Optical fiber cable

Abstract

An optical fiber cable 1 comprises: a plurality of coated optical fiber ribbons 50; and a press winding 80 having a housing space 5 that houses the plurality of coated optical fiber ribbons 50. When the housing space 5 is divided into unit spaces 6, each 1 mm square, in vertical section, and the fiber density ρ of optical fibers 51 in each unit space 6 is measured, a first coefficient of variation CV1 satisfies expression (1).　(1): CV1 = σ1 / x1 < 0.20 In formula (1), x1 is the average value of the fiber density ρ for all the unit spaces 6 other than unit spaces 6B including the press winding 80, and σ1 is the standard deviation of the fiber density ρ for all the unit spaces 6 other than the unit spaces 6B including the press winding 80.

Description

fiber optic cable

[0001] The present invention relates to an optical fiber cable. For designated states where incorporation by reference of documents is permitted, the content of Japanese Patent Application No. 2023-216049 filed in Japan on December 21, 2023 is incorporated by reference into this specification and made a part of the description of this specification.

[0002] An optical fiber cable is known that includes a plurality of optical fiber units each having a plurality of optical fiber ribbon core wires, a pressure winding member that covers the plurality of optical fiber units, and an outer jacket that covers the plurality of optical fiber units and the pressure windings (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2020-112644

[0004] In the above-mentioned optical fiber cable, an optical fiber unit is formed by bundling a plurality of optical fiber ribbons with a bundling material. Therefore, in the accommodation space of the optical fiber cable accommodating a plurality of optical fiber units, the density of the optical fibers is high within each optical fiber unit, but the density of the optical fibers between the optical fiber units is low. Therefore, when stress is applied to the optical fiber cable, there is a problem that the transmission characteristics may be degraded in the areas where the optical fibers are densely packed.

[0005] An object of the present invention is to provide an optical fiber cable that can improve transmission characteristics.

[0006] [1] Aspect 1 of the present invention is an optical fiber cable including a plurality of optical fiber ribbons and a protective layer having an accommodation space for accommodating the plurality of optical fiber ribbons, wherein, in a vertical cross section perpendicular to the longitudinal direction of the optical fiber cable, the accommodation space is divided into 1 mm square unit spaces, and when a fiber density ρ of the optical fiber in the unit space is measured, a first coefficient of variation CV １ is an optical fiber cable that satisfies the following formula (1). １ = σ １ / x １<0.20 ... (1) However, in the above formula (1), x １ is the average value of the fiber density ρ for all the unit spaces excluding the unit space containing the protective layer, and σ １ is the standard deviation of the fiber density ρ for all the unit spaces excluding the unit space containing the protective layer.

[0007] [2] Aspect 2 of the present invention may be an optical fiber cable according to aspect 1, wherein the fiber density ρ of all the unit spaces excluding the unit space including the protective layer satisfies the following formula (2): ２ ≦ρ≦17 fibers / mm ２ … (2)

[0008] [3] Aspect 3 of the present invention is the optical fiber cable of aspect 1 or 2, wherein the first coefficient of variation CV １ The optical fiber cable may be an optical fiber cable whose CV satisfies the following formula (3): １ <0.10 … (3)

[0009] [4] Aspect 4 of the present invention is the optical fiber cable of any one of aspects 1 to 3, wherein the optical fiber cable has an inclusion other than the optical fiber in the accommodation space, and a second coefficient of variation CV ２ The optical fiber cable may be an optical fiber cable whose CV satisfies the following formula (4): ２ = σ ２ / x ２ ≦0.15 (4) However, in the above formula (4), x ２ is the average value of the fiber density ρ for the unit space including the inclusion, and σ ２ is the standard deviation of the fiber density ρ for the unit space including the inclusion.

[0010] [5] Aspect 5 of the present invention is the optical fiber cable of aspect 4, wherein the second coefficient of variation CV ２ The optical fiber cable may be an optical fiber cable whose CV satisfies the following formula (5): ２ ≦0.10 … (5)

[0011] [6] Aspect 6 of the present invention is an optical fiber cable according to any one of aspects 1 to 5, wherein the third coefficient of variation CV ３ The optical fiber cable may be an optical fiber cable whose CV satisfies the following formula (6): ３ = σ ３ / x ３ ≦0.30 (6) However, in the above formula (6), x ３ is the average value of the fiber density ρ for a unit space including the protective layer, and σ ３ is the standard deviation of the fiber density ρ for a unit space including the protective layer.

[0012] [7] A seventh aspect of the present invention is an optical fiber cable according to any one of the first to sixth aspects, wherein a fourth coefficient of variation CV ４ The optical fiber cable may be an optical fiber cable whose CV satisfies the following formula (7): ４ = σ ４ / x ４ ≦0.20 (7) However, in the above formula (7), x ４ is the average value of the fiber density ρ over all the unit spaces, and σ ４ is the standard deviation of the fiber density ρ over all the unit spaces.

