JP2023146629A - Screening method and manufacturing method for optical fiber strand - Google Patents

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

The present invention relates to a screening method and a manufacturing method for optical fiber strands.

An optical fiber usually includes a core, a cladding surrounding the core, and a resin coating surrounding the cladding (Patent Documents 1 and 2). As a screening method for ensuring the long-term mechanical reliability of an optical fiber having such a resin coating layer, there is a method of applying tensile force to the optical fiber to give it tensile strain. When a tensile strain is applied to the optical fiber strand, the portion with weak mechanical strength breaks, so it can be removed in advance from the optical fiber strand that will become the product. Such a screening method is also called a proof test. As a method for applying a tensile force to a bare optical fiber, for example, the ITU-T G. As shown in 650.1, there is a method of holding both ends of a part of the optical fiber using a capstan roller or the like and applying a load between the ends.

On the other hand, multi-core fibers capable of high-capacity transmission through spatial multiplexing are being considered as optical fibers for use in wiring within devices.

Special Publication No. 2020-513469 International Publication No. 2020/250838

Optical fibers used for wiring within devices are required to be resistant to breakage and have high mechanical reliability because the bending diameter is reduced.

However, since the multi-core fiber strand includes a plurality of core parts, the cladding diameter of the cladding part may be larger than 125 μm, which is the cladding diameter of a standard optical fiber strand. In particular, when the number of core portions is seven or more, the cladding diameter is often larger than 125 μm. In the case of optical fiber wires with large cladding diameters such as multi-core fiber wires, the tensile force that must be applied to ensure the same mechanical reliability will be large, so the resin in the part that is held down to apply the tensile tension will be There is a risk that the coating may be damaged and the optical fiber cannot be accurately screened.

The present invention has been made in view of the above, and the object thereof is to provide a screening method for optical fibers that can more accurately screen optical fibers regardless of the cladding diameter, and a method for screening optical fibers using the same. An object of the present invention is to provide a method for manufacturing an optical fiber.

In order to solve the above-mentioned problems and achieve the objectives, one aspect of the present invention includes a feeding step of feeding out an optical fiber strand, and applying bending stress to the fed-out optical fiber strand at a bending stress applying section. The bending stress applying section includes a bending stress applying step and a winding step of winding the optical fiber strand to which the bending stress has been applied, and the bending stress applying section includes a plurality of pulleys, and in the bending stress applying step, the plurality of A method for screening an optical fiber strand in which the bending stress is applied by contacting the side surfaces of the plurality of pulleys at different positions in the circumferential direction of the side surfaces of the optical fiber strand by changing the directions of rotation axes of the pulleys, respectively. be.

In the bending stress application step, the rotational axes of the three or more pulleys are directed in different directions, and the side surfaces of the three or more pulleys are placed at three or more different positions in the circumferential direction of the side surface of the optical fiber strand. It may also be something that makes contact.

The optical fiber strand includes a core portion, a cladding portion surrounding the core portion, and a resin coating portion surrounding the cladding portion, and the cladding diameter of the cladding portion is larger than 125 μm, and in the bending stress application step, The cladding diameter may be 125 μm and bending stress may be applied so as to obtain a breakage rate equivalent to that of a silica-based glass optical fiber at a predetermined proof level.

The outer diameter of the plurality of pulleys may be 5.2 mm or more and 12.4 mm or less.

The time period for which each side surface of the plurality of pulleys is brought into contact with the side surface of the optical fiber may be 1 second or more.

One aspect of the present invention includes a drawing step of heating and melting an optical fiber preform to draw a multi-core fiber having a plurality of core portions and a cladding portion surrounding the plurality of core portions, and coating the multi-core fiber with a resin. A method for manufacturing an optical fiber, comprising: a coating step of forming a multi-core fiber strand into a multi-core fiber strand, and a screening step of performing the optical fiber strand screening method on the multi-core fiber strand.

