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

Abstract

This optical fiber is provided with: a glass fiber that includes at least one core and a cladding covering the core, and that extends in the longitudinal direction; and a coating part that includes at least one layer of a coating resin that is coated on the outer periphery of the glass fiber. The glass fiber has directionality with respect to a rotation direction with the longitudinal direction as an axis. A marking associated with the directionality of the glass fiber with respect to the rotation direction is provided on the outer periphery of the coating part, and the marking is formed by laser marking.

Description

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

[0001] This disclosure relates to an optical fiber, an optical fiber manufacturing method, a tape fiber, and a tape fiber manufacturing method. This application claims priority to Japanese Application Nos. 2024-019279 and 2024-019281, both filed on February 13, 2024, and the entire contents of the aforementioned Japanese applications are incorporated by reference.

[0002] Patent Document 1 discloses various multi-core fibers having a predetermined directionality with respect to the rotation direction, in which cores are arranged asymmetrically with respect to an arbitrary rotation direction.

[0003] Japanese Patent Application Publication No. 2021-155308 Japanese Patent Publication No. 11-513130 ​​Japanese Patent Application Publication No. 2018-062448 US Patent Application Publication No. 2016 / 0223774

[0004] An optical fiber according to an embodiment of the present disclosure includes a glass fiber including at least one core and a cladding covering the core, extending in a longitudinal direction, and a coating including at least one coating resin layer covering the outer periphery of the glass fiber. The glass fiber has directionality relative to a rotation direction about an axis of the longitudinal direction. In this optical fiber, a marking associated with the directionality relative to the rotation direction of the glass fiber is provided on the outer periphery of the coating. The marking is formed by laser marking.

[0005] FIG. 1 is a perspective view including a cross section of an optical fiber according to one embodiment. FIG. 2 is a perspective view including a cross section of an optical fiber according to another embodiment. FIG. 3 is a perspective view including a cross section of an optical fiber according to another embodiment. Parts (a), (b), and (c) of FIG. 4 are schematic diagrams each showing an example of markings formed on an optical fiber. FIG. 5 is a perspective view showing both end facets of an optical fiber according to another embodiment. FIG. 6 is a schematic diagram showing an example of a method for manufacturing an optical fiber. FIG. 7 is a cross-sectional view showing an example of markings on an optical fiber manufactured by the optical fiber manufacturing method shown in FIG. 6. FIG. 8 is a cross-sectional view showing another example of markings on an optical fiber manufactured by the optical fiber manufacturing method shown in FIG. 6. FIG. 9 is a schematic diagram showing another example of a method for manufacturing an optical fiber. FIG. 10 is a cross-sectional view showing an example of markings on an optical fiber manufactured by the optical fiber manufacturing method shown in FIG. 9. Parts (a) and (b) of FIG. 11 are schematic diagrams each showing a modified example of markings formed on an optical fiber. FIG. 12 is a perspective view including a cross section of a tape fiber according to one embodiment. FIG. 13 is a schematic diagram showing the tape fiber shown in FIG. 12 from above. FIG. 14 is a schematic diagram showing a modified example of the position of the marking on the tape fiber. FIG. 15 is a schematic diagram showing another modified example of the position of the marking on the tape fiber. FIG. 16 is a schematic diagram showing a modified example of the marking on the tape fiber. FIG. 17 is a perspective view including a cross section of a tape fiber according to another embodiment. FIG. 18 is a schematic diagram showing an example of a method for manufacturing the tape fiber shown in FIG. 12. Part (a) of FIG. 19 is a diagram explaining details of a detection device in the manufacturing apparatus shown in FIG. 18, and part (b) of FIG. 19 is a diagram showing an example of marking on the tape fiber detected by the detection device. FIG. 20 is a diagram explaining an example of measuring the shape of the optical fiber in the tape fiber of FIG. 17 using the detection device shown in FIG. 18.

[0006] [Problems to be Solved by the Present Disclosure] The optical fiber described in Patent Document 1 is formed as a fiber having directionality in the rotation direction. Such an optical fiber, or a ribbon fiber including a plurality of such optical fibers, requires rotational alignment to align each core with the mating core during optical splicing. It is conceivable to use each core as a marker for such alignment. However, because the difference in refractive index between the core and the cladding is small, it is difficult to distinguish the core. Furthermore, if a colored layer is provided on the outermost layer of the optical fiber, it is impossible to distinguish the core in the first place. Furthermore, in the case of a ribbon fiber, alignment is required for each optical fiber, which further increases the burden of the alignment work. Therefore, there is a need for a method that can easily align optical fibers having directionality in the rotation direction, and a method that can easily align a ribbon fiber including multiple optical fibers, each of which has directionality in the rotation direction.

[0007] Note that Patent Document 2 describes applying a ring-shaped color mark to the coating, Patent Document 3 describes applying marking to the coating with a laser, and Patent Document 4 describes applying a color mark to the coating layer of a multi-core fiber that has directionality with respect to the rotation direction.

[0008] According to one aspect of the present disclosure, it is possible to easily align an optical fiber that has directionality relative to the rotation direction. According to another aspect of the present disclosure, it is possible to easily align a ribbon fiber that includes multiple optical fibers, each of which has directionality relative to the rotation direction.

[0009] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. (1) An optical fiber according to one embodiment includes a glass fiber including at least one core and a cladding covering the core, extending in a longitudinal direction, and a coating including at least one coating resin layer covering the outer periphery of the glass fiber. The glass fiber has directionality with respect to a rotation direction about the longitudinal axis. In this optical fiber, a marking associated with the directionality of the glass fiber with respect to the rotation direction is provided on the outer periphery of the coating. The marking is formed by laser marking.

[0010] In this optical fiber, a marking associated with the orientation of the glass fiber relative to the rotational direction is provided on the outer periphery of the coating that coats the outer periphery of the glass fiber. In this case, the marking allows the orientation of the glass fiber relative to the rotational direction to be known from the outside. Therefore, this optical fiber allows easy rotational alignment of an optical fiber that has orientation relative to the rotational direction when fusion splicing with optical fibers of the same type, fixing to an optical connector or ferrule, connecting to a transmitting / receiving transceiver, or manufacturing an optical fiber ribbon in which optical fibers are arranged. Note that the "optical fiber that has orientation relative to the rotational direction" referred to here includes at least a multicore fiber (also referred to as "MCF") in which multiple cores are arranged in a single cladding, but is not limited thereto, and also includes polarization-maintaining fiber (also referred to as "PMF"), hole-assisted fiber (also referred to as "HAF"), and hole-core fiber (also referred to as "HCF"), which require rotational alignment.

[0011] Furthermore, in this optical fiber, the markings are formed by laser marking. When marking is performed using inkjet or other methods, the position of the markings on the optical fiber is likely to vary, and the ink may cause the outer surface of the optical fiber to become bulged or foreign matter may adhere to it. Furthermore, there is a possibility that the markings may be lost due to wear of the ink. In contrast, when using laser marking, such problems are less likely to occur, and suitable markings can be formed.

[0012] (2) In the optical fiber of (1) above, the marking may be formed as a dotted line. A continuous line marking may cause degradation and breakdown of the colored layer or coating starting from the marked point, depending on the material used. A dotted line marking can reduce such degradation and breakdown. It also broadens the range of materials available for the coating.

[0013] (3) In the optical fiber of (1) or (2), the marking may be formed to indicate information about the optical fiber. In this case, the information about the optical fiber, such as the type of optical fiber, the arrangement of cores, the number of cores, etc., can be recognized from the outside, and optical splicing work (fusion splicing, etc.) of the optical fibers can be performed, thereby simplifying the work.

[0014] (4) In any of the optical fibers described in (1) to (3), the marking may be formed to have a refractive index different from that of the other portions of the coating. In this case, when aligning the optical fiber in the rotational direction, for example, when performing image processing, the marking can be clearly detected by applying appropriate transmitted illumination due to the difference in illumination brightness caused by the difference in refractive index between the marking and the coating. Furthermore, markings made of materials that are difficult to color, such as transparent coatings, and markings that appear the same color as the coating can be detected.

