires such as multi-core fibers without individually rotating and aligning the multi-core fibers.

[0020]

[10] In the optical fiber ribbon according to any one of [1] to [9] above, the first glass fiber may be a multicore fiber including a plurality of first cores, and the first cladding of the first glass fiber may be provided with at least one air hole extending along the plurality of first cores. In this case, the use of the air hole increases the difference in refractive index with the glass, allowing the position of the air hole to be measured with high accuracy from the side of the optical fiber. This allows the orientation of the glass fiber in the rotational direction to be adjusted based on the air hole, thereby providing an optical fiber ribbon with higher alignment accuracy.

[0021]

[11] In the optical fiber ribbon according to

[10] , the at least one hole may include a first hole and a second hole provided at positions facing each other across the central axis of the first glass fiber. In this case, the orientation of the glass fiber in the rotational direction can be adjusted based on the two holes provided at the opposing positions, thereby providing an optical fiber ribbon with higher alignment accuracy.

[0022]

[12] In the optical fiber ribbon according to

[10] or

[11] , the first flat fiber may have a cross-sectional flat shape including a minor axis and a major axis, and a flat portion may be formed in a region where an imaginary line passing through the central axis of at least one of the first glass fiber and the second glass fiber and extending along the minor axis intersects with the outer periphery of the first flat fiber, and the holes may be provided between the flat portion and the central axis. In this case, the directionality of the first glass fiber and the second glass fiber in the rotational direction can be reliably detected from the flat portion using optical means. Moreover, the directionality of the glass fiber in the rotational direction can be adjusted based on the holes. Therefore, this optical fiber ribbon can further improve the alignment accuracy when tape-forming multiple glass fibers having directionality relative to the rotational direction.

[0023]

[13] In the optical fiber ribbon according to any one of [1] to

[12] above, the first flat fiber may have a coating covering the outer periphery of at least one of the first glass fiber and the second glass fiber, and the coating may contain a colorant. In this case, each glass fiber in the optical fiber ribbon can be easily identified. In addition, the coloring step can be omitted.

[0024]

[14] In the optical fiber ribbon according to any one of [1] to

[13] above, the first flat wire may have a cross-sectional flat shape including a minor axis and a major axis, and the first flat wire may be provided with markers at positions asymmetric with respect to a reference line that passes through the center of the wire in the direction along the major axis and extends along the minor axis. In this case, the major axis, minor axis, etc. of the first flat wire can be identified by the markers, and the ribbon can be easily formed.

[0025]

[15] In the optical fiber ribbon according to any one of [1] to

[14] above, the first flat wire may have a flat cross-sectional shape including a minor axis and a major axis, and the first flat wire may have a recess formed inward along the minor axis at a connection between the first glass fiber and the second glass fiber. In this case, the minor axis and other details of the first flat wire can be identified by the recess, making it easy to tape. Also, the glass fibers in the optical fiber ribbon can be easily separated.

[0026]

[16] In the optical fiber ribbon according to any one of the above [1] to

[15] , the first glass fiber may be a multi-core fiber including a plurality of first cores, and the number of the plurality of first cores may be 12 or more. In this case, the optical fiber ribbon may be an optical fiber ribbon using a multi-core glass fiber.

[0027]

[17] In the optical fiber ribbon according to any one of [1] to

[16] above, the number of cores or the characteristics of the first glass fiber may be different from the number of cores or the characteristics of the second glass fiber. In this case, the optical fiber ribbon may have different settings.

[0028]

[18] In the optical fiber ribbon according to any one of [1] to

[17] above, the number of cores or characteristics of the first glass fiber may be different from the number of cores or characteristics of the third glass fiber. In this case, the optical fiber ribbon may be configured with different settings.

[0029]

[19] In the optical fiber ribbon according to any one of [1] to

[18] above, the first flat wire may include at least one fifth core and a fifth cladding covering the fifth core, and may further include a fifth glass fiber extending in the longitudinal direction, and the fifth glass fiber may have directionality with respect to a rotation direction about a central axis of the longitudinal direction. In the first flat wire, the first glass fiber, the second glass fiber, and the fifth glass fiber may be arranged in parallel and connected to each other so that the maximum value of the difference between the first reference angle in the rotation direction of the first glass fiber, the second reference angle in the rotation direction of the second glass fiber, and the fifth reference angle in the rotation direction of the fifth glass fiber is equal to or less than a certain value. In this case, an optical fiber ribbon can be formed using three flat wires, and a larger number of glass fibers can be connected.

[0030]

[20] Another aspect of the present disclosure relates to a method for manufacturing an optical fiber ribbon, comprising the steps of simultaneously drawing a first glass fiber including at least one first core and a first cladding covering the first core and extending in the longitudinal direction, and a second glass fiber including at least one second core and a second cladding covering the second core and extending in the longitudinal direction, to produce a first flat strand including at least the first glass fiber and the second glass fiber, simultaneously drawing a third glass fiber including at least one third core and a third cladding covering the third core and extending in the longitudinal direction, and a fourth glass fiber including at least one fourth core and a fourth cladding covering the fourth core and extending in the longitudinal direction, to produce a second flat strand including at least the third glass fiber and the fourth glass fiber, and arranging the first flat strand and the second flat strand in parallel and connecting them to each other with a connecting resin. The first glass fiber, the second glass fiber, the third glass fiber, and the fourth glass fiber have directionality with respect to a rotation direction around their respective longitudinal axes. In the step of producing a first flat wire, the first glass fiber and the second glass fiber are drawn so as to be arranged in parallel and connected to each other so that a difference between a first reference angle in the rotation direction of the first glass fiber and a second reference angle in the rotation direction of the second glass fiber is equal to or less than a certain value. In the step of producing a second flat wire, the third glass fiber and the fourth glass fiber are drawn so as to be arranged in parallel and connected to each other so that a difference between a third reference angle in the rotation direction of the third glass fiber and a fourth reference angle in the rotation direction of the fourth glass fiber is equal to or less than a certain value.

[0031] According to the manufacturing method of the optical fiber ribbon described above in

[20] , the first flat wire and the second flat wire in the optical fiber ribbon can be formed by simultaneously drawing the respective glass fibers in the same drawing apparatus. This facilitates achieving the same reference angle for each glass fiber in each flat wire. Note that "simultaneously" here means drawing at the same time and is not limited to perfectly synchronized timing. Furthermore, forming a flat wire containing each glass fiber in one go by this drawing method allows the flat wire to be formed before twisting occurs during winding after drawing, which also facilitates achieving the same reference angle for each glass fiber. Furthermore, forming a flat wire containing each glass fiber in one go by this drawing method allows the reference angle to be adjusted before the outer periphery of the glass fiber is coated with resin, which facilitates alignment, which also facilitates achieving the same reference angle for each glass fiber.