[0013] [8] Aspect 8 of the present invention may be an optical fiber cable according to any one of aspects 1 to 7, wherein the optical fiber cable comprises a plurality of optical fiber units each including the optical fiber ribbon, and the plurality of optical fiber units includes three or more optical fiber units gathered around an imaginary point in the vertical cross section, and the three or more optical fiber units include a first optical fiber unit having a first boundary that bends around the imaginary point at a first bend angle, and a second optical fiber unit having a second boundary that bends around the imaginary point at a second bend angle, and the first bend angle is an acute angle, and the second bend angle is an obtuse angle.

[0014] [9] A ninth aspect of the present invention may be the optical fiber cable of the eighth aspect, wherein the first bending angle is 45° or less.

[0015]

[10] Aspect 10 of the present invention may be an optical fiber cable according to aspect 8 or 9, wherein the portion that bends at the first bending angle at the first boundary is the portion where the trajectory of the optical fiber ribbon core wire provided in the first optical fiber unit bends.

[0016]

[11] Aspect 11 of the present invention may be an optical fiber cable according to any one of aspects 1 to 10, wherein the optical fiber cable comprises third and fourth optical fiber units each having the optical fiber ribbon core wire and adjacent to each other in the vertical cross section, the third boundary of the third optical fiber unit having a convex portion protruding toward the fourth optical fiber unit, and the fourth boundary of the fourth optical fiber unit having a concave portion into which the convex portion is recessed.

[0017]

[12] Aspect 12 of the present invention is an optical fiber cable according to any one of aspects 1 to 11, wherein the optical fiber cable comprises a plurality of optical fiber units each including the optical fiber ribbon core wire, and the plurality of optical fiber units may be open-type optical fiber units that are not constrained by a bundling material.

[0018]

[13] Aspect 13 of the present invention may be an optical fiber cable in which, in any one of aspects 1 to 12, the optical fiber ribbon comprises a plurality of sub-tape core wires, each of which comprises two or more optical fibers, and the plurality of sub-tape core wires are intermittently connected in the longitudinal direction of the optical fiber ribbon core wire.

[0019] According to the present invention, the first coefficient of variation CV １ satisfies the above formula (1), and the density of the optical fibers is made uniform in the vertical cross section of the optical fiber cable, so that the transmission characteristics of the optical fiber cable can be improved.

[0020] Fig. 1 is a cross-sectional view showing an optical fiber cable according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing an optical fiber unit according to an embodiment of the present invention. Fig. 3 is a perspective view showing an optical fiber ribbon according to an embodiment of the present invention. Fig. 4 is a cross-sectional view showing an optical fiber unit according to an embodiment of the present invention. Fig. 5 is an enlarged view of part V in Fig. 1. Fig. 6 is an enlarged view of part VI in Fig. 1. Fig. 7 is an enlarged view of part VII in Fig. 1. Fig. 8 is an enlarged view of part VIII in Fig. 1. Fig. 9 is a perspective view showing a modified example of an optical fiber ribbon according to an embodiment of the present invention.

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] Fig. 1 is a cross-sectional view showing an optical fiber cable 1 according to this embodiment, Fig. 2 is a cross-sectional view showing an optical fiber unit 30A according to this embodiment, Fig. 3 is a perspective view showing an optical fiber ribbon 50 according to this embodiment, Fig. 4 is a cross-sectional view showing an optical fiber unit 40A according to this embodiment, and Figs. 5 to 8 are enlarged views of parts V to VIII in Fig. 1. Note that Fig. 1 shows the optical fiber unit 20 in a simplified manner. Fig. 3 also shows the optical fiber ribbon 50 in an unfolded state.

[0023] As shown in Fig. 1, the optical fiber cable 1 in this embodiment includes an optical fiber assemblage 10, a pressure winding 80, a sheath 90, and a tension member 100. This optical fiber cable 1 is a cable extending in the normal direction to the plane of the paper in Fig. 1, and Fig. 1 shows a cross section perpendicular to the longitudinal direction (axial direction) of the optical fiber cable 1.

[0024] The configuration of the optical fiber cable 1 is not particularly limited to the above. For example, the optical fiber cable 1 may not include the pressure wrap 80. The optical fiber cable 1 may also include a rip cord between the pressure wrap 80 and the sheath 90. The optical fiber cable 1 may also include a reinforcing sheet interposed between the optical fiber assemblage 10 and the sheath 90, and this reinforcing sheet may have a corrugated shape. The optical fiber cable 1 may also include an inner sheath interposed between the optical fiber assemblage 10 and the sheath 90. Although the optical fiber cable 1 shown in FIG. 1 has a circular cross-sectional shape, the cross-sectional shape of the optical fiber cable 1 is not particularly limited thereto and may, for example, have a rectangular cross-sectional shape.