[0015] (5) In any of the optical fibers (1) to (4), the marking may form a waveguide. In this case, by transmitting visible light or infrared light for identification through the waveguide marking and detecting the light leaking from the end face or side face, it is possible to easily identify the rotation direction, for example, during fusion splicing.

[0016] (6) In any of the optical fibers described in (1) to (5), the marking may be recessed from the outer periphery of the coating resin layer. In this case, even in a coating resin layer that is difficult to color with a laser, the reference for the rotation direction can be clearly determined by the uneven shape. Furthermore, even in an optical fiber in which a protruding surface may increase microbend loss, a reference based on the shape can be obtained.

[0017] (7) In any one of the optical fibers (1) to (6), the marking may be raised from the outer periphery of the coating resin layer. In this case, even in the coating resin layer, which is difficult to color with a laser, the uneven shape makes it possible to clearly determine the reference for the rotation direction.

[0018] (8) In any of the optical fibers described in (1) to (7) above, the glass fiber does not need to be provided with a marker that serves as a reference for the rotation direction. With this optical fiber, even if the glass fiber does not have a marker, a reference for the rotation direction can be obtained by marking the coating. Furthermore, since the glass fiber does not have a marker, the marker does not affect the transmission characteristics of the core, and the cores can be arranged more densely.

[0019] (9) In the optical fiber according to any one of (1) to (8), the coating may have a colored coating resin layer as an outermost layer, and the marking may be provided on the colored coating resin layer. In this case, the color difference between the colored resin and the marking can improve the visibility of the marking. Furthermore, the colored coating resin layer easily absorbs laser light, making it easy to perform marking.

[0020] (10) In the optical fiber of (9), the coating may have a colored outermost layer and an inner layer in contact with the inner side of the outermost layer. The marking may be formed by removing the outermost layer to expose the inner coating layer. In this case, selective removal of the colored layer, which has a large removal effect by the laser, can prevent a significant impact on the inner coating layer, thereby maintaining the protective function of the coating on the glass.

[0021] (11) In the optical fiber of (10), the inner layer may have a color different from that of the colored outermost layer, or may be transparent. Even in the case of an optical fiber having a colored layer that is difficult to color with a laser, the difference in color between the colored layer and the coating layer from which the colored layer has been removed makes it possible to recognize the marking not only by shape but also by color. For example, if the colored layer is a chromatic color and the coating layer is a black colored secondary, the marking can be clearly seen as a black mark on a chromatic color.

[0022] In any of the optical fibers (1) to (11) above, the markings may be formed along the longitudinal direction. Optical fibers may be cut to perform optical connection (rotational alignment) during installation, etc., and since the markings are formed along the longitudinal direction, the degree of freedom in selecting the locations for cutting and rotational alignment can be improved. Furthermore, multiple markings may be formed along the longitudinal direction. By providing multiple markings, it is possible to distinguish between end faces (end A and end B) where the core arrangement is mirror-symmetrical. Furthermore, in multi-core ribbons and multi-core cables, the number of distinguishable fibers can be increased even in colored layers of the same color by combining the number and type of markings. Examples of multiple distinguishable markings include different colors or widths, dotted and continuous lines, and different dotted line pitches.

[0023] (12) According to one embodiment, a method for manufacturing an optical fiber includes the steps of drawing a glass fiber including at least one core and a cladding covering the core, forming a coating including at least one coating resin layer covering the outer periphery of the glass fiber, and forming a marking on the outer periphery of the coating that is associated with the directionality relative to the rotation direction of the glass fiber. The marking is formed by laser marking. This method allows for the simple manufacture of an optical fiber that can be easily rotated and aligned.

[0024] In addition, in this optical fiber manufacturing method, the markings are formed by laser marking. When markings are formed using inkjet or other methods, the position of the markings on the optical fiber is likely to vary, and the ink may cause protrusions on the outer surface of the optical fiber or foreign matter to adhere to the surface. Furthermore, when marking with ink, the high drawing speed of the optical fiber may be hindered, and a line length must be ensured for the ink to dry. In contrast, when marking with laser, such problems are less likely to occur and markings can be formed efficiently.

[0025] (13) In the optical fiber manufacturing method of (12) above, in the step of forming the marking, the marking may be performed immediately after the resin material for forming the coating is applied to the fiber. In this case, vibration of the drawn fiber is reduced, allowing for more accurate marking. Furthermore, in this case, marking is performed before the resin material for forming the coating is applied to the fiber and hardens. Therefore, stress and shape changes caused in the coating material by laser marking are alleviated by the flow of the liquid coating material, thereby preventing cracks and fractures in the coating material due to residual stress. Furthermore, a marking with a smooth surface can be obtained.

[0026] (14) In the method for manufacturing an optical fiber according to (12), marking may be performed after the resin material for forming the coating is applied to the fiber and cured, when the conveying direction is changed by a roller located immediately below the drawing furnace. In this case, vibration of the drawn fiber is reduced, allowing for more accurate marking.

[0027] (15) In the method for manufacturing an optical fiber according to any one of (12) to (14), the step of forming the coating may include a step of forming a colored outermost layer and a step of forming an inner layer in contact with the inner side of the outermost layer. In the step of forming the marking, the marking may be formed on the outermost layer. In this case, an optical fiber with improved visibility of the marking can be manufactured due to the color difference between the colored resin and the marking. Furthermore, the colored coating resin layer easily absorbs laser light, making marking easy to perform.

[0028] (16) In the method for manufacturing an optical fiber according to any one of (12) to (15) above, the step of forming the coating may include a step of forming a colored outermost layer and a step of forming an inner layer that contacts the inside of the outermost layer. In the step of forming the marking, the marking may be applied to the inner layer. In this case, the optical fiber can have the same appearance as an optical fiber without a marking when visually inspected. Meanwhile, when it is necessary to identify the rotation direction during fusion splicing, for example, the mark on the inner layer of the colored layer can be recognized by applying transmitted illumination, making it possible to identify the rotation direction.

[0029] (17) In the optical fiber manufacturing method according to any one of (12) to (16), the step of forming the coating may include a step of forming a colored outermost layer and a step of forming an inner layer in contact with the inner side of the outermost layer. The inner layer may have a color different from that of the colored outermost layer, or may be transparent. In the step of forming the marking, the marking may be formed by removing the outermost layer. This optical fiber manufacturing method makes it possible to manufacture an optical fiber having a colored layer that is difficult to color with a laser, in which the marking can be recognized not only by shape but also by color due to the difference in color between the colored layer and the coating layer from which the colored layer has been removed. For example, if the colored layer is a chromatic color and the coating layer is a black colored secondary, it is possible to manufacture an optical fiber in which the marking is clearly visible as a black mark on the chromatic color.

[0030] (18) In the optical fiber manufacturing method according to any one of (12) to (17), the step of forming the colored outermost layer may be performed during the drawing step. By checking the rotation direction of the glass before coating on the drawing tower, further adjusting the rotation direction as necessary, and quickly marking the colored coating after coating, a colored optical fiber with markings accurately aligned with the rotation direction can be obtained.

[0031] (19) A tape fiber according to one embodiment includes a plurality of optical fibers. The plurality of optical fibers include glass fibers each including at least one core and a cladding covering the core, extending in a longitudinal direction, and a coating portion including at least one coating resin layer covering the outer periphery of the glass fiber. The plurality of optical fibers are arranged side by side in a horizontal direction intersecting the longitudinal direction. The glass fibers have directionality relative to a rotation direction about the longitudinal direction. In this tape fiber, the outer periphery of each coating portion is provided with a marking associated with the directionality relative to the rotation direction of the glass fiber. The marking is formed by laser marking.

