Optical fiber cable

Abstract

This optical fiber cable comprises: a plurality of coated optical fibers; a cable jacket covering the plurality of coated optical fibers; and a plurality of tension member groups embedded in the cable jacket and each including a plurality of tension members. A plurality of groups of the tension members are arranged along the circumferential direction of the cable jacket in a cross section perpendicular to the axial direction of the optical fiber cable. Given that the outer diameter of the tension member is R, the shortest distance D between adjacent tension member groups among the tension member groups satisfies the condition 3R < D ≤ 7R.

Description

fiber optic cable

[0001] This application claims priority to Japanese Patent Application No. 2023-212967, filed December 18, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 discloses an optical fiber cable having a structure in which adjacent groups of tension members are spaced apart from each other in order to obtain sufficient straightness and flexibility.

[0003] International Publication No. 2023 / 120483

[0004] The optical fiber cable of the present disclosure is an optical fiber cable comprising a plurality of optical fiber cores, a cable outer sheath covering the plurality of optical fiber cores, and a plurality of tension member groups embedded in the cable outer sheath, each of which includes a plurality of tension members, wherein the plurality of tension member groups are arranged along the circumferential direction of the cable outer sheath in a cross section perpendicular to the axial direction of the optical fiber cable, and when the outer diameter of the tension member is R, the shortest distance D between adjacent tension member groups among the plurality of tension member groups satisfies the condition 3R<D≦7R.

[0005] According to the present disclosure, an optical fiber cable with small anisotropy in the bending direction can be provided.

[0006] 1 is a cross-sectional view of an optical fiber cable according to an embodiment of the present disclosure, and FIG. 2 is a cross-sectional view of an optical fiber cable according to a comparative example.

[0007] [Problem to be Solved by the Present Disclosure] It is desirable for an optical fiber cable for air pumping to have a long pumping distance when laid in a duct. To extend the pumping distance, it is important that the optical fiber cable has sufficient straightness and flexibility, and that the bending stiffness of the optical fiber cable is the same regardless of the direction in which the optical fiber cable is bent, i.e., that the anisotropy in the bending direction is small. However, conventional optical fiber cables have a large bending directionality, which can result in a short pumping distance.

[0008] [Advantages of the Present Disclosure] According to the present disclosure, an optical fiber cable with small anisotropy in the bending direction can be provided.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described below. The optical fiber cable of the present disclosure is: (1) an optical fiber cable including a plurality of optical fiber cores, a cable jacket covering the plurality of optical fiber cores, and a plurality of tension member groups embedded in the cable jacket, each of the tension member groups including a plurality of tension members, wherein the plurality of tension member groups are arranged along the circumferential direction of the cable jacket in a cross section perpendicular to the axial direction of the optical fiber cable, and when the outer diameter of each tension member is R, the shortest distance D between adjacent tension member groups among the plurality of tension member groups satisfies the condition 3R<D≦7R.

[0010] The optical fiber cable has sufficient flexibility by satisfying the condition 3R<D. Furthermore, by satisfying the condition D≦7R, an optical fiber cable with small anisotropy in the bending direction can be obtained.

[0011] (2) In the above (1), the number of the tension member groups may be two.

[0012] By using two tension member groups, the tension members can be more uniformly arranged along the circumferential direction of the cable cross section, resulting in an optical fiber cable with excellent temperature characteristics and tensile strength.

[0013] (3) In the above (1) or (2), a tear cord may be disposed between adjacent groups of tension members.

[0014] By disposing the tear cord between the tension members, the tear cord can be positioned away from the tension members, making it easier to dispose the tear cord within the cable jacket. Also, the tension members do not get in the way when tearing the jacket.

[0015] (4) In any one of the above (1) to (3), the tension members included in the tension member group may not be in contact with each other, and the shortest distance between adjacent tension members may be 0.05 mm or more.

[0016] By making the shortest distance between adjacent tension members 0.05 mm or more, it is possible to maintain sufficient adhesion between each tension member and the cable jacket, and to effectively prevent expansion and contraction of the cable jacket due to temperature changes.

[0017] [Details of the embodiments of the present disclosure] Specific examples of the optical fiber cable 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.

[0018] Fig. 1 is a cross-sectional view showing an optical fiber cable 1 according to this embodiment. The cross section of the optical fiber cable 1 shown in Fig. 1 is a cross section perpendicular to the axial direction of the optical fiber cable 1. As shown in Fig. 1, the optical fiber cable 1 includes a plurality of optical fiber cores 3, a water-absorbing tape 8, a tear string 7, a cable jacket 5, and a plurality of tension member groups 6a, 6b. The outer diameter of the optical fiber cable 1 is, for example, 5 mm or more and 20 mm or less.

