Optical cable

Abstract

To provide an optical cable that maintains excellent optical characteristics and has excellent waterproofness.SOLUTION: An optical cable has multiple optical fiber units, a water absorption material, a water absorption tape, and a sheath, the water absorption tape is disposed inside the sheath, the multiple optical fiber units and the water absorption material are housed in a unit housing section that is a space wrapped in the sheath and the water absorption tape, the unit housing section includes a center section located in the center side of the cable relative to a boundary and a peripheral section located outside the cable relative to the boundary with 1 / 2 in the radial direction of the cable as the boundary, and a ratio of the sectional area of the water absorption material disposed in the unit housing section to the sectional area of the unit housing section is less than 9% and a ratio of the sectional area of the water absorption material disposed in the center section to the sectional area of the center section is equal to or more than 3% in a section of the optical cable.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Optical cables that use water-absorbing materials to improve waterproofing have been known. Patent Document 1 discloses an optical cable in which water-stopping materials are arranged on the outside and inside of the fiber unit. Patent Document 2 discloses an optical cable in which water-absorbing processing is applied to the inside of the housing groove. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-88542 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-75815 Summary of the Invention [Problem to be solved by the invention]

[0004] Optical cables are now required to have higher waterproofing properties. For example, waterproofing can be improved by increasing the amount of water-absorbing material placed inside the cable. However, if the amount of water-absorbing material is too high, the packaging density will increase, which may result in a deterioration of optical properties.

[0005] An object of the present disclosure is to provide an optical cable that maintains good optical properties and also has excellent waterproof properties. [Means for solving the problem]

[0006] The optical cable of the present disclosure is an optical cable having a plurality of optical fiber units, a water-absorbing material, a water-absorbing tape, and a sheath, the absorbent tape is disposed inside the sheath; the plurality of optical fiber units and the water-absorbing material are accommodated in a unit accommodating section, which is a space surrounded by the sheath and the water-absorbing tape; the unit accommodating portion includes a central portion located closer to the center of the cable than half of the boundary in the radial direction of the cable, and a peripheral portion located outside the boundary, In a cross section of the optical cable, a ratio of a cross-sectional area of ​​the water absorbent material disposed in the unit accommodating portion to a cross-sectional area of ​​the unit accommodating portion is less than 9%; The ratio of the cross-sectional area of ​​the water-absorbent material disposed at the center to the cross-sectional area of ​​the center is 3% or more. [Effects of the Invention]

[0007] According to the present disclosure, an optical cable that maintains good optical properties and also has excellent waterproof properties can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of an optical cable 1 according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view illustrating the central portion of the unit housing portion of the optical cable 1. As shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of an optical cable 2 according to another embodiment of the present disclosure. [Figure 4] FIG. 4 is a cross-sectional view illustrating the central portion of the unit housing portion of the optical cable 2. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. The optical cable of the present disclosure comprises: (1) An optical cable having a plurality of optical fiber units, a water-absorbing material, a water-absorbing tape, and a sheath, the absorbent tape is disposed inside the sheath; the plurality of optical fiber units and the water-absorbing material are accommodated in a unit accommodating section, which is a space surrounded by the sheath and the water-absorbing tape; the unit accommodating portion includes a central portion located closer to the center of the cable than half of the boundary in the radial direction of the cable, and a peripheral portion located outside the boundary, In a cross section of the optical cable, a ratio of a cross-sectional area of ​​the water absorbent material disposed in the unit accommodating portion to a cross-sectional area of ​​the unit accommodating portion is less than 9%; The ratio of the cross-sectional area of ​​the water-absorbent material disposed at the center to the cross-sectional area of ​​the center is 3% or more.

[0010] According to this configuration, the ratio of the water-absorbing material to the cross-sectional area of ​​the unit housing section is less than 9%, so the mounting density is not too high and good optical characteristics can be maintained. Also, although it is difficult to stop water that has penetrated into the center with the water-absorbing tape placed on the outside of the unit housing section, by setting the ratio of the water-absorbing material placed in the center to 3% or more, excellent waterproofing is also achieved.