[0032] In the ribbon fiber of (19) above, markings associated with the orientation of the optical fiber relative to the rotational direction are provided on the outer periphery of the coating that coats the outer periphery of each glass fiber. In this case, the orientation of the optical fiber relative to the rotational direction can be known from the outside by each marking. Therefore, this ribbon fiber makes it easy to perform rotational alignment of multiple optical fibers that have orientation relative to the rotational direction when fusion splicing with optical fibers of the same type, fixing to an optical connector or ferrule, connecting to a transmitting / receiving transceiver, or manufacturing an optical fiber ribbon in which optical fibers are arranged. Note that the term "fiber having orientation relative to the rotational direction" as used herein includes at least a multicore fiber (also referred to as "MCF") in which multiple cores are arranged in a single cladding, but is not limited thereto, and also includes polarization-maintaining fiber (also referred to as "PMF"), hole-assisted fiber (also referred to as "HAF"), and hole-core fiber (also referred to as "HCF"), which require rotational alignment.

[0033] Furthermore, in this ribbon fiber, the markings are formed by laser marking. When marking is performed by inkjet or the like, the position of the marking is likely to vary in a ribbon fiber having multiple optical fibers, and the ink may cause the outer surface of the ribbon fiber to bulge or foreign matter to adhere. Furthermore, there is a possibility that the markings may disappear due to ink wear. In contrast, when using laser marking, such problems are less likely to occur and suitable markings can be formed.

[0034] (20) In the ribbon fiber of (19), the markings on the plurality of optical fibers may be arranged so as to be in the same position on each corresponding optical fiber. In this case, the orientation of the plurality of optical fibers in the rotation direction is aligned, and when optically splicing the ribbon fiber to another ribbon fiber, etc., splicing work including rotational alignment can be easily performed.

[0035] In any of the above-described ribbon fibers, each of the markings may be formed along the longitudinal direction. During installation, the ribbon fiber may be cut to perform optical splicing (rotational alignment and fusion splicing). Since the markings are formed along the longitudinal direction, the flexibility in selecting the locations for cutting and rotational alignment can be improved. Furthermore, the markings on the multiple optical fibers may be formed so as to indicate information about the ribbon fiber as a whole. In this case, information about the ribbon fiber, such as the type of each optical fiber, the number of optical fibers, the core arrangement, the number of cores, etc., can be recognized from the outside to perform the optical splicing work (fusion splicing, etc.) of the ribbon fiber, thereby simplifying the work.

[0036] In any of the above-described tape fibers, the marking may be recessed from the outer periphery of the plurality of optical fibers. In this case, by fitting the marking in an uneven shape to the coating resin layer (tape coating) that coats the outer periphery of the glass fiber, it is possible to prevent the optical fiber from changing in the rotation direction after being tapered. Furthermore, even in a coating resin layer that is difficult to color with a laser, the uneven shape allows the reference for the rotation direction to be clearly determined. On the other hand, the marking may be raised from the outer periphery of the plurality of optical fibers. In this case, by fitting the marking in an uneven shape to the coating resin layer (tape coating) that coats the outer periphery of the glass fiber, it is possible to prevent the optical fiber from changing in the rotation direction after being tapered. Furthermore, even in a coating resin layer that is difficult to color with a laser, the uneven shape allows the reference for the rotation direction to be clearly determined. Furthermore, a reference based on shape can be obtained even in optical fibers in which a raised surface may increase microbend loss.

[0037] (21) A method for manufacturing a tape fiber according to one embodiment includes the steps of preparing a plurality of optical fibers, arranging the plurality of optical fibers laterally and adjusting the plurality of optical fibers so that they are oriented in a predetermined rotational direction, and connecting the plurality of optical fibers to each other with a connecting portion. The plurality of optical fibers prepared in the preparing step include glass fibers including at least one core and a cladding that covers the core, and coating portions including at least one coating resin layer that covers the outer periphery of the glass fiber. Furthermore, markings associated with the orientation relative to the rotational direction of the glass fiber are formed on the outer periphery of the coating portions of the plurality of optical fibers by laser marking. In the adjusting step, the markings on the plurality of optical fibers are adjusted so that they are positioned in a predetermined position in the rotational direction. This method makes it possible to simply manufacture a tape fiber that can be easily rotated.

[0038] Furthermore, in this method for manufacturing a tape fiber, the markings are formed by laser marking. When markings are formed using inkjet or the like, the position of the markings on the tape fiber is likely to vary, and the ink may cause protrusions on the outer surface of the tape fiber or foreign matter to adhere to the surface. Furthermore, when marking with ink, it is necessary to set a line length to allow the ink to dry and to hinder the high drawing speed of the optical fiber that forms the tape fiber. In contrast, when marking with laser marking, such problems are less likely to occur and markings can be formed efficiently.

[0039] (22) In the manufacturing method of the ribbon fiber of (21), in the adjusting step, the position of the marking in the rotational direction may be detected after the material for forming the joint portion is applied and before the applied material is hardened, and the rotational direction of the corresponding optical fiber among the plurality of optical fibers may be adjusted based on the detected rotational position. In this case, the relationship between the directionality of each optical fiber in the rotational direction and the marking can be more reliably established.

[0040] (23) In the method for manufacturing a ribbon fiber according to (21) or (22), the adjustment step may include adjusting the angle of the running surface of the twist adjustment roller that guides each of the optical fibers for each optical fiber. In this case, the rotation direction of each optical fiber running at high speed can be adjusted with high precision.

[0041] (24) In the ribbon fiber manufacturing method of (23) above, the optical fibers may be passed through an extended pass line, which causes the optical fibers to travel back and forth between rollers multiple times before passing through the twist adjustment rollers. In this case, the twist imparted by winding is restored to a twist-free state within the extended pass line section by releasing the torsional stress of the optical fibers. This facilitates subsequent adjustment of the rotation direction.

[0042] (25) In the manufacturing method of any one of (22) to (24) above for a ribbon fiber, the adjusting step may include photographing the color, surface condition, or uneven shape of the marking with a camera to detect the position of the marking in the rotation direction. In this case, the position of the marking can be detected using a simple device without touching the optical fiber.

[0043] (26) In any of the ribbon fiber manufacturing methods (22) to (24) above, the adjusting step may involve detecting the uneven shape of the marking using a surface shape sensor to detect the position of the marking in the rotation direction. Detection methods using a camera may result in detection failure due to focus shifting. Furthermore, the optical fiber may be displaced due to running. However, detection methods using a surface shape sensor do not result in focus shifting, and the position of the marking with an uneven shape can be detected with high accuracy even if the optical fiber is displaced due to running.

[0044] (27) In the manufacturing method of any one of (21) to (26) above, in the adjusting step, the position of the marking in the rotational direction may be detected before the material for forming the splice portion is applied, and the rotational direction of the corresponding optical fiber among the plurality of optical fibers may be adjusted based on the detected rotational position. In this case, since the position of the marking is detected before the splice portion is formed, the position of the marking can be detected with high accuracy. In addition, the options for the material for the splice portion can be increased.

[0045] (28) In the manufacturing method of the ribbon fiber described in (27) above, in the adjusting step, the positions of the markings in the rotational direction may be detected at multiple locations before the material for forming the splice portion is applied, and the rotational direction of corresponding optical fibers among the multiple optical fibers may be adjusted based on the detected rotational positions. In this case, the amount of misalignment at the splice position can be calculated and predicted by the control device based on the amount of misalignment detected by each detection means and the difference between the amounts of misalignment. Therefore, the position of the marking can be detected with even greater accuracy.

[0046] [Details of the embodiments of the present disclosure] Specific examples of optical fibers, optical fiber manufacturing methods, tape fibers, and tape fiber manufacturing methods 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 redundant 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.