[0019] The optical fiber cable 1 is an optical fiber cable for air pressure feeding that is air pressure fed through a duct such as a microduct. A plurality of optical fiber cores 3 are housed in a housing space 10 of the optical fiber cable 1. The plurality of optical fiber cores 3 extend along the axial direction of the optical fiber cable 1. The plurality of optical fiber cores 3 may also be twisted spirally along the axial direction. The optical fiber core 3 has a glass fiber and a resin coating that covers the glass fiber. The glass fiber has at least one core through which signal light propagates and a cladding that covers the core. The refractive index of the core is greater than the refractive index of the cladding.

[0020] In this example, a plurality of individual optical fiber cores 3 are accommodated in the accommodation space 10, but a plurality of optical fiber ribbons, each including a plurality of optical fiber cores 3, may also be accommodated in the accommodation space 10. In this case, the optical fiber ribbon may be, for example, an intermittently bonded optical fiber ribbon in which, among a plurality of parallelly arranged optical fiber cores, adjacent optical fiber cores are intermittently bonded along the axial direction. Also, a plurality of optical fiber ribbons may be twisted spirally along the axial direction of the optical fiber cable 1.

[0021] The water-absorbing tape 8 is wound around the entirety of the multiple optical fiber cores 3, for example, longitudinally or spirally. The water-absorbing tape 8 is made, for example, of a polyester-containing base fabric to which water-absorbing powder has been applied to provide a water-absorbing finish. The tear cord 7 is used to tear the cable jacket 5 and is embedded in the cable jacket 5. In this example, two tear cords 7 are provided in the optical fiber cable 1. By pulling out the tear cords 7, the cable jacket 5 can be torn in the axial (longitudinal) direction, allowing the optical fiber cores 3 to be removed. The tear cords 7 are made, for example, of a tensile-resistant plastic material (e.g., polyester).

[0022] The cable jacket 5 is provided so as to cover the periphery of the plurality of coated optical fibers 3. The cable jacket 5 is formed of a resin such as polyvinyl chloride (PVC) or polyethylene (PE). The resin of the cable jacket 5 may have a Young's modulus of 500 MPa or more. The cable jacket 5 may also contain a silicone-based lubricant. The silicone-based lubricant may be contained in a proportion of, for example, 2% by mass or more, or in a proportion of 3% by mass or more and 5% by mass or less.

[0023] The cable jacket 5 may also be formed from a highly flame-retardant resin. For example, the cable jacket 5 is formed from flame-retardant PVC, flame-retardant polyethylene, or the like, with an oxygen index of 50 or higher. This allows the optical fiber cable 1 to comply with the UL1666 riser grade of the North American NEC (National Electrical Code) standard and the Cca class of the European CPR (Construction Products Regulation) standard. The cable jacket 5 is formed from, for example, a thermoplastic resin by extrusion molding the resin onto the multiple optical fiber cores 3 around which the water-absorbing tape 8 is wound.

[0024] The two tension member groups 6a and 6b are embedded in the cable jacket 5. The tension member groups 6a and 6b are arranged along the circumferential direction D1 of the cable jacket 5 in the cross section of the optical fiber cable 1 in Figure 1. Each of the tension member groups 6a and 6b includes seven tension members 4.

[0025] The tension members 4 are made of a tensile strength material. Specifically, the tension members 4 may be made of fiber-reinforced plastic (FRP) such as aramid FRP, glass FRP, or carbon FRP. The cross section of each tension member 4 is approximately circular. The outer diameter R of each tension member 4 is, for example, 0.2 mm or more and 2 mm or less. Each tension member 4 extends along the axial direction of the optical fiber cable 1. The tension members 4 included in the tension member groups 6a and 6b do not contact each other. For example, the shortest distance between adjacent tension members 4 is 0.05 mm or more.

[0026] The shortest distance between adjacent tension members 4 is different from the shortest distance D between adjacent tension member groups. More specifically, the shortest distance between adjacent tension members 4 is smaller than the shortest distance D between adjacent tension member groups 6a, 6b. In this way, the tension member group defined in this embodiment is a group in which multiple tension members included in the tension member group are closely packed together.

[0027] Adjacent tension member groups 6a and 6b are spaced apart from each other. As shown in Figure 1, the shortest distance D between adjacent tension member groups 6a and 6b satisfies the condition 3R<D≦7R. As mentioned above, R represents the outer diameter of the tension member 4.

[0028] The optical fiber cable 1 according to this embodiment has multiple tension member groups, and the distance D between the tension member groups satisfies the condition 3R<D, thereby improving flexibility while adequately maintaining the straightness of the optical fiber cable 1. Furthermore, the distance D between the tension member groups satisfies the condition D≦7R, thereby reducing the anisotropy in the bending direction of the optical fiber cable 1. The reduced anisotropy in the bending direction allows for a longer pumping distance when the optical fiber cable 1 is introduced into a duct.

