Optical fiber cable

Abstract

This optical fiber cable comprises: a cable core (10) that contains a plurality of optical fiber cores (11); a tensile strength member (30) that is disposed along the cable core (10); and a sheath (20) that covers the cable core (10) and encloses the tensile strength member (30). The sheath (20) contains a flame-retardant material; the cable core (10) has a high flame-retardant fiber having a limiting oxygen index of at least 40; and the core density provided by dividing the number of optical fiber cores (11) by the cross-sectional area of the cable is at least 1.5 cores / mm2.

Description

fiber optic cable

[0001] The present disclosure relates to fiber optic cables.

[0002] Patent Document 1 describes an optical fiber cable including a plurality of optical fibers, an outer jacket covering the optical fibers, and a set of strength members enclosed by the outer jacket. The outer jacket contains a flame-retardant material.

[0003] International Publication No. 2022 / 004666

[0004] An optical fiber cable according to one aspect of the present disclosure comprises: a cable core including a plurality of optical fiber cores; strength members arranged along the plurality of optical fiber cores; and an outer jacket covering the cable core and enclosing the strength members, wherein the outer jacket includes a flame-retardant material, the cable core includes highly flame-retardant fibers having a limit oxygen index of 40 or more, and a core density, calculated by dividing the number of cores in the optical fiber cores by the cross-sectional area of ​​the cable, of 1.5 cores / mm ２ That's all.

[0005] Fig. 1 is a cross-sectional view of an optical fiber cable according to the present embodiment. Fig. 2 is a cross-sectional view of an end portion of the optical fiber cable according to the present embodiment. Fig. 3 is a diagram illustrating the positional relationship between a strength member, a center of cross section, and a center of rigidity in an optical fiber cable. Fig. 4 is a diagram illustrating the bending radius of an optical fiber cable.

[0006] (Problem to be Solved by the Present Disclosure) In a slotless cable, as in Patent Document 1, strength members may be arranged in two or more locations on the outer sheath. Also, in a flame-retardant cable, the outer periphery of the cable may be covered with a resin containing a flame-retardant material, and if a flammable material such as strength members is arranged inside the outer sheath or in the cable core, it is necessary to increase the thickness of the outer sheath to increase the distance from the flammable material.

[0007] As described above, in a flame-retardant slotless cable such as that disclosed in Patent Document 1, it is necessary to ensure a sufficient coating thickness, making it difficult to reduce the diameter and increase the density of the optical fiber cable.

[0008] Effect of the Present Disclosure According to the present disclosure, an optical fiber cable that ensures flame retardancy and can be made smaller in diameter can be provided.

[0009] (Explanation of Embodiments of the Present Disclosure) First, embodiments of the present disclosure will be listed and explained. (1) An optical fiber cable according to one aspect of the present disclosure comprises: a cable core including a plurality of coated optical fibers; a strength member arranged along the cable core; and an outer jacket covering the cable core and enclosing the strength member, wherein the outer jacket contains a flame-retardant material, the cable core has highly flame-retardant fibers with a limit oxygen index of 40 or more, and a core density, calculated by dividing the number of fibers in the coated optical fibers by the cross-sectional area of ​​the cable, of 1.5 fibers / mm ２ According to the above optical fiber cable, the flame-retardant material is dispersed in the cable core and the jacket, so that the thickness of the jacket can be reduced while ensuring the flame retardancy of the optical fiber cable, thereby enabling the optical fiber cable to be made smaller in diameter.

[0010] (2) In the optical fiber cable according to (1), the strength member may be disposed at only one location on the jacket. By disposing the strength member at only one location on the jacket, the center of rigidity of the optical fiber cable is located close to the strength member. This reduces bending strain on the strength member that occurs when the optical fiber cable is bent, and suppresses buckling of the strength member.

[0011] (3) In the optical fiber cable according to (1) or (2), the distance between the strength members and the outer surface of the jacket may be 0.6 mm or more. According to the above configuration, the distance between the strength members and the outer surface of the jacket is 0.6 mm or more, making the strength members less likely to ignite. This improves the flame retardancy of the optical fiber cable.

[0012] (4) In the optical fiber cable according to any one of (1) to (3), the highly flame-retardant fiber may be a polyparaphenylene benzobisoxazole (PBO) fiber. PBO fiber is not only flame-retardant but also has excellent strength and elasticity, making it possible to increase the bending strength of the entire optical fiber cable while maintaining flame retardancy.

