Method for measuring amount of twist of optical fiber, and method for manufacturing optical fiber

Abstract

This method for measuring the amount of twist of an optical fiber is a method for measuring, during line drawing, the amount of change in a coating eccentricity angle of an optical fiber that includes a glass fiber and a coating resin layer disposed on the outer periphery of the glass fiber, the method including: a step for imaging the optical fiber from a plurality of mutually different directions at a first position in a direction of travel of the optical fiber, and for measuring a first coating eccentricity angle, which is the coating eccentricity angle at the first position; a step for imaging the optical fiber from a plurality of mutually different directions at a second position in the direction of travel, which differs from the first position, and for measuring a second coating eccentricity angle, which is the coating eccentricity angle at the second position; a step for calculating, on the basis of the first coating eccentricity angle and the second coating eccentricity angle, the amount of change in the coating eccentricity angle of the optical fiber between the first position and the second position; and a step for calculating, on the basis of the calculated amount of change, the amount of twist of the optical fiber.

Description

Method for Measuring Twist Amount of Optical Fiber and Method for Manufacturing Optical Fiber

[0001] The present disclosure relates to a method for measuring the twist amount of an optical fiber and a method for manufacturing an optical fiber. This application claims priority based on Japanese Patent Application No. 2024-186709 filed on October 23, 2024, and incorporates all the descriptions described in the above Japanese application.

[0002] Patent Document 1 discloses a method for measuring the twist applied to an optical fiber. In this method, the eccentricity between the core and cladding of the fiber is determined as a cross-sectional eccentricity that is a function of the position in the fiber length direction, and it is confirmed whether there is twist applied to the optical fiber from the cross-sectional eccentricity.

[0003] Japanese Patent Application Laid-Open No. 2004-233364

[0004] A method for measuring the twist amount of an optical fiber according to one aspect of the present disclosure is a method for measuring the twist amount of an optical fiber including a glass fiber and a coating resin layer provided on the outer periphery of the glass fiber by measuring the change amount of the coating eccentricity angle of the optical fiber during drawing. This method for measuring the change amount of the coating eccentricity angle includes a step of imaging the optical fiber from a plurality of different directions at a first position in the traveling direction of the optical fiber to measure a first coating eccentricity angle that is the coating eccentricity angle at the first position, a step of imaging the optical fiber from a plurality of different directions at a second position different from the first position in the traveling direction to measure a second coating eccentricity angle that is the coating eccentricity angle at the second position, a step of calculating the change amount of the coating eccentricity angle of the optical fiber between the first position and the second position based on the first coating eccentricity angle and the second coating eccentricity angle, and a step of calculating the twist amount of the optical fiber based on the calculated change amount.

[0005] Figure 1 is a schematic diagram of a manufacturing apparatus used in the optical fiber manufacturing method according to the embodiment. Figure 2 is a flowchart of the optical fiber manufacturing method according to the embodiment. Figure 3 is a cross-sectional view of the glass fiber and the coating resin layer. Figure 4 is a partially enlarged view of the manufacturing apparatus shown in Figure 1. Figure 5 is a diagram illustrating the twisting process. Figure 6 is another diagram illustrating the twisting process. Figure 7 is another cross-sectional view of the glass fiber and the coating resin layer. Figure 8 is a diagram showing the relationship between the coating eccentricity angle and the hole rotation angle. Figure 9 is another diagram showing the relationship between the coating eccentricity angle and the hole rotation angle.

[0006] The method described in Patent Document 1 does not measure the amount of twisting of the optical fiber during wiring. Therefore, it is desirable to measure the amount of twisting of the optical fiber during wiring.

[0007] This disclosure aims to provide a technology capable of measuring the amount of twisting of an optical fiber during wiring.

[0008] This disclosure provides a technology capable of measuring the amount of twist in an optical fiber during wiring.

[0009] [Description of Embodiments of the Disclosure] First, embodiments of the disclosure will be listed and described.

[0010] (1) A method for measuring the amount of twist of an optical fiber according to one aspect of the present disclosure is a method for measuring the amount of twist of an optical fiber, which includes a glass fiber and a coating resin layer provided on the outer circumference of the glass fiber, by measuring the change in the coating eccentricity angle of the optical fiber during line drawing, and comprising the steps of: imaging the optical fiber from a plurality of different directions at a first position in the direction of travel of the optical fiber to measure a first coating eccentricity angle, which is the coating eccentricity angle at the first position; imaging the optical fiber from a plurality of different directions at a second position different from the first position in the direction of travel to measure a second coating eccentricity angle, which is the coating eccentricity angle at the second position; calculating the amount of change in the coating eccentricity angle of the optical fiber between the first position and the second position based on the first coating eccentricity angle and the second coating eccentricity angle; and calculating the amount of twist of the optical fiber based on the calculated amount of change.

[0011] The inventors of this invention conducted research on a technique for measuring the amount of twisting of an optical fiber during wiring. As a result, the inventors newly discovered the following: The change in the coating eccentricity angle of an optical fiber during wiring serves as an indicator of the amount of twisting of the optical fiber during wiring. For example, if the change in the coating eccentricity angle of the optical fiber between one position and another in the direction of the optical fiber's movement is large, the amount of twisting of the optical fiber during wiring will be large. Therefore, it is possible to measure the amount of twisting of the optical fiber by calculating the change in the coating eccentricity angle of the optical fiber and then calculating the amount of twisting of the optical fiber based on the calculated change in the coating eccentricity angle.

[0012] In the above method for measuring the amount of twist in an optical fiber, the optical fiber is imaged from multiple different directions at both the first and second positions, allowing for the measurement of the first and second coating eccentricity angles. Furthermore, based on the measured first and second coating eccentricity angles, the change in the coating eccentricity angle of the optical fiber between the first and second positions is calculated. As described above, the change in the coating eccentricity angle of the optical fiber during wiring is an indicator of the amount of twist in the optical fiber during wiring. Therefore, by calculating the change in the coating eccentricity angle of the optical fiber between the first and second positions, and then calculating the amount of twist in the optical fiber based on the calculated change in coating eccentricity angle, the amount of twist in the optical fiber during wiring can be measured.

