Fiber optic cable

Abstract

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 parts embedded in the cable sheath. The plurality of tension parts are arranged along the circumferential direction of the optical fiber cable, largely without a space therebetween, so as to surround the plurality of optical fiber cores.

Description

[Technical Field]

[0001] This disclosure relates to optical fiber cables. [Background technology]

[0002] As disclosed in Patent Document 1, optical fiber cables are known that are laid by air-pressure transport inside ducts such as microducts. In the air-pressure transport optical fiber cable disclosed in Patent Document 1, multiple tension members made of tensile strength material such as fiber-reinforced plastic (FRP) are embedded in the cable sheath in order to improve the stretchability of the optical fiber cable. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-197655 [Overview of the Initiative]

[0004] An optical fiber cable according to one aspect of the present disclosure comprises a plurality of optical fiber cores, a cable sheath covering the plurality of optical fiber cores, and a plurality of tension members embedded within the cable sheath. The plurality of tension members are arranged without gaps along the circumferential direction of the optical fiber cable so as to surround the plurality of optical fiber cores. [Brief explanation of the drawing]

[0005] [Figure 1] This is a cross-sectional view showing an example of an optical fiber cable according to the embodiments of this disclosure. [Figure 2] This figure schematically shows a side view of an optical fiber cable according to an embodiment of the present disclosure. [Figure 3] This is a cross-sectional view showing an example of a modified optical fiber cable. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] In the optical fiber cable described in Patent Document 1, four tension members are arranged at equal intervals of 90 degrees along the circumferential direction of the optical fiber cable. As a result, the spacing between adjacent tension members in the circumferential direction becomes wide, causing an unevenness in the radial bending stiffness of the optical fiber cable throughout its entire circumference. Consequently, the optical fiber cable becomes more prone to bending in a specific radial direction, which may cause it to buckle in the middle of the duct when being air-pressurized or pushed in. From this perspective, there is room for consideration of an optical fiber cable structure that can be suitably air-pressurized into a duct cable.

[0007] First, the contents of the embodiments of this disclosure will be listed and explained. (1) Multiple optical fiber cores, a cable sheath covering the multiple optical fiber cores, and the cable outer To embedded rectangular An optical fiber cable comprising a plurality of tension members, wherein the plurality of tension members are arranged without gaps along the circumferential direction of the optical fiber cable so as to surround the plurality of optical fiber cores. Ori , The plurality of tension members are twisted along the longitudinal direction of the optical fiber cable. Fiber optic cable.

[0008] According to the above configuration, multiple tension members are arranged without gaps along the circumferential direction of the optical fiber cable so as to surround multiple optical fiber cores. Therefore, unevenness in the radial bending stiffness of the optical fiber cable is effectively suppressed over the entire circumference of the optical fiber cable. As a result, situations in which the optical fiber cable is bent in a specific radial direction are effectively prevented, so that the optical fiber cable can be effectively pneumatically transported into a duct such as a microduct. Note that "multiple tension members are arranged without gaps" does not mean that there are absolutely no gaps between adjacent tension members. In this respect, there may be gaps of about 0.5 mm between adjacent tension members. Furthermore, with the above configuration, since multiple tension members are twisted along the longitudinal direction, the unevenness in the radial bending stiffness of the optical fiber cable is reduced. In this way, buckling and breakage of the optical fiber cable can be effectively suppressed.

[0009] (2) The optical fiber cable described in item (1), wherein the plurality of tension members are made of fiber-reinforced plastic.

[0010] With the above configuration, the optical fiber cable is lighter compared to when the tension member is made of a metal material, so the optical fiber cable can be suitably pumped under air pressure into the duct cable.

[0013] ( 3 ) The plurality of tension members comprises a plurality of inner tension members arranged along the circumferential direction so as to surround the plurality of optical fiber cores, and a plurality of outer tension members arranged along the circumferential direction so as to surround the plurality of inner tension members, item (1) or item( 2) The fiber optic cable described.