The multi-core fiber wire has seven or more core portions, the outer diameter of the cladding portion is 135 μm or more and 250 μm or less, and the resin coating portion includes a primary layer and a secondary layer surrounding the primary layer. The primary layer may have an elongation at break of 50% or more and 300% or less, and the secondary layer may have an elongation at break of 2.5% or more and 50% or less.

Advantageous Effects of Invention According to the present invention, it is possible to more accurately screen optical fibers regardless of the cladding diameter.

FIG. 1 is a flow diagram of a method for manufacturing an optical fiber wire. FIG. 2 is a schematic diagram of an optical fiber drawing and coating apparatus. FIG. 3 is a schematic cross-sectional view of an optical fiber. FIG. 4 is a diagram showing an example of the refractive index profile of the core. FIG. 5 is a schematic diagram of a screening device for optical fiber strands. FIG. 6 is a diagram illustrating the positional relationship between the optical fiber wire and the pulley.

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Furthermore, in each drawing, the same or corresponding components are designated by the same reference numerals, and redundant explanations are omitted as appropriate.

(Embodiment)
FIG. 1 is a flow diagram of a method for manufacturing an optical fiber strand according to an embodiment. In this manufacturing method, a wire drawing and coating process is performed in step S101. The drawing process is a process of drawing an optical fiber from an optical fiber preform. The coating step is a step of forming a resin coating layer on the drawn optical fiber. As a result, an optical fiber strand is formed. Subsequently, in step S102, a screening process is performed on the formed optical fiber strand. As a result, an optical fiber strand as a product is manufactured.

FIG. 2 is a schematic diagram of an optical fiber drawing and coating apparatus 100 used to carry out the method for manufacturing an optical fiber strand according to the embodiment. As shown in FIG. 2, the lower end of the optical fiber preform P is heated and melted by the heater 101a of the optical fiber drawing furnace 101, and the optical fiber 1 is drawn. Thereafter, as a coating step, a resin coating layer is formed on the outer periphery of the drawn optical fiber 1 by the coating forming device 102 to form the optical fiber strand 2. The optical fiber strand 2 is taken up by a capstan roller 103 and wound up by a winding bobbin 105 via a guide roll 104 .

FIG. 3 is a schematic cross-sectional view of the optical fiber 2. As shown in FIG. The optical fiber wire 2 is a multi-core fiber wire, and includes a multi-core fiber comprising seven core portions 21 as a plurality of core portions, a cladding portion 22 surrounding the core portions 21, and a resin coating portion surrounding the multi-core fiber. 23. Note that the number of core portions 21 is not limited to seven.

FIG. 4 is a diagram showing an example of the refractive index profile of the core portion. The core portion 21 includes 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 to which germanium (Ge) is added to increase the refractive index. For example, the intermediate layer is made of pure silica glass. Pure silica glass is extremely pure silica glass that does not substantially contain dopants that change the refractive index and has a refractive index of about 1.444 at a wavelength of 1550 nm. For example, the trench layer is made of silica-based glass doped with fluorine (F) to lower its refractive index. For example, the cladding portion 22 is made of pure silica glass. The outer diameter (cladding diameter) of the cladding portion 22 is larger 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 FIG. 4 .

The resin coating portion 23 includes 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 curing 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 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. Further, the additives are not limited to those mentioned above, and a wide variety of conventionally known additives used for ultraviolet curing resins and the like can be used.

In the resin coating portion 23, for example, the primary layer 23a has an elongation at break of 50% or more and 300% or less, and the secondary layer 23b has an elongation at break of 2.5% or more and 50% or less.

Next, a method of screening the optical fiber 2 will be explained.

FIG. 5 is a schematic diagram of a screening device for optical fiber strands. This screening device 200 includes a payout bobbin 10, a capstan roller 20, pulley groups 30, 40, 50, a capstan roller 60, and a take-up bobbin 70. The pulley groups 30, 40, and 50 are examples of bending stress applying units.

