Optical fiber cable

Abstract

To provide an optical fiber cable having a small-diameter and capable of mounting an optical fiber core wire with high density.SOLUTION: An optical fiber cable includes: a cable core including a plurality of optical fiber core wires; at least one tensile strength body arranged along the cable core; and a jacket covering the cable core from the outside and including the tensile strength body. The cable core has a non-circular shape; and when using the thickness of the jacket in a place where the thickness of the jacket is the thickest at a position including the tensile strength body in a cross-sectional view as a first jacket thickness and using the thickness of the jacket at a position sandwiching the cable core and facing the tensile strength body as a second jacket thickness, the first jacket thickness is thicker than the second jacket thickness.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 including a plurality of optical fiber cores, a strength member, and an outer jacket that covers the plurality of optical fiber cores from the outside and encases the strength member. The strength member makes the cable relatively easy to bend and provides the cable with tensile strength and anti-buckling properties. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 6,137,936 Summary of the Invention [Problem to be solved by the invention]

[0004] When an optical fiber cable has a structure in which strength members are located on both sides of the jacket around the cable core, it tends to bend easily in a 90-degree direction relative to the line connecting the strength members in a cross-sectional view, and tends to have low bending rigidity in that direction. On the other hand, it tends to bend less easily in the direction of the strength members, and tends to have high bending rigidity in that direction. In other words, an optical fiber cable with the above structure has bending anisotropy. When such an optical fiber cable is compressed air fed or pushed through a duct, it tends to bend in the direction of low bending rigidity, and there is a risk of buckling midway through the duct.

[0005] Optical fiber cables are also known in which three or more strength members are arranged at equal intervals in the jacket when viewed in cross section. However, in such optical fiber cables, the distance between the strength members embedded in the jacket and the bending center (which in this case coincides with the center of the cable) is large. Therefore, when the cable is bent to a small diameter, compressive stress is applied to the inside of the bend, making the strength members arranged on the inside more likely to buckle, break, and collapse. Furthermore, because it is difficult to bend the cable to a small diameter, a large space is required to store the cable.

[0006] Optical fiber cables are preferably made thinner and lighter in order to pack the optical fiber cores at high density, and the optical fiber diameter has been reduced from the conventional 250 μm to 200 μm. To achieve high density, it is effective to make the outer jacket thinner, but as the outer jacket becomes thinner, the protective function of the outer jacket decreases when the cable is bent to a small diameter, making the tensile members placed inside more susceptible to buckling.

[0007] Furthermore, in a configuration in which the cable core is perfectly circular and the outer sheath encloses the strength members, it is difficult to reduce the diameter of the entire cable if one tries to ensure the same thickness of the outer sheath at all points, including the thickness from the strength members to the outer edge of the outer sheath, where the strength members are enclosed, based on the thinnest part of the outer sheath in cross section.Furthermore, under the constraint of a perfectly circular cable core, it is difficult to ensure a large space occupied by the cable core relative to the entire cable in cross section.

[0008] An object of the present disclosure is to provide an optical fiber cable that has a small diameter and allows optical fiber cores to be mounted at a high density. [Means for solving the problem]

[0009] The optical fiber cable of the present disclosure comprises: a cable core including a plurality of optical fiber cores; at least one strength member disposed along the cable core; an outer jacket that covers the cable core from the outside and encloses the strength members, the cable core has a non-circular shape; When viewed in cross section, the thickness of the outer sheath at a position including the strength member where the thickness is greatest is defined as a first outer sheath thickness, and the thickness of the outer sheath at a position facing the strength member across the cable core is defined as a second outer sheath thickness, the first outer sheath thickness is thicker than the second outer sheath thickness. [Effects of the Invention]

[0010] According to the present disclosure, an optical fiber cable can be provided that is thin and capable of mounting optical fiber cores at a high density. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable according to a comparative example. [Figure 3] FIG. 3 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable according to the first modification. [Figure 4] FIG. 4 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable according to the second modification. [Figure 5] FIG. 5 is a schematic diagram illustrating an evaluation experiment of water-stopping ability. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Description of Embodiments 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: a cable core including a plurality of optical fiber cores; at least one strength member disposed along the cable core; an outer jacket that covers the cable core from the outside and encloses the strength members, the cable core has a non-circular shape; When viewed in cross section, the thickness of the outer sheath at a position including the strength member where the thickness is greatest is defined as a first outer sheath thickness, and the thickness of the outer sheath at a position facing the strength member across the cable core is defined as a second outer sheath thickness, the first outer sheath thickness is thicker than the second outer sheath thickness.