[0047] [Structure of Optical Fiber] An example of an optical fiber according to an embodiment will be described with reference to FIG. 1 . FIG. 1 is a perspective view including a cross section of the optical fiber according to an embodiment. As shown in FIG. 1 , the optical fiber 1 is, for example, a multi-core fiber, and includes a glass fiber 4 including a plurality of cores 2 and a cladding 3 covering the plurality of cores 2, a primary resin layer 5 (coating resin layer) that coats the outer periphery of the glass fiber 4, a secondary resin layer 6 (coating resin layer) that coats the outer periphery of the primary resin layer 5, and a colored layer 7 (coating resin layer) that coats the outer periphery of the secondary resin layer 6. The primary resin layer 5, the secondary resin layer 6, and the colored layer 7 form a coating portion 8 that coats the outer periphery of the glass fiber 4 in the optical fiber 1. In this case, the secondary resin layer 6 is an inner layer that contacts the inside of the colored layer 7, which is the outermost layer. The optical fiber 1 has a fiber structure that is directional with respect to the rotation direction. "Directional with respect to the rotation direction" means that the cross-sectional structure (e.g., the position of the core in a multi-core fiber) changes during one rotation. The optical fiber 1 is not limited to an MCF, but may be a PMF, HAF, or HCF that requires alignment in the rotational direction.

[0048] The core 2 is made of pure silica (SiO ２ ) glass or silica glass doped with germanium dioxide or elemental fluorine. The cladding 3 has a refractive index lower than that of the core 2. The cladding 3 is formed, for example, from pure silica glass or silica glass doped with elemental fluorine. A trench having a refractive index lower than that of the cladding 3 may be provided between each core 2 and the cladding 3. A glass fiber 4 is formed from multiple cores 2 and claddings 3. The glass fiber 4 may or may not have markers that serve as references for rotational alignment. If there are no markers in the glass, the markers will not affect the transmission characteristics of the cores 2, and the cores 2 can be arranged more densely.

[0049] The primary resin layer 5 coats the outer periphery of the clad 3 of the glass fiber 4. More specifically, the primary resin layer 5 is in contact with the outer periphery of the clad 3 and coats the entire clad 3. The secondary resin layer 6 further coats the outer periphery of the primary resin layer 5. More specifically, the secondary resin layer 6 is in contact with the outer periphery of the primary resin layer 5 and coats the entire primary resin layer 5.

[0050] The primary resin layer 5 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 that can be used include urethane (meth)acrylate and epoxy (meth)acrylate. The primary resin layer 5 has a lower modulus of elasticity (Young's modulus) than the secondary resin layer 6, and is softer than the secondary resin layer 6. For example, the Young's modulus of the primary resin layer 5 at 23°C is 0.1 MPa or more and 5 MPa or less. This provides the optical fiber 1 with lateral pressure resistance, preventing an increase in transmission loss in the optical fiber 1 even when lateral pressure is applied.

[0051] The secondary resin layer 6 is formed by curing a resin composition containing urethane (meth)acrylate, a monomer, and a photopolymerization initiator with ultraviolet light. The secondary resin layer 6 has a higher elasticity (Young's modulus) than the primary resin layer 5, and is harder than the primary resin layer 5. For example, the Young's modulus of the secondary resin layer 6 at 23°C is 1200 MPa or more and 2800 MPa or less. The thickness of each of the primary resin layer 5 and the secondary resin layer 6 is, for example, 5 μm or more and 50 μm or less.

[0052] The colored layer 7 is formed by curing a UV-curable resin composition containing a pigment or dye with UV light. This resin composition preferably contains titanium oxide. Titanium oxide changes color from white to gray when irradiated with a short-pulse UV laser, allowing color development without significantly affecting the resin of the colored layer 7. Furthermore, titanium oxide scatters UV laser light near the surface, allowing the colored layer 7 to be selectively colored, removed, or raised without significantly affecting the inner coating resin. The UV laser used here is, for example, a THG-YAG laser or THG-YVO4 laser with a wavelength of 300 nm to 410 nm, more preferably 355 nm. The pulse width of the UV laser is 10 ps to 100 ns, more preferably 1 ns to 50 ns. Such a short-pulse UV laser does not thermally affect the resin, allowing marking to be performed without significantly affecting the resin except for the marking area. The thickness of the colored layer 7 is, for example, 3 μm to 10 μm. By making the thickness of the colored layer 7 3 μm or more, the color of the optical fiber (core wire) becomes sufficiently dark in appearance, improving its distinguishability.

[0053] The optical fiber 1 according to this embodiment further has a marking 10 formed on the outer periphery of the coating 8 (on the outer periphery of the colored layer 7 in the example of FIG. 1 ) that extends linearly along the longitudinal direction. This marking 10 serves as a reference when rotationally aligning the glass fiber 4 of the optical fiber 1, and is provided, for example, at a position corresponding to the center lines of the two cores 2 on each side shown in FIG. 1 . This marking 10 functions as a marking associated with the orientation relative to the rotational direction of the glass fiber 4. Therefore, an operator can perform rotational alignment, etc. of the optical fiber 1 based on the position of this marking 10.

[0054] Furthermore, as in the optical fiber 1A shown in FIG. 2 , the marking 10A may be formed in a dotted line shape or may be formed so as to be recessed from the outer periphery of the coating. Conversely, the marking 10A may be formed so as to be raised from the outer periphery of the coating. This optical fiber 1A, like the optical fiber 1 shown in FIG. 1 , includes multiple cores 2, cladding 3, and primary resin layer 5. By forming the marking 10A in an uneven shape, even in a coating resin layer that is difficult to color with a laser, the uneven shape allows for a clear determination of the reference for the rotation direction, thereby facilitating rotational alignment of the optical fiber 1. When the marking 10A is recessed, it is possible to form the marking 10A in a way that prevents an increase in microbending loss even in an optical fiber whose surface is likely to increase microbending loss. Like the marking 10, the marking 10A serves as a reference for rotational alignment of the glass fiber 4 of the optical fiber 1, and is provided, for example, at a position corresponding to the center lines of the two cores 2 on the left and two cores 2 on the right and two cores 2 on the left and two cores 2 on the right as shown in FIG. 2 .

[0055] A similar marking 10B is also provided on the optical fiber 1B shown in FIG. 3. Like the optical fiber 1 shown in FIG. 1, the optical fiber 1B includes multiple cores 2, a cladding 3, and a primary resin layer 5. The optical fiber 1B also includes a secondary resin layer 6A, but differs from the optical fiber 1 in that the secondary resin layer 6A contains a pigment or dye and also functions as the colored layer 7. The primary resin layer 5 and the secondary resin layer 6A form a coating 8A that coats the outer periphery of the glass fiber 4 in the optical fiber 1B. In this case, the primary resin layer 5 serves as an inner layer that contacts the inside of the secondary resin layer 6, which functions as the colored layer 7. In the optical fiber 1B, the marking 10B is provided on the outer periphery of the secondary resin layer 6A in the coating 8A. The marking 10B in the example shown in FIG. 3 is formed as a dotted or wavy line along the longitudinal direction. Like the marking 10, the marking 10B serves as a reference when rotationally aligning the glass fiber 4 of the optical fiber 1, and is provided, for example, at a position corresponding to the center line of each of the two cores 2 on the left and right sides as shown in Figure 3.

[0056] In the optical fiber, the structure of the marking associated with the directionality relative to the rotation direction of the glass fiber 4 is not limited to the above. For example, as shown in parts (a) and (b) of Figure 4, markings 10C and 10D may be formed by continuously forming a large number of dots on a line at predetermined intervals. Also, as shown in part (c) of Figure 4, marking 10E may be formed by forming a large number of dots on a line so that they overlap each other. The markings 10, 10A, 10B, 10C, 10D, and 10E described above may have the shape of yet another marking that is a combination of each other's shapes.