[0011] (2) In the above (1), the unit accommodating portion may have an outer diameter of 30 mm or less.

[0012] According to this configuration, an optical cable having a small diameter and excellent optical properties and waterproof properties can be obtained.

[0013] (3) In the above (1) or (2), the ratio of the cross-sectional area of ​​the water-absorbent material disposed in the center to the cross-sectional area of ​​the center may be 5% or more.

[0014] According to this configuration, the proportion of the water-absorbing material disposed in the center is large, which further improves the waterproofing properties.

[0015] (4) In any of (1) to (3) above, the ratio of the cross-sectional area of ​​the absorbent material arranged in the center to the cross-sectional area of ​​the center may be greater than the ratio of the cross-sectional area of ​​the absorbent material arranged in the unit accommodating section to the cross-sectional area of ​​the unit accommodating section.

[0016] According to this configuration, the proportion of the water-absorbing material disposed in the center is large, which further improves the waterproofing properties.

[0017] (5) In any of the above (1) to (4), a packing density, which is a ratio of the sum of the cross-sectional areas of the plurality of optical fiber units to the cross-sectional area of ​​the unit housing portion, may be 40% or more and 50% or less.

[0018] According to this configuration, an optical cable having high packaging density and excellent waterproof properties can be obtained.

[0019] [Details of the embodiments of the present disclosure] Specific examples of the optical 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.

[0020] (First embodiment) 1 is a cross-sectional view of an optical cable 1 according to this embodiment. As shown in FIG. 1, the optical cable 1 includes a plurality of optical fiber units 10, a water-absorbing yarn 20, a slot rod 30, a water-absorbing tape 40, and a sheath 50.

[0021] The slot rod 30 has a plurality of ribs 31 and a plurality of slot grooves 32. A plurality of optical fiber units 10 are arranged in each slot groove 32. In other words, the optical cable 1 is an example of a slotted cable.

[0022] Each optical fiber unit 10 includes a plurality of optical fiber cores. The optical fiber unit 10 may include an optical fiber ribbon in which a plurality of optical fiber cores are intermittently connected. The optical fiber unit 10 is formed by bundling and twisting a plurality of optical fiber cores or optical fiber ribbons. Each of the optical fiber ribbons included in the optical fiber unit 10 may be in a rounded shape in cross section. Furthermore, a plurality of optical fiber cores or optical fiber ribbons may be bundled together so that the outer shape of each optical fiber unit 10 is round in cross section. Adjacent optical fiber units 10A and 10B may be in contact with each other.

[0023] The water-absorbing yarn 20 is wound around at least one of the multiple optical fiber units 10. The water-absorbing yarn 20 is an example of a water-absorbing material. In the optical cable 1 shown in Fig. 1, of the multiple optical fiber units 10, the water-absorbing yarn 20 is wound around the optical fiber unit 10A, but the water-absorbing yarn 20 is not wound around the optical fiber unit 10B.

[0024] The sheath 50 covers the slotted rod 30 and houses multiple optical fiber units 10 inside. Any sheath commonly used for optical cable sheaths can be used as the sheath 50, for example, a polyethylene sheath. A water-absorbing tape 40 is arranged inside the sheath 50 to cover the multiple optical fiber units 10 and the slotted rod 30 collectively.

[0025] 1, the optical cable 1 may include a tension member 60. The tension member 60 is made of, for example, steel wire or fiber-reinforced plastic (FRP), and prevents excessive tension from being applied to the optical fiber core when tension is applied to the optical cable 1. The number and positions of the tension members 60 are not particularly limited.