[0025] The optical fiber assemblage 10 includes a plurality of (12 in this embodiment) optical fiber units 20 and a plurality of (two in this embodiment) second inclusions 70. The optical fiber units 20 include two types of optical fiber units 30 and 40. That is, the plurality of optical fiber units 20 includes a plurality of (five in this embodiment) optical fiber units 30 and a plurality of (seven in this embodiment) optical fiber units 40. Note that the optical fiber assemblage 10 does not necessarily have to include the second inclusions 70, i.e., the optical fiber cable 1 does not necessarily have to include the second inclusions 70.

[0026] The optical fiber units 20 constitute two unit layers 11 and 12. That is, the optical fiber assemblage 10 comprises an inner unit layer 11 and an outer unit layer 12. The inner unit layer 11 is composed of three optical fiber units 20. The inner unit layer 11 is formed by arranging these three optical fiber units 20 in a ring shape. These three optical fiber units 20 include three optical fiber units 30.

[0027] On the other hand, the outer unit layer 12 is composed of nine optical fiber units 20. The outer unit layer 12 is formed by arranging these nine optical fiber units 20 in a ring shape. These nine optical fiber units 20 include two optical fiber units 30 and seven optical fiber units 40. The outer unit layer 12 is arranged outside the inner unit layer 11 and surrounds the inner unit layer 11.

[0028] The number of optical fiber units 20 included in the optical fiber assemblage 10 is not particularly limited to the above. Moreover, the number of optical fiber units 30, 40 included in the optical fiber assemblage 10 is also not particularly limited to the above. For example, the optical fiber assemblage 10 may not include the optical fiber unit 30, that is, the optical fiber cable 1 may not include the first inclusion 60 (described later). Although not particularly limited, for example, all the optical fiber units 20 included in the optical fiber assemblage 10 may be optical fiber units 40 that do not include the first inclusion 60. Moreover, the optical fiber assemblage 10 may include, in addition to the optical fiber units 20, optical fiber units in which a plurality of optical fibers are bundled with a bundling material.

[0029] Furthermore, the number of optical fiber units 30, 40 included in the inner unit layer 11 is not particularly limited to the above. For example, the inner unit layer 11 may include an optical fiber unit 40, or the inner unit layer 11 may not include an optical fiber unit 30. Similarly, the number of optical fiber units 30, 40 included in the outer unit layer 12 is not particularly limited to the above. The outer unit layer 12 may not include an optical fiber unit 30, or the outer unit layer 12 may not include an optical fiber unit 40. Furthermore, the number of unit layers included in the optical fiber assemblage 10 is not particularly limited to the above, and the optical fiber assemblage 10 may include three or more unit layers. It is noted that the optical fiber assemblage 10 does not have to have the layer structure as described above.

[0030] As shown in Fig. 2, each optical fiber unit 30 includes one optical fiber ribbon 50 and a first inclusion 60. Note that Fig. 2 shows, as an example of the optical fiber unit 30, the optical fiber unit 30A located in the central portion of the optical fiber assemblage 10 in Fig. 1.

[0031] 3, the optical fiber ribbon 50 includes a plurality of optical fibers (optical fiber strands) 51 extending in the longitudinal direction of the optical fiber cable 1. Although not particularly limited, the optical fiber ribbon 50 of this embodiment includes 72 optical fibers 51. The number N of the optical fibers 51 included in the optical fiber ribbon 50 is preferably 48 or more and 144 or less (48≦N≦144), and more preferably 60 or more and 108 or less (60≦N≦108).

[0032] The optical fiber ribbon 50 is an intermittently fixed optical fiber ribbon in which 72 optical fibers 51 are arranged in parallel and intermittently connected. Specifically, adjacent optical fibers 51 are connected by first connecting portions 52 at predetermined intervals in the longitudinal direction of the optical fiber ribbon 50. The first connecting portions 52 are formed of, for example, an ultraviolet-curable resin or a thermoplastic resin. Adjacent first connecting portions 52 in the longitudinal direction of the optical fiber ribbon 50 are shifted in the width direction of the optical fiber ribbon 50. Regions of the optical fiber ribbon 50 other than the first connecting portions 52 are non-connected regions in which adjacent optical fibers 51 are not constrained. Therefore, the optical fiber ribbon 50 can be bent at the first connecting portions 52, allowing a large number of optical fibers 51 to be bundled at high density.

[0033] The arrangement of the first connecting portions 52 is not limited to the above and can be set arbitrarily. The interval between adjacent optical fibers 51 can also be set arbitrarily, and adjacent optical fibers 51 may be in contact with each other.

[0034] Furthermore, instead of the intermittently fixed optical fiber ribbon described above, a continuously fixed optical fiber ribbon in which a plurality of optical fibers 51 are bonded over the entire longitudinal length thereof may be used as the optical fiber ribbon 50. In this case, the connecting portions may have sufficient flexibility so that the optical fiber ribbon 50 can be folded as described below, or the connecting portions may be formed in a folded state of the optical fiber ribbon 50.