[0057] 5 is a diagram showing an optical fiber 1C having multiple markings. The optical fiber 1C has, for example, four cores 2A, 2B, 2C, and 2D, and is provided with two types of markings: a straight line marking 10 and a dotted line marking 10B. In this case, if the solid line marking 10 is used as a reference, it can be determined that the core closer to the dotted line marking 10B is the core 2C. Therefore, when both end faces are viewed side by side, the arrangement of the cores at both ends of the optical fiber is an inverted mirror image, but the positions of the cores 2A, 2B, 2C, and 2D can be distinguished.

[0058] [Method of Manufacturing Optical Fiber] To manufacture the optical fibers 1, 1A, 1B, and 1C having the markings 10, 10A, 10B, 10C, 10D, and 10E extending along the longitudinal direction, for example, as shown in FIG. 6 , first, a glass fiber 4 including a plurality of cores 2 and a cladding 3 covering the plurality of cores 2 is drawn from a preform P for MCF that is heated and melted in a drawing furnace 20. The drawn glass fiber 4 is cooled by a cooling device 21. Then, a twist, such as the rotational position of the cores 2 in the glass fiber 4, is detected by a twist detection device 22 that detects the twist in the rotational direction of the glass fiber 4. The rotational direction of the glass fiber 4 may be adjusted depending on the detected twist.

[0059] Next, the drawn glass fiber 4 is passed through a die 23 to form a primary resin layer 5 so as to coat the outer periphery of the glass fiber 4 with a coating material. At the same time, secondary resin layers 6, 6A are formed so as to coat the outer periphery of the primary resin layer 5 with a different coating material. In the example shown in Figure 6, both resin layers are formed using one die 23, but two or more dies may be arranged in sequence to form each layer in turn. In addition, the colored layer 7 is also formed on the secondary resin layer 6 in a similar manner when these resin layers are formed.

[0060] Next, after the coating 8, which is the primary resin layer 5, the secondary resin layers 6, 6A, and the colored layer 7 (all before hardening) is formed around the outer periphery of the glass fiber 4, the laser marking device 24 forms predetermined markings 10, 10A, 10B, 10C, 10D, and 10E along the longitudinal direction of the outer periphery of the coating 8, 8A of the optical fiber 1, 1A, 1B, and 1C. Since vibration of the optical fiber is significantly reduced after the resin is applied by the die 23, marking can be performed at such a location to achieve more accurate marking. The marking by the laser marking device 24 may be performed by color development or a shape change such as depression or protrusion. Color development may be achieved by any of foaming, condensation, carbonization, and chemical changes, and is not particularly limited. Depression is achieved, for example, by laser ablation of the coating 8 with a laser. Protrusion is achieved, for example, by foaming the coating 8 with a laser, causing volume expansion.

[0061] Before forming the colored layer 7 or the secondary resin layer 6A, predetermined markings 10, 10A, 10B, 10C, 10D, and 10E may be formed on the outer periphery of the optical fiber 1, 1A, 1B, and 1C using a laser marking device 24. In this case, the markings are formed on the outer periphery of the secondary resin layer 6 or the primary resin layer 5. By doing so, the optical fiber (core wire) has the same appearance as an unmarked optical fiber when visually inspected. When it is necessary to identify the rotation direction during fusion splicing, for example, the markings on the inner layer of the colored layer can be recognized by irradiating the optical fiber with transmitted light, making it possible to identify the rotation direction. Furthermore, the secondary resin layer 6 or the primary resin layer 5 may be transparent or may have a color different from that of the colored layer 7 or the secondary resin layer 6A. Laser marking on the colored layer 7 or the secondary resin layer 6A may expose the inner layer, i.e., the secondary resin layer 6 or the primary resin layer 5. Even if it is difficult to color the colored layer 7 or the secondary resin layer 6A with a laser, the difference in color between the colored layer and the inner layer from which the colored layer has been removed makes it possible to recognize the marking not only by shape but also by color.

[0062] When marking using the laser marking device 24, the drawing speed (drawing speed) can be set to, for example, 2000 m / min or more. Furthermore, because marking using the laser marking device 24 is performed along the drawing direction, the markings 10, 10A, 10B, 10C, 10D, and 10E on the optical fibers 1, 1A, 1B, and 1C can be easily formed along the longitudinal direction of the optical fibers 1, 1A, 1B, and 1C. Dotted lines or dot-shaped markings can be formed by intermittently irradiating the laser marking device. The coating 8 marked by the laser marking device 24 is cured by the UV curing device 25 and then wound around the take-up roller 27 via the direct below roller 26. The marking position by the laser marking device 24 may be adjusted depending on the degree of twist detected by the twist detection device 22.

[0063] By using such a laser marking device 24 to perform laser irradiation L before curing and then UV curing, an optical fiber 1D can be obtained that includes a marking 10F with a refractive index difference, as shown in FIG. 7. That is, by laser marking each coating material before curing, regions with different refractive indices can be easily formed within the transparent coating material. L1 is the laser-passing region. Marking 10F based on such a refractive index difference reduces the impact on the appearance, and the marking 10F can be identified by transmitted light even without color development. Furthermore, by marking as close as possible to the twist detection device 22, the marking position can be accurately adjusted according to the degree of twist. Stress and shape changes caused by laser marking in the coating material are alleviated by the flow of the liquid coating material, preventing cracking and fracture of the coating material due to residual stress. Furthermore, a smooth surface marking can be obtained.

[0064] As shown in Figure 8, a marking 10G may be formed inside the secondary resin layer 6, 6A. In this case, the marking 10G is formed inside the secondary resin layer 6, 6A by focusing the laser irradiation L inside the secondary resin layer 6, 6A. L2 is a laser passing region. This marking 10G may form a waveguide. By forming a waveguide, visible light or infrared light for identification can be propagated through the waveguide, and leakage light from the end face or side surface can be detected, making it easy to identify the rotation direction during fusion splicing, etc.

[0065] Furthermore, the method for manufacturing an optical fiber having such markings is not limited to the above-described method, and various methods can be employed. For example, as shown in FIG. 9, a glass fiber 4 drawn in the same manner as described above is passed through a die 23, and a resin material for forming the coatings 8, 8A is applied and cured. Then, when the conveying direction is changed by a roller 26 located immediately below the drawing furnace 20, marking may be performed by a laser marking device 24 to form the marking. In this case, marking is performed after the coating material has cured. Furthermore, since vibration of the optical fiber is significantly reduced at the roller 26 located immediately below, marking at such a location allows for more accurate marking.

[0066] When laser irradiation and UV curing are performed using such a laser marking device 24, a marking 10H is formed on the colored layer 7 or a portion of the secondary resin layer 6A having the function of a colored layer in the optical fiber 1E, as shown in FIG. 10 . The marking 10H extends in the longitudinal direction (the direction perpendicular to the paper). In this case, the action of the laser marking device 24 remains on the surface side of the optical fiber 1C, so the influence on the glass fiber 4 is significantly reduced. When forming a marking on the colored layer 7 or the secondary resin layer 6A having the function of a colored layer using a laser, the marking may be formed by removing the color (ink). In this case, removing the colored layer 7 or the secondary resin layer 6A exposes the inner coating layer that contacts the inside of the colored layer 7 or the secondary resin layer 6A, thereby forming the marking. In this case, the inner layer may be transparent or a color different from that of the colored layer 7 or the secondary resin layer 6A. By using this structure, even in the case of a colored layer that is difficult to color with a laser, the difference in color between the colored layer and the covering layer from which the colored layer has been removed makes it possible to recognize the marking not only by shape but also by color.

[0067] As described above, in the optical fibers 1, 1A, 1B, 1C, 1D, and 1E according to this embodiment, markings 10, 10A to 10H associated with the directionality of the glass fiber 4 relative to the rotational direction are provided on the outer periphery of the coating 8, 8A that coats the outer periphery of the glass fiber 4. These markings 10, 10A to 10H allow the rotational adjustment position of the glass fiber 4 to be known from the outside in the optical fibers 1, 1A, 1B, 1C, 1D, and 1E. Therefore, the optical fibers 1, 1A, 1B, 1C, 1D, and 1E can easily perform rotational alignment of the optical fibers 1, 1A, 1B, 1C, 1D, and 1E, which have directionality relative to the rotational direction. Furthermore, the above-described manufacturing method makes it possible to easily fabricate such optical fibers 1, 1A, 1B, 1C, 1D, and 1E.