[0026] In the optical cable 1 shown in FIG. 1, the slot groove 32 is a space in which the optical fiber unit 10 is accommodated. In the following description, the slot groove 32 may be referred to as the unit accommodating section A. FIG. 2 is a cross-sectional view of the optical cable 1 illustrating the center A1 and peripheral section A2 of the unit accommodating section A. The optical fiber unit 10 and the water-absorbing yarn 20 are not shown in FIG. 2. Taking the unit accommodating section A located at the top of the page in FIG. 2 as an example, the unit accommodating section A, the center A1, and the peripheral section A2 will be described in detail. As shown in FIG. 2, the unit accommodating section A includes a center A1 located closer to the center of the cable than the boundary at half the radial direction of the cable, and a peripheral section A2 located outside the boundary. The center A1 and the peripheral section A2 are defined merely to conceptually distinguish between regions within the unit accommodating section A, and no physical partition is required between the center A1 and the peripheral section A2. More specifically, in the case of a slotted cable such as the optical cable 1, the center A1 and the peripheral section A2 are defined as follows: 2, the bottom 32a of the slot groove 32 is used as the reference for height (position in the cable radial direction), and the top end 32b, which is the highest position of the slot rod 30 from the bottom 32a, is defined as the height h of the slot groove 32. Then, a portion of the unit accommodating section A that is equal to or less than a height h / 2, which is half the height h of the slot groove 32, is defined as a center A1, and a portion higher than the height h / 2 is defined as a peripheral portion A2. Note that the unit accommodating section A refers to the space in which the optical fiber unit 10 is accommodated, and does not include, for example, the main body of the slot rod 30 or the tension member 60. Also, while FIG. 2 shows the center A1 and peripheral portion A2 only for the unit accommodating section A located at the top of the page, the other unit accommodating sections A (slot grooves 32) also similarly include a center A1 and peripheral portion A2.

[0027] In conventional optical cables, a water-absorbing tape is wrapped around the slotted rod and multiple optical fiber units to cover them collectively. When water seeps into the slotted grooves, the water is absorbed by the water-absorbing tape to stop the water from seeping in. However, in cables with deep grooves, such as ultra-high-core cables, the water-absorbing effect of the water-absorbing tape does not reach the groove bottom, which can result in insufficient water-stopping. While waterproofing can be improved by inserting water-absorbing yarns into the grooves, increasing the number of inserted water-absorbing yarns or using thicker water-absorbing yarns to ensure waterproofing increases the packaging density, which can apply lateral pressure to the optical fiber cores and deteriorate the optical properties.

[0028] The optical cable of the present disclosure ensures that a sufficient amount of water-absorbing material is disposed in the center A1 of the unit accommodating section A while preventing the amount of water-absorbing material from being excessively large relative to the entire unit accommodating section A. Specifically, in the optical cable 1 shown in FIG. 1, an optical fiber unit 10A wound with a water-absorbing yarn 20 is disposed in the center A1 (the groove bottom of the slot groove 32), and an optical fiber unit 10B not wound with a water-absorbing yarn 20 is disposed in the peripheral section A2. With this configuration, in the cross section of the optical cable 1, the ratio (S2 / S1) of the cross-sectional area S2 of the water-absorbing material disposed in the unit accommodating section A to the cross-sectional area S1 of the unit accommodating section A is less than 9%. Furthermore, the ratio (S4 / S3) of the cross-sectional area S4 of the water-absorbing material disposed in the center A1 to the cross-sectional area S3 of the center A1 is 3% or more.

[0029] According to the above configuration, the ratio of the cross-sectional area S2 of the water-absorbing material arranged in the unit accommodating section A to the cross-sectional area S1 of the unit accommodating section A is less than 9%, so that transmission loss is small and optical characteristics can be maintained well.