[0035] The first inclusion 60 is a fibrous inclusion extending in the longitudinal direction of the optical fiber cable 1. The first inclusion 60 extends along the optical fiber ribbon 50. The first inclusion 60 is composed of, for example, a yarn made of a resin material such as nylon, polyester (PE), or polypropylene (PP), a yarn made of aramid fiber (aromatic polyamide resin) or glass fiber, or cotton thread. The first inclusion 60 has water-absorbing properties to improve the waterproofing of the inside of the optical fiber cable 1. Note that the first inclusion 60 does not necessarily have to have water-absorbing properties.

[0036] 2 , the optical fiber unit 30 is formed by folding one optical fiber ribbon 50 so that the optical fiber ribbon 50 surrounds the entire periphery of the first inclusion 60 in a cross section perpendicular to the longitudinal direction of the optical fiber cable 1 (hereinafter also simply referred to as a "vertical cross section") As described above, in this embodiment, since the optical fiber ribbon 50 surrounds the first inclusion 60, movement of the first inclusion 60 within the optical fiber cable 1 can be suppressed.

[0037] 1 each include one first inclusion 60, the optical fiber unit 30 may include multiple first inclusions 60. In this case, too, the multiple first inclusions 60 are surrounded by one optical fiber ribbon 50.

[0038] The optical fiber unit 30 can be manufactured by feeding the optical fiber ribbon 50 and the first inclusions 60 from their respective feeders and passing them through a jig provided in a molding device. Here, the jig is, for example, a former (die) that guides the first inclusions 60 into the optical fiber ribbon 50 and molds the optical fiber ribbon 50 so as to wrap the first inclusions 60.

[0039] In contrast, each optical fiber unit 40 includes only one optical fiber ribbon 50, as shown in Fig. 4. Note that Fig. 4 shows the optical fiber unit 40A located at the rightmost part of the optical fiber assemblage 10 in Fig. 1 as an example of the optical fiber unit 40. This optical fiber unit 40 has a configuration similar to the optical fiber unit 30 described above, except that it does not include an inclusion. That is, in this optical fiber unit 40, the optical fiber ribbon 50 does not surround the first inclusion 60.

[0040] In the known optical fiber unit, a plurality of bundled optical fiber ribbons are bound by a bundling material (bundling material) or a tube, or are inserted into slot grooves of a slot core. That is, the known optical fiber unit is a constrained unit in which the plurality of optical fiber ribbons are constrained in a standalone state (before being incorporated into the optical fiber cable 1, or after being removed from the optical fiber cable 1).

[0041] In contrast, as described above, the optical fiber unit 30 is simply a single optical fiber ribbon 50 wrapped around the first inclusion 60. The optical fiber unit 40 is also composed of only one optical fiber ribbon 50. In this embodiment, the optical fiber ribbon 50 is not covered with a bundling material or a tube, and is not inserted into the slot groove of the slot core. That is, the optical fiber unit 20 of this embodiment is a release-type (non-constrained) optical fiber unit in which the optical fiber ribbon 50 is not constrained in a standalone state. Therefore, the optical fiber cable 1 includes a release-type optical fiber unit 20 in which the optical fiber ribbon 50 is not constrained.

[0042] In this way, by employing an open-type unit as the optical fiber unit 20, it is possible to improve the productivity of the optical fiber cable 1 and reduce the number of parts. For example, when bundling multiple optical fiber ribbons with a bundling material, a process of winding the bundling material is required. In contrast, by employing an open-type unit as the optical fiber unit 20, not only is the bundling material itself unnecessary, but the winding process is also unnecessary, allowing for a faster drawing speed when manufacturing the optical fiber cable 1.

[0043] 1, the outer shape of the optical fiber unit 20 described above has a shape corresponding to the outer shapes of the other optical fiber units 20, the second inclusions 70, and the pressure windings 80 adjacent to the optical fiber unit 20. In particular, since the optical fiber unit 20 of this embodiment is an open-type optical fiber unit as described above, the outer shape of the optical fiber unit 20 is greatly dependent on the outer shapes of the other optical fiber units 20, the second inclusions 70, and the pressure windings 80 adjacent to the optical fiber unit 20, and has a distorted shape. Therefore, the 12 optical fiber units 20 shown in FIG. 1 do not have a specific outer shape, but each has an outer shape that is significantly different from the others.

[0044] The second inclusion 70 is a fibrous inclusion extending in the longitudinal direction of the optical fiber cable 1, similar to the above-described first inclusion 60. This second inclusion 70 is not present within the optical fiber unit 20, but is interposed between the optical fiber units 20. Specifically, as shown in FIG. 1 , this second inclusion 70 is disposed near the center of the optical fiber assemblage 10, or is sandwiched between three optical fiber units 20. Note that this second inclusion 70 may be sandwiched between two or four or more optical fiber units 20, or may be sandwiched between an optical fiber unit 20 and a pressure winding 80. In this way, by providing the optical fiber assemblage 10 with the second inclusion 70 that is not surrounded by the optical fiber ribbon 50, movement of the optical fiber units 20 within the optical fiber cable 1 can be suppressed.

