Optical fiber cable

Abstract

To provide an optical fiber cable that can lengthen a pressure-feeding distance while making a sheath hard to be damaged and that is reduced in diameter.SOLUTION: An optical fiber cable comprises: a cable core including a plurality of coated optical fibers; at least one tension member disposed along an axis of the cable core; and a sheath covering the cable core from the outside and incorporating the tension member. In a cross-sectional view orthogonal to an axis of the optical fiber cable, the sheath is set to be flat so that a long axis thereof overlaps a position where the tension members are disposed relative to the cable core. A circularity ratio of an outer diameter of the cable core is larger than a circularity ratio of a surface layer of the sheath and, in the cross-sectional view, the circularity ratio of the surface layer of the sheath is 85% or more and 96% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an optical fiber cable that is laid in a duct such as a microduct by an air pumping method. In the optical fiber cable of Patent Document 1, the roundness of the surface layer of the jacket is 85% or more in a cross section perpendicular to the axis of the optical fiber cable. This configuration improves the airtightness between the optical fiber cable and the inner surface of the cable insertion tube of the cable pumping machine, thereby enabling the pumping distance of the optical fiber cable to be extended. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 120478 Summary of the Invention [Problem to be solved by the invention]

[0004] In optical fiber cables whose jackets contain tension members (hereinafter also referred to as TMs), the thickness of the jacket between the tension members and the outer layer of the jacket (hereinafter referred to as the TM outer jacket) in the direction from the tension members to the outer layer of the jacket in a cross-sectional view perpendicular to the axis of the optical fiber cable must be thicker than the thickness specified by the standard. Furthermore, when pressure is applied to the optical fiber cable from the outside, the tension members may press against the jacket between the tension members and the cable core in the direction from the tension members to the cable core in a cross-sectional view (hereinafter referred to as the TM inner jacket). If the TM inner jacket becomes too thin, damage such as cracks may occur.

[0005] Furthermore, if the overall thickness of the outer sheath is increased in order to make the TM outer sheath and the TM inner sheath thicker than a predetermined thickness, the average outer diameter of the cable will increase, making it difficult to reduce the diameter of the cable.

[0006] An object of the present disclosure is to provide a thin-diameter optical fiber cable whose outer sheath is less susceptible to damage and whose pumping distance can be extended. [Means for solving the problem]

[0007] The optical fiber cable of the present disclosure is an optical fiber cable comprising: a cable core containing a plurality of optical fiber cores; at least one strength member arranged along the axis of the cable core; and an outer jacket that covers the cable core from the outside and encloses the strength member, wherein, in a cross-sectional view perpendicular to the axis of the optical fiber cable, the outer jacket is flattened so that its long axis overlaps with the position where the strength member is arranged relative to the cable core, the circularity of the outer diameter of the cable core is greater than the circularity of the surface layer of the outer jacket, and the circularity of the surface layer of the outer jacket is 85% or more and 96% or less in the cross-sectional view. [Effects of the Invention]

[0008] According to the present disclosure, a thin-diameter optical fiber cable is provided, the outer jacket of which is less susceptible to damage and which allows for an extended pumping distance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of an optical fiber cable according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Description of one embodiment of the present disclosure) First, embodiments of the present disclosure will be listed and described. (1) An optical fiber cable according to one embodiment of the present disclosure includes: An optical fiber cable comprising: a cable core containing a plurality of optical fiber cores; at least one strength member arranged along the axis of the cable core; and an outer jacket that covers the cable core from the outside and encases the strength member, wherein, in a cross-sectional view perpendicular to the axis of the optical fiber cable, the outer jacket is flattened so that its major axis coincides with the position where the strength member is arranged relative to the cable core, the circularity of the outer diameter of the cable core is greater than the circularity of the surface layer of the outer jacket, and the circularity of the surface layer of the outer jacket is 85% or more and 96% or less in the cross-sectional view.