An optical fiber wire 2 is wound around the feeding bobbin 10. The capstan roller 20 unwinds the optical fiber 2 wound around the unwinding bobbin 10 (unwinding step), and sends it out to the pulley group 30 .

The pulley group 30 includes three pulleys 31, 32, and 33 in this embodiment. The pulleys 31, 32, and 33 apply bending stress to the optical fiber strand 2 by bringing their side surfaces into contact with each other (bending stress application step).

The pulley group 40 includes three pulleys 41, 42, and 43 in this embodiment. The pulleys 41, 42, and 43 apply bending stress to the optical fiber strand 2 by bringing their side surfaces into contact with each other (bending stress application step).

The pulley group 50 includes three pulleys 51, 52, and 53 in this embodiment. The pulleys 51, 52, and 53 apply bending stress to the optical fiber strand 2 by bringing their side surfaces into contact with each other (bending stress application step).

The capstan roller 60 takes out the optical fiber 2 to which bending stress has been applied at the pulley groups 30, 40, and 50. The winding bobbin 70 winds up the optical fiber 2 taken up by the capstan roller 60 (winding process).

(Screening by applying bending stress)
Screening by applying bending stress using pulley groups 30, 40, and 50 will be described.

As mentioned above, in the case of an optical fiber with a large cladding diameter, the tensile force that must be applied to ensure the same mechanical reliability will be large, so the resin coating of the part that is held down to apply the tensile force is Otherwise, the optical fiber may not be properly screened.

On the other hand, in the screening device 200, by applying bending stress and applying bending strain to perform screening, bending strain can be applied without strongly suppressing the resin coating, so that unintended damage to the resin coating can occur. Therefore, screening of optical fibers can be performed more accurately.

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

Here, if there is a flaw in a certain part of the cladding part of the optical fiber, the optical fiber will break when the optical fiber is bent so that the part with the flaw is on the outer circumferential side. However, when the optical fiber is bent so that the scratched part is on the inner circumferential side, the optical fiber is difficult to break.
Therefore, in the screening device 200, in the above-mentioned bending stress application process, the directions of the rotation axes of the plurality of pulleys are made different, and the side surfaces 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 2. to apply bending stress. As a result, the optical fiber 2 can be bent at various positions in the circumferential direction so that the positions are on the outer circumferential side, so that screening can be performed more accurately.

To explain with reference to FIG. 5, the normal N3 of the plane P3 formed by the traveling path of the optical fiber 2 in the pulleys 31, 32, 33 of the pulley group 30 is aligned with the rotation axis of each of the pulleys 31, 32, 33. parallel. Similarly, in the pulleys 41, 42, 43 of the pulley group 40, the normal N4 to the plane P4 formed by the traveling path of the optical fiber 2 is parallel to the rotation axis of each of the pulleys 41, 42, 43. Similarly, the normal N5 of the plane P5 formed by the travel path of the optical fiber 2 in the pulleys 51, 52, 53 of the pulley group 50 is parallel to the rotation axis of each of the pulleys 51, 52, 53. In this case, for example, the rotational axes of the pulleys 31, 32, and 33 of the pulley group 30 are different in direction from those of the other pulleys of the pulley groups 40 and 50, respectively.

FIG. 6 is a diagram illustrating an example of the positional relationship between the optical fiber wire and the pulley. FIG. 6 shows the position where each pulley hits in the circumferential direction when the optical fiber strand 2 is viewed in the traveling direction, that is, the position on the inner circumferential side when the optical fiber strand 2 is bent. .

As shown in FIG. 6, for example, three pulleys 31, 42, and 51 are arranged so that the rotation axes shown by dashed lines in the figure are in different directions, and are arranged around the side surface of the optical fiber 2. Each side surface is in contact with three different positions PO1, PO2, PO3 in the direction.

Further, like the pulley 31, the pulley 33 has its side surface in contact with the position PO1 in the circumferential direction of the side surface of the optical fiber strand 2. Further, like the pulley 51, the pulley 53 has its side surface in contact with the position PO3 in the circumferential direction of the side surface of the optical fiber strand 2.

