Optical fiber cable

Abstract

This optical fiber cable comprises: a cable core that includes a plurality of optical fiber core wires; a plurality of tensile bodies that are arranged along the cable core; and an outer sheath that covers the cable core and encloses the tensile bodies. The tensile bodies each have an exposed part that is exposed from the outer sheath to the inside of the cable core. In a cross-sectional view of the optical fiber cable, the exposed part includes a portion where a line segment connecting the center of the tensile body and the center of the optical fiber cable intersects with the outer periphery of the tensile body, and the plurality of tensile bodies are arranged on a diagonal line.

Description

Optical fiber cable

[0001] This disclosure relates to an optical fiber cable. This application claims priority based on Japanese Application No. 2024-221363 filed on December 18, 2024, and incorporates all the descriptions set forth in the said Japanese application.

[0002] Patent Document 1 discloses an optical fiber cable including a cable core containing a plurality of optical fiber cores, a tensile strength member, and an outer sheath covering the cable core. In this optical fiber cable, a tension member as the tensile strength member is enclosed in the outer sheath.

[0003] Japanese Patent Application Laid-Open No. 2023-73421

[0004] The optical fiber cable of the present disclosure is an optical fiber cable comprising a cable core containing a plurality of optical fiber cores, a plurality of tensile strength members arranged along the cable core, and an outer sheath covering the cable core and enclosing the tensile strength members, wherein the tensile strength member has an exposed portion exposed from the outer sheath to the inside of the cable core, and the exposed portion includes a portion where a line segment connecting the center of the tensile strength member and the center of the optical fiber cable intersects with the outer periphery of the tensile strength member in a cross-sectional view of the optical fiber cable, and the plurality of tensile strength members are arranged diagonally.

[0005] FIG. 1 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable according to a comparative example. FIG. 3 is a diagram for explaining the problems of the optical fiber cable according to the comparative example shown in FIG. 2. FIG. 4 is a cross-sectional view for explaining a state in which an external pressure is applied to the optical fiber cable according to an embodiment of the present disclosure. FIG. 5 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable according to a modified example of the embodiment of the present disclosure. FIG. 6 is a diagram for explaining the situation when the optical fiber cable shown in FIG. 5 is bent.

[0006] External pressure may be applied to the optical fiber cable along the direction connecting the tensile strength material enclosed within the outer sheath to the vicinity of the optical fiber cable's center. In such cases, the tensile strength material presses against the outer sheath between the tensile strength material and the cable core, and if the outer sheath in this area is thin, damage such as cracks may occur. Furthermore, the part of the outer sheath where the tensile strength material is located is difficult to bend, so if the tensile strength material is unevenly distributed in the outer sheath of the optical fiber cable, the direction in which it bends will not be determined, which may make the optical fiber cable difficult to handle.

[0007] This disclosure aims to provide an optical fiber cable that is easy to handle and can prevent damage to its outer sheath when external pressure is applied to the optical fiber cable.

[0008] According to this disclosure, the cable is easy to handle and can prevent damage to the outer sheath when external pressure is applied to the optical fiber cable.

[0009] First, embodiments of the present disclosure will be listed and described. (1) An optical fiber cable according to an embodiment of the present disclosure is an optical fiber cable comprising: a cable core including a plurality of optical fiber cores; a plurality of tensile strength members arranged along the cable core; and an outer sheath covering the cable core and enclosing the tensile strength members, wherein the tensile strength members have exposed portions that are exposed from the outer sheath into the interior of the cable core, and the exposed portions include a portion where, in a cross-sectional view of the optical fiber cable, a line segment connecting the center of the tensile strength member and the center of the optical fiber cable intersects with the outer circumference of the tensile strength member, and the plurality of tensile strength members are arranged diagonally.

[0010] With this configuration, even if external pressure is applied to the optical fiber cable along the direction connecting the center of the tensile strength body to the vicinity of the center of the optical fiber cable, there is no outer sheath between the cable core and the tensile strength body. This prevents the tensile strength body from pressing against the outer sheath between itself and the cable core, thus preventing damage to the outer sheath. Furthermore, the optical fiber cable is easily bent around an axis centered on the diagonal where the multiple tensile strength bodies are arranged, making the optical fiber cable easier to handle.

[0011] (2) In the optical fiber cable described in (1) above, the width of the exposed portion relative to the outer circumference of the cable core in a cross-sectional view of the optical fiber cable may be in the range of 0.5% to 6%.

[0012] This configuration prevents the tensile strength member from pressing against the sheath between itself and the cable core, and also prevents the tensile strength member from completely detaching from the sheath.