[0032] 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, identical elements or elements having identical functions will be designated by the same reference numerals, and duplicated explanations will be omitted. Note that 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.

[0033] First Embodiment An example of an optical fiber ribbon according to the first embodiment will be described with reference to FIG. 1 . FIG. 1 is a cross-sectional view of the optical fiber ribbon according to the first embodiment. As shown in FIG. 1 , the optical fiber ribbon 1 includes a plurality of flat wires 10 (first flat wire, second flat wire) and a connecting member 15 connecting the flat wires 10. In the optical fiber ribbon 1 shown in FIG. 1 , five flat wires 10 are connected, but this is not limited thereto; two or more flat wires 10 may be connected. The flat wires 10 included in the optical fiber ribbon 1 are arranged in two-core units. Each of the flat wires 10 extends in the longitudinal direction, is arranged side by side in a horizontal direction perpendicular to (intersecting) the longitudinal direction, and is connected (fixed) to each other by a connecting member 15. The connecting member 15 is formed from a tape-forming resin (connecting resin). For example, an ultraviolet-curable resin can be used as the tape-forming resin.

[0034] 1 and 2, the flat wire 10 has a plurality of optical fibers 20 and a connecting member 30 that connects the optical fibers 20. The flat wire 10 is a member having a flat cross-sectional shape that includes a minor axis S and a major axis T. The plurality of optical fibers 20 extend in the longitudinal direction along a central axis G that is perpendicular to the minor axis S and the major axis T. The number of optical fibers 20 included in the flat wire 10 is not limited to two, and may be two or more, and may be three or four.

[0035] Each optical fiber 20 is, for example, a multi-core fiber, and includes glass fibers 23 (first, second, third, and fourth glass fibers) each including a plurality of cores 21 and a cladding 22 covering the plurality of cores 21, a primary resin layer 24 that coats the outer periphery of the glass fiber 23, and a secondary resin layer 25 that coats the outer periphery of the primary resin layer 24. When the outer diameter of the glass fiber 23 is 125 μm, the outer diameter of the secondary resin layer 25 may be 250 μm, and when the outer diameter of the glass fiber 23 is 180 μm, the outer diameter of the secondary resin layer 25 may be 250 μm. The primary resin layer 24 and the secondary resin layer 25 form a coating portion that coats the outer periphery of the glass fiber 23 in the optical fiber 20. For example, if the outer diameter of the glass fiber 23 is as large as 180 μm, the microbending resistance is improved, so the thickness of the primary resin layer can be set to about 20 μm and the thickness of the secondary resin layer to about 15 μm to thin the coating, making the overall outer diameter the same as that of a standard fiber (250 μm). In this way, by keeping the outer diameter of the optical fiber at 250 μm, the same as conventional optical fibers, and setting the ribbon fiber pitch to 250 μm, it is possible to maintain compatibility with existing products.

[0036] The optical fiber 20 has a plurality of cores 21 arranged in the cladding 22 at a predetermined interval and angle, and has a fiber configuration that has directionality in the rotation direction. Note that "having directionality in the rotation direction" means that the cross-sectional structure (e.g., the position of the cores of a multi-core fiber) changes during one rotation. The optical fiber 20 (glass fiber 23) is not limited to an MCF, and may be a PMF, HAF, or HCF that requires alignment in the rotation direction. When the optical fiber 20 is such an optical fiber, the number of cores 21 may be at least one.

[0037] The core 21 is made of pure silica (SiO ２The cladding 22 is made of silica glass or silica glass doped with germanium dioxide or fluorine. The cladding 22 has a refractive index lower than that of the cores 21. The cladding 22 is made of, for example, pure silica glass or silica glass doped with fluorine. A trench having a refractive index lower than that of the cladding 22 may be provided between each core 21 and the cladding 22. A glass fiber 23 is formed from multiple cores 21 and claddings 22.

[0038] The primary resin layer 24 (first coating portion, second coating portion) coats the outer periphery of the clad 22 of the glass fiber 23. Specifically, the primary resin layer 24 is in contact with the outer periphery of the clad 22 and coats the entire circumferential surface of the clad 22. The secondary resin layer 25 further coats the outer periphery of the primary resin layer 24. Specifically, the secondary resin layer 25 is in contact with the outer periphery of the primary resin layer 24 and coats the entire circumferential surface of the primary resin layer 24.

[0039] The primary resin layer 24 is formed by curing, with ultraviolet light, 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 primary resin layer 24 has a lower elastic modulus (Young's modulus) than the secondary resin layer 25 and is softer than the secondary resin layer 25. For example, the Young's modulus of the primary resin layer 24 at 23°C is 0.1 MPa or more and 5 MPa or less. This provides the optical fiber 20 with lateral pressure resistance, thereby preventing an increase in transmission loss in the optical fiber 20 even when lateral pressure is applied.

[0040] The secondary resin layer 25 (third covering portion, fourth covering portion) is formed by curing a resin composition containing urethane (meth)acrylate, a monomer, and a photopolymerization initiator with ultraviolet light. The secondary resin layer 25 has a higher elasticity (Young's modulus) than the primary resin layer 24, and is harder than the primary resin layer 24. For example, the Young's modulus of the secondary resin layer 25 at 23°C is 1200 MPa or more and 2800 MPa or less. The thickness of each of the primary resin layer 24 and the secondary resin layer 25 is, for example, 5 μm or more and 50 μm or less.

[0041] In the flat wire 10 shown in FIG. 1 , a pair of (two) optical fibers 20 (glass fibers 23) are arranged in parallel in the horizontal direction and connected to each other so that the difference in the arrangement angles of the cores 21 of the two left and right glass fibers 23 in the rotational direction around the central axis G is equal to or less than a certain value. The arrangement angles here refer to a first reference angle, a second reference angle, a third reference angle, and a fourth reference angle. As described below, the flat wire 10 is manufactured by drawing both built-in optical fibers 20 simultaneously using the same drawing device, which makes it easy to reduce the difference in their arrangement angles. Specifically, the difference in the arrangement angles of both optical fibers 20 included in the flat wire 10 may be, for example, 5 degrees or less, 2 degrees or less, or 1 degree or less. If the difference in the arrangement angles is 1 degree or less, angle adjustment between the flat wires 10 is unnecessary or simplified when connecting the flat wires 10 to each other with a connecting member 15 (tape-formed resin) in the manufacturing method described below, thereby improving manufacturing efficiency.