[0014] With the above configuration, since multiple inner tension members and multiple outer tension members are embedded in the cable sheath, it is possible to further increase the radial bending rigidity of the optical fiber cable, and it is also possible to further suppress the unevenness in the radial bending rigidity of the optical fiber cable around its entire circumference.

[0015] ( 4 The plurality of inner tension members are twisted in a first rotational direction along the longitudinal direction of the optical fiber cable, and the plurality of outer tension members are twisted in a second rotational direction opposite to the first rotational direction along the longitudinal direction, item ( 3 The fiber optic cable described in ).

[0016] With the above configuration, since the inner tension member and the outer tension member are twisted in different rotational directions, the unevenness in the radial bending stiffness of the optical fiber cable is further reduced. In this way, buckling and breakage of the optical fiber cable can be more effectively suppressed.

[0017] ( 5 ) The cable jacket has an inner cable jacket and an outer cable jacket covering the inner cable jacket, and the plurality of tension members are disposed between the inner cable jacket and the outer cable jacket. The outer cable jacket is made of flame-retardant polyethylene to which a lubricant is added, according to any one of items (1) to item ( 4 ) of the optical fiber cable described above.

[0018] According to the above configuration, since the outer cable jacket is made of flame-retardant polyethylene to which a lubricant is added, the flame retardancy of the optical fiber cable can be ensured, and the friction generated between the optical fiber cable and the inner surface of the duct can be reduced. Thus, while ensuring the flame retardancy of the optical fiber cable, the optical fiber cable can be suitably pneumatically conveyed into the duct. Here, the "lubricant" is added to the flame-retardant polyethylene for the purpose of reducing the friction on the surface of the cable jacket, not for the purpose of improving the extrusion processability. For example, a silicone-based material is used as the lubricant.

[0019] ( 6 ) The inner cable jacket is made of flame-retardant polyethylene to which no lubricant is added, according to item ( 5 ) described above of the optical fiber cable.

[0020] According to the above configuration, the inner cable jacket is made of flame-retardant polyethylene to which no flammable lubricant used for reducing the surface friction is added. Therefore, the flame retardancy of the inner cable jacket can be made higher than that of the outer cable jacket. Thus, the flame retardancy of the optical fiber cable as a whole can be sufficiently ensured.

[0021] ( 7 ) Over the entire circumference of the optical fiber cable, the bending rigidity in the radial direction of the optical fiber cable is 1.0 N·m 2 or more and 9.0 N·m 2 or less, according to any one of items (1) to item ( 6A fiber optic cable as described in any one of the items listed above.

[0022] According to the above configuration, the radial bending stiffness of the optical fiber cable is 1.0 N·m over its entire circumference. 2 More than 9.0N m 2 Since the following range is maintained, both the stretchability and flexibility of the optical fiber cable can be sufficiently ensured, and the optical fiber cable can be suitably transported under air pressure into the duct.

[0023] ( 8 ) The difference between the maximum and minimum values ​​of the radial bending stiffness of the optical fiber cable over its entire circumference is 0.5 N·m 2 More than 1.0N m 2 The range is as follows, from item (1) to item ( 7 A fiber optic cable as described in any one of the items listed above.

[0024] According to the above configuration, the unevenness in the radial bending stiffness of the optical fiber cable is suppressed throughout its entire circumference, thus effectively preventing the optical fiber cable from being bent in a specific radial direction. In this way, the optical fiber cable can be effectively air-pressurized into a duct such as a microduct.

[0025] [Effects of this disclosure] According to this disclosure, it is possible to provide an optical fiber cable that can suitably suppress the unevenness in the radial bending stiffness of the optical fiber cable over its entire circumference.

[0026] [Description of Embodiments in this Disclosure] Hereinafter, an optical fiber cable 1 according to an embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described with reference to Figure 1. The dimensions of each component shown in each drawing may differ from the actual dimensions of each component for the sake of explanation. In this embodiment, the X-axis direction, Y-axis direction, and Z-axis direction set for the optical fiber cable 1 shown in Figure 1 will be referred to as appropriate. Each of the X-axis direction, Y-axis direction, and Z-axis direction is perpendicular to the other two directions. For example, the X-axis direction is perpendicular to the Y-axis direction and the Z-axis direction. The Z-axis direction corresponds to the longitudinal direction (axial direction) of the optical fiber cable 1.

