Method for screening and manufacturing optical fiber strands

Abstract

To provide a screening method for optical fiber strand capable of performing screening of an optical fiber strand more accurately without reference to its clad diameter, and a manufacturing method for optical fiber strand using the same.SOLUTION: A screening method for optical fiber strand comprises: a payoff process of paying off an optical fiber strand; a bending stress application process of applying bending stress to the paid-off optical fiber strand by a bending stress application part; and a take-up process of taking up the optical fiber strand applied with the bending stress, wherein the bending stress application part comprises a plurality of pulleys, and in the bending stress application process, rotary shafts of the plurality of pulleys are made different in direction and side faces of the plurality of pulleys are thus brought into contact with circumferentially different positions on the side face of the optical fiber strand so as to apply the bending stress.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a screening method and a manufacturing method for optical fiber element wires.

Background Art

[0002] Optical fiber element wires usually include a core part, a cladding part surrounding the core part, and a resin coating part surrounding the cladding part (Patent Documents 1 and 2). As a screening method for ensuring the long-term mechanical reliability of an optical fiber element wire having such a resin coating layer, there is a method of applying a tensile stress to the optical fiber element wire to give tensile strain. When tensile strain is applied to the optical fiber element wire, a portion with weak mechanical strength breaks, so it can be removed in advance from the optical fiber element wire that becomes a product. Such a screening method is also called a proof test. As a method of applying a tensile stress to the optical fiber element wire, for example, as shown in ITU-T G.650.1 of the International Telecommunication Union (ITU), both ends of a part of the optical fiber element wire are held by a capstan roller or the like, and a load is applied between both ends.

[0003] On the other hand, as an optical fiber used for in-device wiring, a multi-core fiber capable of high-capacity transmission by spatial multiplexing is being studied.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the bending diameter of the optical fiber used for in-device wiring is reduced, it is required to be highly resistant to breakage and have high mechanical reliability.

[0006] However, because multicore fiber optic strands contain multiple cores, the cladding diameter of the cladding portion may be larger than the standard cladding diameter of 125 μm for standard fiber optic strands. In particular, when the number of cores is seven or more, the cladding diameter is often larger than 125 μm. In the case of fiber optic strands with large cladding diameters, such as multicore fiber optic strands, the tensile tension that must be applied to ensure the same mechanical reliability becomes larger. This can damage the resin coating of the portion that is being held down to apply the tensile tension, potentially making it impossible to accurately screen the fiber optic strands.

[0007] The present invention has been made in view of the above, and its object is to provide a method for screening optical fiber strands that can screen optical fiber strands more accurately regardless of the cladding diameter, and a method for manufacturing optical fiber strands using the same. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, one aspect of the present invention is a method for screening optical fiber strands, comprising: a feeding step of feeding out optical fiber strands; a bending stress application step of applying bending stress to the fed-out optical fiber strands using a bending stress application unit; and a winding step of winding up the optical fiber strands to which the bending stress has been applied, wherein the bending stress application unit comprises a plurality of pulleys, and in the bending stress application step, the orientation of the rotation axes of the plurality of pulleys is made different for each of them, so that the sides of the plurality of pulleys come into contact with different positions in the circumferential direction of the side surface of the optical fiber strand to apply the bending stress.

[0009] In the bending stress application step, the orientation of the rotation axes of the three or more pulleys may be different, so that the sides of the three or more pulleys come into contact with three or more different positions in the circumferential direction of the side surface of the optical fiber strand.

[0010] The optical fiber strand comprises a core portion, a cladding portion surrounding the core portion, and a resin coating portion surrounding the cladding portion, wherein the cladding diameter of the cladding portion is greater than 125 μm, and in the bending stress application process, bending stress may be applied such that a fracture rate equivalent to that of a quartz glass optical fiber strand with a cladding diameter of 125 μm at a predetermined proof level is obtained.

[0011] The outer diameter of the aforementioned multiple pulleys may be between 5.2 mm and 12.4 mm.

[0012] The time during which each side of the plurality of pulleys is in contact with the side of the optical fiber strand may be 1 second or more.

[0013] One aspect of the present invention is a method for manufacturing an optical fiber, comprising: a drawing step of heating and melting an optical fiber base material to draw a multicore fiber having a plurality of core portions and a cladding portion surrounding the plurality of core portions; a coating step of forming a resin coating portion on the multicore fiber to form a multicore fiber strand; and a screening step of performing a screening method on the multicore fiber strand.