[0011] According to the present disclosure, the jacket is flattened so that its major axis overlaps the position where the strength members are located relative to the cable core in a cross-sectional view. The circularity of the outer diameter of the cable core is greater than the circularity of the surface layer of the jacket (hereinafter also referred to as the circularity of the jacket), and the circularity of the jacket is 96% or less. This allows the TM outer jacket to be thicker than the thickness specified by the standard. Furthermore, the TM inner jacket can also be thickened, making the TM inner jacket less likely to be damaged even when pressure is applied from the outside. Since the circularity of the jacket is 85% or more, the airtightness between the cable and the inner surface of the cable insertion tube of the cable pumping machine is less likely to be impaired, thereby extending the pumping distance. Furthermore, compared to when the circularity of the outer diameter of the cable core and the circularity of the jacket are both large, the jacket is thicker only at the locations where the strength members are located, resulting in a thinner average jacket thickness and making it easier to reduce the cable diameter.

[0012] (2) In the above (1), the tension members may be arranged at two locations facing each other across the cable core in the cross-sectional view.

[0013] According to the present disclosure, the outer diameter of the tension members can be made smaller than when the tension members are arranged in one location, making it easier to further reduce the diameter of the cable.

[0014] (3) In the above (1) or (2), the outer jacket may be made of high-density polyethylene.

[0015] According to the present disclosure, since the outer jacket is formed from high-density polyethylene, the mechanical strength of the outer jacket is high and the outer jacket is resistant to crushing.

[0016] (4) In any one of the above (1) to (3), the tension members may be made of fiber-reinforced plastic, and the outer diameter of the tension members may be 1.9 mm or less.

[0017] According to the present disclosure, since the tension members are formed from fiber reinforced plastic, the strength of the optical fiber cable can be increased even when the outer diameter of the tension members is as small as 1.9 mm or less.

[0018] [Details of the embodiment] An optical fiber cable 1 according to an embodiment of the present disclosure (hereinafter referred to as the present embodiment) will be described below with reference to Fig. 1. For the sake of convenience, the dimensions of each component shown in each drawing may differ from the actual dimensions of each component.

[0019] FIG. 1 is a cross-sectional view illustrating 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 axis of the optical fiber cable 1. As shown in FIG. 1, the optical fiber cable 1 includes a cable core 11, at least one tensile member 12, an outer jacket 13, a holding tape 14, and at least one tear cord 15. The optical fiber cable 1 is, for example, a slotless optical fiber cable, and is a cable for air pressure feeding that is air pressure fed through a duct such as a microduct. The average outer diameter of the optical fiber cable 1 is, for example, 17.5 mm.

[0020] The cable core 11 includes a plurality of optical fiber cores or a plurality of optical fiber ribbons 100. In this embodiment, the cable core 11 has six optical fiber units 10, each having, for example, 12 optical fiber ribbons 100. One optical fiber ribbon 100 includes, for example, 12 optical fiber cores. The outer diameter of each optical fiber core is, for example, 250 μm. The 12 optical fiber cores are arranged in a direction perpendicular to the axis. At least some of the adjacent optical fiber cores in the optical fiber ribbon 100 may have connected portions where the adjacent optical fiber cores are connected and unconnected portions where the adjacent optical fiber cores are not connected, intermittently provided in the longitudinal direction of the optical fiber cores.

[0021] Each of the optical fiber ribbons 100 included in the optical fiber unit 10 may be rounded in cross section. Alternatively, a plurality of optical fiber cores or a plurality of optical fiber ribbons may be bundled together so that the outer shape of each optical fiber unit 10 is round in cross section. Note that FIG. 1 is a diagram showing a schematic diagram of the cable structure and is not intended to show the specific arrangement or dimensions of each component. For example, the optical fiber unit 10 may be housed inside the holding winding tape 14 so that the gap around the optical fiber unit 10 is smaller.

[0022] The cable core 11 has an outer diameter of, for example, 12.7 mm. The cable core 11 may include a plurality of water-absorbent members 16 in addition to the optical fiber units 10.