[0027] Figure 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 Figure 1 is perpendicular to the Z-axis direction of the optical fiber cable 1. As shown in Figure 1, the optical fiber cable 1 comprises a plurality of optical fiber ribbon cores 4, a plurality of tension members 2, a water-absorbing tape 6, and a cable sheath 7.

[0028] The optical fiber cable 1 is, for example, an optical fiber cable for pneumatic transport that is carried by air pressure inside a duct such as a microduct. Multiple optical fiber ribbons 4 are housed in a housing space S of the optical fiber cable 1. Each optical fiber ribbon has multiple optical fiber cores 3 arranged in parallel. Each optical fiber ribbon 4 may be an intermittently bonded type of optical fiber ribbon, for example, in which at least some of the adjacent optical fiber cores among the multiple optical fiber cores 3 arranged in parallel are intermittently bonded along the Z-axis direction. Note that for an intermittently bonded type of optical fiber ribbon, it is sufficient that the optical fiber cores are intermittently connected along the longitudinal direction, and the manufacturing method is not limited.

[0029] Multiple optical fiber ribbon fibers 4 extend along the Z-axis direction. In particular, the multiple optical fiber ribbon fibers 4 may be twisted spirally along the Z-axis direction. The type of twist may be S-twist, Z-twist, or SZ-twist, which alternates between S-twist and Z-twist.

[0030] The optical fiber core 3 comprises a glass fiber and a resin coating covering the glass fiber. The glass fiber has at least one core through which signal light propagates, and a cladding covering the core. The refractive index of the core is greater than the refractive index of the cladding. In this example, multiple optical fiber ribbons 4 are housed in the optical fiber cable 1, but instead of the optical fiber ribbons 4, multiple isolated single-core optical fiber cores 3 may be housed in the optical fiber cable 1.

[0031] Multiple tension members 2 are embedded within the cable sheath 7. As shown in Figure 2, the multiple tension members 2 extend along the Z-axis direction. In particular, the multiple tension members 2 may be twisted spirally along the Z-axis direction. In this case, because the multiple tension members 2 are twisted, the unevenness in the radial bending stiffness of the optical fiber cable 1 is reduced. In this way, buckling and breakage of the optical fiber cable 1 can be effectively suppressed.

[0032] In the cross-section of the optical fiber cable 1 shown in Figure 1, the multiple tension members 2 are arranged almost seamlessly along the circumferential direction D1 of the optical fiber cable 1, surrounding a bundle of multiple optical fiber ribbon cores 4 (or a bundle of multiple optical fiber cores 3). Here, the multiple tension members 2 may be arranged along the circumferential direction D1 without any gaps at all. In this case, adjacent tension members may be in contact with each other. Alternatively, the multiple tension members 2 may be arranged along the circumferential direction D1 with some gaps between them. In this case, the gap C between adjacent tension members 2 may be in the range of 0.1 mm to 1.0 mm.

[0033] The tension member 2 is made of a tensile strength material that has resistance to tension and compression. Specifically, the tension member 2 may be made of fiber-reinforced plastic (FRP) such as aramid FRP, glass FRP, or carbon FRP. When the tension member 2 is made of FRP, the optical fiber cable 1 is lighter compared to when the tension member 2 is made of a metal material, so the optical fiber cable 1 can be suitably air-fed into the duct.

[0034] In this example, the cross-section of each tension member 2 is approximately rectangular. When the cross-section of the tension member 2 is rectangular, the opposing sides of adjacent tension members 2 come into contact with each other, making it possible to arrange the tension members 2 without any gaps. Also, for example, if the inner diameter of the optical fiber cable 1 is 10.1 mm and the outer diameter of the optical fiber cable 1 is 13.5 mm, the width dimension of the tension member 2 may be 1.5 mm and the thickness dimension of the tension member 2 may be 0.5 mm. Note that the cross-section of the tension member 2 is not particularly limited and may be approximately elliptical, for example.