[0013] (3) In either of the optical fiber cables described in (1) or (2) above, the outer sheath may be made of a flame-retardant material.

[0014] This configuration makes it possible to obtain a fiber optic cable structure that is resistant to combustion. Furthermore, although flame retardancy decreases as the outer sheath becomes thinner, in the parts of the outer sheath where the tensile strength material is placed, the tensile strength material is exposed inside the cable core as described above, and the outer sheath made of flame retardant material is thicker in the parts where the tensile strength material is placed, so the flame retardancy does not decrease easily.

[0015] (4) In any of the optical fiber cables described in (1) to (3) above, the thickness of the outer sheath may be 2.5 mm or more in a cross-sectional view of the optical fiber cable.

[0016] This configuration prevents the outer sheath from becoming too thin in the areas where the tensile strength material is placed, resulting in a fiber optic cable structure that is less prone to burning.

[0017] (5) In any of the optical fiber cables described in (1) to (4) above, the distance between the outer circumference of the outer sheath and the tensile strength member in a cross-sectional view of the optical fiber cable may be 0.8 mm or more.

[0018] This configuration makes it possible to obtain a fiber optic cable structure that is less prone to burning.

[0019] Specific examples of the optical fiber cables of this disclosure will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to include all modifications within the meaning and scope of the claims as indicated by the claims.

[0020] [Configuration of the Optical Fiber Cable] Figure 1 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 1 according to an embodiment of the present disclosure. The optical fiber cable 1 is, for example, a slotless optical fiber cable for pneumatic transmission. As shown in Figure 1, the optical fiber cable 1 comprises a cable core 11, a plurality of tensile strength members 12, and an outer sheath 13. The optical fiber cable 1 is substantially circular in cross-sectional view.

[0021] The cable core 11 is approximately circular in cross-section. The cable core 11 also includes a plurality of optical fiber ribbons 10 and a retaining tape 14 that covers the plurality of optical fiber ribbons 10. The cable core 11 shown in Figure 1 has, as an example, 36 optical fiber ribbons 10. Each optical fiber ribbon 10 includes, for example, 12 optical fiber cores 21.

[0022] In each optical fiber ribbon 10, multiple optical fiber cores 21 are arranged in parallel in a direction perpendicular to the longitudinal direction of the optical fiber ribbon 10. For example, in these multiple optical fiber cores 21, connecting portions where adjacent optical fiber cores 21 are connected and unconnected portions where adjacent optical fiber cores 21 are not connected are intermittently provided along the longitudinal direction. Each optical fiber ribbon 10 is housed in a rolled-up state when viewed in cross-section.

[0023] The outer sheath 13 covers the cable core 11 from the outside and encloses a plurality of tensile strength members 12. The outer sheath 13 is made of, for example, polyethylene resin. The plurality of tensile strength members 12 are arranged along the cable core 11. The tensile strength members 12 are circular in cross-section. Note that "enclosed" includes not only the state in which all of the tensile strength members 12 are contained within the outer sheath 13, but also the state in which only a portion of the tensile strength members 12 are contained within the outer sheath 13.

[0024] The tensile strength member 12 is formed from, for example, a flammable fiber-reinforced plastic (FRP). Specifically, the tensile strength member 12 is formed from fiber-reinforced plastics such as aramid FRP, glass FRP, or carbon FRP. This makes it possible to obtain an optical fiber cable structure using a tensile strength member 12 that is relatively rigid and resistant to buckling.

[0025] Each tensile strength member 12 has an exposed portion 22 that is exposed from the outer sheath 13 into the interior of the cable core 11. In a cross-sectional view of the optical fiber cable 1, this exposed portion 22 includes the intersection A1 of the outer circumference of the tensile strength member 12 with the line segment L1 connecting the center O1 of the tensile strength member 12 and the center O2 of the optical fiber cable 1. Alternatively, the tensile strength member 12 may be positioned such that the exposed portion 22 including the intersection A1 is located closer to the center O2 of the optical fiber cable 1 than to the outer circumference of the cable core 11. As a result, a portion of the retaining tape 14 on the cable core 11 protrudes closer to the center O2 of the optical fiber cable 1.

[0026] Furthermore, it is preferable that the tensile strength member 12 is exposed inside the cable core 11 along its entire length in the longitudinal direction. If the exposed portion 22 is provided intermittently along the longitudinal direction of the cable core 11, there is a risk of injury in the unexposed areas.