[0013] (2) In (1) above, the distance between the first position and the second position in the direction of travel may be 50 mm or more and 20 m or less. In this case, the amount of twist of the optical fiber during drawing can be measured with high accuracy.

[0014] (3) In (1) or (2) above, the amount of coating eccentricity of the optical fiber in a cross section perpendicular to the direction of travel may be 0.1 μm or more. In this case, the measurement of the first coating eccentricity angle and the measurement of the second coating eccentricity angle can be easily performed.

[0015] (4) In any one of (1) to (3) above, the step of calculating the amount of change may be to calculate the amount of change based on the first coating eccentricity angle and the second coating eccentricity angle measured by imaging the optical fiber at the first position and the second position at the same time. In this case, for example, the amount of change in the coating eccentricity angle of the optical fiber between the first position and the second position can be accurately calculated.

[0016] (5) A method for manufacturing an optical fiber according to one aspect of the present disclosure comprises the steps of: melting an optical fiber base material and drawing a glass fiber; applying a resin composition to the outer circumference of the glass fiber; curing the applied resin composition to form an optical fiber including the glass fiber and a coating resin layer formed by curing the resin composition; and measuring the amount of change in the coating eccentricity angle of the optical fiber during drawing, wherein the measuring step involves imaging the optical fiber from a plurality of different directions at a first position in the direction of travel of the optical fiber, and measuring the amount of change in the coating eccentricity angle at the first position The method includes the steps of: measuring a first coating eccentricity angle, which is the coating eccentricity angle of the optical fiber; imaging the optical fiber from a plurality of different directions at a second position different from the first position in the travel direction, and measuring a second coating eccentricity angle, which is the coating eccentricity angle of the optical fiber at the second position; calculating the amount of change in the coating eccentricity angle of the optical fiber between the first position and the second position based on the first and second coating eccentricity angles; and calculating the amount of twist of the optical fiber based on the calculated amount of change.

[0017] In the optical fiber manufacturing method described above, the optical fiber is imaged from multiple different directions at both the first and second positions, allowing for the measurement of the first and second coating eccentricity angles. Furthermore, based on the measured first and second coating eccentricity angles, the change in the coating eccentricity angle of the optical fiber between the first and second positions is calculated. As mentioned above, the change in the coating eccentricity angle of the optical fiber during wiring is an indicator of the amount of twisting of the optical fiber during wiring. Therefore, by calculating the change in the coating eccentricity angle of the optical fiber between the first and second positions, and then calculating the amount of twisting of the optical fiber based on the calculated change in coating eccentricity angle, the amount of twisting of the optical fiber during wiring can be measured.

[0018] (6) In (5) above, the distance between the first position and the second position in the direction of travel may be 50 mm or more and 20 m or less. In this case, the amount of twist of the optical fiber during drawing can be measured with high accuracy.

[0019] (7) In (5) or (6) above, the coating eccentricity of the optical fiber in a cross section perpendicular to the direction of travel may be 0.1 μm or more. In this case, the first coating eccentricity angle and the second coating eccentricity angle can be easily measured.

[0020] (8) In any one of (5) to (7) above, the step of calculating the amount of change may be calculated based on the first and second coating eccentricity angles measured by imaging the optical fiber at the first and second positions at the same time. In this case, for example, the amount of change in the coating eccentricity angle of the optical fiber between the first and second positions can be accurately calculated.

[0021] (9) Any one of (5) to (8) above may further include a step of imparting twist to the optical fiber by adjusting the position or angle of the guide roller based on the calculated amount of twist of the optical fiber. In this case, if a twist that cancels out the twist occurring in the optical fiber is imparted to the optical fiber, an optical fiber with reduced twist can be manufactured. It is also possible to manufacture an optical fiber with a desired periodic twist or random twist.

[0022] [Details of Embodiments of the Disclosure] Specific examples of the method for measuring the torsion of an optical fiber and the method for manufacturing an optical fiber according to the Disclosure will be described below with reference to the drawings. However, the Disclosure is not limited to these examples, and is intended to include all changes within the meaning and scope of the claims as indicated by the claims. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0023] Figure 1 is a schematic diagram of a manufacturing apparatus used in the optical fiber manufacturing method according to the embodiment. As shown in Figure 1, the manufacturing apparatus 1 comprises a heating furnace 2, a cooling device 3, a die 4, an ultraviolet irradiation device 5, a measuring unit 6, a guide roller 7, a capstan 8, a winding drum 9, and a control unit 10.

[0024] In this embodiment, an XYZ coordinate system is set for the manufacturing apparatus 1. The X-axis direction represents one direction in the horizontal direction. The Y-axis direction represents a direction perpendicular to the X-axis direction in the horizontal direction. The Z-axis direction represents the vertical direction. In the following explanation, the XYZ coordinate system may be used for explanation.

[0025] The optical fiber 20 manufactured by the manufacturing apparatus 1 includes a glass fiber 21 and a coating resin layer 22 (see Figure 3) provided on the outer circumference of the glass fiber 21. Examples of optical fibers 20 include, for example, single-mode optical fibers for communication, multi-core optical fibers, and polarization-maintaining optical fibers.

[0026] The glass fiber 21 includes a core and a cladding. The glass fiber 21 may include multiple cores. In the glass fiber 21, the cladding surrounds the core. The core and cladding mainly consist of glass such as quartz glass. For example, germanium-doped quartz glass or pure quartz glass can be used for the core. Pure quartz glass or fluorine-doped quartz glass can be used for the cladding. Here, pure quartz glass refers to quartz glass that is substantially free of impurities. The diameter (glass diameter) of the glass fiber 21 may be, for example, 125 ± 1 μm. The diameter (fiber diameter) of the optical fiber 20 may be, for example, 250 ± 1 μm.