[0035] The length of the tension member 2 in the Z-axis direction may be shorter than the length of the optical fiber core 3 in the Z-axis direction. In this case, since there is excess length in each optical fiber core 3, the tension member 2 is loaded before excessive tension is generated in each optical fiber core 3 when the optical fiber cable 1 is pulled. This effectively prevents each optical fiber core 3 from breaking.

[0036] The absorbent tape 6 is wound around a bundle of multiple optical fiber ribbon cores 4 (or a bundle of multiple optical fiber cores 3), for example, by vertical or horizontal winding. The absorbent tape 6 is made of a base fabric made of polyester or the like, to which absorbent powder has been applied to give it absorbent properties. Although not shown in Figure 1, a coarse winding thread may also be wound around the bundle of multiple optical fiber ribbon cores 4.

[0037] The tear cord 8 is used to tear the cable sheath 7 and is embedded within the cable sheath 7. In this example, two tear cords 8 are provided inside the optical fiber cable 1. By pulling out the tear cords 8, the cable sheath 7 can be torn along the Z-axis, and as a result, the optical fiber core 3 can be extracted. The tear cord 8 is made of, for example, a plastic material that is resistant to tension (e.g., polyester).

[0038] The cable sheath 7 is provided to cover a bundle of multiple optical fiber ribbon cores 4 (or a bundle of multiple optical fiber cores 3). The cable sheath 7 is made of a flame-retardant resin such as flame-retardant polyethylene. In this embodiment, the cable sheath 7 is composed of an inner cable sheath 7b and an outer cable sheath 7a that covers the inner cable sheath 7b. In the radial direction of the optical fiber cable 1 (hereinafter simply referred to as the radial direction), each tension member 2 is positioned between the inner cable sheath 7b and the outer cable sheath 7a.

[0039] The inner cable sheath 7b is located radially between the water-absorbing tape 6 and the plurality of tension members 2, and is made of flame-retardant polyethylene without a silicone-based lubricant added, for example. The outer cable sheath 7a is provided to cover the plurality of tension members 2, and is made of flame-retardant polyethylene (particularly flame-retardant high-density polyethylene) with a silicone-based lubricant added. The silicone-based lubricant may be included in a proportion of 2 wt% or more, preferably 3 wt% to 5 wt%, relative to the flame-retardant polyethylene.

[0040] In this embodiment, the outer cable sheath 7a is made of flame-retardant polyethylene with added lubricant, thereby ensuring the flame retardancy of the optical fiber cable 1 and suppressing friction between the optical fiber cable 1 and the inner surface of the duct. In this way, the optical fiber cable 1 can be suitably air-pressurized into the duct while ensuring the flame retardancy of the optical fiber cable 1.

[0041] On the other hand, since the inner cable sheath 7b is made of flame-retardant polyethylene without added flammable lubricants, the flame retardancy of the inner cable sheath 7b can be further enhanced compared to the outer cable sheath 7a. In this way, sufficient flame retardancy of the optical fiber cable 1 as a whole can be ensured.

[0042] Furthermore, the manufacturing process for the optical fiber cable 1 begins with preparing a cable core consisting of a bundle of multiple optical fiber ribbon cores 4 and a water-absorbing tape 6. Next, with the cable core inserted into a first extruder, an inner cable sheath 7b covering the cable core is formed by extrusion molding using the first extruder. Subsequently, a winding device wraps multiple tension members 2 around the cable core so as to cover the outer circumference of the inner cable sheath 7b. Finally, with the cable core inserted into a second extruder, an outer cable sheath 7a covering the multiple tension members 2 is formed by extrusion molding using the second extruder. In this way, the optical fiber cable 1 shown in Figure 1 is manufactured through the above manufacturing process.