Further, unlike the pulley 31, the pulley 32 has a side surface in contact with a position PO4 (a position opposite to the position PO1) in the circumferential direction of the side surface of the optical fiber strand 2. Moreover, unlike the pulley 42, the pulleys 41 and 43 have their side surfaces in contact with the circumferential position PO5 (the position opposite to the position PO2) of the side surface of the optical fiber 2. Further, unlike the pulley 51, the pulley 52 has a side surface in contact with a position PO6 (a position opposite to the position PO3) in the circumferential direction of the side surface of the optical fiber strand 2.

That is, in the screening device 200, the respective side surfaces of the pulleys 31 to 33, 41 to 43, and 51 to 53 are brought into contact with six different positions PO1 to PO6 in the circumferential direction of the side surface of the optical fiber strand 2.

Note that it is preferable that the time period for which each side surface of the pulley is brought into contact with the side surface of the optical fiber strand 2 is 1 second or more. This allows more accurate screening. However, in consideration of fatigue of the optical fiber 2 due to screening, it is better to shorten the contact time.

(Screening level setting)
Setting of the screening level in the screening device 200 will be explained. For example, in the conventional method of applying tensile stress to the optical fiber strand, the screening level is defined as the rate at which tensile stress is applied to the extent that the optical fiber strand stretches at a certain rate. be. For example, if the elongation rate is 1%, it is called 1% screening. In response to such screening, it is known that optical fiber strands break at a predetermined breakage rate. The rupture rate can be derived, for example, by the following equation (1) (Griffioen, W., Greven, W., Jonker, J., Zandberg, S., Kuyt, G., and Overton, B., (See “Reliability of bend insensitive fibers”, Proceedings of the 58th International Wire and Cable Symposium, (2009-11), pp.251-257.)

式（１）において、各パラメータは以下の通りである。
Ｌ ：ファイバ長
Ｎ_ｐ０ ：プルーフテスト時破断回数
ｍ_１ ：ワイブル分布係数（弱強度分布）
ｎ ：ファイバ実使用時の疲労係数
ｔ_ｐ ：プルーフテスト時印加時間
ｔ_ｓ ：ファイバ実使用時間
σ_ａ ：敷設時のファイバ曲げ応力
σ_ｐ ：プルーフ印加応力
σ_ｐ０ ：スケーリング係数

In formula (1), each parameter is as follows.
L: Fiber length N _p0 : Number of breaks during proof test m ₁ : Weibull distribution coefficient (weak strength distribution)
n: Fatigue coefficient during actual use of the fiber t _p : Application time during proof test t _s : Actual use time of the fiber σ _a : Fiber bending stress during installation σ _p : Proof applied stress σ _p0 : Scaling coefficient

For example, for a silica 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 (pound force per square inch) is 6894.76 Pa (pascal).

With the conventional method, a silica-based glass optical fiber with a cladding diameter different from 125 µm has the same mechanical reliability as a silica-based glass optical fiber with a cladding diameter of 125 µm that is screened with a tensile stress of 100 kpsi. To ensure this, the following steps were taken: In other words, in order to obtain a breakage rate equivalent to the breakage rate when screening a silica glass optical fiber with a cladding diameter of 125μm under a tensile stress of 100 kpsi, the light of a silica glass whose cladding diameter is different from 125μm is to be obtained. Screening was performed by applying tensile stress to the fiber.

On the other hand, in the screening device 200, a silica-based glass optical fiber with a cladding diameter different from 125 µm is screened using the same machine as that used when screening a silica-based glass optical fiber with a cladding diameter of 125 µm at a tensile stress of 100 kpsi. To ensure the reliability of the information, the following steps can be taken. That is, in order to obtain a fracture rate equivalent to that obtained when a silica-based glass optical fiber with a cladding diameter of 125 μm is screened with a tensile stress of 100 kpsi, a silica-based glass optical fiber with a cladding diameter different from 125 μm is used. Screening may be performed by applying bending stress to the optical fiber. 1% screening (screening at 100 kpsi tensile stress) is an example of a predetermined proof level.