[0027] The coating resin layer 22 includes, for example, multiple resin layers. In one example, the coating resin layer 22 includes a primary resin layer and a secondary resin layer. The primary resin layer is in contact with the outer circumferential surface of the cladding and covers the entire cladding. The secondary resin layer is in contact with the outer circumferential surface of the primary resin layer and covers the entire primary resin layer. The secondary resin layer is the outermost layer of the coating resin layer. The coating resin layer 22 consists of a cured product of an ultraviolet-curable resin composition.

[0028] Figure 2 is a flowchart illustrating a method for manufacturing an optical fiber according to an embodiment. As shown in Figure 2, the method for manufacturing an optical fiber according to an embodiment includes a drawing step S1, a coating step S3, a curing step S4, and a measurement step S5. The method for manufacturing an optical fiber according to an embodiment may further include a cooling step S2, a twisting step S6, and a winding step S7. Steps S1 to S7 are shown in order when focusing on a certain point in the longitudinal direction of the optical fiber 20. In other words, a certain point in the longitudinal direction of the optical fiber 20 is manufactured by sequentially going through steps S1 to S7.

[0029] The drawing process S1 is a process of melting the optical fiber preform 23 and drawing the glass fiber 21. In the drawing process S1, the optical fiber preform 23 is melted by the heating furnace 2 and the glass fiber 21 is drawn. The heating furnace 2 includes a cylindrical furnace core tube 2a into which the optical fiber preform 23 is supplied, and a heating element 2b surrounding the furnace core tube 2a. The heating furnace 2 melts the end of the optical fiber preform 23 by heating. From the end of the optical fiber preform 23 melted by the heating furnace 2, the glass fiber 21 is drawn downward along the Z axis.

[0030] Cooling step S2 is a step in which the glass fiber 21 drawn from the end of the optical fiber preform 23 is cooled. In cooling step S2, the glass fiber 21 is cooled by the cooling device 3. The cooling device 3 is located downstream of the heating furnace 2 in the direction A in which the optical fiber 20 travels. In this embodiment, the direction A is downward along the Z axis and coincides with the axis of the optical fiber 20.

[0031] The coating step S3 is a step of applying a resin composition to the outer circumference of the glass fiber 21. In the coating step S3, a die 4 applies an ultraviolet-curable resin composition that will become a coating resin layer 22 to the outer circumference of the glass fiber 21. The die 4 is located downstream of the cooling device 3 in the travel direction A. The die 4 is a coating device for applying the resin composition. In this embodiment, a resin composition that will become the primary resin layer and a resin composition that will become the secondary resin layer are applied sequentially to the outer surface of the glass fiber 21.

[0032] The above resin composition includes, for example, a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator. Here, (meth)acrylate means acrylate or the corresponding methacrylate. As the monomer, a monofunctional monomer having one polymerizable group or a polyfunctional monomer having two or more polymerizable groups can be used. Two or more glass species of monomer may be mixed and used. As the photopolymerization initiator, it can be appropriately selected from known radical photopolymerization initiators. The resin composition may further contain a silane coupling agent, a photoacid generator, a leveling agent, an antifoaming agent, and an antioxidant.

[0033] The curing step S4 is a step in which the applied resin composition is cured. In the curing step S4, the ultraviolet irradiation device 5 cures the ultraviolet-curable resin composition. The ultraviolet irradiation device 5 is located downstream of the die 4 in the traveling direction A. The ultraviolet irradiation device 5 irradiates the resin composition with ultraviolet light. The resin composition is cured by the irradiation of ultraviolet light, forming a coating resin layer 22. This results in an optical fiber 20 comprising a glass fiber 21 and a coating resin layer 22. In other words, the curing step S4 is a step in which the applied resin composition is cured to produce an optical fiber 20 containing a glass fiber 21 and a coating resin layer 22 formed from the cured resin composition.

[0034] In the optical fiber 20, the non-circularity of the glass fiber 21 in a cross-section perpendicular to the running direction A may be 0.1% or more. Alternatively, the non-circularity of the glass fiber 21 may be 0.05% or more, or 0.03% or more. The non-circularity of the glass fiber 21 is defined by the value obtained by dividing the difference in length between the major axis and the minor axis of the glass fiber 21 by the length of the major axis. The above non-circularity of the glass fiber 21 may be 0.1% or more, 0.05% or more, or 0.03% or more at the time the curing process S4 is completed. The non-circularity of the glass fiber 21 may be higher than the non-circularity of the coating resin layer 22. In the coating process S3, the resin composition is easily applied uniformly, so the coating resin layer 22 tends to exhibit a circular shape in a cross-section perpendicular to the running direction A.

[0035] In the optical fiber 20, the coating eccentricity of the optical fiber 20 in a cross section perpendicular to the direction of travel A may be 0.1 μm or more, or 1.0 μm or more. The coating eccentricity of the optical fiber 20 may be 20 μm or less, or 17.5 μm or less. The coating eccentricity of the optical fiber 20 is defined as the distance from the central axis with respect to the outer circumference of the coating resin layer 22 to the central axis of the glass fiber 21. For example, in a cross section perpendicular to the direction of travel A, the difference between the center with respect to the outer circumference of the coating resin layer 22 and the center of the glass fiber 21 is the coating eccentricity.

[0036] Measurement step S5 is a step in which the amount of twist of the optical fiber 20 is measured while drawing the fiber. Measuring the amount of twist of the optical fiber 20 while drawing the fiber can also be said to be measuring the amount of twist of the optical fiber 20 online. Therefore, measurement step S5 can also be said to be a step in which the amount of twist of the optical fiber 20 is measured online.