[0030] Furthermore, since the ratio (S4 / S3) of the cross-sectional area S4 of the water-absorbing material arranged at the center A1 to the cross-sectional area S3 of the center A1 is 3% or more, water can be effectively stopped even when water penetrates into the center A1. In other words, an optical cable with excellent waterproofing is obtained. The ratio (S4 / S3) of the cross-sectional area S4 of the water-absorbing material arranged at the center A1 to the cross-sectional area S3 of the center A1 may be 5% or more. There is no particular upper limit to the ratio (S4 / S3) of the cross-sectional area S4 of the water-absorbing material arranged at the center A1 to the cross-sectional area S3 of the center A1, but it is, for example, 30% or less from the viewpoint of packaging density.

[0031] In this embodiment, the ratio (S4 / S3) of the cross-sectional area S4 of the water absorbent material arranged in the central portion A1 to the cross-sectional area S3 of the central portion A1 may be larger than the ratio (S2 / S1) of the cross-sectional area S2 of the water absorbent material arranged in the unit accommodating portion A to the cross-sectional area S1 of the unit accommodating portion A. When the ratio S4 / S3 is larger than the ratio S2 / S1, the density of the water absorbent material in the central portion A1 is increased, further improving waterproofness.

[0032] In a slotted cable, the cross-sectional areas S1, S2, S3, and S4 of each slot are generally substantially the same. Therefore, good optical and waterproof properties can be achieved as long as the ratios S2 / S1 and S4 / S3 calculated using the cross-sectional areas S1, S2, S3, and S4 of one slot are within the ranges specified above. However, if the cross-sectional areas S1, S2, S3, and S4 of the slots are different, good optical and waterproof properties can be achieved as long as the ratios S2 / S1 and S4 / S3 calculated using the cross-sectional areas S1, S2, S3, and S4 of at least one slot are within the ranges specified above. The ratios S2 / S1 and S4 / S3 may be within the ranges specified above for all slots.

[0033] The optical cable 1 may have a unit accommodating section outer diameter of 30 mm or less. A unit accommodating section outer diameter of 30 mm or less is thin and preferable. In a slotted cable such as the optical cable 1, the unit accommodating section outer diameter means the outer diameter of an imaginary circle that passes through the tip of the rib 31 of the slotted rod 30.

[0034] The mounting density of the optical cable 1 may be 40% or more and 50% or less. A mounting density of 40% or more ensures high transmission capacity. A mounting density of 50% or less prevents a significant increase in transmission loss due to bending, etc. In this disclosure, the mounting density refers to the ratio of the sum of the cross-sectional areas of the multiple optical fiber units 10 to the cross-sectional area of ​​the unit accommodating section A.

[0035] (Second embodiment) Next, an optical cable 2 according to a second embodiment of the present disclosure will be described. Fig. 3 is a cross-sectional view showing the optical cable 2. The optical cable 2 includes a plurality of optical fiber units 10, a water-absorbing yarn 20, a water-absorbing tape 40, a sheath 50, and a tension member 60. Of the components of the optical cable 2, parts that are common to the components of the optical cable 1 according to the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0036] The optical cable 2 does not have a slot rod, and the space (core) inside the sheath 50 is not divided. In other words, the optical cable 2 is an example of a slotless cable. The optical cable 2 houses an optical fiber unit throughout the core. Therefore, in the optical cable 2, the entire core corresponds to the unit housing section A. A water-absorbing tape 40 is arranged inside the sheath 50, covering the multiple optical fiber units 10 and the water-absorbing yarn 20 collectively.

[0037] The optical cable 2 includes an optical fiber unit 10A wound with a water-absorbing yarn 20 and an optical fiber unit 10B not wound with the water-absorbing yarn 20. As shown in Fig. 3, in the optical cable 2, the optical fiber unit 10A is arranged near the center of the unit accommodating section A, and the optical fiber unit 10B is arranged near the periphery of the unit accommodating section A.