[0042] The connecting member 30 is a member for connecting and fixing the optical fibers 20 to each other. The connecting member 30 is disposed between the optical fibers 20 to connect them. The connecting member 30 may cover the entire circumferential surface of the optical fiber 20 or may cover only a portion of the optical fiber 20. The connecting member 30 may be formed so as to extend continuously along the longitudinal direction of the optical fiber 20, or may be formed so as to extend intermittently along the longitudinal direction. The connecting member 30 also has flat portions 31, 32 formed on its outer periphery. The flat portions 31, 32 are formed so as to extend to a region where an imaginary line L, which passes through the central axis G of each glass fiber 23 and extends along the minor axis S, intersects with the outer periphery of the flat fiber 10. The provision of such flat portions 31, 32 makes it easier to optically detect the arrangement angle of the cores 21 of the optical fiber 20.

[0043] The connecting member 30 is formed, for example, from a resin tape. The connecting member 30 is formed by curing an ultraviolet-curable resin, which is the resin tape, with ultraviolet light or the like. The resin tape has a lower elasticity (Young's modulus) than the secondary resin layer 25, and is softer than the secondary resin layer 25.

[0044] Next, a method for producing the flat fiber 10 will be described with reference to Figures 3 and 4A to 4C. The drawing apparatus 100 shown in Figure 3 is configured to simultaneously draw two optical fibers 20 and to ensure that the core positions of the two optical fibers 20 are within a certain range. The drawing apparatus 100 includes a pair of furnaces 101, a pair of glass outer diameter measuring devices 102, a pair of twist detection devices 103, a pair of coating application devices 104, a pair of hardening devices 105, a pair of direct-below rollers 106, a dual-core concentrator 107, a hardening device 108, an inspection device 109, and a capstan 110. In a production method using this drawing apparatus 100, a pair of glass preforms P are placed in the corresponding furnaces 101, and the tip ends of the glass preforms P are heated to a predetermined melting temperature. As shown in Figure 4A, the glass preforms P have core portions P1 corresponding to the cores 21 and cladding portions P2 corresponding to the cladding 22 and covering the multiple core portions P1.

[0045] Next, when the tip of each glass preform P is heated and melted to a state where it can be drawn, drawing is started and the portion corresponding to the glass fiber 23 is drawn out of the furnace 101. The glass fiber 23 then passes through a glass outer diameter measuring instrument 102 to measure the outer diameter. Based on the measured outer diameter of the glass fiber 23, the heating temperature of the furnace 101, the drawing speed, etc. are adjusted.

[0046] Next, the drawn glass fiber 23 enters the twist detection device 103, where the twist of the glass fiber 23 around the central axis G, which corresponds to the arrangement angle of the cores 21, is detected. Because this is a stage before the glass fiber 23 is coated with resin, twist detection can be easily performed. Based on the detected twist value, the angle of the immediately below roller 106, which will be described later, is adjusted so that the difference in the arrangement angles of both glass fibers 23 in the rotation direction is equal to or less than a certain value. Specifically, the twist of the glass fiber 23 is adjusted by rotating the rotation axis of the immediately below roller 106 around the vertical axis or tilting it from the horizontal direction. This adjustment ensures that the difference in the arrangement angles of both glass fibers 23 is equal to or less than 5 degrees. The rotation angle or tilt angle of the immediately below roller 106 may be adjusted so that the difference in the arrangement angles is equal to or less than 2 degrees, or the rotation angle or tilt angle of the immediately below roller 106 may be fine-tuned so that the difference in the arrangement angles is equal to or less than 1 degree. Note that other members (for example, the coating application device 104 and the preform holding device) may be further adjusted to adjust the arrangement angle in the rotation direction of the glass fibers 23. This allows the difference in the arrangement angles of both glass fibers 23 to be adjusted with higher precision.

[0047] Furthermore, each glass fiber 23 whose twist has been adjusted by passing through the twist detection device 103 enters a corresponding coating application device 104, where a coating resin is applied to the outer periphery of the glass fiber 23. The glass fiber 23 then enters a curing device 105, where the coating resin is hardened by ultraviolet light, heat, or both. By applying and hardening the resin in this manner, a primary resin layer 24 and a secondary resin layer 25 are formed. Note that various known methods can be used to form the coating resin layers.

[0048] Next, the optical fiber 20, with the resin coated on the outer periphery of the glass fiber 23, advances toward the dual-fiber concentrator 107. As it advances toward the dual-fiber concentrator 107, both optical fibers 20 move toward each other and are arranged adjacent to each other in a horizontal direction, as shown in FIG. 4B . In the dual-fiber concentrator 107, both optical fibers 20 are arranged in parallel so that the difference in the arrangement angles of the cores 21 is equal to or less than a certain value. In this state, a resin (e.g., a tape-formed resin) used for the connecting member 30 is applied. The tape-formed resin may be the same material as the secondary resin. Then, in the curing device 108, the resin is hardened by ultraviolet light, heat, or both, to form the flat fiber 10 shown in FIG. 4C . In the dual-fiber concentrator 107, both optical fibers 20 may be connected by being arranged in parallel so that the outer peripheries of the both optical fibers are in contact with each other, or they may be connected by being arranged in parallel so that a gap is provided between the outer peripheries of the both optical fibers 20 (i.e., the both optical fibers are spaced apart).

[0049] After the flat wire 10 is produced, an inspection device 109 inspects whether the difference in the arrangement angles of the cores 21 of both optical fibers 20 in the flat wire 10 is equal to or less than a predetermined value. If necessary, a rotation angle control signal is sent to a device that controls controlled objects such as the directly below roller 106, and the inclination angle of the directly below roller 106, etc. is adjusted under control of the control device. The inspection device 109 may also inspect other configurations of the flat wire 10. After the inspection is completed, the flat wire 10 passes through a capstan 110 and is taken up by a take-up roller (not shown). In this way, in this method of producing the flat wire 10, the difference in the arrangement angles of the cores of the two optical fibers 20 is adjusted before being taken up by the take-up roller, so that twists that occur during winding occur in the same way in both optical fibers 20. Therefore, when an optical fiber ribbon is produced using the flat wire 10, the work can be performed without worrying about the difference in the arrangement angles of the optical fibers within the flat wire 10. Furthermore, because the optical fibers 20 are drawn at the same time by the drawing apparatus 100 with the optical fibers 20 aligned at the same angle, the deviation in the arrangement angles of the cores 21 of both optical fibers 20 tends to be the same, making it easy to adjust the difference in the arrangement angles of the cores 21 of the optical fibers 20 when producing the flat fiber 10. While it is necessary to adjust the arrangement angle of the cores 21 based on the central axis G of the glass fiber 23, angle adjustment based on the contact surface (bottom surface) is also effective when collecting multiple optical fibers 20 into a tape. Adjustment based on the central axis G of the glass fiber 23 serves as a management index for V-groove positioning and connector hole insertion when fusion splicing or manufacturing a multi-core connector after the coating is removed and the optical fibers are in a glass fiber state. Adjusting the core arrangement angle based on the bottom surface is effective when collecting multiple flat fiber strands into a tape.