[0013] The cable core according to the present disclosure has a non-circular shape, and the first jacket thickness is greater than the second jacket thickness in a cross-sectional view. Therefore, the optical fiber cable according to the present disclosure can have a smaller diameter while ensuring the area occupied by the cable core in the cross-sectional view compared to when the cable core is perfectly circular.

[0014] (2) In the above (1), the tension member may be provided at one location on the jacket in a cross-sectional view.

[0015] According to the present disclosure, when an optical fiber cable is bent, the center of bending is closer to the strength member, and the distance between the strength member and the bending center is shorter. Therefore, compared to when the strength member is embedded in two or more locations in the jacket, the strength member is less likely to buckle even when the optical fiber cable is bent to a small diameter. Furthermore, because the optical fiber cable can be easily bent to a small diameter, the storage capacity of the optical fiber cable is improved.

[0016] (3) In the above (2), the outer periphery of the cable core has, in the cross-sectional view, two arc-shaped portions: a first arc-shaped portion close to the tension member and a second arc-shaped portion far from the tension member; the first arc portion and the second arc portion are each arcs that are convex outward from the center of the optical fiber cable, The radius of curvature of the first arcuate portion may be greater than the radius of curvature of the second arcuate portion.

[0017] The cable core of the present disclosure has an outer periphery that has a first arcuate portion with a relatively large radius of curvature and a second arcuate portion with a relatively small radius of curvature. Because the cable core has such a non-circular shape, it is possible to pack optical fiber cores at a high density and realize an optical fiber cable with a small diameter.

[0018] (4) In the above (2), the outer periphery of the cable core has, in the cross-sectional view, two arc-shaped portions: a first arc-shaped portion close to the tension member and a second arc-shaped portion far from the tension member; the first arc portion is an arc that is convex toward the center of the optical fiber cable, the second arc portion is an arc that is convex outward from the center of the optical fiber cable, The radius of curvature of the first arcuate portion may be smaller than the radius of curvature of the second arcuate portion.

[0019] The cable core of the present disclosure has an outer periphery that has a first arc portion with a relatively small radius of curvature and a second arc portion with a relatively large radius of curvature. Because the cable core has such a non-circular shape, the area occupied by the cable core can be maximized and a thin optical fiber cable can be realized.

[0020] (5) In any one of the above (1) to (4), the first outer covering thickness may be the thickest in the outer covering in the cross-sectional view.

[0021] According to the present disclosure, the first outer sheath has the largest thickness in cross-sectional view, so that the outer sheath can be secured around the tensile member.

[0022] (Details of the first embodiment of the present disclosure) Specific examples of the optical fiber cable according to the first embodiment of the present disclosure will be described with reference to the drawings. Note that the present disclosure 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.

[0023] (Optical fiber cable structure) An optical fiber cable 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the optical fiber cable 1 taken perpendicular to its longitudinal direction.

[0024] As shown in Fig. 1, the optical fiber cable 1 includes a cable core 11, one tensile member 12, an outer jacket 13, and a pressure winding tape 14. The optical fiber cable 1 is circular in cross section. The outer diameter of the optical fiber cable 1 is, for example, 10 mm. The optical fiber cable 1 of this embodiment is a slotless optical fiber cable and a cable for air pressure transmission.

[0025] The cable core 11 includes a plurality of optical fiber ribbons 10. In this embodiment, the cable core 11 has 24 optical fiber ribbons 10. The optical fiber ribbon 10 includes 12 optical fiber cores. The outer diameter of each optical fiber core is relatively thin, for example, 165 μm or more and 250 μm or less. The 12 optical fiber cores are arranged in a direction perpendicular to the longitudinal direction. At least some adjacent optical fiber cores in the optical fiber ribbon 10 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. The optical fiber ribbon 10 is an example of a plurality of optical fiber cores.

[0026] The cable core 11 has a non-circular shape in a cross-sectional view. More specifically, the outer periphery of the cable core 11 has two arc portions in a cross-sectional view: a first arc portion 111 close to the strength members 12 and a second arc portion 112 far from the strength members 12. The first arc portion 111 and the second arc portion 112 are each arcs that convex outward from the center C of the optical fiber cable. In other words, the first arc portion 111 is an arc that convex toward a first jacket portion 13U described later. The second arc portion 112 is an arc that convex toward a second jacket portion 13D described later. Thus, the direction in which the first arc portion 111 is convex is different from the direction in which the second arc portion 112 is convex.