[0013] (5) In the optical fiber cable according to any one of (1) to (4), the cable core may include a water-absorbent fiber only in the center of the cable core, and the plurality of optical fibers may be arranged around the water-absorbent fiber. The plurality of optical fibers may be arranged around the water-absorbent fiber arranged only in the center of the cable core. Compared to a water-absorbent tape that covers the optical fiber, the water-absorbent fiber can improve the water absorption of the optical fiber cable while reducing the area occupied by the inner core in cross-section. Furthermore, by arranging a flammable water-absorbent fiber in the center, flame retardancy can be improved. Note that "only in the center of the cable core" means that the water-absorbent fiber is arranged only in the range from the center of the cable core to a position r1 / 2, where r1 is the diameter of the cable core.

[0014] (6) In the optical fiber cable according to any one of (1) to (5), the strength members may not buckle even when bent with a bending diameter 10 times the diameter of the optical fiber cable. With the above optical fiber cable, an optical fiber cable in which the strength members are less likely to buckle can be obtained.

[0015] (7) In the optical fiber cable according to any one of (1) to (6) above, the jacket may be made of a material having a flame retardancy with a limit oxygen index of 40 or more. Since the jacket is made of a material having a flame retardancy with a limit oxygen index of 40 or more, the flame retardancy of the entire optical fiber cable can be ensured.

[0016] (8) In the optical fiber cable according to any one of (1) to (7), the base material of the jacket may be ethylene-vinyl acetate copolymer (EVA) resin. EVA resin has excellent elasticity and flexibility, allowing the optical fiber cable to be bent to a smaller diameter. Furthermore, with the optical fiber cable, the tensile strength members are less likely to buckle.

[0017] (9) In the optical fiber cable according to any one of (1) to (8), the room-temperature Young's modulus of the jacket may be 400 MPa or more and 800 MPa or less. By setting the room-temperature Young's modulus of the jacket to 800 MPa or less, the jacket can be made soft, making it easier for inorganic flame-retardant materials such as magnesium hydroxide to disperse, and improving the flame retardancy of the jacket. Furthermore, by setting the room-temperature Young's modulus of the jacket to 400 MPa or more, rigidity can be ensured, and the occurrence of kinking during air pumping can be suppressed.

[0018] (10) In the optical fiber cable according to any one of (1) to (9), the softening point temperature of the jacket may be in the range of 40°C or higher and 70°C or lower. By using a material with a softening temperature of 70°C or lower for the jacket, the jacket can be softened, making it easier for inorganic flame retardants such as magnesium hydroxide to disperse, thereby improving the flame retardancy of the jacket. Furthermore, by setting the softening temperature of the jacket to 40°C or higher, softening of the jacket at room temperature can be suppressed.

[0019] (11) In the optical fiber cable according to any one of (1) to (10), the optical fiber cable may be used for compressed air transmission. The optical fiber cable having the above configuration can have a thin outer jacket while maintaining flame retardancy, making it suitable for use as an optical fiber cable for compressed air transmission.

[0020] (12) In the optical fiber cable according to any one of (1) to (11) above, a multi-fiber connector may be connected to an end of the optical fiber cable. Since the multi-fiber connector is connected to the end of the optical fiber cable, it becomes easy to connect the optical fiber cable to other optical fiber cables.

[0021] (Details of the embodiment of the present disclosure) Specific examples of optical fiber cables according to the embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0022] 1 is a cross-sectional view of an optical fiber cable 1. As illustrated in FIG. 1, the optical fiber cable 1 includes a cable core 10, an outer jacket 20, and a strength member 30.

[0023] The cable core 10 includes a plurality of optical fibers 11, water-absorbent fibers 12, and highly flame-retardant fibers 13. In this embodiment, the optical fiber 11 forms an optical fiber ribbon 11a in which 12 optical fibers 11 are connected in parallel. The cable core 10 may be composed of, for example, 24 optical fiber ribbons 11a, which may be twisted together. In the optical fiber ribbon 11a, adjacent optical fibers 11 may be intermittently connected at a predetermined interval in the longitudinal direction of the optical fiber ribbon 11a. The optical fiber 11 may be a single fiber without forming an optical fiber ribbon. The optical fiber 11 includes a glass fiber having a core and a cladding, and a resin layer covering the glass fiber. The diameter of the glass fiber is typically approximately 125 μm. The diameter of the optical fiber 11 is, for example, 180 μm or more and 220 μm or less, and is 200 μm in this example.