[0050] Next, once the production of the flat wire 10 is completed, a predetermined number of such flat wires 10 are prepared. The flat wires 10 are then arranged in parallel with one another and connected to one another with a tape-forming resin. Various known methods can be used for this tape-forming process. In this manner, the optical fiber ribbon 1 shown in FIG. 1 can be produced. In this manufacturing method, the flat wires 10 in which the rotational alignment of the multiple optical fibers 20 contained therein is performed are treated as one unit, and these units are connected to produce the optical fiber ribbon 1. Therefore, when the optical fiber ribbon 1 is produced, the deviation in the arrangement angle of the cores 21 of each optical fiber 20 is reduced.

[0051] As described above, in the optical fiber ribbon 1 according to the first embodiment, the flat wires 10 are arranged and connected to each other so that the difference in the arrangement angles of the glass fibers 23 in the rotation direction is equal to or less than a certain value. The flat wires 10 having such differences in arrangement angles held to a certain value or less are further arranged in parallel and connected to each other with a tape-forming resin. By connecting the flat wires 10 having such differences in arrangement angles held to a certain value or less in the rotation direction around the central axis G, the alignment accuracy can be improved when tape-forming the optical fibers 20 (glass fibers 23), each of which has directionality relative to the rotation direction around the central axis G in its longitudinal direction. In other words, an optical fiber ribbon 1 with high alignment accuracy can be provided.

[0052] Although not limited to this, by drawing the glass fibers 23 of each flat strand 10 in the optical fiber ribbon 1 at the same time using the same drawing device 100, it becomes easy to make the arrangement angles of the glass fibers 23 forming each flat strand 10 similar. Furthermore, when the flat strand 10 including each glass fiber 23 is formed in one go by drawing in this manner, the flat strand 10 can be formed before twisting occurs during winding after drawing, which also makes it easy to make the arrangement angles of the glass fibers 23 similar. Furthermore, when the flat strand 10 including each glass fiber 23 is formed in one go by drawing in this manner, the arrangement angles can be adjusted before the outer periphery of the glass fibers 23 is coated with resin, which makes alignment easier, which also makes it easy to make the arrangement angles of the glass fibers 23 similar.

[0053] Here, modified examples of the flat fiber 10 that can be used in the optical fiber ribbon 1 according to the first embodiment will be described with reference to FIGS. 5A to 5C and FIGS. 6A to 6B.

[0054] The flat wire 10A shown in FIG. 5A includes a pair of optical fibers 20, a connecting member 30A connecting the optical fibers 20, and a marker 33. In this flat wire 10A, the connecting member 30A has a recess 34 formed on the lower side. This allows the flat wire 10A to easily distinguish between the up and down directions. The depth of the recess 34 may be, for example, 10% or more of the thickness of the optical fiber 20. When the thickness of the optical fiber 20 is 250 μm, the depth of the recess 34 may be 25 μm or more. In addition, in the flat wire 10A, the marker 33 is provided above the center of the wire on the longitudinal axis T of the connecting member 30A. This allows the flat wire 10A to easily distinguish between the up and down directions. The marker 33 can be identified, for example, by utilizing a reaction in which the coating changes color in the irradiated area upon laser irradiation of the coating. Unlike ink application, the thickness of the marker is not increased by applying the marker, and the visibility required for the marker function can be achieved by discoloring a specific region inside the coating. Of course, this can be achieved by applying ink or the like.

[0055] 5B has a pair of optical fibers 20, a connecting member 30A that connects the optical fibers 20 together, and a marker 33, similar to the flat wire 10A described above. However, in the flat wire 10B, the marker 33 is arranged above one of the optical fibers 20 (on the left side in the figure) so as to be asymmetric with respect to the center of the optical fiber on the longitudinal axis T of the connecting member 30A. As a result, in the flat wire 10B, even after the flat wire 10B is separated into single fibers, the two optical fibers can be easily identified by the presence or absence of the marker.

[0056] The flat wire 10C shown in Fig. 5C has a pair of optical fibers 20 and a connecting member 30C that connects the optical fibers 20 together. Similar to the connecting member 30A, the connecting member 30C has a recess 34 formed on the bottom. Furthermore, in the flat wire 10C, the connecting member 30C is formed by two-color molding, and the colored portions 35 and 36 are given different colors. In other words, a coloring agent is used in the coating. This makes it easy to determine the up and down directions of the flat wire 10C.

[0057] The flat fiber 10D shown in FIG. 6A includes a pair of optical fibers 20 and a connecting member 30D that connects the optical fibers 20 together. In the flat fiber 10D, the connecting member 30D is formed from an intermittent tape-forming resin that is provided intermittently in the longitudinal direction. The connecting member 30D is provided only in the upper portion of the gap between the optical fibers 20. That is, the connecting member 30D has a weaker force for connecting and fixing the optical fibers 20 than the connecting member 30 of the flat fiber 10 or the like. This allows the optical fibers 20 to be easily separated during use when the flat fiber 10D is used to fabricate an optical fiber ribbon 1. This improves workability.

[0058] The flat wire 10E shown in Fig. 6B has a pair of optical fibers 20, a connecting member 30D that connects the optical fibers 20 together, and a marker 33. When this flat wire 10E is used to fabricate an optical fiber ribbon 1, the optical fibers 20 can be easily separated during use, similar to the flat wire 10D. This improves workability. Furthermore, by providing the marker 33, the up and down directions of the flat wire 10E can be easily identified. The marker 33 may be formed by laser irradiation, as described above.

[0059] Second Embodiment Next, an optical fiber ribbon 1A according to a second embodiment will be described with reference to FIG. 7 . FIG. 7 is a cross-sectional view of the optical fiber ribbon 1A according to the second embodiment. As shown in FIG. 7 , the optical fiber ribbon 1A includes a plurality of flat wires 10F (first flat wire, second flat wire) and a connecting member 15 that connects the flat wires 10F. The flat wires 10F included in the optical fiber ribbon 1A are arranged in two-core units. Each of the flat wires 10F extends in the longitudinal direction, is arranged side by side in a horizontal direction perpendicular to (intersecting) the longitudinal direction, and is connected (fixed) to each other by the connecting member 15. The connecting member 15 is formed from a tape-forming resin.