[0014] The multicore fiber strand may have seven or more core portions, the outer diameter of the cladding portion being 135 μm or more and 250 μm or less, and the resin coating portion having a primary layer and a secondary layer surrounding the primary layer, the elongation at break of the primary layer being 50% or more and 300% or less, and the elongation at break of the secondary layer being 2.5% or more and 50% or less. [Effects of the Invention]

[0015] The present invention offers the advantage of enabling more accurate screening of optical fiber strands regardless of cladding diameter. [Brief explanation of the drawing]

[0016] [Figure 1]FIG. 1 is a flowchart of a method for manufacturing an optical fiber element wire. [Figure 2] FIG. 2 is a schematic diagram of a wire drawing and coating apparatus for an optical fiber. [Figure 3] FIG. 3 is a schematic cross-sectional view of an optical fiber element wire. [Figure 4] FIG. 4 is a diagram showing, as an example, the refractive index profile of a core. [Figure 5] FIG. 5 is a schematic diagram of a screening apparatus for an optical fiber element wire. [Figure 6] FIG. 6 is a diagram for explaining the positional relationship between an optical fiber element wire and a pulley. BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Also, in each drawing, the same or corresponding components are appropriately denoted by the same reference numerals, and redundant descriptions are omitted as appropriate.

[0018] (Embodiment) [ FIG. 1 is a flowchart of a method for manufacturing an optical fiber element wire according to an embodiment. In this manufacturing method, in step S 101, a wire drawing and coating process is performed. The wire drawing process is a process of wire drawing an optical fiber from an optical fiber base material. The coating process is a process of forming a resin coating layer on the wire-drawn optical fiber. Thereby, an optical fiber element wire is formed. Subsequently, in step S 102, a screening process is performed on the formed optical fiber element wire. Thereby, an optical fiber element wire as a product is manufactured.

[0019] Figure 2 is a schematic diagram of an optical fiber drawing and coating apparatus 100 used in carrying out the manufacturing method of optical fiber strands according to the embodiment. As shown in Figure 2, the lower end of the optical fiber base material P is heated and melted by the heater 101a of the optical fiber drawing furnace 101 to draw the optical fiber 1. Subsequently, in the coating process, a resin coating layer is formed on the outer circumference of the drawn optical fiber 1 by a coating forming apparatus 102 to form an optical fiber strand 2. The optical fiber strand 2 is picked up by a capstan roller 103 and wound onto a winding bobbin 105 via a guide roll 104.

[0020] Figure 3 is a schematic cross-sectional view of the optical fiber strand 2. The optical fiber strand 2 is a multicore fiber strand comprising a multicore fiber having seven core portions 21, which are multiple core portions, and a cladding portion 22 surrounding the core portions 21, and a resin coating portion 23 surrounding the multicore fiber. Note that the number of core portions 21 is not limited to seven.

[0021] Figure 4 shows an example of the refractive index profile of the core. The core 21 comprises a center core, an intermediate layer surrounding the center core, and a trench layer surrounding the intermediate layer. For example, the core diameter of the center core is 2a, the outer diameter of the intermediate layer is 2b = 2a × 1.8, and the outer diameter of the trench layer is 2c = 2a × 2.8. For example, the center core is made of quartz glass with a higher refractive index due to the addition of germanium (Ge). For example, the intermediate layer is made of pure quartz glass. Pure quartz glass is an extremely high-purity quartz glass that substantially does not contain dopants that change the refractive index and has a refractive index of approximately 1.444 at a wavelength of 1550 nm. For example, the trench layer is made of quartz glass with a lower refractive index due to the doping of fluorine (F). For example, the cladding 22 is made of pure quartz glass. The outer diameter (cladding diameter) of the cladding portion 22 is greater than 125 μm, for example, 135 μm or more, and for example, 250 μm or less. Note that the refractive index profile of the core portion is not limited to that shown in Figure 4.