[0045] The optical fiber assemblage 10 is formed by twisting together the optical fiber unit 20 and the second inclusion 70 described above. Specific examples of twisting methods for the optical fiber assemblage 10 include SZ twisting and unidirectional twisting. SZ twisting is a twisting method in which multiple linear bodies are twisted together while reversing the twisting direction at predetermined intervals. In contrast, unidirectional twisting is a twisting method in which multiple linear bodies are twisted in only one direction, that is, a twisting method in which multiple linear bodies are twisted together in a spiral shape.

[0046] In this case, as described above, since the optical fiber unit 20 is an open-type optical fiber unit, the outer shape of the optical fiber unit 20 is largely dependent on the outer shapes of the other optical fiber units 20 adjacent to the optical fiber unit 20, the second intervening material 70, and the pressure winding 80.

[0047] 5, the optical fiber units 20A to 20C are gathered around an imaginary point VP in the vertical cross section. The boundary 201A of the optical fiber unit 20A is bent at a bending angle θ around the imaginary point VP. １ The boundary 201B of the optical fiber unit 20B is bent at a bending angle θ around the virtual point VP. ２The boundary 201C of the optical fiber unit 20C is bent at a bending angle θ around the virtual point VP. ３ In this embodiment, the bending angle θ １ is an acute angle (θ １ <90°). Although not particularly limited, this bending angle θ １ is preferably 45° or less (θ １ ≦45°). In contrast, the bending angle θ ２ , θ ３ is an obtuse angle (θ ２ >90°, θ ３ >90°).

[0048] The boundary of the optical fiber unit 20 is an imaginary line that separates the optical fiber unit 20 from other optical fiber units 20 adjacent to the optical fiber unit 20 (or the second inclusion 70 adjacent to the optical fiber unit 20). Specifically, this boundary is an imaginary line that connects the centers of the optical fibers 51 that face the other optical fiber unit 20 adjacent to the optical fiber unit 20 (or the second inclusion 70 adjacent to the optical fiber unit 20) among the optical fibers 51 included in the optical fiber unit 20.

[0049] Here, if the bending angles of all three or more optical fiber units gathered around the imaginary point VP in the vertical cross section are obtuse angles, wide gaps are likely to form between the optical fiber units. In this case, waterproof performance may be affected and untwisting may be more likely to occur in the optical fiber assemblage 10. On the other hand, if the bending angles of all three or more optical fiber units are acute angles, a large number of optical fiber units must be arranged around the imaginary point VP, and the shape of each optical fiber unit becomes elongated and unstable, which may affect the transmission characteristics of the optical fiber cable 1.

[0050] In contrast to this, in this embodiment, the three or more optical fiber units 20 gathered around the imaginary point VP in the vertical cross section include both the optical fiber unit 20A having an acute bending angle and the optical fiber units 20B and 20C having obtuse bending angles. This makes it possible to reduce the gaps between the optical fiber units 20A to 20C and stabilize the shapes of the optical fiber units 20A to 20C. In particular, the bending angle θ of the optical fiber unit 20A having an acute angle １ is 45° or less, the above-mentioned effect can be enhanced. The imaginary point VP is an arbitrary point around which three or more optical fiber units are gathered within the accommodation space 5. The optical fiber unit 20A corresponds to an example of a "first optical fiber unit" in the aspects of the present invention, and the optical fiber unit 20B or 20C corresponds to an example of a "second optical fiber unit" in the aspects of the present invention.

[0051] As shown in FIG. 5, an acute angle θ １ The bent portion is formed by a bent portion of the trajectory 501 of the optical fiber ribbon 50 included in the optical fiber unit 20A. As a result, the optical fiber 51 located at the apex is held by the adjacent optical fibers 51 on both sides via the connecting portions 52, so that distortion occurring in the optical fiber 51 can be suppressed.

[0052] The locus 501 of the optical fiber ribbon 50 is an imaginary line connecting the multiple optical fibers 51 constituting the optical fiber ribbon 50 from one end (e.g., the first end 502 in FIGS. 2 and 4 ) to the other end (e.g., the second end 503 in FIGS. 2 and 4 ) of the optical fiber ribbon 50 in accordance with the arrangement of the multiple optical fibers 51. This locus 501 passes through the centers of the multiple optical fibers 51 constituting the optical fiber ribbon 50. The arrangement of the optical fibers 51 is the order in which the optical fibers 51 are arranged adjacent to each other via the connecting portions 52 in the optical fiber ribbon 50. In other words, the locus 501 is an imaginary line formed by connecting unit imaginary lines connecting the centers of adjacent optical fibers 51 via the connecting portions 52 from one end to the other end.