[0068] The optical fibers 1, 1A, 1B, 1C, 1D, and 1E and the manufacturing method of the optical fiber 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, while the optical fibers described above have direct or dotted line markings, markings having structures shown in parts (a) and (b) of FIG. 11 may also be used. For example, the marking 10J shown in part (a) of FIG. 11 further adds predetermined additional information (e.g., identification information of the optical fibers 1, 1A, 1B, 1C, 1D, and 1E) to the marking using Morse code. Similarly, the marking 10K shown in part (b) of FIG. 11 may be digitally expressed, thereby adding predetermined additional information. Such additional information may be, for example, identification information of the optical fibers 1, 1A, 1B, 1C, 1D, and 1E, such as the type of optical fiber, core arrangement, number of cores, and core spacing. In this case, the optical fiber identification information can be recognized externally (in some cases, using a reader) to perform optical splicing work (fusion splicing, etc.), which simplifies the work. The identification information may be information for tracing, such as the serial number of the optical fiber.

[0069] Furthermore, in the above-described embodiment, an example in which one marking is formed on one optical fiber has been described, but this is not limiting. That is, two or more markings may be formed on one optical fiber. Such two or more markings may be positioned so that, when the optical fiber is viewed in cross section, the angle formed by the lines connecting each of the two markings with the center of the optical fiber is 90 degrees or more (for example, 180 degrees). In this case, even if one marking is positioned so that the other marking is hidden, the worker can easily see the other marking, thereby improving work efficiency. Alternatively, the two or more markings may be positioned so as to disrupt the symmetry of the structural arrangement inside the glass as viewed in the cross section. For example, in the case of a multicore fiber, the core arrangement at both ends of the optical fiber is a mirror image, so it is necessary to distinguish the end faces. However, two or more asymmetric markings make it possible to determine which end face is which.

[0070] (Structure of Tape Fiber) An example of a tape fiber according to one embodiment will be described with reference to Fig. 12 . Fig. 12 is a perspective view including a cross section of the tape fiber according to one embodiment. As shown in Fig. 12 , the tape fiber 100 includes a plurality of optical fibers 1F (four optical fibers 1F in the example shown in Fig. 12 ). Each optical fiber 1F 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 one another. This connection is achieved by a connecting portion (not shown) made of resin or the like.

[0071] Each optical fiber 1F forming the tape fiber 100 is, for example, a multi-core fiber, and includes a glass fiber 4 including a plurality of cores 2 and a cladding 3 covering the plurality of cores 2, a primary resin layer 5 (coating resin layer) that coats the outer periphery of the glass fiber 4, and a secondary resin layer 6 (coating resin layer) that coats the outer periphery of the primary resin layer 5. The primary resin layer 5 and the secondary resin layer 6 form a coating portion 8 that coats the outer periphery of the glass fiber 4 in the optical fiber 1F. The coating portion 8 may further include a colored layer (not shown) that coats the outer periphery of the secondary resin layer 6. The secondary resin layer 6 may also be colored. The optical fiber 1F has a fiber configuration that is directional with respect to the rotation direction. Note that "directional with respect to 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 1F (glass fiber 4) is not limited to an MCF, but may also be a PMF, HAF, or HCF that requires alignment in the rotation direction.

[0072] Each optical fiber 1F of the tape fiber 100 according to this embodiment further has a marking 10 formed on the outer periphery of each coating 8 (on the outer periphery of each secondary resin layer 6 in the example of FIG. 12 ) that extends linearly along the longitudinal direction. The marking 10 serves as a reference for rotational alignment of the glass fiber 4 of the optical fiber 1F, and is provided, for example, at a position corresponding to a line connecting the two upper and lower cores 2 shown in FIG. 12 . The marking 10 functions as a marking associated with the directionality relative to the rotational direction of the glass fiber 4 (for example, the rotational positions of the multiple cores 2). Therefore, an operator can perform rotational alignment of the tape fiber 100 including multiple optical fibers 1F based on the position of this marking 10. Such marking 10 is formed by laser marking.

[0073] 12 and 13, in the tape fiber 100, when viewed from above, each marking 10 extends in the longitudinal direction so as to pass through the center in the width direction (lateral direction) of each optical fiber. As described above, each marking 10 is arranged so as to be at the same position (the line connecting the two upper and lower cores 2, which is on the center line of the optical fiber 1F) in the corresponding optical fiber 1F. Therefore, in the tape fiber 100, the optical fibers 1F are aligned with the arrangement of the multiple cores 2 aligned.

[0074] However, the arrangement of the markings 10 on each optical fiber 1F of the tape fiber 100 is not limited to the arrangement shown in Figures 12 and 13. That is, as shown in Figure 14, in the tape fiber 100A, when viewed from above, the markings 10 associated with the directionality with respect to the rotation direction of the glass fiber 4 may be provided beside (on the side of) each optical fiber 1F of the tape fiber 100A. In this case, too, each marking 10 is arranged so as to be in the same position (on the side) on each corresponding optical fiber 1F.

[0075] Furthermore, as shown in FIG. 15 , in the tape fiber 100B, when viewed from above, the marking 10 may be provided laterally (sideways) on one optical fiber 1F (second from the top) of the tape fiber 100B, and may be provided so as to pass through the center in the width direction on the remaining three optical fibers 1F. In this case, the optical fibers 1F having different marking 10 arrangements may be used to impart predetermined information about the tape fiber 100B (e.g., identification information of the tape fiber 100B, information such as a serial number, or the number of optical fibers included in the tape fiber) that has meaning as a whole. In the example shown in FIG. 15 , for example, when the marking 10 is arranged at the center of the optical fiber 1F, it is treated as a data "1," and when the marking 10 is arranged to the side of the optical fiber 1F, it is treated as a data "0," and binary information such as "1011" can be added to the tape fiber. In this case, too, the marking 10 is formed at a predetermined position relative to the core 2, and in the tape fiber 100B, the optical fibers 1F are arranged with the arrangement of multiple cores 2 aligned.

[0076] Furthermore, the shape of the marking 10 is not limited to a straight line. For example, as shown in FIG. 16 , a tape fiber 100C may be used in which the marking 10L applied to each optical fiber 1F is a dotted or dashed line. The marking 10L may be a linear dotted line indicating Morse code or digital information. Such marking 10L can provide optical fiber identification information, such as the type of optical fiber 1F, core arrangement, number of cores, and core spacing. In this case, the optical fiber identification information can be recognized externally (possibly using a reader) to perform optical fiber splicing (fusion splicing, etc.), thereby simplifying the work.

[0077] The markings 10, 10L may have a shape that is depressed or elevated relative to the outer periphery of the optical fiber 1F. The markings 10, 10L may be formed on a colored layer that covers the outer periphery of the secondary resin layer 6 (coating resin layer).

[0078] Here, with reference to FIG. 17 , a tape fiber 100D, which is another embodiment, will be described. The optical fiber 1G is, for example, a multicore fiber, and includes a glass fiber 4 including multiple cores 2 and cladding 3, a primary resin layer 5 covering the glass fiber 4, a secondary resin layer 6 covering the primary resin layer 5, and a colored coloring layer 7 covering the secondary resin layer 6. In the optical fiber 1G, the marking 10M is formed by removing part or all of the coloring layer 7 in the thickness direction, or even a part of the secondary resin layer 6 in the thickness direction, so that the outer periphery of the coating resin layer has a depressed, concave shape. In the tape fiber 100D, multiple optical fibers 1G are arranged so that the markings 10M are in the same rotational position, and the entirety of the optical fibers 1G is coated with a tape coating resin 9. The tape coating resin 9 penetrates into the depressed shape of the markings 10M, preventing the optical fibers 1G from rotating inside the tape fiber 100D.