[0022] The resin coating portion 23 has a primary layer 23a and a secondary layer 23b surrounding the primary layer 23a. The resin constituting the resin coating portion 23 is, for example, an ultraviolet-curable resin. The ultraviolet-curable resin is a mixture of various resin materials and additives, such as oligomers, diluent monomers, photopolymerization initiators, silane coupling agents, sensitizers, and lubricants. As the oligomer, conventionally known materials such as polyether-based urethane acrylate, epoxy acrylate, polyester acrylate, and silicone acrylate can be used. As the diluent monomer, conventionally known materials such as monofunctional monomers and polyfunctional monomers can be used. Furthermore, the additives are not limited to those mentioned above, and a wide range of conventionally known additives used for ultraviolet-curable resins can be used.

[0023] In the resin-coated portion 23, for example, the primary layer 23a has a break elongation of 50% to 300%, and the secondary layer 23b has a break elongation of 2.5% to 50%.

[0024] Next, we will explain the screening method for optical fiber strand 2.

[0025] Figure 5 is a schematic diagram of a screening device for optical fiber strands. This screening device 200 comprises a feeding bobbin 10, a capstan roller 20, pulley groups 30, 40, and 50, a capstan roller 60, and a winding bobbin 70. The pulley groups 30, 40, and 50 are examples of bending stress application sections.

[0026] The feed bobbin 10 has optical fiber strands 2 wound on it. The capstan roller 20 feeds out the optical fiber strands 2 wound on the feed bobbin 10 (feeding process) and sends them to the pulley group 30.

[0027] In this embodiment, the pulley group 30 comprises three pulleys 31, 32, and 33. The pulleys 31, 32, and 33 apply bending stress to the optical fiber strand 2 by bringing their sides into contact (bending stress application step).

[0028] In this embodiment, the pulley group 40 comprises three pulleys 41, 42, and 43. The pulleys 41, 42, and 43 apply bending stress to the optical fiber strand 2 by bringing their sides into contact (bending stress application step).

[0029] In this embodiment, the pulley group 50 comprises three pulleys 51, 52, and 53. The pulleys 51, 52, and 53 apply bending stress to the optical fiber strand 2 by bringing their sides into contact (bending stress application step).

[0030] The capstan roller 60 takes in the optical fiber strands 2 that have been subjected to bending stress in the pulley groups 30, 40, and 50. The winding bobbin 70 winds up the optical fiber strands 2 that have been taken in by the capstan roller 60 (winding process).

[0031] (Screening by applying bending stress) This section describes screening by applying bending stress using pulley groups 30, 40, and 50.

[0032] As mentioned above, in the case of optical fiber strands with a large cladding diameter, the tensile tension that must be applied to ensure the same mechanical reliability increases. This can damage the resin coating in the area where the tensile tension is applied, potentially preventing proper screening of the optical fiber strands.

[0033] In contrast, the screening device 200 applies bending stress to create bending strain during screening. This allows for bending strain to be applied without having to strongly restrain the resin coating, thus enabling more accurate screening of optical fiber strands without unintended damage to the resin coating.

[0034] The magnitude of the applied bending stress or bending strain can be adjusted by adjusting the outer diameter of each pulley in pulley groups 30, 40, and 50.

[0035] Here, if there is a scratch in a certain part of the cladding of an optical fiber strand, the optical fiber strand is likely to break when bent so that the scratched part faces the outer circumference, but it is less likely to break when bent so that the scratched part faces the inner circumference. Therefore, in the screening device 200, during the bending stress application process described above, the orientation of the rotation axes of the multiple pulleys is made different for each of them, and the sides of the multiple pulleys are brought into contact with different positions in the circumferential direction of the side surface of the optical fiber strand 2 to apply bending stress. This makes it possible to bend the optical fiber strand 2 at various positions in the circumferential direction so that the location becomes the outer circumference, thus enabling more accurate screening.

[0036] Referring to Figure 5, in pulleys 31, 32, and 33 of pulley group 30, the normal N3 to the plane P3 formed by the propagation path of the optical fiber strand 2 is parallel to the respective rotation axes of pulleys 31, 32, and 33. Similarly, in pulleys 41, 42, and 43 of pulley group 40, the normal N4 to the plane P4 formed by the propagation path of the optical fiber strand 2 is parallel to the respective rotation axes of pulleys 41, 42, and 43. Similarly, in pulleys 51, 52, and 53 of pulley group 50, the normal N5 to the plane P5 formed by the propagation path of the optical fiber strand 2 is parallel to the respective rotation axes of pulleys 51, 52, and 53. In this case, for example, the rotation axes of pulleys 31, 32, and 33 of pulley group 30 are oriented differently from those of the other pulleys in pulley groups 40 and 50.