[0027] The radius of curvature of the first arc portion 111 is larger than the radius of curvature of the second arc portion 112. The radius of curvature of the second arc portion 112 may be close to the radius of curvature of the outer edge of the jacket 13 of the optical fiber cable 1. The second arc portion 112 forms half of the entire cable core 11 (the lower half in FIG. 1 ) that is far from the tensile strength member 12. A pressure winding tape 14 is wound around the outer periphery of the cable core 11. Instead of the pressure winding tape 14, a bundling string may be wound around the outer periphery of the cable core 11.

[0028] The strength members 12 are arranged along the cable core 11. The strength members 12 may be arranged linearly along the cable core 11 in the longitudinal direction of the optical fiber cable 1. Furthermore, the strength members 12 are provided at one location on the jacket 13 in a cross-sectional view.

[0029] 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, 2 mm.

[0030] The jacket 13 is provided to cover the cable core 11 from the outside and to enclose the tensile members 12. The base resin of the jacket 13 in this embodiment is ethylene-vinyl acetate copolymer resin (EVA resin). The jacket 13 may contain a flame-retardant inorganic material. As the flame-retardant inorganic material, the jacket 13 contains, for example, magnesium hydroxide or aluminum hydroxide.

[0031] In a cross-sectional view, the thickness of the jacket 13 is not uniform. The jacket 13 has a first jacket portion 13U that is thicker and a second jacket portion 13D that is thinner. The first jacket portion 13U is a jacket that encases the strength members 12. In a cross-sectional view, the first jacket portion 13U is a jacket portion that occupies half of the entire optical fiber cable 1 (the upper half in FIG. 1 ) and is closer to the strength members 12 than the second jacket portion 13D. In the first jacket portion 13U, the thickness of the jacket at a position including the strength members 12 where the thickness of the jacket 13 (the distance from the inner edge to the outer edge of the jacket 13) is the thickest is defined as a first jacket thickness 131. When a line connecting the center 12C of the strength members 12 and the center C of the optical fiber cable 1 is defined as L, the first jacket thickness 131 is the thickness of the first jacket portion 13U on this line L.

[0032] The second jacket thickness 132 is the thickness of the jacket at a position in the second jacket portion 13D facing the strength members 12 across the cable core 11. In a cross-sectional view, the second jacket portion 13D is located between the outer edge of the optical fiber cable 1 and the holding winding tape 14 corresponding to the second arc portion 112 of the cable core 11. In other words, the second jacket portion 13D is not only located on the opposite side of the strength members 12 across the cable core 11 in a cross-sectional view, but also is a jacket portion in the other half (the lower half in FIG. 1 ) of the entire optical fiber cable 1 that is farther from the strength members 12 than the first jacket portion 13U. The thickness of the second jacket portion 13D may be uniform across half of the entire optical fiber cable 1. In this embodiment, "uniform" does not only refer to a case where the thickness is strictly uniform, but also includes a case where the difference between the thicknesses is sufficiently small and the thickness is evaluated as substantially uniform.

[0033] In this embodiment, the first outer sheath thickness 131 is thicker than the second outer sheath thickness 132. The second outer sheath thickness 132 is, for example, 1 mm. The first outer sheath thickness 131 is, for example, 1.1 to 2.8 times the diameter of the tensile member 12. In this embodiment, the first outer sheath thickness 131 is the thickest of the outer sheath 13 in a cross-sectional view.

[0034] Next, the area occupied by the cable core 11 in the optical fiber cable 1 of this embodiment will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber cable 1Z according to a comparative example. In the configuration shown in Fig. 2, the same components as those shown in Fig. 1 are given the same reference numerals, and their description will be omitted. In Fig. 2, the unfilled areas (white areas) indicate the outer sheath that should be provided to protect the cable core 11.

[0035] As shown in FIG. 2, the optical fiber cable 1Z according to the comparative example has a circular cable core 11Z, unlike the cable core 11 having a non-circular shape. Furthermore, in the optical fiber cable 1Z, the center CZ of the optical fiber cable 1Z, the center 12C of the strength member 12, and the center 11CZ of the cable core 11Z are aligned on a straight line LZ, and the strength member 12 and the cable core 11Z are in contact with each other on the straight line LZ. The radius of the cable core 11Z is r, the radius of the strength member 12 is t, and the radius of the circle formed by adding the diameters of the cable core 11Z and the strength member 12 is R. The area of ​​the grayed-out portion in FIG. 2 is the area of ​​the circle with radius R minus the area of ​​the strength member 12 and the area of ​​the cable core 11Z, which is 2πtr. Thus, if the cable core 11Z were a perfect circle, the area of ​​2πtr would not be usable for the cable core 11Z. As a result, it is difficult to increase the density of the optical fiber cable 1Z.