[0079] [Method for Manufacturing Tape Fiber] To manufacture a tape fiber 100 including a plurality of optical fibers 1F having markings 10 extending along the longitudinal direction, a glass fiber 4 including a plurality of cores 2 and a cladding 3 covering the plurality of cores 2 is first drawn from a preform for MCF that is heated and melted in a drawing furnace. The drawn glass fiber 4 is then cooled, and a coating material is then applied to the outer periphery of the glass fiber 4 to form a primary resin layer 5. Similarly, another coating material is applied to the outer periphery of the primary resin layer 5 to form a secondary resin layer 6. The markings 10 described above are then formed along the longitudinal direction (drawing direction) on the outer periphery of the secondary resin layer 6 (coating 8) of the optical fiber 1F using a laser marking device. The coating 8 on which the markings 10 are formed may then be cured using a UV curing device. Alternatively, the coating 8 may be cured before the markings 10 are formed. In this manner, a plurality of optical fibers 1F having markings 10 formed along the longitudinal direction are obtained.

[0080] Next, as shown in FIG. 18 , once preparation of the multiple optical fibers 1F (optical fibers 1a, 1b, 1c, and 1d) on which the markings 10 are formed is complete, the multiple optical fibers 1a to 1d wound around each of the supply rollers 30a, 30b, 30c, and 30d are arranged side by side and transported using multiple rollers 31 that function as an extension path line. By running the optical fibers along the extension path line, which reciprocates between these rollers 31 multiple times, the torsional stress generated in each of the optical fibers 1a to 1d when they were wound around the supply rollers 30a to 30d is released. Furthermore, during this transport, the rotational direction of the multiple optical fibers 1a to 1d is adjusted so that the markings 10 on each of the multiple optical fibers 1a to 1d are positioned at predetermined positions in the rotational direction. For example, as shown in FIG. 13 , the predetermined positions are arranged so that each marking 10 passes through the center line of the corresponding optical fiber 1F. However, this is not limited to this, and the arrangements shown in FIG. 14 or FIG. 15 may also be used. Furthermore, the rotational direction of the optical fibers 1a to 1d can be adjusted by adjusting the roller angles or conveying speed of the supply rollers 30a to 30d or the rollers 32a and 32b. The roller 32a may be, for example, a twist adjustment roller provided for each optical fiber. By using the twist adjustment roller, the angles of the optical fibers 1a to 1d are individually adjusted according to the rotational direction adjustment required for each optical fiber. In this angle adjustment, the angle of the running surface of the twist adjustment roller that guides each of the optical fibers 1a to 1d is adjusted for each optical fiber. The roller 32b may be a twist adjustment roller provided for each optical fiber, or both the rollers 32a and 32b may be twist adjustment rollers.

[0081] Detectors 40, 41 are provided on the transport path of the optical fibers 1a to 1d transported from roller 32a to roller 32b to detect the position of the marking 10 in the rotational direction. A detector 42 is also provided on the transport path of the optical fibers 1a to 1d transported from roller 32b to direction-changing roller 35 to detect the position of the marking 10 in the rotational direction. These detectors 40, 41, 42 detect the degree of deviation (amount of deviation) of the position of the marking 10 in the width direction of each optical fiber from a set position (e.g., centerline or lateral). The detectors 40, 41, 42 output the detected deviation amount to a control device (not shown). The control device, which acquires this detection information, controls the roller angle of the supply rollers 30a to 30d or rollers 32a, 32b, the transport speed, etc., based on the acquired information. Three detectors 40, 41, 42, or one or two of these detectors may be provided.

[0082] When multiple detectors 40 and 41 are disposed at positions before the optical fibers 1F are spliced, the control device can calculate and predict the amount of misalignment at the spliced ​​position based on the misalignment detected by the detectors 40 and 41 and the difference between these misalignments. This enables splicing without misalignment. Furthermore, when the detector 42 is disposed at a position after the optical fibers 1F are spliced, it can inspect the degree of misalignment at the spliced ​​position. In this case, if the inspected misalignment is large, the calculation of the predicted misalignment can be appropriately corrected. In this way, by disposing multiple detectors 40 and 41 before splicing and disposing the detectors 40, 41, and 42 before and after splicing, a spliced ​​ribbon fiber with minimal misalignment can be obtained.

[0083] Between the roller 32b on which the detection device 42 is disposed and the direction-changing roller 35, there are further provided a die 33 onto which a resin material for a connecting portion for connecting the parallel-arranged optical fibers 1F is applied, and a UV curing device 34 for curing the resin material. In other words, the detection device 42 is disposed between the die 33 and the UV curing device 34. In the die 33, the multiple optical fibers 1F are passed through holes for applying resin, thereby reducing vibration of the transported optical fibers 1F. Therefore, by detecting the position of the marking 10 in the rotational direction immediately after it passes through the die 33, detection accuracy can be improved. The detection device 42 may be disposed behind the UV curing device 34. When the detection device 42 is disposed behind the UV curing device 34, the detection device 42 can detect the alignment state fixed by the UV curing device 34 and determine whether the alignment is good or bad. After the resin material for the connecting portions is cured by the UV curing device 34, the conveying direction is changed by a direction changing roller 35, and the tape fiber 100 is taken up by a take-up roller 36. It will be clear to those skilled in the art that the tape fibers 100A, 100B, 100C, and 100D can also be manufactured in a similar manner, and detailed description thereof will be omitted.

[0084] FIG. 19 ( a ) shows an example of the detection devices 40, 41, and 42. The detection devices include a camera 50 that captures images from a direction perpendicular to the direction in which the optical fibers 1F run, an illumination device 51 that irradiates light from a direction diagonally intersecting the optical fibers 1F, and an illumination device 52 that irradiates light from a direction opposite to the camera 50. When the optical fibers 1F are illuminated from the opposite directions, images of the markings 10 with different colors and brightness are obtained due to differences in color and transmittance between the markings 10 and the surrounding coating resin layer, as shown in FIG. 19 ( b ). In other words, the camera 50 captures the color, surface condition, and uneven shape of the markings 10. This allows the position of the markings 10 in the rotational direction to be detected. When the optical fibers 1F are illuminated from the illumination device 51 from a diagonally intersecting direction and an image is obtained in which the interior and boundary of the markings 10 have different brightness from the surrounding coating resin layer due to scattering and shadows created by the uneven shape of the markings 10. This allows the position of the marking 10 in the rotational direction to be detected.

[0085] Furthermore, a surface shape sensor that detects the surface shape may be used as the detection device instead of the camera 50. In the case of an uneven marking (for example, the marking 10M shown in FIG. 17), when this surface shape sensor measures the optical fiber 1G of the ribbon fiber shown in FIG. 20, for example, a surface shape output such as that shown in FIG. 20 is obtained. In other words, the uneven shape of the marking 10M is detected by the surface shape sensor. The position of the marking 10M is detected from the position of the depression on the surface. Because the sensor that detects the surface shape is used to measure the height direction of the surface, it is not affected by changes in the distance between the sensor and the optical fiber due to vibration of the optical fiber 1G as it travels, and the position of the marking 10M can be stably detected.

[0086] As described above, in the tape fibers 100, 100A, 100B, 100C, and 100D according to the present embodiment, markings 10, 10L, and 10M associated with the orientation (position in the rotational direction) of the glass fiber 4 relative to the rotational direction are provided on the outer periphery of the coating 8 that coats the outer periphery of each glass fiber 4. These markings 10, 10L, and 10M allow the orientation of the glass fiber 4 relative to the rotational direction to be known from the outside. Therefore, the tape fibers 100, 100A, 100B, 100C, and 100D facilitate the alignment of multiple optical fibers 1F and 1G that have orientation relative to the rotational direction. Furthermore, the above-described manufacturing method makes it possible to easily fabricate such tape fibers 100, 100A, 100B, 100C, and 100D.