[0037] Figure 6 illustrates an example of the positional relationship between an optical fiber strand and a pulley. In Figure 6, when the optical fiber strand 2 is viewed in the direction of travel, the positions where each pulley makes contact with it in the circumferential direction, i.e., the positions that become the inner circumference when the optical fiber strand 2 is bent, are shown.

[0038] As shown in Figure 6, for example, the three pulleys 31, 42, and 51 are arranged so that their rotation axes, indicated by dashed lines in the figure, are oriented in different directions, and each pulley contacts one of three different positions PO1, PO2, and PO3 in the circumferential direction of the side surface of the optical fiber strand 2.

[0039] Furthermore, pulley 33, like pulley 31, has its side in contact with position PO1 in the circumferential direction on the side surface of the optical fiber strand 2. Similarly, pulley 53, like pulley 51, has its side in contact with position PO3 in the circumferential direction on the side surface of the optical fiber strand 2.

[0040] Furthermore, unlike pulley 31, pulley 32 has its side surface in contact with position PO4 (opposite position PO1) in the circumferential direction on the side surface of the optical fiber strand 2. Also, unlike pulley 42, pulleys 41 and 43 have their side surfaces in contact with position PO5 (opposite position PO2) in the circumferential direction on the side surface of the optical fiber strand 2. Also, unlike pulley 51, pulley 52 has its side surface in contact with position PO6 (opposite position PO3) in the circumferential direction on the side surface of the optical fiber strand 2.

[0041] In other words, in the screening device 200, the sides of the pulleys 31-33, 41-43, and 51-53 are brought into contact with six different positions PO1-PO6 in the circumferential direction on the side surface of the optical fiber strand 2.

[0042] Furthermore, it is preferable that the contact time between each side of the pulley and the side of the optical fiber strand 2 be 1 second or longer. This allows for more accurate screening. However, considering the fatigue of the optical fiber strand 2 due to screening, a shorter contact time is preferable.

[0043] (Setting the screening level) The setting of the screening level in the screening device 200 will be explained. For example, in the conventional method of applying tensile tension to optical fiber strands, the screening level can be defined by the percentage of tensile stress applied that causes the optical fiber strands to elongate at a certain rate. For example, if the elongation rate is 1%, it is called 1% screening. It is known that optical fiber strands will break at a predetermined break rate under such screening. The break rate can be derived, for example, by the following equation (1) (see Griffioen, W., Greven, W., Jonker, J., Zandberg, S., Kuyt, G., and Overton, B., “Reliability of bend insensitive fibers”, Proceedings of the 58th International Wire and Cable Symposium, (2009-11), pp.251-257).

[0044]

number

[0045] For example, in a silica-based glass optical fiber with a cladding diameter of 125 μm, a tensile stress of 100 kpsi is applied to perform 1% screening, and a tensile stress of 200 kpsi is applied to perform 2% screening. Note that 1 psi (pounds per square inch) is equal to 6894.76 Pa (Pascals).

[0046] In conventional methods, to ensure the same mechanical reliability for silica-based glass optical fibers with a cladding diameter different from 125 μm as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, the following procedure was followed: Specifically, tensile stress was applied to the silica-based glass optical fiber with a cladding diameter different from 125 μm, and screening was performed, so that a fracture rate equivalent to that obtained when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi was obtained.

[0047] On the other hand, in the screening device 200, in order to ensure the same mechanical reliability for a silica-based glass optical fiber with a cladding diameter different from 125 μm as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi, the following procedure should be followed. That is, a bending stress should be applied to the silica-based glass optical fiber with a cladding diameter different from 125 μm, and the screening should be performed, so that a fracture rate equivalent to that obtained when screening a silica-based glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi is obtained. 1% screening (screening with a tensile stress of 100 kpsi) is an example of a predetermined proof level.

[0048] Below, we will describe examples of screening conditions for various cladding diameters of the optical fiber strand 2 shown in Figures 2 and 3.

[0049] (Example with a cladding diameter of 150 μm and a bending radius of 10 mm during installation) In the case of the optical fiber strand 2 shown in Figures 2 and 3, where the cladding diameter is 150 μm, in order to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 180 kpsi must be applied.