[0036] On the other hand, in the optical fiber cable 1 of this embodiment, the cable core 11 has a non-circular shape. More specifically, the outer periphery of the cable core 11 has a first arc portion 111 close to the strength members 12 and a second arc portion 112 far from the strength members 12. The first arc portion 111 and the second arc portion 112 are each arcs that convex outward from the center C of the optical fiber cable 1. The radius of curvature of the first arc portion 111 is larger than the radius of curvature of the second arc portion 112. Because the cable core 11 has such a non-circular shape, the area occupied by the cable core 11 relative to the entire optical fiber cable 1 in a cross-sectional view can be secured to be larger, up to a maximum of 2πtr, compared to when the cable core is a perfect circle. This makes it easier to increase the density of the optical fiber cable 1.

[0037] Furthermore, in this embodiment, in a cross-sectional view, the first outer sheath thickness 131 is thicker than the second outer sheath thickness 132. Therefore, the outer sheath 13 around the strength member 12 can be secured.

[0038] (Variation 1) An optical fiber cable 1A according to Modification 1 will be described with reference to Fig. 3. In the configuration shown in Fig. 3, the same components as those shown in Fig. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

[0039] Fig. 3 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 1A. In the cable core 11 illustrated in Fig. 1, the first arc portion 111 and the second arc portion 112 are each arcs that convex outward from the center C of the optical fiber cable 1. On the other hand, in the cable core 11A of the optical fiber cable 1A illustrated in Fig. 3, the first arc portion 111A is an arc that convex outward from the center CA of the optical fiber cable 1A, and the second arc portion 112A is an arc that convex outward from the center CA of the optical fiber cable 1A. In other words, the first arc portion 111A and the second arc portion 112A are arcs that convex outward from the second jacket portion 13D.

[0040] Furthermore, in the cable core 11A of the optical fiber cable 1A, the first arc portion 111A is provided so as to surround from the outside a part of the outer periphery of the tension member 12. The radius of curvature of the first arc portion 111A is smaller than the radius of curvature of the second arc portion 112A.

[0041] According to this modification, the area occupied by the cable core 11A in the optical fiber cable 1A can be maximized.

[0042] (Variation 2) An optical fiber cable 1B according to Modification 2 will be described with reference to Fig. 4. In the configuration shown in Fig. 4, the same components as those shown in Fig. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

[0043] Fig. 4 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 1B. The optical fiber cable 1 illustrated in Fig. 1 includes one strength member 12. In contrast, the optical fiber cable 1B illustrated in Fig. 4 has two strength members 12B provided at one location on the jacket 13 in the cross-sectional view.

[0044] The two strength members 12B form a pair of strength member sets 12S. This pair of strength member sets 12S is provided at one location on the outer sheath 13. The two strength members 12B may be in contact with each other or may be spaced apart. Each strength member 12B is circular in cross section. The diameter of each strength member 12B is, for example, 1.2 mm.

[0045] In the second modification, the outer sheath 13 has a first outer sheath portion 13UB having a larger thickness and a second outer sheath portion 13D having a smaller thickness. The first outer sheath portion 13UB contains two strength members 12B. The thickness of the outer sheath 13 at the thickest point in the first outer sheath portion 13UB, which includes the strength member set 12S, is defined as a first outer sheath thickness 131B.

[0046] In the optical fiber cable 1B of this modification, two strength members 12B (a pair of strength member sets 12S) are also provided at one location in the jacket 13. Therefore, when the optical fiber cable 1B is bent, the bending center is closer to the two strength members 12B, and the distance between the two strength members 12B and the bending center is shorter. Therefore, the two strength members 12B are less likely to buckle. Since the optical fiber cable 1B can be easily bent to a small diameter, the storage ability of the optical fiber cable 1B is also improved.

[0047] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure.

[0048] The jacket 13 of the optical fiber cable 1, the optical fiber cable 1A, and the optical fiber cable 1B can be formed by drop extrusion. More specifically, in drop extrusion, resin is drawn down from a resin flow path between a point and a die, and the resin coats the cable cores 11, 11A from the outside and also coats the tensile strength members 12 so as to enclose them. In this case, the shape of the die opening through which the cable cores 11, 11A pass is noncircular. By making the die opening noncircular in this way, the shape of the cable cores 11, 11A as exemplified in this embodiment can be formed.