[0023] A holding winding tape 14 is wound around the outer periphery of the cable core 11. The holding winding tape 14 may be a tape of nonwoven fabric, or a laminate of a base material such as polyethylene terephthalate (PET) and nonwoven fabric. The holding winding tape 14 may be given the function of a water-absorbing material by using a water-absorbing powder or the like. If the holding winding tape 14 functions as a water-absorbing material, the water-absorbing member 16 does not need to be disposed. Instead of the holding winding tape 14, a bundling string may be wound around the outer periphery of the cable core 11.

[0024] At least one strength member 12 is arranged along the cable core 11. The strength members 12 may be arranged linearly along the axis of the cable core 11 in the axis of the optical fiber cable 1. The strength members 12 are provided so as to be embedded inside the jacket 13. It is preferable that the strength members 12 are arranged inside the jacket 13 at a position close to the cable core 11, rather than on the surface layer of the jacket 13.

[0025] The tension members 12 are made of fiber reinforced plastic (FRP). Examples of fiber reinforced plastic include aramid FRP, glass FRP, and carbon FRP. The tension members 12 are circular in cross section. The diameter of the tension members 12 is, for example, 1.8 mm or more and 1.9 mm or less.

[0026] In this embodiment, the strength members 12 are provided in pairs. In the following description, two paired strength members 12 are collectively referred to as a strength member set 120. In this embodiment, in a cross-sectional view, the strength member sets 120 are arranged at two locations facing each other across the cable core 11 (positions symmetrical with respect to the cable center). Furthermore, in one strength member set 120, the two paired strength members 12 are spaced apart from each other by, for example, 0.3 mm or more.

[0027] The tear cords 15 are provided to tear the jacket 13 and extract the optical fiber units 10 inside the cable core 11, and are arranged along the cable core 11. In this embodiment, the tear cords 15 are arranged at two locations facing each other across the cable core 11. Each tear cord 15 is arranged at approximately the middle position between the two tensile member sets 120. The tear cords 15 are fibrous and made of, for example, a plastic material that is resistant to tension.

[0028] The jacket 13 is provided to cover the cable core 11 from the outside and to enclose the tensile strength members 12 and the tear cord 15. The base resin of the jacket 13 in this embodiment is made of high-density polyethylene. The jacket 13 may contain a flame-retardant inorganic material. Examples of the flame-retardant inorganic material that the jacket 13 contains include magnesium hydroxide or aluminum hydroxide.

[0029] In this embodiment, in a cross-sectional view perpendicular to the axis of the optical fiber cable 1, the jacket 13 is flattened so that its major axis coincides with the position where the strength member set 120 is arranged relative to the cable core 11. In other words, the jacket 13 has an elliptical shape, and the major axis of the jacket 13 is on a line passing through the centers of the two strength member sets 120 arranged on either side of the cable core 11. For example, the jacket 13 is flattened so that the major axis of the jacket 13 is approximately on a line connecting the center 11C of the cable core 11 and the middle 120C of the two strength members 12 that make up a pair in one strength member set 120.

[0030] The jacket 13 includes a TM outer jacket 13o and a TM inner jacket 13i. In a cross-sectional view perpendicular to the axis of the optical fiber cable 1, the TM outer jacket 13o is the jacket portion between the strength members 12 and the surface layer 13s of the jacket 13 in the direction from the strength members 12 toward the surface layer 13s of the jacket 13. More specifically, the TM outer jacket 13o is the jacket portion between the strength members 12 and the surface layer 13s of the jacket 13 on a line passing through the center 11C of the cable core 11 and the center 12C of the strength members 12 in the cross-sectional view. The thickness of the TM outer jacket 13o is, for example, 0.67 mm. The TM inner jacket 13i is the jacket portion between the strength members 12 and the cable core 11 in the direction from the strength members 12 toward the cable core 11 in the cross-sectional view. More specifically, in a cross-sectional view, the TM inner outer jacket 13i is the outer jacket portion between the strength member 12 and the cable core 11 on a line passing through the center 11C of the cable core 11 and the center 12C of the strength member 12. The thickness of the TM inner outer jacket 13i is, for example, 0.36 mm.