[0053] Furthermore, since the optical fiber unit 20 is an open-type optical fiber unit, for example, as shown in Fig. 6, the boundary 201D of the optical fiber unit 20D has a convex portion 202, and the boundary 201E of the optical fiber unit 20E adjacent to the optical fiber unit 20D has a concave portion 203. The convex portion 202 of the optical fiber unit 20D protrudes toward the optical fiber unit 20D and enters the concave portion 203 of the optical fiber unit 20D. With this configuration, the shapes of the optical fiber units 20D and 20E are stabilized, so that it is possible to further suppress the occurrence of variations in density of the optical fibers 51 in the optical fiber assemblage 10. The optical fiber unit 20D corresponds to an example of a "third optical fiber unit" in this aspect of the present invention, and the optical fiber unit 20E corresponds to an example of a "fourth optical fiber unit" in this aspect of the present invention.

[0054] 1, the optical fiber assemblage 10 described above is covered with a pressure winding 80. Specifically, the pressure winding 80 forms a storage space 5 surrounding the periphery of the optical fiber assemblage 10, and the optical fiber assemblage 10 is stored in this storage space 5.

[0055] In this embodiment, the first coefficient of variation CV １ satisfies the following formula (8). １ 1, in the vertical cross section of the optical fiber cable 1, the accommodation space 5 is divided into unit spaces 6 of 1 mm square, and the fiber density ρ of the optical fibers 51 in the unit spaces 6 is measured. More specifically, a mesh (lattice) is created on the accommodation space 5, the accommodation space 5 is divided into unit spaces (unit lattices) 6 of 1 mm square, and the fiber density ρ of the optical fibers 51 in each unit space 6 is measured. In this embodiment, the first coefficient of variation CV １ By satisfying the following formula (8), the density of the optical fibers 51 can be made uniform in the vertical cross section of the optical fiber cable 1, and the transmission characteristics of the optical fiber cable 1 can be improved. １It is preferable that the following formula (9) be satisfied, which can further improve the transmission characteristics of the optical fiber cable 1. It is preferable that the following formulas (8), (9), and (12) to (16) be satisfied over the entire area of ​​the optical fiber cable 1 in the longitudinal direction.

[0056] CV １ = σ １ / x １ <0.20... (8) CV １ <0.10 … (9)

[0057] However, in the above formula (8), x １ is the average value of the fiber density ρ for all unit spaces 6 except for the unit space 6 containing the pressure winding 80. １ is the standard deviation of the fiber density ρ for all unit spaces 6 excluding the unit space 6 including the pressure winding 80. Generally, when the number of unit spaces 6 is n, the average value x of the fiber density ρ is expressed by the following formula (10), and the standard deviation σ of the fiber density ρ is expressed by the following formula (11). In the following formulas (10) and (11), the fiber density ρ ｉ represents the fiber density ρ of the i-th unit space 6 among the n unit spaces 6.

[0058]

[0059] Specifically, the fiber density ρ is calculated as follows: First, the number m of optical fibers 51 contained in the unit space 6 is counted. In this case, if 80% or more of the area of ​​the optical fibers 51 is contained in the unit space 6, it is counted as "1 fiber." If more than 20% but less than 80% of the area of ​​the optical fibers 51 is contained in the unit space 6, it is counted as "0.5 fibers." If only 20% or less of the area of ​​the unit space 6 is contained, it is counted as "0 fibers."

[0060] Next, the number m of optical fibers 51 included in the unit space 6 is calculated by dividing the number m by the area (cross-sectional area) S of the accommodation space 5 in the unit space 6 (ρ=m / S). The area S of the accommodation space 5 is the area of ​​the space in which the optical fibers 51 can exist in the unit space 6.

[0061] For example, in this embodiment, as shown in Figures 7 and 8, there are three types of unit spaces 6A to 6C as the unit space 6. Specifically, the first unit space 6A is a unit space 6 that does not include the inclusions 60, 70 and the pressure winding 80. In contrast, the second unit space 6B is a unit space 6 that includes the pressure winding 80. Furthermore, the third unit space 6C is a unit space 6 that includes the inclusions 60, 70. All of the unit spaces 6 include a portion of the accommodation space 5.

[0062] When calculating the fiber density ρ of the first unit space 6A, the occupied area S is the total area (1 mm ２ On the other hand, when calculating the fiber density ρ of the second unit space 6B, the total area (1 mm ２ ) minus the area of ​​the portion outside the accommodation space 5 (the portion outside the inner surface 80a of the pressure winding 80). When calculating the fiber density ρ of the third unit space 6C, the occupied area S is the total area (1 mm ２ ) minus the area of ​​the inclusions 60 and 70.

[0063] Here, although not particularly limited, it is preferable that the fiber density ρ of all unit spaces 6 (i.e., all first unit spaces 6A and all third unit spaces 6C) excluding the second unit space 6B including the pressure winding 80 satisfies the following formula (12): ２ By satisfying the above, it is possible to make the pull-out force of the optical fiber ribbon 50 appropriate, and to suppress movement of the optical fiber ribbon 50. The pull-out force is the force required to start relative movement of the optical fiber ribbon with respect to the optical fiber cable when the optical fiber ribbon is pulled. On the other hand, when the fiber density ρ is 17 fibers / mm ２ By satisfying the condition below, good transmission characteristics of the optical fiber cable 1 can be ensured.