[0043] In this embodiment, multiple tension members 2 are arranged almost seamlessly along the circumferential direction D1 so as to surround a bundle of multiple optical fiber cores 3. Therefore, unevenness in the radial bending stiffness of the optical fiber cable 1 is effectively suppressed over the entire circumference of the optical fiber cable 1. As a result, situations in which the optical fiber cable 1 is bent in a specific radial direction are effectively prevented, allowing the optical fiber cable 1 to be effectively air-pressurized into a duct such as a microduct.

[0044] Furthermore, in this embodiment, the radial bending rigidity is 1.0 N·m over the entire circumference of the optical fiber cable 1. 2 More than 9.0N m 2 Since the values ​​fall within the following range, both the stretchability and flexibility of the optical fiber cable 1 can be sufficiently ensured, and the optical fiber cable 1 can be suitably pumped into the duct under air pressure. The measurement of the bending stiffness value conforms to IEC60794 Stiffness (Method E17A).

[0045] Furthermore, the difference between the maximum value and the minimum value of the radial bending stiffness over the entire circumference of the optical fiber cable 1 is 0.5 N·m 2 or more and 1.0 N·m 2 or less, and the deviation of the radial bending stiffness is suppressed. For this reason, a situation where the optical fiber cable 1 is bent in a specific radial direction (particularly, the radial direction in which the bending stiffness is small) is preferably prevented, and the optical fiber cable 1 can be preferably pneumatically conveyed in the duct.

[0046] (Modified Example) Next, referring to FIG. 3, the optical fiber cable 1a according to a modified example of the present embodiment will be described below. FIG. 3 is a cross-sectional view showing an example of the optical fiber cable 1a according to the modified example. The cross-section of the optical fiber cable 1a shown in FIG. 3 is a cross-section perpendicular to the Z-axis direction of the optical fiber cable 1a. In the following description, the description of members having the same reference numerals as those already described in the above embodiment will be omitted as appropriate.

[0047] As shown in FIG. 3, the optical fiber cable 1a is different from the optical fiber cable 1 in that the tension member has a two-layer structure. In this regard, the tension member 20 has a plurality of inner tension members 20b and a plurality of outer tension members 20a. The plurality of inner tension members 20b are arranged along the circumferential direction D1 so as to surround a bundle of a plurality of optical fiber cores 3. The plurality of outer tension members 20a are arranged along the circumferential direction D1 so as to surround the plurality of inner tension members 20b.

[0048] The inner tension member 20b and the outer tension member 20a are embedded within the cable sheath 7. The inner tension member 20b and the outer tension member 20a extend along the Z-axis direction. In particular, the inner tension member 20b and the outer tension member 20a may be twisted spirally along the Z-axis direction. In this respect, the inner tension member 20b is twisted in either a clockwise or counterclockwise direction (an example of a first rotation direction), while the outer tension member 20a is twisted in the other clockwise or counterclockwise direction (an example of a second rotation direction). That is, the direction of twist of the inner tension member 20b is opposite to the direction of twist of the outer tension member 20a. In this way, because the inner tension member 20b and the outer tension member 20a are twisted in different directions, the bias in the radial bending stiffness of the optical fiber cable 1a is reduced. Therefore, buckling and breakage of the optical fiber cable 1a can be more effectively suppressed.

[0049] The distance between each inner tension member 20b and the inner surface 72 of the cable sheath 7 in the radial direction (hereinafter simply referred to as the radial direction) of the optical fiber cable 1a is shorter than the distance between each outer tension member 20a and the inner surface 72. That is, the inner tension members 20b are located radially inward from the outer tension members 20a. Along the circumferential direction D1, the inner tension members 20b and outer tension members 20a are arranged alternately. That is, each inner tension member 20b is adjacent to two outer tension members 20a in the circumferential direction D1, while each outer tension member 20a is adjacent to two inner tension members 20b in the circumferential direction D1.