[0037] Here, the coating eccentricity angle will be explained in more detail with reference to Figure 3. Figure 3 is a cross-sectional view of the glass fiber and the coating resin layer. For the sake of explanation, the hatching of the glass fiber 21 and the coating resin layer 22 has been omitted in Figure 3.

[0038] In one example, the coating eccentricity angle is defined by angle θ1, as shown in Figure 3. Angle θ1 is the angle between line segment L1 and line L2, which represents the diameter of the glass fiber 21. Line segment L1 is the line segment connecting the central axis C1 of the glass fiber 21 and the central axis C2 of the coating resin layer 22. Line L2, which represents the diameter, is the line representing the diameter of the glass fiber 21 along the X-axis direction. Alternatively, the coating eccentricity angle may be defined by angle θ2. Angle θ2 is the angle between line segment L1 and line L3, which represents the diameter of the coating resin layer 22. Line L3, which represents the diameter, is the line representing the diameter of the coating resin layer 22 along the X-axis direction.

[0039] In measurement step S5, the amount of twist of the optical fiber 20 is measured by the measurement unit 6 and control unit 10 shown in Figure 1. The measurement unit 6 is located downstream of the ultraviolet irradiation device 5 and upstream of the guide roller 7 in the travel direction A. The measurement unit 6 includes, for example, four imaging devices. In this embodiment, the measurement unit 6 includes a first imaging device 61, a second imaging device 62, a third imaging device 63, and a fourth imaging device 64. In this embodiment, each of the first imaging device 61 to the fourth imaging device 64 is located downstream of the ultraviolet irradiation device 5 and upstream of the guide roller 7 in the travel direction A.

[0040] In this embodiment, the measurement step S5 includes a first measurement step S51, a second measurement step S52, a change amount calculation step S53, and a torsion amount calculation step S54. The first measurement step S51, the second measurement step S52, the change amount calculation step S53, and the torsion amount calculation step S54 are performed, for example, in this order.

[0041] The first measurement step S51 is a step of measuring the first coating eccentricity angle. In the first measurement step S51, the optical fiber 20 is imaged using the first imaging device 61 and the second imaging device 62 shown in Figure 4. Figure 4 is a partially enlarged view of the manufacturing apparatus shown in Figure 1. Specifically, Figure 4 is an enlarged view of the portion of Figure 1 in which the first imaging device 61, the second imaging device 62, the third imaging device 63, and the fourth imaging device 64 are arranged, and is a perspective view of that portion. As shown in Figure 4, the first imaging device 61 is located at the first position P1. The first position P1 is located downstream of the ultraviolet irradiation device 5 in the travel direction A. The optical axis 61a of the first imaging device 61 intersects the travel direction A, for example. In this embodiment, the optical axis 61a is perpendicular to the travel direction A.

[0042] The first coating eccentricity angle is the coating eccentricity angle of the optical fiber 20 at a first position P1 in the travel direction A. In the first measurement step S51, the optical fiber 20 is imaged from two different directions at the first position P1 to measure the first coating eccentricity angle. In other words, the first measurement step S51 can be said to include the steps of imaged from two different directions at the first position P1 and the steps of measuring the first coating eccentricity angle.

[0043] The first imaging device 61 is disposed at the first position P1 such that the optical axis 61a thereof extends along the X-axis. In the present embodiment, the first imaging device 61 is disposed at the first position P1 such that the optical axis 61a coincides with a line L3 indicating the diameter of the coating resin layer 22. The first imaging device 61 images the optical fiber 20 at the first position P1. The first imaging device 61 transmits the captured image of the optical fiber 20 to the control unit 10.

[0044] The second imaging device 62 is disposed at the first position P1 in the same manner as the first imaging device 61. The optical axis 62a of the second imaging device 62 intersects, for example, the traveling direction A. In the present embodiment, the optical axis 62a is orthogonal to the traveling direction A. The optical axis 62a of the second imaging device 62 intersects the optical axis 61a. In the present embodiment, the optical axis 62a is orthogonal to the optical axis 61a.

[0045] The second imaging device 62 is disposed at the first position P1 such that the optical axis 62a thereof extends along the Y-axis. In the present embodiment, the second imaging device 62 is disposed at the first position P1 such that the optical axis 62a is orthogonal to a line L3 indicating the diameter of the coating resin layer 22. The second imaging device 62 images the optical fiber 20 from a direction different from that of the first imaging device 61 at the first position P1. The second imaging device 62 transmits the captured image of the optical fiber 20 to the control unit 10. Thus, in the first measurement step S51, at the first position P1, the optical fiber 20 is imaged by the first imaging device 61 and the second imaging device 62 from two different directions.

[0046] In the first measurement step S51, the control unit 10 measures the first coating eccentricity angle. In this embodiment, the control unit 10 measures the first coating eccentricity angle based on images of the optical fiber 20 received from the first imaging device 61 and the second imaging device 62. In this embodiment, the control unit 10 measures the first coating eccentricity angle as follows, for example. In this example, the angle θ1 is measured as the first coating eccentricity angle. First, the control unit 10 calculates the coordinates of the central axis C2 of the coating resin layer 22 by analyzing the received images. The calculated coordinates of the central axis C2 are coordinates in a coordinate system with the central axis C1 of the glass fiber 21 as the origin. Next, the control unit 10 calculates the tangent (tan) of the calculated coordinates of the central axis C2. Next, the control unit 10 calculates the angle corresponding to the calculated tangent. Next, the control unit 10 calculates the angle obtained by subtracting the calculated angle from 180° as the first coating eccentricity angle. If the angle θ2 is measured as the first coating eccentricity angle, the control unit 10 may calculate the angle corresponding to the calculated tangent as the first coating eccentricity angle.

[0047] The control unit 10 may be a computer system including, for example, a processor such as a CPU (Central Processing Unit), RAM (Random Access Memory) and ROM (Read Only Memory), input / output devices such as a touch panel, mouse, keyboard, and display, and communication devices such as a network card. The control unit 10 provides its functions by operating each piece of hardware under the control of the processor based on a computer program stored in memory.