[0064] 11 fibers / mm ２ ≦ρ≦17 fibers / mm ２… (12)

[0065] After calculating the fiber density ρ for all unit spaces 6 in the accommodation space 5, the above average value x １ and standard deviation σ １ Specifically, the average value x １ is the average value for all unit spaces 6 excluding the second unit space 6B (i.e., all first unit spaces 6A and all third unit spaces 6C). １ is also the standard deviation for all unit spaces 6 excluding the second unit space 6B (i.e., all first unit spaces 6A and all third unit spaces 6C). １ and standard deviation σ １ From the first coefficient of variation CV １ Calculate.

[0066] In addition, when other members than the optical fiber 51 are present in the accommodation space 5, the occupied area S is the total area of ​​the unit space 6 (1 mm ２ The fiber density ρ is calculated using a value obtained by subtracting the area of ​​the other components from the area of ​​the first and second inclusions 60, 70. Specific examples of the other components present in the accommodation space 5 include the strength members and ripcords present in the accommodation space 5, in addition to the first and second inclusions 60, 70 described above. The other components present in the accommodation space 5 correspond to examples of "inclusions" in this aspect of the present invention. In other words, the "inclusions" in this aspect of the present invention is a concept that encompasses the first and second inclusions 60, 70, the strength members, and the ripcords.

[0067] Although not particularly limited, the second coefficient of variation CV ２ It is preferable that the following formula (13) is satisfied, and it is more preferable that the following formula (14) is satisfied. In the optical fiber cable equipped with the above-mentioned constrained type optical fiber unit, gaps tend to occur around the inclusions, but the second coefficient of variation CV ２ By satisfying the following formula (13), the fiber density ρ can be made uniform even around the inclusions 60 and 70. ２By satisfying the following formula (14), the fiber density ρ can be made even more uniform around the inclusions 60 and 70.

[0068] CV ２ = σ ２ / x ２ ≦0.15... (13) CV ２ ≦0.10 … (14)

[0069] However, in the above formula (13), x ２ is the average value of the fiber density ρ for all the third unit spaces 6C including the inclusions 60 and 70. ２ is the standard deviation of the fiber density ρ for all the third unit spaces 6C including the inclusions 60, 70.

[0070] In addition, although not particularly limited, the third coefficient of variation CV ３ It is preferable that the following formula (15) is satisfied: In the optical fiber cable provided with the above-mentioned constrained type optical fiber unit, gaps tend to occur near the pressure winding, but the third coefficient of variation CV ３ By satisfying the following formula (15), the fiber density ρ can be made uniform even in the vicinity of the pressure winding 80.

[0071] CV ３ = σ ３ / x ３ ≦0.30 … (15)

[0072] However, in the above formula (15), x ３ is the average value of the fiber density ρ for all the second unit spaces 6B including the pressure winding 80. ３ is the standard deviation of the fiber density ρ for all second unit spaces 6B including the pressure winding 80.

[0073] In addition, although not particularly limited, the fourth coefficient of variation CV ４ It is preferable that the fourth coefficient of variation CV satisfies the following formula (16): ４ By satisfying the following formula (16), the fiber density ρ can be made uniform in the entire unit space 6, including the areas around the inclusions 60, 70 and in the vicinity of the pressure winding 80.

[0074] CV ４ = σ ４ / x ４ ≦0.20 … (16)

[0075] However, in the above formula (16), x ４ is the average value of the fiber density ρ for all unit spaces 6 (i.e., all first unit spaces 6A, all second unit spaces 6B, and all third unit spaces 6C). ４ is the standard deviation of the fiber density ρ for all unit spaces 6 (i.e., all first unit spaces 6A, all second unit spaces 6B, and all third unit spaces 6C).

[0076] When the optical fiber cable 1 does not have a pressure wrap 80, the internal space 91 of the sheath 90 becomes the storage space 5 that stores the optical fiber assemblage 10. When the optical fiber cable 1 does not have a pressure wrap 80 but has a reinforcing sheet interposed between the optical fiber assemblage 10 and the sheath 90, the space surrounded by this reinforcing sheet becomes the storage space 5. When the optical fiber cable 1 does not have a pressure wrap 80 but has an inner sheath interposed between the optical fiber assemblage 10 and the sheath 90, the space surrounded by this inner sheath becomes the storage space 5.

[0077] In this embodiment, the pressure winding 80 is formed by longitudinally wrapping a pressure winding tape 81 around the outer periphery of the optical fiber assemblage 10. Specifically, the pressure winding tape 81 is wound around the outer periphery of the optical fiber assemblage 10 in a state in which the longitudinal direction of the pressure winding tape 81 substantially coincides with the longitudinal direction of the optical fiber cable 1 and the width direction of the pressure winding tape 81 substantially coincides with the circumferential direction of the optical fiber cable 1. Note that the winding method of the pressure winding tape 81 is not limited to longitudinally wrapping, and may be, for example, horizontally wrapping (spiral winding).