[0031] Next, the circularity in this embodiment will be described. In this embodiment, for example, in the case of the circularity of the surface layer of the jacket 13, the "circularity" is defined by the ratio ((minor diameter / major diameter) x 100%) between the longest diameter (hereinafter referred to as the major diameter) and the shortest diameter (hereinafter referred to as the minor diameter) of the outer diameters of the surface layer of the jacket 13 in a cross section perpendicular to the axis of the optical fiber cable 1. The same is true for the circularity of the cable core 11, which is defined by the ratio ((minor diameter / major diameter) x 100%) between the major diameter and the minor diameter of the outer diameter of the cable core 11. The larger the value of the circularity of the outer diameter of the cable core 11, the closer the outer shape of the cable core 11 is to a perfect circle.

[0032] In this embodiment, in a cross-sectional view perpendicular to the axis of the optical fiber cable 1, the circularity of the outer diameter of the cable core 11 is greater than the circularity of the jacket 13. Furthermore, in the cross-sectional view, the circularity of the jacket 13 is 85% or more and 96% or less. For example, the circularity of the outer diameter of the cable core 11 is 100%, and the circularity of the jacket 13 is 96%.

[0033] As described above, in this embodiment, in a cross-sectional view of the optical fiber cable 1, the jacket 13 is flattened so that its major axis coincides with the position where the tensile members 12 are arranged relative to the cable core 11. Furthermore, the circularity of the outer diameter of the cable core 11 is greater than the circularity of the jacket 13, and in a cross-sectional view, the circularity of the jacket 13 is 85% or more and 96% or less.

[0034] In an optical fiber cable 1 in which the sheath 13 contains the strength members 12, the thickness of the TM outer sheath 13o in cross section must be a standard thickness, for example, 0.5 mm or more. Furthermore, when pressure is applied to the optical fiber cable 1 from the outside, the strength members 12 may press against the TM inner sheath 13i in cross section. If the TM inner sheath 13i becomes thin, the pressure from the strength members 12 may cause damage such as cracks in the TM inner sheath 13i.

[0035] Furthermore, if the overall thickness of the jacket 13 is increased in order to make the thickness of the TM outer jacket 13o and the thickness of the TM inner jacket 13i greater than a predetermined value, the average outer diameter of the optical fiber cable 1 increases, making it difficult to reduce the diameter of the optical fiber cable 1. However, according to this embodiment, an optical fiber cable 1 having a reduced diameter is provided, in which the jacket 13 is less susceptible to damage and the pumping distance can be extended.

[0036] (Evaluation experiment 1) The present embodiment will be described in more detail below by showing the results of evaluation tests using examples and comparative examples according to the present embodiment. Note that the present disclosure is not limited to these examples.

[0037] In Evaluation Experiment 1, we conducted actual measurements and simulations to evaluate whether damage to the TM inner jacket 13i would occur when external pressure was applied to the optical fiber cable 1. More specifically, we first prepared actual optical fiber cable samples 1 and 2 as comparative examples. We applied an external force of 2200 N for one minute, and measured the thickness of the TM inner jacket 13i and the deformation of the average outer diameter of the jacket 13 when cracks occurred in the TM inner jacket 13i. The presence or absence of cracks was confirmed by visually inspecting the cross section of the optical fiber cable and using a microscope, and derived a relationship between the thickness of the TM inner jacket 13i and the deformation of the average outer diameter of the jacket 13 to prevent cracks from occurring. Furthermore, we conducted simulations to prepare Samples 3 and 4 as examples, and calculated the deformation of the average outer diameter of the jacket 13 under conditions where cracks would not occur in the TM inner jacket 13i even when an external force of 2200 N was applied to the optical fiber cable 1 for one minute. The results of the actual measurements and simulations are shown in Table 1. [Table 1]

[0038] Sample No. 1 and Sample No. 2 are comparative examples, and show evaluation results based on actual measurements. In Sample No. 1 and Sample No. 2, the cable core 11 is flattened, and the jacket 13 is also flattened.

[0039] In sample No. 1, the limit value for the amount of change in the average outer diameter of the outer jacket 13 when no cracks occurred in the TM inner jacket 13i was 1 mm. In sample No. 1, the amount of change in the average outer diameter of the outer jacket 13 when a force of 2200 N was applied for one minute was 6.07 mm, so the pressure applied to the optical fiber cable exceeded the limit value, and cracks occurred in the TM inner jacket 13i.