[0038] Fig. 4 is a cross-sectional view illustrating a central portion A1 and a peripheral portion A2 of the unit accommodating portion A of the optical cable 2. The optical fiber unit 10 and the water-absorbing yarn 20 are not shown in Fig. 4. As shown in Fig. 4, the unit accommodating portion A of the optical cable 2, like the optical cable 1 in the first embodiment, includes a central portion A1 located closer to the center of the cable than the boundary located halfway in the radial direction of the cable, and a peripheral portion A2 located outside the boundary. More specifically, in the case of a slotless cable such as the optical cable 2, the central portion A1 is defined as a circle located at the center of the unit accommodating portion A and has a radius half (r / 2) of the core radius r, and the portion other than the central portion A1 is defined as the peripheral portion A2.

[0039] In the optical cable 2 according to this embodiment, the ratio (S2 / S1) of the cross-sectional area S2 of the water absorbent material arranged in the unit accommodating section A to the cross-sectional area S1 of the unit accommodating section A is less than 9%. Furthermore, the ratio (S4 / S3) of the cross-sectional area S4 of the water absorbent material arranged in the center A1 to the cross-sectional area S3 of the center A1 is 3% or more.

[0040] According to the above configuration, the ratio of the cross-sectional area S2 of the water absorbent material arranged in the unit accommodating section A to the cross-sectional area S1 of the unit accommodating section A is less than 9%, so that transmission loss is small and excellent optical characteristics are obtained. Furthermore, the ratio (S4 / S3) of the cross-sectional area S4 of the water absorbent material arranged in the center A1 to the cross-sectional area S3 of the center A1 is 3% or more, so that water can be effectively stopped even when water penetrates into the center A1. Thus, in a slotless cable such as optical cable 2, as in the slotted cable of the first embodiment, excellent optical characteristics and waterproofness can be obtained by setting the cross-sectional area ratio of the water absorbent material in the unit accommodating section and the cross-sectional area ratio of the water absorbent material in the center within a predetermined range. [Example]

[0041] The optical cable of the present disclosure will be further described below with reference to examples. In the following description, the cross-sectional area of ​​one slot groove (unit accommodating section A) in a slotted cable may be referred to as the "groove cross-sectional area S1." The cross-sectional area of ​​the center A1 of one slot groove (unit accommodating section A) in a slotted cable may be referred to as the "groove bottom cross-sectional area S3." The cross-sectional area of ​​the unit accommodating section A in a slotless cable may be referred to as the "core cross-sectional area S1." The cross-sectional area of ​​the center A1 of the unit accommodating section A in a slotless cable may be referred to as the "center cross-sectional area S3." The cross-sectional area of ​​one slot groove in a slotted cable or the water-absorbing yarn in the unit accommodating section A of a slotless cable may be referred to as the "water-absorbing yarn cross-sectional area S2." The cross-sectional area of ​​the water-absorbing yarn in the center A1 of one slot groove in a slotted cable or the center A1 of a slotless cable may be referred to as the "groove bottom (center) water-absorbing yarn cross-sectional area S4."

[0042] [Optical cable manufacturing] (Examples 1 to 4) We fabricated slotted cables containing multiple optical fiber units and water-absorbing yarns inside a sheath. The number of slots was six. In each optical cable, the same amount of water-absorbing yarn was housed in each slot, and the arrangement of the water-absorbing yarn was changed in three ways so that the amount of water-absorbing yarn placed in the center of each slot was different. Table 1 shows the outer diameter of the unit housing section (outer diameter of the slot rod) for each cable in Examples 1 to 4, as well as the groove cross-sectional area S1, water-absorbing yarn cross-sectional area S2, groove bottom cross-sectional area S3, and groove bottom water-absorbing yarn cross-sectional area S4 of each slot. In Table 1, for example, Example 1-1 refers to the first slot in the cable in Example 1, and Example 1-2 refers to the second slot in the cable in Example 1.

[0043] (Examples 5 to 7) We fabricated slotless cables with multiple optical fiber units and water-absorbing yarns housed inside a sheath. The core cross-sectional area S1, water-absorbing yarn cross-sectional area S2, center cross-sectional area S3, and center water-absorbing yarn cross-sectional area S4 of each optical cable are shown in Table 2.