[0029] Although the optical fiber cable 1 of this embodiment has two tension member groups, the number of tension member groups in the optical fiber cable of the present disclosure is not particularly limited and may be, for example, two to four. When there are three or more tension member groups, the shortest distance D between any two adjacent tension member groups satisfies the condition 3R<D≦7R. The spacing between the tension member groups along the circumferential direction of the optical fiber cable may be the same or different, but in either case, the shortest distance D between adjacent tension member groups satisfies the condition 3R<D≦7R. Note that when the number of tension member groups is two, the tension members can be more evenly arranged along the circumferential direction of the cable cross section, thereby improving the temperature characteristics and tensile strength of the optical fiber cable.

[0030] In this embodiment, each of the tension member groups 6a and 6b includes seven tension members, but the number of tension members included in each tension member group is not particularly limited. If each tension member group includes three or more tension members, the straightness of the optical fiber cable is further improved. In particular, when there are two tension member groups, if each tension member group includes six or more tension members, an optical fiber cable with excellent straightness can be obtained.

[0031] In the optical fiber cable 1 of this embodiment, a tear cord 7 is disposed between adjacent tension member groups 6a, 6b. The distance between adjacent tension member groups 6a, 6b is greater than the distance between adjacent tension members 4 belonging to one tension member group, so disposing the tear cord 7 between the tension member groups 6a, 6b makes it easier to dispose the tear cord 7 within the cable jacket 5. Furthermore, the tension members do not get in the way when tearing the jacket. Note that in the optical fiber cable of the present disclosure, tear cords do not need to be disposed between all adjacent tension member groups; it is sufficient that a tear cord is disposed between at least one of the adjacent tension member groups.

[0032] Next, an optical fiber cable 1a according to a comparative example will be described with reference to Fig. 2. Components common to the optical fiber cable 1 are assigned the same reference numerals and will not be described again. As shown in Fig. 2, in the optical fiber cable 1a according to the comparative example, tension members 4 are arranged along the circumferential direction of the cable jacket 5. Each of the tension member groups 16a and 16b includes five tension members 4. In the optical fiber cable 1a, the relationship between the distance D between the tension member groups 16a and 16b and the outer diameter R of the tension members 4 is D > 7R. Because the optical fiber cable 1a has the relationship D > 7R, the anisotropy in the bending direction of the cable is increased, and the pumping distance when introduced into a duct is shortened.

[0033] In the optical fiber cable configuration shown in Figure 1, multiple optical fiber cables with different shortest distances D between tension member groups were prepared, and each optical fiber cable was introduced into the following test route using a pumping device to measure the pumping distance. The outer diameter of the optical fiber cable was 13 mm. The tension members were made of aramid FRP, had a diameter of 0.5 mm, there were seven tension members, and there were two tension member groups. The ratio (D / R) of the shortest distance D between the tension member groups to the outer diameter R of the tension member of each optical fiber cable and the measurement results of the pumping distance are shown in Table 1. In Table 1, "TM" means tension member. (Test route) Total route length: 2200 m Circumference: 500 m Number of 90° curves per revolution: 8 Number of 180° curves per revolution: 2 Curve curvature radius: 1 m Duct inner diameter: 18 mm

[0034]

[0035] As shown in Table 1, optical fiber cables that satisfied the condition D≦7R had a good pumping distance of 700 m or more. From these results, it can be seen that by making the shortest distance D between tension member groups and the outer diameter R of the tension member satisfy the condition D≦7R, an optical fiber cable with small anisotropy in the bending direction and a long pumping distance can be obtained.

[0036] 1, 1a Optical fiber cable 3 Optical fiber core 4 Tension member 5 Cable jacket 6a, 6b Tension member group 7 Tear string 8 Water-absorbing tape 10 Storage space 16a, 16b Tension member group R Outer diameter of tension member D Shortest distance between adjacent tension member groups D1 Circumferential direction of cable jacket

Claims

1. An optical fiber cable comprising: a plurality of optical fiber cores; a cable sheath covering the plurality of optical fiber cores; and a plurality of tension member groups embedded in the cable sheath, each of the tension member groups including a plurality of tension members, wherein the plurality of tension member groups are arranged circumferentially around the cable sheath in a cross section perpendicular to the axial direction of the optical fiber cable, and wherein, when the outer diameter of the tension member is R, the shortest distance D between adjacent tension member groups among the plurality of tension member groups satisfies the condition 3R<D≦7R.

2. The optical fiber cable according to claim 1, wherein the number of said tension member groups is two.

3. An optical fiber cable as described in claim 1 or claim 2, wherein a tear cord is disposed between adjacent groups of tension members.

4. An optical fiber cable as described in any one of claims 1 to 3, wherein each of the multiple tension members included in the tension member group is not in contact with each other, and the shortest distance between adjacent tension members is 0.05 mm or more.

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