Examples of screening conditions for various cladding diameters of the optical fiber 2 shown in FIGS. 2 and 3 will be described below.

(Example where the cladding diameter is 150μm and the bending radius during installation is 10mm)
When the cladding diameter of the optical fiber strand 2 shown in FIGS. 2 and 3 is 150 μm, tensile stress is applied and screening is performed on a silica glass optical fiber with a cladding diameter of 125 μm at a tensile stress of 100 kpsi. To obtain the same rupture rate, a tensile stress of 180 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 150 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 8.8 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 180 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 180 kpsi.

As a comparative example, an optical fiber with a cladding diameter of 150 μm was manufactured with the structure shown in FIGS. 2 and 3, and screening was performed over a length of 1000 km using a conventional screening device to apply a tensile stress of 180 kpsi. Breakage occurred due to damage to the resin coating.

On the other hand, as Example 1, an optical fiber 2 with a cladding diameter of 150 μm was manufactured with the structure shown in FIGS. When screening was performed over a length of 1000 km using the screening device 200 that applies , it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example when the cladding diameter is 200μm and the bending radius during installation is 10mm)
When the cladding diameter of the optical fiber 2 is 200 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi. To obtain this, a tensile stress of 220 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 200 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 9.6 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 220 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 220 kpsi.

As Example 2, an optical fiber with a cladding diameter of 200 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 9.6 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 250μm and the bending radius during installation is 10mm)
When the cladding diameter of the optical fiber 2 is 250 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi. To obtain , a tensile stress of 341 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 250 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 7.7 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 341 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 341 kpsi.

As Example 3, an optical fiber with a cladding diameter of 250 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 7.7 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 150μm and the bending radius during installation is 20mm)
When the cladding diameter of the optical fiber 2 is 150 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica-based glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi. To obtain this, a tensile stress of as much as 150 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 150 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 10.5 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 150 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 150 kpsi.

As Example 4, an optical fiber with a cladding diameter of 150 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 10.5 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 200μm and the bending radius during installation is 20mm)
When the cladding diameter of the optical fiber 2 is 200 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi. To obtain this, a tensile stress of 170 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 200 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 12.4 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 170 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 170 kpsi.

As Example 5, an optical fiber with a cladding diameter of 200 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 12.4 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 250μm and the bending radius during installation is 20mm)
When the cladding diameter of the optical fiber 2 is 250 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 100 kpsi. To obtain this, a tensile stress of 251 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 250 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 10.5 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 251 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 251 kpsi.

As Example 6, an optical fiber having a cladding diameter of 250 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 10.5 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 135μm and the bending radius during installation is 10mm)
When the cladding diameter of the optical fiber strand 2 is 135 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica-based glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 200 kpsi. To obtain this, a tensile stress of 220 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 135 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 6.5 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 220 kpsi, it is possible to perform screening equivalent to applying a tensile stress of 220 kpsi.

As Example 7, an optical fiber with a cladding diameter of 135 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 6.5 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

(Example where the cladding diameter is 150μm and the bending radius during installation is 10mm)
When the cladding diameter of the optical fiber 2 is 150 μm, the rupture rate is the same as the rupture rate when applying tensile stress and screening a silica-based glass optical fiber with a cladding diameter of 125 μm with a tensile stress of 200 kpsi. To obtain this, a tensile stress of 301 kpsi must be applied.

On the other hand, in the screening device 200, when the cladding diameter of the optical fiber 2 is 150 μm, the outer diameter of the pulleys 31 to 33, 41 to 43, and 51 to 53 is set to 5.2 mm, and the bending stress is reduced by the pulleys. By applying a tensile stress of 301 kpsi, it is possible to perform screening equivalent to screening performed by applying a tensile stress of 301 kpsi.