[0087] The above has described in detail the tape fibers 100, 100A, 100B, 100C, and 100D according to the embodiments of the present disclosure, and the method for manufacturing the tape fibers. However, the present invention is not limited to the above embodiments, and can be applied to various embodiments and modifications.

[0088] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G... Optical fiber 1a, 1b, 1c, 1d... Optical fiber 2, 2A, 2B, 2C, 2D... Core 3... Cladding 4... Glass fiber 5... Primary resin layer (coating resin layer) 6, 6A... Secondary resin layer (coating resin layer) 7... Colored layer (coating resin layer) 8, 8A... Coating portion 9... Tape coating resin 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10J, 10K, 10L, 10M... Marking 20... Drawing furnace 21... Cooling device 22... Twist detection device 23... Die 24... Laser marking device 25... UV curing device 26... Directly below roller 27... Take-up roller 30a, 30b, 30c, 30d... Supply roller REFERENCE SIGNS 31: Roller 32a, 32b: Rollers 33: Die 34: UV curing device 35: Direction change roller 36: Winding roller 40, 41, 42: Detection device 50: Camera 51, 52: Lighting device L: Laser irradiation L1, L2: Laser passing area P: Base material

Claims

1. An optical fiber comprising: a glass fiber including at least one core and a cladding covering the core, extending in a longitudinal direction; and a coating including at least one coating resin layer covering the outer periphery of the glass fiber, wherein the glass fiber has an orientation relative to a rotation direction about the longitudinal direction as an axis, and a marking associated with the orientation of the glass fiber relative to the rotation direction is provided on the outer periphery of the coating, the marking being formed by laser marking.

2. The optical fiber according to claim 1, wherein the marking is formed as a dotted line.

3. The optical fiber according to claim 1 or claim 2, wherein the marking is formed to indicate information about the optical fiber.

4. The optical fiber according to any one of claims 1 to 3, wherein the marking is formed so as to have a refractive index different from that of other parts of the coating.

5. The optical fiber according to any one of claims 1 to 4, wherein the marking forms a waveguide.

6. The optical fiber according to any one of claims 1 to 5, wherein the marking is recessed from the outer periphery of the coating resin layer.

7. The optical fiber according to any one of claims 1 to 6, wherein the marking is raised from the outer periphery of the coating resin layer.

8. An optical fiber according to any one of claims 1 to 7, wherein the glass fiber is not provided with a marker that serves as a reference for the rotation direction.

9. The optical fiber according to any one of claims 1 to 8, wherein the coating portion has the colored coating resin layer as an outermost layer, and the marking is provided on the colored coating resin layer.

10. The optical fiber according to claim 9, wherein the coating comprises a colored outermost layer and an inner layer in contact with the inside of the outermost layer, and the marking is formed by removing the outermost layer to expose the inner coating layer.

11. The optical fiber according to claim 10, wherein the inner layer has a color different from the outermost layer, which is colored, or is transparent.

12. A method for manufacturing an optical fiber, comprising: a step of drawing a glass fiber including at least one core and a cladding that covers the core; a step of forming a coating portion including at least one coating resin layer that covers the outer periphery of the glass fiber; and a step of forming a marking on the outer periphery of the coating portion that is associated with the directionality relative to the rotation direction of the glass fiber, wherein the marking is formed by laser marking.

13. The method for manufacturing an optical fiber according to claim 12, wherein in the step of forming the marking, the marking is performed immediately after a resin material for forming the coating is applied to the glass fiber.

14. A method for manufacturing an optical fiber according to claim 12 or claim 13, wherein in the step of forming the marking, the marking is performed after a resin material for forming the coating has been applied to the glass fiber and hardened, and when the conveying direction is changed by a roller located immediately below the drawing furnace that performs the drawing.

15. A method for manufacturing an optical fiber according to any one of claims 12 to 14, wherein the step of forming the coating comprises the steps of forming a colored outermost layer and forming an inner layer in contact with the inside of the outermost layer, and the step of forming a marking comprises marking the outermost layer.

16. A method for manufacturing an optical fiber according to any one of claims 12 to 15, wherein the step of forming the coating comprises the steps of forming a colored outermost layer and forming an inner layer in contact with the inside of the outermost layer, and the step of forming a marking comprises marking the inner layer.

17. A method for manufacturing an optical fiber as set forth in any one of claims 12 to 16, wherein the step of forming the coating comprises the steps of forming a colored outermost layer and forming an inner layer in contact with the inside of the outermost layer, the inner layer having a color different from the colored outermost layer or being transparent, and the step of forming the marking involves removing the outermost layer to form the marking.

18. A method for manufacturing an optical fiber according to any one of claims 12 to 17, wherein the step of forming a colored outermost layer is carried out during the drawing step.

19. A tape fiber comprising a plurality of optical fibers, wherein the plurality of optical fibers comprise: a glass fiber including at least one core and a cladding covering the core, extending in a longitudinal direction; and a coating portion including at least one coating resin layer covering the outer periphery of the glass fiber; the plurality of optical fibers are arranged so as to be aligned in a horizontal direction intersecting the longitudinal direction; the glass fiber has directionality with respect to a rotation direction about the longitudinal direction as an axis; and a marking associated with the directionality of the glass fiber with respect to the rotation direction is provided on the outer periphery of each of the coating portions, and the marking is formed by laser marking.

20. The tape fiber according to claim 19, wherein the markings provided on the plurality of optical fibers are arranged so as to be at the same positions on each corresponding optical fiber.

21. A method for manufacturing a tape fiber, comprising: a step of preparing a plurality of optical fibers; a step of arranging the plurality of optical fibers horizontally and adjusting the plurality of optical fibers so that they are oriented in a predetermined rotation direction; and a step of connecting the plurality of optical fibers to each other with a connecting portion, wherein the plurality of optical fibers prepared in the preparing step comprise: a glass fiber including at least one core and a cladding that covers the core; and a coating portion including at least one coating resin layer that covers the outer periphery of the glass fiber, and markings associated with orientations relative to the rotation direction of the glass fiber are formed on the outer periphery of the coating portion of the plurality of optical fibers by laser marking, and the adjusting step adjusts the markings of the plurality of optical fibers so that they are at predetermined positions in the rotation direction.

22. A method for manufacturing a tape fiber as described in claim 21, wherein in the adjusting step, the position of the marking in the rotational direction is detected after the material forming the connecting portion is applied and before the applied material is hardened, and the rotational direction of a corresponding optical fiber among the plurality of optical fibers is adjusted based on the detected rotational position.

23. A method for manufacturing a ribbon fiber according to claim 21 or 22, wherein in the adjusting step, the angle of the running surface of a twist adjusting roller that guides each of the plurality of optical fibers is adjusted for each of the optical fibers.

24. The method for producing a ribbon fiber according to claim 23, wherein the plurality of optical fibers travel on an extended pass line that reciprocates between rollers multiple times before traveling over the twist adjustment rollers.

25. A method for manufacturing a tape fiber according to any one of claims 21 to 24, wherein in the adjusting step, the color, surface condition or uneven shape of the marking is photographed with a camera to detect the position of the marking in the rotation direction.

26. A method for manufacturing a tape fiber according to any one of claims 21 to 24, wherein in the adjusting step, a surface shape sensor detects the uneven shape of the marking to detect the position of the marking in the rotation direction.

27. A method for manufacturing a tape fiber as described in claim 21, wherein in the adjusting step, the position of the marking in the rotational direction is detected before applying the material that forms the connecting portion, and the rotational direction of the corresponding optical fiber among the plurality of optical fibers is adjusted based on the detected rotational position.

28. A method for manufacturing a tape fiber as described in claim 27, wherein in the adjusting step, the position of the marking in the rotational direction is detected at multiple points before applying the material that forms the connecting portion, and the rotational direction of corresponding optical fibers among the multiple optical fibers is adjusted based on the detected rotational positions.

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