[0040] In sample No. 2, the limit value for the amount of change in the average outer diameter of the outer jacket 13 when no cracks occurred in the TM inner jacket 13i was 3.6 mm. In sample No. 2, the amount of change in the average outer diameter of the outer jacket 13 when a force of 2200 N was applied for one minute was 5.78 mm, so the pressure applied to the optical fiber cable exceeded the limit value, and cracks occurred in the TM inner jacket 13i.

[0041] From Sample No. 1 and Sample No. 2, the following Equation 1 was derived as the relationship between the thickness of the TM inner jacket 13i and the change in the average outer diameter of the jacket 13, which is the limit value at which cracks do not occur. In Equation 1, x is the thickness of the TM inner jacket 13i. y is the change in the average outer diameter of the jacket 13 [mm], which is the limit value at which cracks do not occur when an external force of 2200 N is applied to the optical fiber cable for one minute. C is a correction coefficient. y=14.943x+C (Formula 1)

[0042] Samples No. 3 and No. 4 are examples and represent simulation results. In Samples No. 3 and No. 4, the major and minor axes of the cable core 11 are both 12.7 mm, and the circularity of the cable core 11 is 100%. In other words, in Samples No. 3 and No. 4, the cable core 11 is perfectly round and not flattened.

[0043] In sample No. 3, the circularity of the outer jacket 13 is 96%, and the outer jacket 13 is flattened. In sample No. 3, the circularity of the cable core 11 (100%) is greater than the circularity of the outer jacket 13 (96%). The thickness of the TM inner outer jacket 13i is 0.36 mm. In sample No. 3, when an external force of 2200 N is applied to the optical fiber cable 1 for one minute, the change in the average outer diameter of the outer jacket 13, which is the limit value at which cracks do not occur, was calculated using equation 1 to be 5.02 mm.

[0044] In sample No. 4, the circularity of the jacket 13 is 85%, and the jacket 13 is flattened. In sample No. 4, the circularity of the cable core 11 (100%) is greater than the circularity of the jacket 13 (85%). The thickness of the TM inner jacket 13i is 0.52 mm. In sample No. 4, when an external force of 2200 N is applied to the optical fiber cable 1 for one minute, the change in the average outer diameter of the jacket 13, which is the limit value at which cracks do not occur, was calculated using equation 1 to be 7.41 mm.

[0045] If the optical fiber cable 1 is considered to be a pipe, the change in the average outer diameter of the jacket 13 when external pressure is applied to the optical fiber cable 1 can be calculated as follows. Specifically, the average outer diameter of the jacket 13 of the optical fiber cable 1 is considered to be the average outer diameter of the pipe, and the average outer diameter of the cable core 11 is considered to be the average inner diameter of the pipe. Furthermore, from Sample No. 1 and Sample No. 2, the following Equation 2 is derived as the relationship between the external force applied to the pipe and the change in the average outer diameter of the pipe. In Equation 2, F is the external load applied to the pipe [kg], which is set to 2200 N / 9.8 = 224.5 kg in this case. OD is the average outer diameter of the pipe, i.e., the average outer diameter [mm] of the jacket 13. ID is the average inner diameter of the pipe, i.e., the average outer diameter [mm] of the cable core 11. E is the Young's modulus of the material of the jacket 13. L is the length [mm] of the pipe along its axis. A is the outer diameter correction coefficient. A*2*F*"π / 8-1 / π"*{"OD+ID" / 4}^3 / [E*L*{"OD-ID" / 2}^3 / 12]...(Formula 2)

[0046] Using Equation 2 derived from Sample No. 1 and Sample No. 2, it is calculated that in Sample No. 3, when an external force of 2200 N is applied to the optical fiber cable 1 for one minute and no cracks occur in the TM inner jacket 13i, the change in average outer diameter of the jacket 13 is 4.82 mm. The calculated value of 4.82 mm is smaller than the change in average outer diameter of the jacket 13 of 5.02 mm when no cracks occur, which was used in Evaluation Experiment 1. Therefore, it was confirmed that no cracks occur in the TM inner jacket 13i in Sample No. 3, even in the evaluation using Equation 2.