[0027] The outer sheath 13 may be formed such that its thickness W1 is 2.5 mm or more in a cross-sectional view of the optical fiber cable 1. This thickness W1 of the outer sheath 13 prevents the outer sheath 13 from becoming too thin in the area where the tensile strength member 12 is located, thereby obtaining an optical fiber cable structure that is less prone to burning.

[0028] Furthermore, the outer sheath 13 may be formed such that, in a cross-sectional view of the optical fiber cable 1, the distance W2 between the outer circumference of the outer sheath 13 and the tensile strength member 12 is, for example, 0.8 mm or more. With such a thickness W2, an optical fiber cable structure that is less prone to burning can be obtained.

[0029] Furthermore, the outer sheath 13 may be formed from a flame-retardant material. For example, the outer sheath 13 can be formed from a flame-retardant polyethylene resin. As the flame-retardant polyethylene resin, for example, flame-retardant polyethylene with an oxygen index (minimum oxygen concentration required for continued combustion) of 35 or higher as specified in JIS K7201 can be used. Note that the flame retardancy decreases as the outer sheath 13 becomes thinner, but in the part of the outer sheath 13 where the tensile strength member 12 is placed, the flame retardancy does not decrease easily because the tensile strength member 12 is exposed inside the cable core 11 as described above.

[0030] Multiple tensile strength members 12 are arranged at two locations on the diagonal in a cross-sectional view of the optical fiber cable 1. In this example, one tensile strength member 12 is arranged at each of the two diagonal locations.

[0031] Here, the portion of the outer sheath 13 where the tensile strength members 12 are located is difficult to bend. If multiple tensile strength members 12 are unevenly arranged, the direction in which the cable bends easily is not determined, which may make the optical fiber cable 1 difficult to handle. In contrast, as shown in Figure 1, if multiple tensile strength members 12 are arranged diagonally in a cross-sectional view of the optical fiber cable 1, the optical fiber cable 1 is easily bent around an axis centered on the diagonal where the multiple tensile strength members 12 are located, making the optical fiber cable 1 easier to handle.

[0032] [Effects on the outer sheath when external pressure is applied to the optical fiber cable] (In the case of the optical fiber cable according to the comparative example) Figure 2 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 51 according to the comparative example. Figure 3 is a diagram for explaining the problems of the optical fiber cable 51 according to the comparative example shown in Figure 2. As shown in Figure 2, in the optical fiber cable 51 according to the comparative example, the entire tensile strength member 12 is enclosed in the outer sheath 13.

[0033] In such an optical fiber cable 51, as shown by the arrow in Figure 3, when external pressure is applied along the direction connecting the tensile strength member 12 and the vicinity of the center of the optical fiber cable 51, the tensile strength member 12 presses against the outer sheath 13 between it and the cable core 11. Therefore, if the outer sheath 13 in the area pressed by the tensile strength member 12 is thin, damage such as cracks may occur in that area.

[0034] (In the case of the optical fiber cable according to the present disclosure) Figure 4 is a cross-sectional view illustrating the state in which external pressure is applied to the optical fiber cable 1 according to an embodiment of the present disclosure. In the optical fiber cable 1 according to the present disclosure, as described above, the exposed portion 22 of the tensile strength member 12 is exposed from the outer sheath 13 into the interior of the cable core 11. That is, there is no outer sheath 13 between the tensile strength member 12 and the cable core 11. Therefore, as shown by the arrow in Figure 4, even when external pressure is applied toward the center of the optical fiber cable 1, cracks in the outer sheath 13 can be prevented.

[0035] Referring again to Figure 1, in a cross-sectional view of the optical fiber cable 1, the width D1 of the exposed portion 22 relative to the outer circumference of the cable core 11 should ideally be within the range of 0.5% to 6%. For example, if the outer diameter of the tensile strength member 12 is 1.8 mm and the outer diameter R1 of the cable core 11 is 11 mm, the width D1 of the exposed portion 22 is formed to be within the range of 0.2 mm to 2.1 mm, that is, within the range of approximately 0.5% to approximately 6% relative to the outer circumference of the cable core 11 (= 11 mm × π). This prevents the tensile strength member 12 from pressing against the sheath 13 between itself and the cable core 11, and also prevents the tensile strength member 12 from completely falling out of the sheath 13. Note that the outer diameter of the tensile strength member 12 is larger than the width D1 of the exposed portion 22.

[0036] [Modified Example] Figure 5 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 31 according to a modified example of the embodiment of the present disclosure. As shown in Figure 5, the number of tensile strength members 12 provided at one location in the cross-sectional view of the optical fiber cable 31 is not limited to one, but may be multiple. In the example shown in Figure 5, two tensile strength members 12 are arranged at one location in the cross-sectional view of the optical fiber cable 31.