[0060] 7 and 8A, the flat wire 10F includes a plurality of optical fibers 20F and a connecting member 30F that connects the optical fibers 20F. The flat wire 10F is a member having a flat cross-sectional shape that includes a minor axis S and a major axis T.

[0061] Each optical fiber 20F is, for example, a multi-core fiber, and includes glass fibers 23 (first glass fiber, second glass fiber, third glass fiber, fourth glass fiber) each including a plurality of cores 21 and a cladding 22 covering the plurality of cores 21, and a primary resin layer 24 covering the outer periphery of the glass fiber 23. In the optical fiber 20F, the primary resin layer 24 forms a coating portion that covers the outer periphery of the glass fiber 23. Similar to the optical fiber 20, the optical fiber 20F has a plurality of cores 21 arranged in the cladding 22 at a predetermined interval and at a predetermined arrangement angle, and has a fiber configuration that has directionality with respect to the rotation direction.

[0062] 8A, a pair of (two-core) optical fibers 20F (glass fibers 23) are arranged in parallel in the horizontal direction and connected to each other so that the difference in the arrangement angles of the cores 21 of the two left and right glass fibers 23 in the rotation direction around the central axis G is a certain value or less, similar to the flat wire 10. The difference in the arrangement angles of both optical fibers 20F included in the flat wire 10F may be, for example, 5 degrees or less, 2 degrees or less, or 1 degree or less.

[0063] The connecting member 30F is a member for connecting and fixing the optical fibers 20F to each other. The connecting member 30F is disposed between the optical fibers 20F to connect them. In the example shown in FIG. 8A , a recess 34 is provided below the connecting member 30F. The connecting member 30F also has a flat portion 31 formed on its outer periphery. Since the optical fiber 20F according to the second embodiment does not have a secondary resin layer, the primary resin layer 24 located on the outermost periphery of each optical fiber 20F is covered with the tape-formed resin that forms the connecting member 30F. Note that the method for manufacturing the optical fiber 20F according to the second embodiment can be substantially the same as the manufacturing method according to the first embodiment, and therefore detailed description thereof will be omitted.

[0064] Here, modified examples of the flat fiber 10F that can be used in the optical fiber ribbon 1A according to the second embodiment will be described with reference to FIGS. 8A to 8C and 9A to 9C.

[0065] 8B, the flat wire 10G includes a pair of optical fibers 20F, a connecting member 30F that connects the optical fibers 20F together, and a marker 33. In this flat wire 10F, the marker 33 is provided above the longitudinal axis of the connecting member 30F near the center of the wire. This makes it easy to determine the up and down directions of the flat wire 10G.

[0066] As shown in Fig. 8C, the flat wire 10H has a pair of optical fibers 20F and a connecting member 30H that connects the optical fibers 20F together. Similar to the connecting member 30F, the connecting member 30H has a recess 34 formed on the bottom. Furthermore, in the flat wire 10H, the connecting member 30H is formed by two-color molding, and the colored portions 35 and 36 are given different colors. This allows the up and down directions of the flat wire 10H to be easily distinguished. Similar to the connecting member 30F, the connecting member 30H is formed from tape-formed resin.

[0067] The flat wires 10J and 10K shown in Figures 9A and 9B correspond to the flat wires 10F and 10G shown in Figures 8A and 8B. In these flat wires 10J and 10K, unlike the flat wires 10F and 10G, the optical fibers 20F are not in contact with each other but are spaced apart and arranged in parallel in the horizontal direction and connected together. Similarly, in the flat wire 10L shown in Figure 9C, the optical fibers 20F are spaced apart and not in contact with each other. The flat wire 10L is configured without providing markers 33 in the flat wires 10J and 10K.

[0068] [Third embodiment] Next, an optical fiber ribbon according to a third embodiment will be described with reference to Figures 10A to 10C. The optical fiber ribbon according to the third embodiment has a configuration similar to that of the optical fiber ribbon according to the second embodiment. However, the configuration of the flat wire included in the optical fiber ribbon according to the third embodiment is slightly different from that of the flat wire 10G included in the optical fiber ribbon 1A according to the second embodiment. Below, the differences will be mainly described.

[0069] 10A , a flat fiber 10M included in the optical fiber ribbon according to the third embodiment has a plurality of optical fibers 20F and a connecting member 30M that connects the optical fibers 20F. In the flat fiber 10M, similar to the flat fiber 10G, a pair (two cores) of optical fibers 20F (glass fibers 23) are arranged in parallel in the horizontal direction and connected to each other so that the difference in the arrangement angle of the cores 21 in the rotation direction around the central axis G of the two left and right glass fibers 23 is equal to or less than a certain value.

[0070] The connecting member 30M is a member for connecting and fixing the optical fibers 20F to each other, and its structure is the same as that of the second embodiment. However, in the third embodiment, the material forming the connecting member 30M is a secondary resin. That is, the connecting member 30M is formed from the secondary resin material that forms the secondary resin layer 25 described above.

[0071] The optical fiber ribbon includes a plurality of flat fibers 10M each having a connecting member 30M formed from a secondary resin, and in addition to the effects described in the first and second embodiments, the ribbon is formed using a secondary resin, resulting in a simple configuration and excellent productivity, which allows for faster manufacturing.

[0072] Here, as shown in Figures 10B and 10C, modified examples of the flat wire 10M included in the optical fiber ribbon according to the third embodiment will be described. In the flat wire 10N shown in Figure 10B, a marker 33 is provided on the side of the flat wire 10N (the side on the left side in the figure). By providing the markers 33 in asymmetric positions like this, the up and down directions of the flat wire 10N can be easily identified. Furthermore, in the flat wire 10P shown in Figure 10C, no marker 33 is provided. When an optical fiber ribbon is formed using such flat wires 10M, 10P, the above-mentioned effects can be obtained.

[0073] [Fourth embodiment] Next, an optical fiber ribbon according to a fourth embodiment will be described with reference to Fig. 11 and Fig. 12A to Fig. 12B. The optical fiber ribbon according to the fourth embodiment can have a configuration substantially similar to that of the optical fiber ribbon according to the first embodiment, etc. However, the optical fiber ribbon according to the fourth embodiment differs in that the optical fibers contained in the flat wire included in the optical fiber ribbon are bunched optical fibers.

[0074] The drawing apparatus 100A shown in FIG. 11 is configured to allow two optical fibers 20 to be drawn simultaneously in the same furnace. The drawing apparatus 100A includes a furnace 101, a twist detector 103, a coating applicator 104, a curing device 105, a roller 106, and a capstan 110. The drawing apparatus 100A may further include an inspection device 109. In a method for producing bunched fiber using the drawing apparatus 100A, a pair of glass preforms P are placed in the furnace 101, and the tips of the glass preforms P are heated to a predetermined melting temperature. As shown in FIG. 12A , the glass preforms P have core portions P1 corresponding to the cores 21 and cladding portions P2 corresponding to the cladding 22 and covering the core portions P1. When placed in the furnace 101, the glass preforms P are placed adjacent to each other so as to be in contact with each other.