[0047] Similarly, using Equation 2, it is calculated that for sample No. 4, when an external force of 2200 N is applied to the optical fiber cable 1 for one minute and no cracks occur in the TM inner jacket 13i, the change in the average outer diameter of the jacket 13 is 7.38 mm. The calculated value of 7.38 mm is smaller than the change in the average outer diameter of the jacket 13 of 7.41 mm when no cracks occur, which was used in Evaluation Experiment 1. Therefore, the evaluation using Equation 2 also confirmed that no cracks occur in the TM inner jacket 13i of sample No. 4.

[0048] As described above, it has been confirmed that if the circularity of the cable core 11 is greater than that of the outer sheath 13 and the circularity of the outer sheath 13 is 85% or more and 96% or less, no cracks will occur in the TM inner outer sheath 13i even if an external force of 2200 N is applied to the optical fiber cable 1 for one minute.

[0049] Although the present embodiment has been described above, it goes without saying that the technical scope of the present invention should not be construed as being limited by the description of the embodiment. The present embodiment is merely an example, and it will be understood by those skilled in the art that various modifications of the embodiment are possible within the scope of the invention described in the claims. Thus, the technical scope of the present invention should be determined based on the scope of the invention described in the claims and its equivalents.

[0050] In the above-described embodiment, the strength member sets 120 are arranged at two locations facing each other across the cable core 11, but the arrangement of the strength members 12 is not limited to this. One strength member 12 may be arranged at two locations facing each other across the cable core 11. In this case, too, the jacket 13 is flattened in the direction in which the two strength members 12 are arranged relative to the cable core 11. In other words, the jacket 13 has an elliptical shape, and the major axis of the jacket 13 is aligned in the direction in which the two strength members 12 arranged across the cable core 11 are aligned.

[0051] One strength member 12 may be disposed in one location within the sheath 13. In this case, too, the sheath 13 is flattened so that the major axis of the sheath 13 lies in the direction from the center 11C of the cable core 11 toward the center of one strength member 12. Similarly, one strength member set 120 may be disposed in one location within the sheath 13. In this case, too, the sheath 13 is flattened so that the major axis of the sheath 13 lies in the direction from the center 11C of the cable core 11 toward the middle 120C of the pair of strength members 12.

[0052] In the above-described embodiment, the two strength members 12 making up a pair in one strength member set 120 are spaced apart from each other, but the arrangement of the two strength members 12 is not limited to this. In one strength member set 120, the two strength members 12 making up a pair may be in contact with each other. [Explanation of symbols]

[0053] 1. Fiber optic cable 10 Optical fiber unit 100 Optical Fiber Ribbons 11 Cable Core 11C Center of cable core 12 Tensile strength body 12C Center of tensile body 120 Tensile Strength Member Set 120C intermediate 13 Outer cover 13i TM inner jacket 13o TM outer jacket 13s surface layer 14 rolls of tape 15 Tear Cord 16 Water-absorbent material

Claims

1. a cable core including a plurality of optical fiber cores; At least one strength member disposed along the axis of the cable core; an outer jacket that covers the cable core from the outside and encloses the strength members, In a cross-sectional view perpendicular to the axis of the optical fiber cable, the jacket is flattened so that its major axis coincides with a position where the tensile strength member is disposed relative to the cable core, the circularity of the outer diameter of the cable core is greater than the circularity of the surface layer of the jacket; An optical fiber cable, wherein the circularity of the surface layer of the jacket is 85% or more and 96% or less in the cross-sectional view.

2. 2. The optical fiber cable according to claim 1, wherein, in the cross-sectional view, the strength members are arranged at two locations facing each other with the cable core interposed therebetween.

3. 3. The optical fiber cable according to claim 1, wherein the jacket is made of high-density polyethylene.

4. the tension member is made of fiber-reinforced plastic, 3. The optical fiber cable according to claim 1, wherein the outer diameter of the tension member is 1.9 mm or less.

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