[0044] [evaluation] (Optical properties) The transmission loss of each optical cable was evaluated. For Examples 1 to 4, if the average transmission loss of the optical fiber in each slot groove was less than 0.3 dB / km at a wavelength of 1.3 μm, it was rated A (good), and if the average transmission loss was 0.3 dB / km or more, it was rated C (poor). For Examples 5 to 7, if the average transmission loss of the optical fiber in each optical cable was less than 0.3 dB / km at a wavelength of 1.3 μm, it was rated A (good), and if the average transmission loss was 0.3 dB / km or more, it was rated C (poor). The results are shown in Tables 1 and 2.

[0045] (waterproof) Tap water was poured into each 3m long optical cable at a head length of 1m for 24 hours, and the water travel velocity was calculated from the permeation length using equation (1). Hydraulic velocity = permeability length [m] / test time (24 hours) [h] (1) A running water velocity of less than 0.10 m / h was rated A (good), a running water velocity of 0.10 m / h or more but less than 0.12 m / h was rated B (acceptable), and a running water velocity of 0.12 m / h or more was rated C (poor). The results are shown in Tables 1 and 2.

[0046] [Table 1]

[0047] [Table 2]

[0048] From the above results, it was found that all optical cables with an S2 / S1 ratio of 9% or less had an optical property evaluation of A, indicating that they had good optical properties. In addition, optical cables with an S4 / S3 ratio of 3% or more had a water-borne velocity evaluation of A or B, indicating that they had excellent waterproof properties.

[0049] In the above embodiment, the water-absorbent yarn is wound around the optical fiber unit, but the optical cable of the present disclosure is not limited to this configuration. For example, the water-absorbent yarn may be contained inside the optical fiber unit by twisting the optical fiber core and the water-absorbent yarn together. Furthermore, the water-absorbent yarn may be placed separately in the unit housing section without being integrated with the optical fiber unit. [Explanation of symbols]

[0050] 1,2 Optical cable 10, 10A, 10B Optical fiber unit 20 Water-absorbing yarn 30 slot rod 31 Ribs 32 slot groove 32a bottom 32b top end 40 Water-absorbing tape 50 sheath 60 tension member A unit housing A1 center A2 Periphery

Claims

1. An optical cable having a plurality of optical fiber units, a water absorbing material, a water absorbing tape, and a sheath, The water-absorbent tape is disposed inside the sheath, the optical fiber units and the water-absorbing material are accommodated in a unit accommodation section, which is a space surrounded by the sheath and the water-absorbing tape; the unit accommodating portion includes a central portion located toward the center of the cable from a boundary that is half the length of the cable in a radial direction, and a peripheral portion located toward an outer side of the cable from the boundary, In a cross section of the optical cable, a ratio of a cross-sectional area of ​​the water absorbent material disposed in the unit accommodating portion to a cross-sectional area of ​​the unit accommodating portion is less than 9%, An optical cable, wherein the ratio of the cross-sectional area of ​​the water absorbent material disposed at the center to the cross-sectional area of ​​the center is 3% or more.

2. 2. The optical cable according to claim 1, wherein the unit accommodating portion has an outer diameter of 30 mm or less.

3. 3. The optical cable according to claim 1, wherein a ratio of a cross-sectional area of ​​the water absorbent material disposed in the central portion to a cross-sectional area of ​​the central portion is 5% or more.

4. 3. The optical cable according to claim 1, wherein the ratio of the cross-sectional area of ​​the absorbent material arranged in the center to the cross-sectional area of ​​the center is greater than the ratio of the cross-sectional area of ​​the absorbent material arranged in the unit accommodating portion to the cross-sectional area of ​​the unit accommodating portion.

5. 3. The optical cable according to claim 1, wherein a packing density, which is a ratio of a sum of cross-sectional areas of the plurality of optical fiber units to a cross-sectional area of ​​the unit housing portion, is 40% or more and 50% or less.

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