[0075] Next, when the tip of each glass preform P is heated and melted to a state where it can be drawn, drawing begins, and a portion corresponding to the glass fiber 23Q is drawn from the furnace 101. In the bunched fiber, the glass fibers 23Q are solid-state bonded to each other at their side surfaces. Specifically, the clads 22Q are solid-state bonded to each other at their opposing ends (see FIG. 12B ). The integrated glass fiber 23Q may then enter a twist detection device 103 to detect the twist around the central axis G corresponding to the arrangement angle of the cores 21 in the glass fiber 23Q. Since the glass preforms P are pre-positioned at a predetermined angle and drawn, drawing can be performed relatively easily while maintaining a misalignment of the arrangement angle of 5 degrees or less. The width and area of ​​the solid-state bond are set so as not to significantly affect the splice loss. The side surfaces of both glass preforms P may be brought into contact with each other for solid-state bonding, or the side surfaces of both glass preforms P may be ground flat in advance, and both flat portions may be solid-state bonded.

[0076] Each glass fiber 23Q enters a coating application device 104, where a coating resin is applied to the outer periphery of the integrated glass fiber 23Q. The glass fiber 23Q then enters a curing device 105, where the coating resin is cured by ultraviolet light, heat, or both. This resin application and curing process forms a primary resin layer 24 and a connecting member 30Q. A secondary resin layer 25 may also be formed. The primary resin layers 24 are connected to each other at their opposing ends to form an integrated structure.

[0077] Next, the optical fiber 20Q, in which the outer periphery of the integrated glass fiber 23Q is coated with resin, passes through the capstan 110 and is taken up by a take-up roller (not shown) in an integrated state. When an optical fiber ribbon is produced using the flat wire 10Q as bunched fibers, the core angle arrangement is determined in the preform setting stage, so that the drawing can be carried out without worrying about deviations in the arrangement angles of the optical fibers 20Q within the flat wire 10Q.

[0078] Next, after the flat wire 10Q is produced, a predetermined number of such flat wires 10Q are prepared. Then, the flat wires 10Q are arranged in parallel with each other and connected to each other with a tape-forming resin. Various known methods can be used for this tape-forming process. In this way, the optical fiber ribbon according to the fourth embodiment can be produced (see also FIGS. 18A and 18B).

[0079] The optical fiber ribbon according to the fourth embodiment uses a flat fiber 10Q having bunched optical fibers 20Q, which further reduces the deviation of the arrangement angle of each optical fiber 20Q (glass fiber 23Q). Other effects are the same as those of the first embodiment.

[0080] Here, as shown in Figures 13A and 13B, a modified example of a flat fiber 10Q included in the optical fiber ribbon according to the fourth embodiment will be described. In the flat fiber 10R shown in Figure 13A, the markers 33 provided on the connecting member 30Q that connects and covers the bunched optical fibers 20Q are arranged in asymmetric positions along the longitudinal axis. By providing the markers 33 in such asymmetric positions, the up and down directions of the flat fiber 10R can be easily identified. In addition, in the flat fiber 10S shown in Figure 13B, the markers 33 are not provided. Instead, the connecting member 30S has colored portions 35, 36 formed in two colors. When an optical fiber ribbon is formed using such flat fiber 10R, 10S, the above-described effects can be similarly obtained.

[0081] Fifth Embodiment Next, with reference to FIG. 14 , an optical fiber ribbon 1B according to a fifth embodiment will be described. The optical fiber ribbon 1B has a configuration substantially similar to that of the optical fiber ribbon 1A according to the second embodiment. The optical fiber ribbon 1B differs from the optical fiber ribbon 1A in that markers 33 are not provided on the flat strands 10T. Although the optical fiber ribbon 1A according to the fifth embodiment does not have markers 33, the connecting member 15 has an asymmetrical shape in the vertical direction, allowing the up-down direction of the flat strands 10T to be identified. Furthermore, all or part of the connecting member 30T, which is the second coating layer of the flat strands, may be colored. Coloring such a coating portion allows identification by color even after separation into two-core units. If further separation of two cores is required for single-core identification, identification may be performed by the broken portion after separation. However, to improve identification, a discolored portion may be formed in one of the coatings using the laser described above. Other advantages are the same as those of the above-described embodiments.

[0082] Here, further modifications of the above-described flat wires will be described with reference to FIGS. 15A and 15B . In the above-described embodiments, for ease of explanation, a two-fiber flat wire has been described as an example, but the present invention is not limited thereto. For example, as shown in FIG. 15A , a flat wire 10U has three optical fibers 20 and a connecting member 30 connecting the three optical fibers 20. Also, as shown in FIG. 15B , a flat wire 10V has four optical fibers 20 and a connecting member 30 connecting the four optical fibers 20. A plurality of flat wires 10U, 10V each having three or four optical fibers 20 may be used to form an optical fiber ribbon 1 such as that shown in FIG. 1 . Even in this embodiment, the optical fibers 20 are arranged in parallel and connected so that the maximum difference in the arrangement angles of the optical fibers 20 is equal to or less than a certain value. Here, the "certain value" may be equal to or less than 5 degrees, equal to or less than 2 degrees, or equal to or less than 1 degree, as described above. It is relatively easy to produce two-, three-, or four-core flat wires by drawing them simultaneously in the same drawing machine. Also, each of the four optical fibers can be identified by a marker or the like.

[0083] The optical fiber ribbons 1, 1A, 1B, etc., the flat wire 10, etc., and their manufacturing methods according to the embodiments of the present disclosure have been described in detail above. However, the present invention is not limited to the above embodiments and can be applied to various embodiments and modifications. For example, the number of cores 21 included in the optical fiber 20 embedded in the flat wire 10, etc., is not limited to the above examples and may be 12 or more, as shown in FIG. 16A. In the optical fiber ribbon 1C shown in FIG. 16A, six flat wires 10W are arranged in parallel and connected by a connecting member 15. Furthermore, as shown in FIG. 16B, an optical fiber ribbon 1D may be formed by eight flat wires 10W arranged in parallel and connected by a connecting member 15.

[0084] 17A , the flat wire 10W includes two optical fibers 20W and a connecting member 30W. Each optical fiber 20W is, for example, a multi-core fiber, and includes a glass fiber 23W including 12 cores 21 and a cladding 22 covering the cores 21, and a primary resin layer 24 that coats the outer periphery of the glass fiber 23W. The optical fiber 20W may further include a secondary resin layer that coats the outer periphery of the primary resin layer 24. Furthermore, the flat wire 10W may or may not have markers 33 at asymmetric positions.