[0050] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 150 μm, applying bending stress to the pulleys with an outer diameter of 8.8 mm for pulleys 31-33, 41-43, and 51-53 allows for screening equivalent to that performed by applying a tensile stress of 180 kpsi.

[0051] As a comparative example, when optical fiber strands with a cladding diameter of 150 μm were manufactured using the structure shown in Figures 2 and 3, and a screening process was performed over a length of 1000 km using a conventional screening device with a tensile stress of 180 kpsi, fracture occurred due to damage to the resin coating.

[0052] On the other hand, in Example 1, optical fiber strands 2 with a cladding diameter of 150 μm were manufactured with the structure shown in Figures 2 and 3, and screening was performed over a length of 1000 km using a screening device 200 that applies bending stress with the outer diameters of pulleys 31-33, 41-43, and 51-53 set to 8.8 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0053] (Example with cladding diameter of 200 μm and bending radius of 10 mm during installation) If the cladding diameter of optical fiber strand 2 is 200 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 220 kpsi must be applied.

[0054] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 200 μm, applying bending stress to the pulleys by setting the outer diameter of pulleys 31-33, 41-43, and 51-53 to 9.6 mm allows for screening equivalent to that performed by applying a tensile stress of 220 kpsi.

[0055] As Example 2, optical fiber strands with a cladding diameter of 200 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 9.6 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0056] (Example with cladding diameter of 250 μm and bending radius of 10 mm during installation) If the cladding diameter of optical fiber strand 2 is 250 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 341 kpsi must be applied.

[0057] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 250 μm, applying bending stress to the pulleys with an outer diameter of 7.7 mm for pulleys 31-33, 41-43, and 51-53 allows for screening equivalent to that performed by applying a tensile stress of 341 kpsi.

[0058] As Example 3, optical fiber strands with a cladding diameter of 250 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 7.7 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0059] (Example with a cladding diameter of 150 μm and a bending radius of 20 mm during installation) If the cladding diameter of optical fiber strand 2 is 150 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 150 kpsi must be applied.

[0060] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 150 μm, applying bending stress to the pulleys by setting the outer diameter of pulleys 31-33, 41-43, and 51-53 to 10.5 mm allows for screening equivalent to that performed by applying a tensile stress of 150 kpsi.

[0061] As Example 4, optical fiber strands with a cladding diameter of 150 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 10.5 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0062] (Example with a cladding diameter of 200 μm and a bending radius of 20 mm during installation) If the cladding diameter of optical fiber strand 2 is 200 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 170 kpsi must be applied.

[0063] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 200 μm, applying bending stress to the pulleys by setting the outer diameter of pulleys 31-33, 41-43, and 51-53 to 12.4 mm allows for screening equivalent to that performed by applying a tensile stress of 170 kpsi.

[0064] As Example 5, optical fiber strands with a cladding diameter of 200 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 12.4 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0065] (Example with a cladding diameter of 250 μm and a bending radius of 20 mm during installation) If the cladding diameter of optical fiber strand 2 is 250 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 100 kpsi, a tensile stress of 251 kpsi must be applied.

[0066] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 250 μm, applying bending stress to the pulleys by setting the outer diameter of pulleys 31-33, 41-43, and 51-53 to 10.5 mm allows for screening equivalent to that performed by applying a tensile stress of 251 kpsi.

[0067] As Example 6, optical fiber strands with a cladding diameter of 250 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 10.5 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0068] (Example with a cladding diameter of 135 μm and a bending radius of 10 mm during installation) If the cladding diameter of optical fiber strand 2 is 135 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 200 kpsi, a tensile stress of 220 kpsi must be applied.

[0069] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 135 μm, applying bending stress to the pulleys with an outer diameter of 6.5 mm for pulleys 31-33, 41-43, and 51-53 will enable screening equivalent to that performed by applying a tensile stress of 220 kpsi.

[0070] As Example 7, optical fiber strands with a cladding diameter of 135 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 6.5 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0071] (Example with a cladding diameter of 150 μm and a bending radius of 10 mm during installation) If the cladding diameter of optical fiber strand 2 is 150 μm, then to obtain the same fracture rate as when screening a silica-based glass optical fiber with a cladding diameter of 125 μm under a tensile stress of 200 kpsi, a tensile stress of 301 kpsi must be applied.