[0024] The core density obtained by dividing the number of cores in the optical fiber core 11 by the cross-sectional area of ​​the cable is 1.5 cores / mm ２ The cable cross-sectional area is the cross-sectional area of ​​the optical fiber cable 1 including the jacket 20.

[0025] The water-absorbent fibers 12 are, for example, plastic fibers coated with water-absorbent powder or fibers that have been given water-absorbency themselves. The water-absorbent fibers 12 are bundled and arranged in the center of the cable core 10, and the multiple optical fiber cores 11 are arranged around the water-absorbent fibers 12.

[0026] The highly flame-retardant fibers 13 are disposed inside the cable core 10. The highly flame-retardant fibers 13 preferably have a limiting oxygen index of 40 or higher. Here, the limiting oxygen index is the minimum oxygen concentration required for continued combustion as defined by JIS K7201. The highly flame-retardant fibers 13 may be, for example, flame-retardant polyparaphenylene benzobisoxazole (PBO) fibers. The highly flame-retardant fibers 13 are disposed between the multiple optical fiber cores 11 and the jacket 20. In the optical fiber cable 1 of this embodiment, four highly flame-retardant fibers 13 are disposed so as to surround the multiple optical fiber cores 11.

[0027] PBO fiber has excellent strength, elasticity, and flame retardancy, but is weak against abrasion. If a water-absorbent sheet is provided to cover the optical fiber 11 instead of the water-absorbent fiber 12, abrasion may occur between the water-absorbent sheet and the highly flame-retardant fiber 13. However, by providing the water-absorbent fiber 12 only in the center so that it is covered by the optical fiber 11, abrasion of the highly flame-retardant fiber 13 is suppressed, and the flame retardancy and water absorption of the optical fiber cable 1 are obtained.

[0028] The outer jacket 20 covers the cable core 10. The outer jacket 20 includes a flame-retardant material. For example, the outer jacket 20 may be made of a flame-retardant material with a limit oxygen index of 40 or higher. The base material of the outer jacket 20 may be an ethylene-vinyl acetate copolymer (EVA) resin. Furthermore, the room temperature Young's modulus of the outer jacket 20 may be 400 MPa or higher and 800 MPa or lower, and the softening point temperature of the outer jacket 20 may be in the range of 40°C or higher and 70°C or lower.

[0029] The strength members 30 are embedded in the jacket 20 and disposed along the cable core 10. In other words, the jacket 20 contains the strength members 30. The strength members 30 are formed, for example, from fiber reinforced plastic (FRP). Examples of fiber reinforced plastic include aramid FRP, glass FRP, and carbon FRP. The outer diameter of the strength members 30 is, for example, 1.2 mm.

[0030] In this embodiment, two tension members 30 are provided side by side. The tension members 30 are preferably disposed at only one location on the outer sheath 20. The distance D between the tension members 30 and the outer surface of the outer sheath 20 is preferably 0.6 mm or more.

[0031] When the optical fiber cable 1 is bent, the tensile strength member 30 may buckle due to bending stress. However, in the optical fiber cable of this embodiment, the tensile strength member does not buckle even when bent with a bending diameter 10 times the diameter of the optical fiber cable.

[0032] 2 illustrates an example of an end of an optical fiber cable 1. A multi-fiber connector 2 and a protective tube 3 are connected to the end of the optical fiber cable 1. The multi-fiber connector 2 may be, for example, a 96-fiber or 144-fiber connector based on an MT connector. The multi-fiber connector 2 may include, for example, four ferrules 2a. The ferrule 2a is, for example, a 12-fiber MT ferrule configured such that the tip of a 12-fiber optical fiber ribbon 11a is inserted and fixed therein.

[0033] The protective tube 3 is made of, for example, metal and includes a flexible portion 3 a and a lid portion 3 b provided at a tip end of the flexible portion 3 a. The protective tube 3 is connected to an end of the optical fiber cable 1, and the optical fiber cable 1 can be used to lay the optical fiber cable 1 in an existing duct by air pressure feeding.

[0034] According to the optical fiber cable 1 of this embodiment, since both the cable core 10 and the outer sheath 20 contain flame-retardant material, the thickness of the outer sheath 20 can be reduced while maintaining the flame retardancy of the optical fiber cable 1, compared to when only one of them contains flame-retardant material, and the diameter of the optical fiber cable 1 can be reduced.