[0048] The second measurement step S52 is a step of measuring the second coating eccentricity angle. The second coating eccentricity angle is the coating eccentricity angle of the optical fiber 20 at the second position P2 in the traveling direction A. The second position P2 is a position different from the first position P1 in the traveling direction A. The second position P2 is arranged downstream of the first position P1 in the traveling direction A. The distance d between the first position P1 and the second position P2 in the traveling direction A is set in consideration of, for example, the length when the optical fiber 20 is twisted once. The distance d is, for example, 50 mm or more and 20 m or less. By setting the distance d to 50 mm or more, the amount of twist of the optical fiber 20 can be accurately measured. The distance d may be 100 mm or more, or may be 150 mm or more. By setting the distance d to 20 m or less, the measurement unit 6 (from the first imaging device 61 to the fourth imaging device 64) can be surely arranged downstream of the ultraviolet irradiation device 5 and upstream of the guide roller 7. The distance d may be 15 m or less, or may be 10 m or less.

[0049] In the second measurement step S52, at the second position P2, the optical fiber 20 is imaged from two different directions to measure the second coating eccentricity angle. That is, the second measurement step S52 can also be said to include a step of imaging the optical fiber 20 from two different directions at the second position P2 and a step of measuring the second coating eccentricity angle.

[0050] In the second measurement step S52, the third imaging device 63 and the fourth imaging device 64 are used to image the optical fiber 20. The third imaging device 63 is arranged at the second position P2. As described above, the second position P2 is arranged downstream of the first position P1 in the traveling direction A. Therefore, the third imaging device 63 is arranged downstream of the first imaging device 61 and the second imaging device 62 in the traveling direction A. For example, the direction of the optical axis 63a of the third imaging device 63 is the same as the direction of the optical axis 61a of the first imaging device 61. That is, the optical axis 63a is, for example, parallel to the optical axis 61a. The optical axis 63a does not have to be parallel to the optical axis 61a. The optical axis 63a may intersect the optical axis 61a when viewed from the traveling direction A.

[0051] In this embodiment, the arrangement of the third imaging device 63 is the same as that of the first imaging device 61, except that it is located at the second position P2. The third imaging device 63 images the optical fiber 20 at the second position P2. The third imaging device 63 transmits the image of the optical fiber 20 that it has captured to the control unit 10.

[0052] The fourth imaging device 64 is positioned at the second position P2, the same as the third imaging device 63. For example, the orientation of the optical axis 64a of the fourth imaging device 64 is the same as the orientation of the optical axis 62a of the second imaging device 62. That is, the optical axis 64a is, for example, parallel to the optical axis 62a. The optical axis 64a does not have to be parallel to the optical axis 62a. The optical axis 64a may intersect the optical axis 62a when viewed from the travel direction A. The optical axis 64a of the fourth imaging device 64 also intersects the optical axis 63a. In this embodiment, the optical axis 64a is perpendicular to the optical axis 63a.

[0053] In this embodiment, the arrangement of the fourth imaging device 64 is the same as that of the second imaging device 62, except that it is located at the second position P2. The fourth imaging device 64 images the optical fiber 20 from a different direction than the third imaging device 63 at the second position P2. The fourth imaging device 64 transmits the image of the optical fiber 20 it has captured to the control unit 10. In this way, in the second measurement step S52, at the second position P2, the optical fiber 20 is imaged by the third imaging device 63 and the fourth imaging device 64 from two different directions.

[0054] In the second measurement step S52, the control unit 10 measures the second coating eccentricity angle. The control unit 10 measures the second coating eccentricity angle based on the images of the optical fiber 20 received from the third imaging device 63 and the fourth imaging device 64. The control unit 10 may measure the second coating eccentricity angle by performing the same process as when measuring the first coating eccentricity angle.

[0055] The change amount calculation step S53 is a step in which the change amount of the coating eccentricity angle of the optical fiber 20 between the first position P1 and the second position P2 is calculated based on the first coating eccentricity angle and the second coating eccentricity angle. In the change amount calculation step S53, the control unit 10 calculates the above change amount of the coating eccentricity angle of the optical fiber 20. Hereafter, "the change amount of the coating eccentricity angle of the optical fiber 20 between the first position P1 and the second position P2" may be simply referred to as "the change amount of the coating eccentricity angle of the optical fiber 20". In the change amount calculation step S53, the control unit 10 calculates the change amount of the coating eccentricity angle of the optical fiber 20 based on the first coating eccentricity angle and the second coating eccentricity angle measured by imaging the optical fiber 20 at the same time at the first position P1 and the second position P2. The same time is not limited to exactly the same time, but may include a predetermined time difference. In other words, there may be a predetermined time difference between the time the optical fiber 20 is imaged at the first position P1 and the time the optical fiber 20 is imaged at the second position P2. This time difference is, for example, less than or equal to the value obtained by dividing the distance d by the velocity v, where v is the drawing speed (meters per second) of the optical fiber 20. That is, the time difference is, for example, less than or equal to d / v (seconds).

[0056] In this embodiment, the control unit 10 calculates the change in the coating eccentricity angle of the optical fiber 20 as the value obtained by dividing the difference between the first coating eccentricity angle and the second coating eccentricity angle by the distance d. In this case, the change in the coating eccentricity angle of the optical fiber 20 may be expressed as the change in coating eccentricity angle per 1 mm. The control unit 10 may also calculate the change in the coating eccentricity angle of the optical fiber 20 as the difference between the first coating eccentricity angle and the second coating eccentricity angle.