As Example 8, an optical fiber with a cladding diameter of 150 μm was manufactured with the structure shown in FIGS. 2 and 3, and bending stress was applied to the pulleys 31 to 33, 41 to 43, and 51 to 53 with outer diameters of 5.2 mm. When screening was performed over a length of 1000 km using the screening device 200, it was confirmed that no breakage occurred and mechanical reliability was ensured.

In the above embodiments and examples, screening using the screening device 200 is performed on optical fibers with a cladding diameter larger than 125 μm; however, screening using the screening device 200 is performed on optical fibers with a cladding diameter of 125 μm or less. It may also be carried out.

Further, in the above embodiments and examples, the side surface of the pulley is brought into contact with six positions in the circumferential direction of the side surface of the optical fiber strand 2, but the number of positions to be brought into contact may be two or more.

Furthermore, the present invention is not limited to the above embodiments. The present invention also includes configurations in which the above-mentioned components are appropriately combined. Moreover, further effects and modifications can be easily derived by those skilled in the art. Accordingly, the broader aspects of the invention are not limited to the embodiments described above, but are capable of various modifications.

1: Optical fiber 2: Optical fiber wire 10: Feeding bobbin 20, 60: Capstan roller 21: Core portion 22: Clad portion 23: Resin coating portion 23a: Primary layer 23b: Secondary layer 30, 40, 50: Pulley group 31, 32, 33, 41, 42, 43, 51, 52, 53: Pulleys 70, 105: Winding bobbin 100: Drawing and coating device 101: Optical fiber drawing furnace 101a: Heater 102: Coating forming device 103: Capstan roller 104: Guide roll 200: Screening device N3, N4, N5: Normal P: Optical fiber base material P3, P4, P5: Plane

Claims (7)

A feeding process of feeding out the optical fiber strand,
a bending stress applying step of applying bending stress to the unwound optical fiber strand at a bending stress applying section;
a winding step of winding the optical fiber to which the bending stress has been applied;
Equipped with
The bending stress applying section includes a plurality of pulleys,
In the bending stress applying step, the rotational axes of the plurality of pulleys are made to have different directions, and the side surfaces 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. A method of screening bare optical fiber. In the bending stress application step, the rotational axes of the three or more pulleys are directed in different directions, and the side surfaces of the three or more pulleys are placed at three or more different positions in the circumferential direction of the side surface of the optical fiber strand. The method for screening an optical fiber wire according to claim 1, wherein the optical fiber is brought into contact with the wire. The optical fiber strand includes a core portion, a cladding portion surrounding the core portion, and a resin coating portion surrounding the cladding portion, the cladding diameter of the cladding portion being larger than 125 μm,
According to claim 1 or 2, in the bending stress application step, bending stress is applied so as to obtain a breakage rate equivalent to a breakage rate at a predetermined proof level in a silica-based glass optical fiber strand with a cladding diameter of 125 μm. screening method for bare optical fiber. The method for screening optical fiber strands according to claim 1, wherein the outer diameter of the plurality of pulleys is 5.2 mm or more and 12.4 mm or less. The method for screening an optical fiber strand according to any one of claims 1 to 4, wherein the time period for which the side surface of each of the plurality of pulleys is brought into contact with the side surface of the optical fiber strand is 1 second or more. a drawing step of heating and melting an optical fiber preform to draw a multi-core 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 on the multi-core fiber to obtain a multi-core fiber wire;
A screening step of performing the optical fiber screening method according to any one of claims 1 to 5 on the multi-core fiber;
A method for manufacturing an optical fiber. The multi-core fiber wire has seven or more core portions, the outer diameter of the cladding portion is 135 μm or more and 250 μm or less, and the resin coating portion includes a primary layer and a secondary layer surrounding the primary layer. The optical fiber strand according to claim 6, wherein the primary layer has an elongation at break of 50% or more and 300% or less, and the secondary layer has an elongation at break of 2.5% or more and 50% or less. Production method.

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