[0085] Furthermore, as shown in FIG. 17B , the optical fiber 20W included in the flat fiber 10W may have holes 26 in the cladding 22 in addition to the cores 21. The pair of holes 26 may be located on an imaginary line L that passes through the central axis G and extends along the minor axis S. Because the refractive index difference between the holes and the glass is large, providing such holes 26 allows for highly accurate measurement of the arrangement angle of the cores 21 of the optical fiber 20W in the rotational direction. As a result, rotation angle control during the drawing process can be easily performed. Instead of the holes 26, low-refractive index markers formed from a low-refractive index material having a refractive index lower than that of the cladding 22 may be provided. The same can be done in this case. A small diameter of the holes makes it easier to control the glass diameter deformation dependent on the holes, so the diameter may be, for example, 10 μm or less, or 5 μm or less.

[0086] 18A and 18B, the number of cores 21 in a bunched optical fiber 20Q may be 12. As shown in Fig. 18A, an optical fiber ribbon 1E may include six flat strands 10X, and as shown in Fig. 18B, an optical fiber ribbon 1F may include eight flat strands 10X.

[0087] In the above-described embodiment, the flat wires included in the optical fiber ribbon have the same number of cores or characteristics, but this is not limiting. For example, the number of cores or characteristics of the optical fibers included in one flat wire may be different from the number of cores or characteristics of the optical fibers included in another flat wire. Furthermore, the number of cores or characteristics of the optical fibers included in one flat wire may be different from each other.

[0088] FIG. 19 shows a cross-sectional view of a flat wire 10Y according to another modification. As shown in FIG. 19, the flat wire 10Y includes multiple optical fibers 20Y and a connecting member 30Y that connects the optical fibers 20Y. The optical fiber 20Y is a so-called multicore fiber, and includes a glass fiber 23Y including three cores 21 and a cladding 22 that covers the cores 21, and a primary resin layer 24Y that coats the outer periphery of the glass fiber 23Y. The optical fiber 20Y may further include a secondary resin layer that coats the outer periphery of the primary resin layer 24Y. The optical fiber 20Y may further include holes 26. In this flat wire 10Y, the primary resin layer 24Y and the connecting member 30Y have a rectangular (polygonal) cross section. That is, the flat wire 10Y is a rectangular wire. The flat wire 10Y may also have another polygonal cross section.

[0089] When a round wire runs on a guide roller or is wound on a reel, vibrations can cause the wire's outer periphery to rotate slightly due to contact vibration and friction with the V-groove wall of the guide roller. In contrast, with a square wire (e.g., rectangular shape) as described above, it is easy to control minute rotations of 20 to 30 degrees or less. As a result, when producing a two-core flat wire, it is possible to effectively align the angle of the precise arrangement.

[0090] In a method for drawing and manufacturing such a two-core flat wire, which is a two-core rectangular wire, two independently coated optical fibers 20Y are first formed using a primary die. Then, during drawing, the two optical fibers 20Y are gathered and arranged in parallel, for example, at a pitch of 250 μm, and the outer periphery of the gathered optical fibers is collectively coated using a secondary die to produce a flat wire. This coating is formed by at least a primary coating on a single optical fiber and a secondary coating that flattens the two fibers. Here, by forming the coating on the single optical fiber with the primary coating in a rectangular shape (for example, 220 μm square), the core arrangement of the multi-core fiber can be measured based on the flat portion of the rectangular shape, making it easy to adjust the rotation. For example, the orientation of the four corners on the outer periphery of the primary coated optical fiber 20Y can be measured using a laser, and by appropriately controlling the die rotation, guide roller rotation, glass preform rotation, or the like based on a specific side, the rotational position of the multi-core fiber relative to the rectangular wire can be rotationally aligned with a specific reference.

[0091] Furthermore, by performing final inspection after forming the two-core flat wire by measuring the core position from outside the flat coating, further fine adjustments (e.g., adjustments of a few degrees or less) can be performed by rotating the die or guide rollers. In particular, by making the grooves of the guide rollers square, the vibration contact rotation that occurs with round wires in the guide grooves can be prevented, enabling stable rotation-controlled manufacturing of multicore fibers. Using the markers made of the holes 26 described above facilitates measurement due to the large refractive index difference. In the configuration shown in FIG. 19 , the primary resin layer 24Y, which is the outer periphery of the square wire, is separated, but it may also be in close contact. Furthermore, as long as a flat portion of a certain length is formed at a specific location, the vicinity of each vertex may be rounded. In this flat wire 10Y, the cores are arranged based on the parallel central axes of the two cores, using the markers made of the holes 26 as a reference. The markers may be solid markers instead of holes. However, the holes 26 are easier to measure. A plurality of such flat fiber 10Y (for example, six) can be arranged in parallel and connected to each other to form an optical fiber ribbon.

[0092] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C, 1D, 1E, 1F... Optical fiber ribbon 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10J, 10K, 10L, 10M, 10N, 10P, 10Q, 10R, 10S, 10T, 10U, 10V, 10W, 10X, 10Y... Flat wire 15... Connecting member 20, 20F, 20Q, 20W, 20Y... Optical fiber 21... Core 22, 22Q... Cladding 23, 23Q, 23W, 23Y... Glass fiber 24, 24Y... Primary resin layer 25... Secondary resin layer 26... Hole DESCRIPTION OF SYMBOLS 30, 30A, 30C, 30D, 30F, 30H, 30M, 30Q, 30S, 30T...Connecting member 31, 32...Flat portion 33...Marker 34...Recess 35, 36...Colored portion 100, 100A...Wire drawing device 101...Furnace 102...Glass outer diameter measuring device 103...Twist detection device 104...Coating application device 105...Hardening device 106...Directly below roller 107...Two-core concentrator 108...Hardening device 109...Inspection device 110...Capstan G...Central axis L...Virtual line P...Glass preform P1...Core portion P2...Clad portion S...Minor axis T...Major axis

Claims

1. A first flat wire comprising at least a first glass fiber including at least one first core and a first clad covering the first core and extending in the longitudinal direction, and a second glass fiber including at least one second core and a second clad covering the second core and extending in the longitudinal direction, and a second flat wire comprising at least a third glass fiber including at least one third core and a third clad covering the third core and extending in the longitudinal direction, and a fourth glass fiber including at least one fourth core and a fourth clad covering the fourth core and extending in the longitudinal direction, wherein the first glass fiber, the second glass fiber, the third glass fiber, and the fourth glass fiber have directionality with respect to the direction of rotation about their respective longitudinal axes, and wherein in the first flat wire, the first glass fiber and the second glass fiber are arranged in parallel and connected to each other so that the difference between a first reference angle in the rotation direction of the first glass fiber and a second reference angle in the rotation direction of the second glass fiber is equal to or less than a certain value, In the second flat wire, the third glass fiber and the fourth glass fiber are arranged in parallel and connected to each other so that a difference between a third reference angle in the rotation direction of the third glass fiber and a fourth reference angle in the rotation direction of the fourth glass fiber is equal to or less than a certain value; and the first flat wire and the second flat wire are further arranged in parallel and connected to each other over their entire length or intermittently by connecting resin, an optical fiber ribbon core wire.