[0037] Thus, even when multiple tensile strength members 12 are arranged at one location in a cross-sectional view of the optical fiber cable 31, each tensile strength member 12 has an exposed portion 22 that is exposed from the outer sheath 13 into the interior of the cable core 11, similar to the optical fiber cable 1 shown in Figure 1. In this case as well, each exposed portion 22 includes the intersection of the line segment connecting the center of the tensile strength member 12 and the center of the optical fiber cable 31 and the outer circumference of the tensile strength member 12. This prevents cracks in the outer sheath 13 even when external pressure is applied toward the center of the optical fiber cable 31. Furthermore, since the optical fiber cable 31 is easily bent around an axis that is the axis of the diagonal line in which the multiple tensile strength members 12 are arranged, the optical fiber cable 31 is easy to handle.

[0038] [Example] The optical fiber cable configured as described above was subjected to impact tests, combustion tests, and small-diameter bending tests in a high-temperature, high-humidity environment.

[0039] Specifically, as shown in Figure 1, an optical fiber cable 1 was fabricated with an outer diameter of 16.4 mm, a thickness W1 of 2.6 mm for the outer sheath 13 made of flame-retardant polyethylene, an outer diameter of 1.8 mm for the tensile strength member 12, and a thickness W2 of 0.9 mm between the outer circumference of the outer sheath 13 and the tensile strength member 12 (0.1 mm of the tensile strength member 12 exposed inside the cable core 11). Inside the cable core 11 of this optical fiber cable 1, twelve units were housed, each consisting of six bundles of optical fiber ribbons 10, each containing 12 optical fiber cores (i.e., a total of 864 optical fiber cores). Impact tests, combustion tests, and small-diameter bending tests under high temperature and high humidity conditions were performed on the optical fiber cable 1 fabricated in this manner.

[0040] Furthermore, as a comparative example shown in Figure 2, an optical fiber cable 51 was fabricated that had the same configuration as the optical fiber cable 1 described above, except that the entire tensile strength member 12 was enclosed within the outer sheath 13, and an impact test and a combustion test were performed on it.

[0041] Further, as the optical fiber cable 31 shown in FIG. 5, an optical fiber cable 31 having the same configuration as the above-described optical fiber cable 1 except that two tensile strength members 12 are arranged at one location was fabricated, and a small-diameter bending test was conducted in a high-temperature and high-humidity environment.

[0042] [Impact Test] In the impact test, the presence or absence of cracks in the outer sheath 13 when external pressure was applied to the optical fiber cable was confirmed. Specifically, an impact energy of 4.4 N·m (the energy when a 3-kg weight was dropped from a height of 0.15 m) was applied, and the presence or absence of cracks was confirmed. In the structure of the optical fiber cable 51 shown in FIG. 2, cracks occurred in the outer sheath 13. In the structure of the optical fiber cable 1 shown in FIG. 1, cracks did not occur in the outer sheath 13.

[0043] [Combustion Test] In the combustion test, a combustion test by a riser combustion test (applicable safety standard UL1666) was carried out. In the structure of the optical fiber cable 51 shown in FIG. 2, the maximum flame height was 185 cm and the maximum temperature was 235.6°C. In the structure of the optical fiber cable 1 shown in FIG. 1, the maximum flame height was 155 cm and the maximum temperature was 215.0°C. Thereby, it was found that the optical fiber cable 1 shown in FIG. 1 has lower maximum flame height and maximum temperature and higher flame retardancy compared with the optical fiber cable 51 shown in FIG. 2.

[0044] [Small-Diameter Bending Test in a High-Temperature and High-Humidity Environment] In the small-diameter bending test, in an environment of a temperature of 85°C and a humidity of 85%, the presence or absence of cracks after bending the optical fiber cable around an axis with a diameter of 60 cm and leaving it for 24 hours was confirmed. Also, in an environment of a temperature of 85°C and a humidity of 85%, the presence or absence of cracks after bending the optical fiber cable around an axis with a diameter of 30 cm and leaving it for 24 hours was confirmed. As shown in FIG. 6, the optical fiber cable was bent around an axis along the diagonal line where the tensile strength member was arranged.