[0057] The twist amount calculation step S54 is a step in which the twist amount of the optical fiber 20 is calculated based on the change in the coating eccentricity angle of the optical fiber 20 calculated in the change amount calculation step S53. In this embodiment, the control unit 10 may calculate the twist amount of the optical fiber 20 directly using the change in the coating eccentricity angle of the optical fiber 20. That is, the twist amount of the optical fiber 20 may be the change in the coating eccentricity angle per 1 mm. The twist amount of the optical fiber 20 may also be the difference between the first coating eccentricity angle and the second coating eccentricity angle. Alternatively, the control unit 10 may calculate the twist amount of the optical fiber 20 by multiplying the change in the coating eccentricity angle of the optical fiber 20 by a predetermined coefficient.

[0058] In this embodiment, the control unit 10 transmits a control signal to the guide roller 7 according to the calculation result. This enables feedback control to the guide roller 7 based on the calculation result of the twist amount of the optical fiber 20. The feedback control will be described later.

[0059] The twisting step S6 is a step of applying twist to the optical fiber 20. In the twisting step S6, the position or angle of the guide roller 7 is adjusted based on the calculated amount of twist of the optical fiber 20. This applies twist to the optical fiber 20. In the twisting step S6, a twist that cancels out the twist occurring in the optical fiber 20 may be applied to the optical fiber 20. In the twisting step S6, a periodic twist or a random twist may be applied to the optical fiber 20. The guide roller 7 is provided downstream of the measuring unit 6 in the running direction A. The guide roller 7 is positioned between the die 4 and the capstan 8 in the running direction A. In this embodiment, the guide roller 7 is positioned between the measuring unit 6 and the capstan 8 in the running direction A. The guide roller 7 is a direct-down roller positioned directly below the optical fiber base material 23 in the Z-axis direction. The guide roller 7 contacts the optical fiber 20, changing the direction of travel A of the optical fiber 20 from the Z-axis direction to a direction different from the Z-axis direction.

[0060] Figure 5 is a diagram illustrating the torsion imparting process. Figure 6 is another diagram illustrating the torsion imparting process. Figure 5 shows a perspective view of the guide roller 7. Figure 6 shows a view of the guide roller 7 from upstream in the travel direction A. As shown in Figures 5 and 6, the guide roller 7 can move, for example, in the axial direction AX of the guide roller 7. The angle of the axis of rotation of the guide roller 7 with respect to a direction perpendicular to the vertical direction (Z-axis direction) can be changed (for example, the angle of the axial direction AX with respect to the X-axis direction when viewed from the Z-axis direction). The guide roller 7 is positioned such that the axial direction AX is perpendicular to the Z-axis direction.

[0061] In the diagram below the arrow in Figure 6, the optical fiber 20 is in contact with the lower (upstream) part of the guide roller 7, and is wound around the guide roller 7, so that it is located in the groove at the upper (downstream) part of the guide roller 7. In this way, if the position where the optical fiber 20 contacts the guide roller 7 at the lower (upstream) part of the guide roller 7 is not in the groove, the optical fiber 20 can change its direction of travel so that it fits into the groove while still in contact with the guide roller 7. At this time, a rotational force R is applied to the optical fiber 20, causing it to twist.

[0062] The twist of the optical fiber 20 is transmitted to the molten part of the optical fiber base material 23. As a result, the optical fiber 20 that has just been drawn from the molten part is also twisted. Unlike the twist that is applied after the optical fiber 20 has cooled and solidified, the twist applied before the optical fiber 20 cools and solidifies does not return to its original state after manufacturing and becomes residual twist. To prevent residual twist, it is necessary to cancel out the twist that occurs in the optical fiber 20 during drawing while the drawing is still in progress. In the guide roller 7, by changing the position of the optical fiber 20 entering the guide roller 7, a twist that cancels out the twist that has occurred in the optical fiber 20 is applied to the optical fiber 20.

[0063] The guide roller 7 may move in the axial direction AX and in the direction AY perpendicular to the axial direction AX. Alternatively, the guide roller 7 may change with respect to the Z-axis direction perpendicular to the axial direction AX and the direction AY. By adjusting the angle of the rotation axis of the guide roller 7 with respect to the direction perpendicular to the vertical direction (Z-axis direction) (for example, the angle of the axial direction AX with respect to the X-axis direction when viewed from the Z-axis direction), the position at which the optical fiber 20 first contacts the guide roller 7 (position on the guide roller 7) may be changed, thereby eliminating the twisting of the optical fiber 20.

[0064] The direction and magnitude of the rotational force R applied to the optical fiber 20 by the guide roller 7 can be adjusted, for example, by the axial position AX of the guide roller 7. For example, as shown in Figure 6, in the lower diagram of Figure 6, the position where the optical fiber 20 first contacts the guide roller 7 is not the groove, and the optical fiber 20 rotates and twists on the guide roller 7 as it is guided into the groove of the guide roller 7. As shown in the upper diagram of Figure 6, if the guide roller 7 is moved so that the position where the optical fiber 20 first contacts the guide roller 7 is the groove, the optical fiber 20 does not twist.

[0065] The control unit 10 transmits a control signal based on the calculation result to the guide roller 7, and adjusts the axial position AX of the guide roller 7 to cancel out the twisting of the optical fiber 20. In other words, feedback control of the twisting is performed on the guide roller 7. The winding process S7 is the process of winding the optical fiber 20 with the winding drum 9. The winding drum 9 is located downstream of the capstan 8 in the travel direction A.

[0066] As described above, in the method for measuring the amount of twist of an optical fiber 20 and the method for manufacturing an optical fiber 20 according to this embodiment, the optical fiber 20 is imaged from multiple directions that are different from each other at both the first position P1 and the second position P2. Therefore, the first coating eccentricity angle and the second coating eccentricity angle can be measured. Furthermore, based on the measured first and second coating eccentricity angles, the amount of change in the coating eccentricity angle of the optical fiber 20 between the first position P1 and the second position P2 is calculated. The amount of change in the coating eccentricity angle of the optical fiber 20 during drawing is an indicator of the amount of twist of the optical fiber 20 during drawing. Therefore, by calculating the amount of change in the coating eccentricity angle of the optical fiber 20 between the first position P1 and the second position P2, the amount of twist of the optical fiber 20 during drawing can be measured.