2. An optical fiber ribbon according to claim 1, wherein the first flat wire has a flat cross-sectional shape including a minor axis and a major axis, and a flat portion is formed in the region where an imaginary line passing through the central axis of at least one of the first glass fiber and the second glass fiber and extending along the minor axis intersects with the outer periphery of the first flat wire.

3. An optical fiber ribbon according to claim 1 or claim 2, wherein the first flat wire has a first coating that coats the outer periphery of the first glass fiber and a second coating that coats the outer periphery of the second glass fiber, and the first coating and the second coating are formed so that their outer peripheries are in contact with each other or are separated from each other.

4. An optical fiber ribbon according to claim 3, wherein the first flat wire has a third coating portion that coats the first coating portion, a fourth coating portion that coats the second coating portion, and a connecting member that covers at least a portion of the third coating portion and the fourth coating portion and connects the third coating portion and the fourth coating portion.

5. The optical fiber ribbon according to claim 3, wherein the first flat wire has a connecting member that covers at least a portion of the first coated portion and the second coated portion and connects the first coated portion and the second coated portion.

6. An optical fiber ribbon according to any one of claims 1 to 5, wherein the first flat strand has a first outermost coating that coats the outer periphery of the first glass fiber and a second outermost coating that coats the outer periphery of the second glass fiber, and the cross-sectional shape of at least one of the first outermost coating and the second outermost coating is polygonal.

7. An optical fiber ribbon according to claim 1 or 2, wherein the first cladding and the second cladding are solid-state bonded.

8. An optical fiber ribbon according to any one of claims 1 to 7, wherein the first glass fiber is a multicore fiber including a plurality of the first cores, the second glass fiber is a multicore fiber including a plurality of the second cores, and the difference between a first arrangement angle of the plurality of first cores, which is the first reference angle, and a second arrangement angle of the plurality of second cores, which is the second reference angle, is 5 degrees or less in the rotation direction based on the central axis.

9. The optical fiber ribbon according to claim 8, wherein the difference between the first arrangement angle and the second arrangement angle is 1 degree or less in the rotation direction around the axis.

10. An optical fiber ribbon according to any one of claims 1 to 9, wherein the first glass fiber is a multi-core fiber including a plurality of the first cores, and the first clad of the first glass fiber is provided with at least one air hole extending along the plurality of first cores.

11. The optical fiber ribbon according to claim 10, wherein the at least one hole includes a first hole and a second hole provided at positions facing each other across the central axis of the first glass fiber.

12. An optical fiber ribbon according to claim 10 or claim 11, wherein the first flat wire has a flat cross-sectional shape including a short axis and a long axis, a flat portion is formed in a region where an imaginary line passing through the central axis of at least one of the first glass fiber and the second glass fiber and extending along the short axis intersects with the outer periphery of the first flat wire, and the air holes are provided between the flat portion and the central axis.

13. An optical fiber ribbon according to any one of claims 1 to 12, wherein the first flat wire has a coating that covers the outer periphery of at least one of the first glass fiber and the second glass fiber, and the coating contains a colorant.

14. An optical fiber ribbon core wire as described in any one of claims 1 to 13, wherein the first flat wire has a flat cross-sectional shape including a short axis and a long axis, and the first flat wire is provided with a marker at an asymmetric position with respect to a reference line that passes through the center of the wire in a direction along the long axis and extends along the short axis.

15. An optical fiber ribbon according to any one of claims 1 to 14, wherein the first flat wire has a flat cross-sectional shape including a short axis and a long axis, and the first flat wire has a recess that is recessed inward along the short axis at the connection between the first glass fiber and the second glass fiber.

16. An optical fiber ribbon according to any one of claims 1 to 15, wherein the first glass fiber is a multi-core fiber including a plurality of the first cores, and the number of the plurality of first cores is 12 or more.

17. An optical fiber ribbon according to any one of claims 1 to 16, wherein the number of cores or characteristics of the first glass fiber are different from the number of cores or characteristics of the second glass fiber.

18. An optical fiber ribbon according to any one of claims 1 to 17, wherein the number of cores or characteristics of the first glass fiber are different from the number of cores or characteristics of the third glass fiber.

19. An optical fiber ribbon according to any one of claims 1 to 18, wherein the first flat wire includes at least one fifth core and a fifth cladding covering the fifth core, and further includes a fifth glass fiber extending in the longitudinal direction, the fifth glass fiber having directionality with respect to a rotation direction about the longitudinal direction as a central axis, and in the first flat wire, the first glass fiber, the second glass fiber, and the fifth glass fiber are arranged in parallel and connected to each other so that the maximum value of the difference between a first reference angle in the rotation direction of the first glass fiber, a second reference angle in the rotation direction of the second glass fiber, and a fifth reference angle in the rotation direction of the fifth glass fiber is equal to or less than a certain value.

20. A method for manufacturing a flat wire comprising: simultaneously drawing a first glass fiber including at least one first core and a first clad covering the first core and extending in the longitudinal direction, and a second glass fiber including at least one second core and a second clad covering the second core and extending in the longitudinal direction, to produce a first flat wire including at least the first glass fiber and the second glass fiber; simultaneously drawing a third glass fiber including at least one third core and a third clad covering the third core and extending in the longitudinal direction, and a fourth glass fiber including at least one fourth core and a fourth clad covering the fourth core and extending in the longitudinal direction, to produce a second flat wire including at least the third glass fiber and the fourth glass fiber; and arranging the first flat wire and the second flat wire in parallel and connecting them to each other with a connecting resin, a first flat wire made by drawing the first glass fiber and the second glass fiber so that a difference between a first reference angle in the rotation direction of the first glass fiber and a second reference angle in the rotation direction of the second glass fiber is a certain value or less; and a second flat wire made by drawing the third glass fiber and the fourth glass fiber so that a difference between a third reference angle in the rotation direction of the third glass fiber and a fourth reference angle in the rotation direction of the fourth glass fiber is a certain value or less.

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