[0050] Multiple inner tension members 20b and outer tension members 20a are arranged almost seamlessly along the circumferential direction D1. However, the multiple inner tension members 20b and outer tension members 20a may be arranged without any gaps along the circumferential direction D1. In this case, adjacent inner tension members 20b and outer tension members 20a may be in contact with each other. Also, adjacent inner tension members 20b and outer tension members 20a may partially overlap radially in the circumferential direction D1. Furthermore, the multiple inner tension members 20b and outer tension members 20a may be arranged along the circumferential direction D1 with some gaps between them. In this case, the gap C1 may be in the range of 0.1 mm to 1.0 mm.

[0051] The cross-sectional shape of the inner tension member 20b may be the same as or different from the cross-sectional shape of the outer tension member 20a. Similarly, the dimensions of the cross-sectional shape of the inner tension member 20b may be the same as or different from the dimensions of the cross-sectional shape of the outer tension member 20a.

[0052] According to this modified example, since the multiple inner tension members 20b and outer tension members 20a are arranged almost without gap along the circumferential direction D1, the unevenness in radial bending stiffness over the entire circumference of the optical fiber cable 1a is effectively suppressed. As a result, situations in which the optical fiber cable 1a is bent in a specific radial direction are effectively prevented, allowing the optical fiber cable 1 to be effectively pneumatically transported into a duct such as a microduct.

[0053] Although this embodiment has been described above, it goes without saying that the technical scope of this disclosure should not be interpreted restrictively by the description of the embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications to the embodiment are possible within the scope of the invention described in the claims. Thus, the technical scope of this disclosure should be determined based on the scope of the invention described in the claims and the scope of its equivalents. [Explanation of Symbols]

[0054] 1, 1a: Fiber optic cable 2: Tension member 3: Optical fiber core 4: Fiber optic ribbon 6: Absorbent tape 7: Cable sheath 7a: Outer cable jacket 7b: Inner cable outer sheath 8: Tear cord 20: Tension member 20a: Outer tension member 20b: Internal tension member 72: Inner self D1: Circumferential direction S: Containment space

Claims

1. Multiple optical fiber cores, A cable sheath covering the plurality of optical fiber cores, Multiple rectangular tension members embedded in the cable sheath, A fiber optic cable equipped with, The plurality of tension members are arranged without gaps along the circumferential direction of the optical fiber cable so as to surround the plurality of optical fiber cores. The plurality of tension members are twisted along the longitudinal direction of the optical fiber cable. Fiber optic cable.

2. The aforementioned plurality of tension members are made of fiber-reinforced plastic. The optical fiber cable according to claim 1.

3. The plurality of tension members are, A plurality of inner tension members arranged along the circumferential direction so as to surround the plurality of optical fiber cores, A plurality of outer tension members are arranged along the circumferential direction so as to surround the plurality of inner tension members, Equipped with, The optical fiber cable according to claim 1 or claim 2.

4. The plurality of internal tension members are twisted in a first rotational direction along the longitudinal direction of the optical fiber cable. The plurality of outer tension members are twisted along the longitudinal direction in a second rotational direction opposite to the first rotational direction. The optical fiber cable according to claim 3.

5. The cable sheath is, The inner cable sheath and, The outer cable sheath covers the inner cable sheath, It has, The plurality of tension members are arranged between the inner cable sheath and the outer cable sheath. The outer cable sheath is made of flame-retardant polyethylene to which a lubricant has been added. An optical fiber cable according to any one of claims 1 to 4.

6. The inner cable sheath is made of flame-retardant polyethylene without added lubricant. The optical fiber cable according to claim 5.

7. The radial bending stiffness of the optical fiber cable is 1.0 N·m along its entire circumference. ２ 9.0N・m or more ２ The following range: An optical fiber cable according to any one of claims 1 to 6.

8. The difference between the maximum and minimum values ​​of the radial bending stiffness of the optical fiber cable over its entire circumference is 0.5 N·m ２ 1.0N・m or more ２ The following range: An optical fiber cable according to any one of claims 1 to 7.

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