[0067] While embodiments have been described above, this disclosure is not necessarily limited to the embodiments described above, and various modifications are possible without departing from its essence.

[0068] In the embodiment described above, the optical fiber 20 is imaged from two different directions at the first position P1 and the second position P2. However, the directions in which the optical fiber 20 is imaged at the first position P1 and the second position P2 are not limited to these two directions. For example, the optical fiber 20 may be imaged from three or more different directions at the first position P1 and the second position P2. That is, the first measurement step S51 may be a step of measuring the first coating eccentricity angle by imagering the optical fiber 20 from a plurality of different directions at the first position P1 in the travel direction A. The second measurement step S52 may be a step of measuring the second coating eccentricity angle by imagering the optical fiber 20 from a plurality of different directions at the second position P2 in the travel direction A. The number of directions in which the optical fiber 20 is imaged at the first position P1 and the number of directions in which the optical fiber 20 is imaged at the second position P2 may be the same or different.

[0069] In this case, the number of imaging devices positioned at the first position P1 may correspond to the number of directions in which the optical fiber 20 is imaged at the first position P1. The number of imaging devices positioned at the second position P2 may correspond to the number of directions in which the optical fiber 20 is imaged at the second position P2. That is, the measuring unit 6 may include multiple imaging devices corresponding to the number of directions in which the optical fiber 20 is imaged at the first position P1 and the second position P2. In addition to the first position P1 and the second position P2, an imaging device may be positioned at a third position, and even more, for example, imaging devices may be positioned at a fourth position and a fifth position. The third position, the fourth position, and the fifth position are different positions from the first position P1 and the second position P2 in the travel direction A. Each of the third position, the fourth position, and the fifth position may be positioned upstream of the first position P1, downstream of the second position P2, or between the first position P1 and the second position P2.

[0070] Next, in order to explain that the change in the coating eccentricity angle of the optical fiber 20 during drawing is an indicator of the amount of twisting of the optical fiber 20 during drawing, we will explain the experiment conducted by the inventors. Specifically, the inventors investigated the relationship between the hole rotation angle and the coating eccentricity angle, and then clarified the relationship between the coating eccentricity angle and the twisting of the optical fiber 20 during drawing by comparing the hole rotation angle and the coating eccentricity angle.

[0071] First, the inventors prepared an optical fiber 20A. Figure 7 is another cross-sectional view of the glass fiber and the coating resin layer. As shown in Figure 7, the optical fiber 20A includes a glass fiber 21A in which holes H are formed and a coating resin layer 22 provided on the outer circumference of the glass fiber 21A. The glass fiber 21A is the same as the glass fiber 21 except that holes H are formed therein. The inventors then measured the hole rotation angle and the coating eccentricity angle offline in a cross section perpendicular to the axial direction of the optical fiber 20A while changing the length position of the optical fiber 20A.

[0072] The hole rotation angle indicates the position of the hole H relative to the central axis C1 of the glass fiber 21A. In one example, the hole rotation angle is defined by angle θ3, as shown in Figure 7. Angle θ3 is the angle between line L2, which represents the diameter of the glass fiber 21A, and line segment L4. Line segment L4 is the line segment that connects the central axis C1 of the glass fiber 21A and the hole H with the shortest distance. Alternatively, the hole rotation angle may be defined by angle θ4. Angle θ4 is the angle between line L3, which represents the diameter of the coating resin layer 22, and line segment L4. The process for measuring the hole rotation angle and the coating eccentricity angle was the same as the process for measuring the coating eccentricity angle in the embodiment described above.

[0073] Here, if twisting occurs in the optical fiber 20A during drawing, the hole rotation angle changes along the length of the optical fiber 20A. On the other hand, if no twisting occurs in the optical fiber 20A during drawing, the hole rotation angle remains approximately constant along the length of the optical fiber 20A. From these observations, if twisting occurs in the optical fiber 20A during drawing, the change in the hole rotation angle between one position and another in the direction A of the optical fiber 20A will be zero or greater. Therefore, the change in the hole rotation angle can be said to be an indicator of the amount of twisting in the optical fiber 20A (optical fiber 20) during drawing.

[0074] The measurement results for the hole rotation angle and the coating eccentricity angle are shown in Figures 8 and 9. Figure 8 is a diagram showing the relationship between the coating eccentricity angle and the hole rotation angle. Figure 9 is another diagram showing the relationship between the coating eccentricity angle and the hole rotation angle. Figure 8 shows the relationship between the coating eccentricity angle and the hole rotation angle when the optical fiber 20A is twisted. Figure 9 shows the relationship between the coating eccentricity angle and the hole rotation angle when the optical fiber 20A is not twisted. The vertical axis in Figures 8 and 9 represents the angle, and the horizontal axis in Figures 8 and 9 represents the position of the optical fiber 20A in the longitudinal direction.

[0075] In Figure 8, change G1 shows the change in the hole rotation angle when the optical fiber 20A is twisted. Change G2 shows the change in the coating eccentricity angle when the optical fiber 20A is twisted. Change G3 shows the difference between change G1 and change G2. That is, change G3 shows the angular difference between the hole rotation angle and the coating eccentricity angle when the optical fiber 20A is twisted. In Figure 9, change G4 shows the change in the hole rotation angle when the optical fiber 20A is not twisted. Change G5 shows the change in the coating eccentricity angle when the optical fiber 20A is not twisted. Change G6 shows the difference between change G4 and change G5. Change G6 shows the angular difference between the hole rotation angle and the coating eccentricity angle when the optical fiber 20A is not twisted.