[0049] (Evaluation experiment) The pumping distance of the optical fiber cable 1 according to the first embodiment was evaluated. The pumping distance was evaluated using a microduct pumping test defined by the IEC (International Electrotechnical Commission). A general-purpose microduct was used in the pumping test. The inner diameter of the duct was 13 mm. The total pumping distance in the duct was set to 1000 m or more, and the duct was arranged so as to turn back every 100 m. The radius of curvature of the duct was 40 times the outer diameter of the duct. The pressure inside the duct was 1.3 MPa to 1.5 MPa. The measurement experiment confirmed that the pumping distance of the optical fiber cable 1 was 1000 m or more.

[0050] Furthermore, the transmission loss characteristics of the optical fiber cable 1 according to the first embodiment were evaluated. As an evaluation method, light having a wavelength of 1.55 μm was incident on the optical fiber cable 1, and it was confirmed that the transmission loss value was 0.25 dB / km or less.

[0051] Furthermore, the watertightness of the optical fiber cable 1 according to the first embodiment was evaluated. FIG. 5 is a schematic diagram illustrating an evaluation experiment of watertightness. As illustrated in FIG. 5, the hose X has a cylindrical portion X1 extending vertically and a cylindrical portion X2 extending horizontally. The diameter of the hose X is larger than the diameter of the optical fiber cable 1. A waterproof seal X3 is provided at the end of the cylindrical portion X2, which holds the optical fiber cable 1 and seals the hose X to prevent leakage of water stored in the hose X. Because this waterproof seal X3 is provided, the hose X is configured to be able to store liquids such as water or artificial seawater in the cylindrical portions X1 and X2.

[0052] In the evaluation experiment, first, a sample optical fiber cable 1 was held at the end of the cylindrical portion X2, and tap water or artificial seawater was filled inside the hose X. At this time, the height H between the center C of the held optical fiber cable 1 and the water surface of the cylindrical portion X1 was 1 m. With tap water or artificial seawater filled inside the hose X, the optical fiber cable 1 was left at room temperature for 24 hours. After that, the optical fiber cable 1 was removed from the end of the cylindrical portion X2, and the length of the optical fiber cable 1 that had been submerged in tap water or artificial seawater in its longitudinal direction was measured. The watertightness of the optical fiber cable 1 was confirmed by the fact that the length of water submersion was 3 m or less. [Explanation of symbols]

[0053] 1,1A,1B,1Z fiber optic cable 10 Optical fiber ribbon 11, 11A, 11Z cable core 111,111A First arc 112,112A Second arc section 12,12B tensile strength body 12S Tensile Strength Member Set 111L,112L part 13 Outer cover 13U,13UB First outer covering part 13D Second outer covering part 131,131B First jacket thickness 132 Second jacket thickness C,12C,CZ,11CZ,CA center L,LZ straight line X1, X2 cylindrical part X3 Waterproof Seal

Claims

1. a cable core including a plurality of optical fiber cores; at least one strength member disposed along the cable core; an outer jacket that covers the cable core from the outside and encloses the strength members, the cable core has a non-circular shape; an optical fiber cable in which, when viewed in cross section, a thickness of the outer covering at a position including the strength member where the thickness of the outer covering is the thickest is defined as a first outer covering thickness, and a thickness of the outer covering at a position facing the strength member across the cable core is defined as a second outer covering thickness, the first outer covering thickness is thicker than the second outer covering thickness.

2. The optical fiber cable according to claim 1 , wherein the strength member is provided at one location on the jacket in a cross-sectional view.

3. an outer periphery of the cable core has, in the cross-sectional view, two arc portions, a first arc portion close to the strength member and a second arc portion far from the strength member; the first arc portion and the second arc portion are each arcs that are convex outward from the center of the optical fiber cable, The optical fiber cable according to claim 2 , wherein the radius of curvature of the first arcuate portion is larger than the radius of curvature of the second arcuate portion.

4. an outer periphery of the cable core has, in the cross-sectional view, two arc portions, a first arc portion close to the strength member and a second arc portion far from the strength member; the first arc portion is an arc that is convex toward the center of the optical fiber cable, the second arc portion is an arc that is convex outward from the center of the optical fiber cable, The optical fiber cable according to claim 2 , wherein the radius of curvature of the first arcuate portion is smaller than the radius of curvature of the second arcuate portion.

5. The optical fiber cable according to claim 1 , wherein the first outer sheath thickness is the thickest in the cross-sectional view.

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