[0035] 3 illustrates the positional relationship between the strength members 30, the cross-sectional center O, and the center of rigidity G in the optical fiber cable 1. FIG. 4 illustrates the bending radius R of the optical fiber cable 1.

[0036] In the optical fiber cable 1 of this embodiment, the strength member 30 is disposed at only one location in the jacket 20. Therefore, the center of rigidity G of the optical fiber cable 1 is located closer to the strength member 30 than the cross-sectional center O of the optical fiber cable 1. On the other hand, if the strength members are located at two locations on either side of the cable core, as in Patent Document 1, the center of rigidity will be located at the cross-sectional center.

[0037] When the optical fiber cable 1 is bent, bending stress occurs in the strength members 30. If the bending stress occurring in the strength members 30 acts as a compressive stress on the strength members 30, there is a possibility that the strength members 30 will buckle.

[0038] Here, the bending strain ε of the strength member 30 is approximately expressed as ε = r / R, where r is the distance from the center of rigidity G to the strength member 30 and R is the bending radius of the optical fiber cable 1. In other words, since the center of rigidity G of the optical fiber cable 1 in this embodiment is located closer to the strength member 30 than the center O of the cross section of the optical fiber cable 1, the distance r is smaller and the strain ε is also smaller. As a result, the strength member 30 of the optical fiber cable 1 in this embodiment is less likely to buckle than when the center of rigidity is at the center of the cross section.

[0039] Since resins containing flame-retardant materials are generally soft, strength members enclosed in a jacket containing flame-retardant materials are prone to buckling. However, with the optical fiber cable 1 of this embodiment, the center of rigidity G of the optical fiber cable 1 is located closer to the strength members 30 than the cross-sectional center O of the optical fiber cable 1, so the strain ε of the optical fiber cable is reduced and the strength members 30 are less likely to buckle.

[0040] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure.

[0041] REFERENCE SIGNS LIST 1 Optical fiber cable 2 Multi-core connector 2a Ferrule 3 Protective tube 3a Flexible portion 3b Lid portion 10 Cable core 11 Optical fiber core 12 Water-absorbent fiber 13 Highly flame-retardant fiber 20 Jacket 30 Tensile member G Center of rigidity O Center of cross section r Distance from center of rigidity to tensile member R Bending radius

Claims

1. A cable comprising: a cable core including a plurality of optical fiber cores; a strength member arranged along the cable core; and an outer jacket covering the cable core and enclosing the strength member, wherein the outer jacket contains a flame-retardant material, the cable core has highly flame-retardant fibers with a limit oxygen index of 40 or more, and the core density, calculated by dividing the number of cores in the optical fiber cores by the cross-sectional area of ​​the cable, is 1.5 cores / mm ２ That's it, fiber optic cable.

2. The optical fiber cable according to claim 1, wherein the strength member is disposed at only one location in the jacket.

3. The optical fiber cable according to claim 1 or 2, wherein the distance between the tension member and the outer surface of the jacket is 0.6 mm or more.

4. The optical fiber cable according to any one of claims 1 to 3, wherein the highly flame-retardant fiber is a polyparaphenylene benzobis oxazole (PBO) fiber.

5. An optical fiber cable as claimed in any one of claims 1 to 4, wherein the cable core has water-absorbent fibers only in the center of the cable core, and the plurality of optical fiber strands are arranged around the water-absorbent fibers.

6. The optical fiber cable according to any one of claims 1 to 5, wherein the tensile member does not buckle even when bent with a bending diameter ten times the diameter of the optical fiber cable.

7. The optical fiber cable according to any one of claims 1 to 6, wherein the jacket is made of a material having a flame retardancy with a limit oxygen index of 40 or more.

8. The optical fiber cable according to any one of claims 1 to 7, wherein the base material of the jacket is an ethylene-vinyl acetate copolymer (EVA) resin.

9. The optical fiber cable according to any one of claims 1 to 8, wherein the room temperature Young's modulus of the outer sheath is 400 MPa or more and 800 MPa or less.

10. An optical fiber cable as claimed in any one of claims 1 to 9, wherein the softening point temperature of the outer jacket is in the range of 40°C or higher and 70°C or lower.

11. The optical fiber cable according to any one of claims 1 to 10, wherein the optical fiber cable is used for air pressure feeding.

12. The optical fiber cable according to any one of claims 1 to 11, wherein a multi-fiber connector is connected to an end of the optical fiber cable.

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