[0076] As described above, if the optical fiber 20A is twisted, the hole rotation angle changes along its length. If the optical fiber 20A is not twisted, the hole rotation angle remains approximately constant along its length. As shown in Figure 8, if the optical fiber 20A is twisted, the coating eccentricity angle also changes along its length, just like the hole rotation angle. Furthermore, change G3, although including fine fluctuations, remains approximately constant along the length of the optical fiber 20A. The fact that change G3 remains approximately constant along the length of the optical fiber 20A indicates that the trends of change G1 and change G2 are consistent. Therefore, in Figure 8, it can be seen that the coating eccentricity angle changes with the same trend as the hole rotation angle.

[0077] As shown in Figure 9, when there is no twisting in the optical fiber 20A, the coating eccentricity angle is approximately constant along the length of the optical fiber 20A, just like the hole rotation angle. Furthermore, change G6 is approximately constant along the length of the optical fiber 20A. The fact that change G6 is approximately constant along the length of the optical fiber 20A, just like change G3, indicates that the trends of change G4 and change G5 are consistent. Therefore, in Figure 9, it can be seen that the coating eccentricity angle changes with the same trend as the hole rotation angle.

[0078] From these observations, it can be seen that the coating eccentricity angle shows the same trend as the hole rotation angle, both when the optical fiber 20A is twisted and when it is not. As mentioned above, the change in the hole rotation angle is an indicator of the amount of twisting of the optical fiber 20A (optical fiber 20) during wiring. Therefore, the change in the coating eccentricity angle, which shows the same trend as the hole rotation angle, can also be said to be an indicator of the amount of twisting of the optical fiber 20A (optical fiber 20) during wiring.

[0079] 1...Manufacturing equipment 2...Heating furnace 2a...Core tube 2b...Heating element 3...Cooling device 4...Die 5...Ultraviolet irradiation device 6...Measurement unit 7...Guide roller 8...Capstan 9...Winding drum 10...Control unit 20...Optical fiber 20A...Optical fiber 21...Glass fiber 21A...Glass fiber 22...Coating resin layer 23...Optical fiber base material 61...First imaging device 61a...Optical axis 62...Second imaging device 62a...Optical axis 63...Third imaging device 63a...Optical axis 64...Fourth imaging device 64a...Optical axis A...Travel direction AX...Axial direction AY...Direction C1...Central axis C2...Central axis d...Distance G1 to G6...Change H...Hole L1...Line segment L2...Line L3...Line L4...Line segment P1...First position P2...Second position R...Rotational force S1...Line drawing process S2...Cooling process S3...Coating process S4...Curing process S5...Measurement process S6...Application process S7...Winding process S51...First measurement process S52...Second measurement process S53...Change amount calculation process S54...Twist amount calculation process θ1 to θ4...Angle

Claims

1. A method for measuring the amount of twist of an optical fiber, which includes a glass fiber and a coating resin layer provided on the outer circumference of the glass fiber, by measuring the change in the coating eccentricity angle of the optical fiber during line drawing, comprising: a step of imaging the optical fiber from a plurality of different directions at a first position in the direction of travel of the optical fiber to measure a first coating eccentricity angle, which is the coating eccentricity angle at the first position; a step of imaging the optical fiber from a plurality of different directions at a second position different from the first position in the direction of travel to measure a second coating eccentricity angle, which is the coating eccentricity angle at the second position; a step of calculating the change in the coating eccentricity angle of the optical fiber between the first position and the second position based on the first and second coating eccentricity angles; and a step of calculating the amount of twist of the optical fiber based on the calculated change.

2. The method for measuring the amount of twist of an optical fiber according to claim 1, wherein the distance between the first position and the second position in the direction of travel is 50 mm or more and 20 m or less.

3. The method for measuring the amount of twist of an optical fiber according to claim 1 or claim 2, wherein the amount of coating eccentricity of the optical fiber in a cross section perpendicular to the direction of travel is 0.1 μm or more.

4. The method for measuring the amount of twist of an optical fiber according to any one of claims 1 to 3, wherein in the step of calculating the amount of change, the amount of change is calculated based on the first coating eccentricity angle and the second coating eccentricity angle measured by imaging the optical fiber at the first position and the second position at the same time.

5. The process comprises: melting an optical fiber base material and drawing a glass fiber; applying a resin composition to the outer circumference of the glass fiber; curing the applied resin composition to form an optical fiber including the glass fiber and a coating resin layer formed by curing the resin composition; and measuring the change in the coating eccentricity angle of the optical fiber during drawing, wherein the measuring process includes: imaging the optical fiber from a plurality of different directions at a first position in the direction of travel of the optical fiber to measure a first coating eccentricity angle, which is the coating eccentricity angle of the optical fiber at the first position; imaging the optical fiber from a plurality of different directions at a second position different from the first position in the direction of travel to measure a second coating eccentricity angle, which is the coating eccentricity angle of the optical fiber at the second position; calculating the change in the coating eccentricity angle of the optical fiber between the first and second positions based on the first and second coating eccentricity angles; and calculating the amount of twist of the optical fiber based on the calculated change. A method for manufacturing optical fibers, including [the specified element].

6. The method for manufacturing an optical fiber according to claim 5, wherein the distance between the first position and the second position in the direction of travel is 50 mm or more and 20 m or less.

7. The method for manufacturing an optical fiber according to claim 5 or claim 6, wherein the coating eccentricity of the optical fiber in a cross section perpendicular to the direction of travel is 0.1 μm or more.

8. The method for manufacturing an optical fiber according to any one of claims 5 to 7, wherein in the step of calculating the amount of change, the amount of change is calculated based on the first coating eccentricity angle and the second coating eccentricity angle measured by imaging the optical fiber at the first and second positions at the same time.

9. A method for manufacturing an optical fiber according to any one of claims 5 to 8, further comprising the step of imparting a twist to the optical fiber by adjusting the position or angle of a guide roller based on the calculated amount of twist of the optical fiber.

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