[0045] When the optical fiber cable was bent with a diameter of 60 cm, no cracks occurred in the outer sheath 13 in both the optical fiber cable 1 shown in FIG. 1 and the optical fiber cable 31 shown in FIG. 5. On the other hand, when the optical fiber cable was bent with a diameter of 30 cm, no cracks occurred in the outer sheath 13 in the optical fiber cable 1 shown in FIG. 1, but cracks occurred in the outer sheath 13 in the optical fiber cable 31 shown in FIG. 5.

[0046] Here, when the optical fiber cable 31 shown in FIG. 6 is bent around an axis along the diagonal line where the tension member 12 is arranged, the tension member 12 is located on the inner side or the outer side of the bend. Also, tensile strain due to bending occurs in the portion of the outer sheath 13 located on the outer side of the bend of the optical fiber cable 31. When the optical fiber cable 31 in such a state is left in a high-temperature and high-humidity environment, the outer sheath 13 becomes soft, and the portion of the outer sheath 13 where tensile strain has occurred cannot hold the tension member 12. In particular, when the optical fiber cable 31 is bent with a diameter of 30 cm, the tensile strain generated in the portion of the outer sheath 13 located on the outer side of the bend is larger than when the optical fiber cable 31 is bent with a diameter of 60 cm. Therefore, in the optical fiber cable 31 shown in FIG. 5, it is considered that cracks occurred in the outer sheath 13 when bent with a diameter of 30 cm.

[0047] In contrast, in the optical fiber cable 1 shown in FIG. 1, one tension member 12 is arranged at one location on the diagonal line. When the optical fiber cable 1 is bent around an axis along the diagonal line, the tension member 12 is located at the center of the bend. That is, since the tension member 12 is not located on the inner side or the outer side of the bend within the outer sheath 13, even if the outer sheath 13 becomes soft in a high-temperature and high-humidity environment, the outer sheath 13 can hold the tension member 12, and it is considered that no cracks occurred in the outer sheath 13.

[0048] As described above, the present disclosure has been described based on specific embodiments, but the present invention is not limited to these examples, and is intended to be shown by the claims and to include all modifications within the meaning and scope equivalent to the claims.

[0049] It should be understood that at least one configuration or feature described in each embodiment and example can be combined with other embodiments and examples, or modified in various ways.

[0050] In the optical fiber cable 31 shown in Figure 5, there are two tensile strength members 12 at one location, but there may be three or more.

[0051] In the optical fiber cable 1 shown in Figure 1 and the optical fiber cable 31 shown in Figure 5, multiple tensile strength members 12 are arranged along one diagonal. However, in the optical fiber cable of this disclosure, the multiple tensile strength members 12 may be arranged along two or more diagonals. For example, in the optical fiber cable 1 shown in Figure 1, in addition to the multiple tensile strength members 12 arranged along the diagonal extending vertically, there may also be multiple tensile strength members 12 arranged along the diagonal extending horizontally.

[0052] 1, 31, 51 Optical fiber cable 10 Optical fiber ribbon 11 Cable core 12 Tensile strength member 13 Outer sheath 14 Retaining tape 21 Optical fiber core 22 Exposed portion A1 Intersection D1 Width of exposed portion L1 Line segment connecting the center of the tensile strength member and the center of the optical fiber cable O1 Center of the tensile strength member O2 Center of the optical fiber cable R1 Outer diameter of the cable core W1 Thickness of the outer sheath W2 Distance between the outer circumference of the outer sheath and the tensile strength member

Claims

1. An optical fiber cable comprising: a cable core containing a plurality of optical fiber cores; a plurality of tensile strength members arranged along the cable core; and an outer sheath covering the cable core and enclosing the tensile strength members, wherein the tensile strength members have exposed portions that are exposed from the outer sheath into the interior of the cable core, and the exposed portions include a portion where, in a cross-sectional view of the optical fiber cable, a line segment connecting the center of the tensile strength member and the center of the optical fiber cable intersects with the outer circumference of the tensile strength member, and the plurality of tensile strength members are arranged diagonally.

2. The optical fiber cable according to claim 1, wherein, in a cross-sectional view of the optical fiber cable, the width of the exposed portion relative to the outer circumference of the cable core is in the range of 0.5% to 6%.

3. The optical fiber cable according to claim 1 or claim 2, wherein the outer sheath is formed of a flame-retardant material.

4. The optical fiber cable according to any one of claims 1 to 3, wherein, in a cross-sectional view of the optical fiber cable, the thickness of the outer sheath is 2.5 mm or more.

5. The optical fiber cable according to any one of claims 1 to 4, wherein, in a cross-sectional view of the optical fiber cable, the distance between the outer circumference of the outer sheath and the tensile strength body is 0.8 mm or more.

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