[0072] In contrast, with the screening device 200, if the cladding diameter of the optical fiber strand 2 is 150 μm, applying bending stress to the pulleys with an outer diameter of 5.2 mm for pulleys 31-33, 41-43, and 51-53 allows for screening equivalent to that performed by applying a tensile stress of 301 kpsi.

[0073] As Example 8, optical fiber strands with a cladding diameter of 150 μm were manufactured using the structure shown in Figures 2 and 3. Screening was performed over a length of 1000 km using a screening device 200 that applied bending stress with pulleys 31-33, 41-43, and 51-53 having outer diameters of 5.2 mm. No breakage occurred, confirming that mechanical reliability was ensured.

[0074] In the above embodiments and examples, screening using the screening device 200 is performed on optical fiber strands with a cladding diameter greater than 125 μm, but it may also be performed on optical fiber strands with a cladding diameter of 125 μm or less.

[0075] Furthermore, in the above embodiments and examples, the side surface of the pulley is in contact with six positions in the circumferential direction on the side surface of the optical fiber strand 2, but it is sufficient to have two or more contact positions.

[0076] Furthermore, the present invention is not limited by the embodiments described above. Configurations that appropriately combine the above-described components are also included in the present invention. Moreover, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible. [Explanation of Symbols]

[0077] 1: Optical fiber 2: Optical fiber strand 10: Feed-out bobbin 20, 60: Capstan Roller 21: Core section 22: Clad section 23: Resin-coated part 23a: Primary layer 23b: Secondary layer 30, 40, 50: Pulley group 31, 32, 33, 41, 42, 43, 51, 52, 53: Pulley 70, 105: Winding bobbin 100: Wire drawing and coating device 101: Optical fiber laying furnace 101a: Heater 102: Coating forming apparatus 103: Capstan Roller 104: Guide Roll 200: Screening device N3, N4, N5: Normal vectors P: Optical fiber base material P3, P4, P5: Plane

Claims

1. The process of unwinding optical fiber strands, A bending stress application step is performed in which bending stress is applied to the extended optical fiber strands at a bending stress application unit, A winding process in which the optical fiber strand to which the aforementioned bending stress has been applied is wound up, Equipped with, The optical fiber strand comprises a core portion, a cladding portion surrounding the core portion, and a resin coating portion surrounding the cladding portion, wherein the cladding diameter of the cladding portion is greater than 125 μm. The bending stress application section comprises a plurality of pulleys, In the bending stress application step, the orientation of the rotation axes of the plurality of pulleys is made different for each of them, and the sides of the plurality of pulleys are brought into contact with different positions in the circumferential direction of the side surface of the optical fiber strand to apply the bending stress, and the bending stress is applied so that a fracture rate equivalent to that of a quartz glass optical fiber strand with a cladding diameter of 125 μm at a predetermined proof level is obtained. A screening method for optical fiber strands.

2. In the bending stress application step, the orientation of the rotation axes of the three or more pulleys is made different, so that the sides of the three or more pulleys come into contact with three or more different positions in the circumferential direction of the side surface of the optical fiber strand. A method for screening optical fiber strands according to claim 1.

3. The outer diameter of the aforementioned plurality of pulleys is between 5.2 mm and 12.4 mm. A method for screening optical fiber strands according to claim 1 or 2.

4. The time during which each side of the plurality of pulleys is in contact with the side of the optical fiber strand is one second or more. A method for screening optical fiber strands according to any one of claims 1 to 3.

5. A drawing process involves heating and melting an optical fiber base material to draw a multicore fiber having multiple core portions and a cladding portion surrounding the multiple core portions, A coating step in which a resin coating portion is formed on the multicore fiber to form a multicore fiber strand, The multicore fiber strand is subjected to a screening step in which the optical fiber strand screening method described in any one of claims 1 to 4 is performed, Equipped with A method for manufacturing optical fiber strands.

6. The multicore fiber strand has seven or more core portions, the outer diameter of the cladding portion is 135 μm or more and 250 μm or less, the resin coating portion has a primary layer and a secondary layer surrounding the primary layer, the elongation at break of the primary layer is 50% or more and 300% or less, and the elongation at break of the secondary layer is 2.5% or more and 50% or less. A method for manufacturing optical fiber strands according to claim 5.

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