[0078] The holding winding tape 81 is made of a nonwoven fabric or a film. Specific examples of the nonwoven fabric that makes up the holding winding tape 81 are not particularly limited, but include nonwoven fabrics made of fibers such as polyester, polyethylene, and polypropylene. On the other hand, specific examples of the film that makes up the holding winding tape 81 are not particularly limited, but include films made of resins such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and nylon.

[0079] When the holding winding tape 81 is made of a nonwoven fabric, water-absorbing powder may be applied to the nonwoven fabric so that it functions as a water-absorbing layer for stopping water from entering the optical fiber cable 1. When water penetrates the optical fiber cable 1, the water-absorbing powder swells and seals gaps in the optical fiber cable 1, thereby stopping water from entering the optical fiber cable 1.

[0080] Specific examples of such water-absorbing powders are not particularly limited, but include, for example, starch-based, cellulose-based, polyacrylic acid-based, polyvinyl alcohol-based, polyoxyethylene-based highly absorbent materials, or mixtures of these, etc. Furthermore, the water-absorbing powder may be applied to the nonwoven fabric by adhering (coating) it on the surface of the nonwoven fabric, or by being interposed between two sheets of nonwoven fabric.

[0081] The sheath (outer jacket) 90 is a tubular member that covers the outer periphery of the pressure winding 80, and the optical fiber assemblage 10 wrapped in the pressure winding 80 is housed in an internal space 91 of the sheath 90. The sheath 90 is made of a resin material such as polyvinyl chloride (PVC), polyethylene (PE), nylon, ethylene fluoride, or polypropylene (PP). A pair of tensile members 100 are embedded in the sheath 90.

[0082] The pair of tension members 100 are linear components that bear the stress applied in the longitudinal direction of the optical fiber cable 1, thereby reducing the load on the optical fiber 51. The tension members 100 are embedded in the sheath 90 so as to extend substantially parallel to each other across the internal space 91 of the sheath 90. Note that the number and arrangement of the tension members 100 provided in the optical fiber cable 1 are not particularly limited to those described above.

[0083] Examples of materials that can be used to form the tension member 100 include non-metallic materials and metallic materials. Specific examples of non-metallic materials include, but are not limited to, glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (KFRP) reinforced with aramid (aromatic polyamide resin), and fiber reinforced plastic (FRP) such as polyethylene fiber reinforced plastic reinforced with polyethylene fibers. Specific examples of metallic materials include, but are not limited to, metal wires such as steel wires.

[0084] As described above, in this embodiment, the first coefficient of variation CV １ satisfies the above formula (8), and the density of the optical fibers 51 is made uniform in the vertical cross section of the optical fiber cable 1, so that an optical fiber cable 1 with good transmission characteristics can be provided.

[0085] It should be noted that the above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, the elements disclosed in the above embodiments are intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0086] For example, the optical fiber unit 20 may be configured using an optical fiber ribbon 50B shown in Fig. 9 instead of the above-described optical fiber ribbon 50. Fig. 9 is a perspective view showing the optical fiber ribbon 50B, which is a modified example of the above-described optical fiber ribbon 50.

[0087] This optical fiber ribbon 50B includes a plurality of sub-tapes 55. Each sub-tape 55 has the same configuration as the above-described optical fiber ribbon 50, except that the number of optical fibers 51 is different. That is, each sub-tape 55 is an intermittently fixed optical fiber ribbon in which a plurality of optical fibers 51 are arranged in parallel and intermittently connected at first connecting portions 52.

[0088] Adjacent sub-tapes 55 are also intermittently connected by second connecting portions 56 at predetermined intervals in the longitudinal direction of the optical fiber ribbon 50. The second connecting portions 56 are formed of, for example, an ultraviolet-curable resin or a thermoplastic resin. In the optical fiber ribbon 50B, the areas other than the second connecting portions 56 are non-connected areas where the sub-tapes 55 are not constrained to each other.

[0089] By providing the optical fiber ribbon 50B with such a plurality of sub-tapes 55, it is possible to provide different identifiers such as ring marks for each sub-tape 55, making it easier to identify the optical fibers 51 within the optical fiber ribbon 50B. Furthermore, while a conventional optical fiber ribbon may be configured with, for example, 4, 8, 12, or 16 optical fibers, by providing the optical fiber ribbon 50B with a plurality of sub-tapes 55, the optical fiber ribbon 50B can be handled with the same ease as the above-described conventional optical fiber ribbon.

[0090] The number of sub-tape fibers 55 included in the optical fiber ribbon 50B is not particularly limited to the above, as long as it is plural. Furthermore, the number of optical fibers 51 included in each sub-tape fiber 55 is not particularly limited, as long as it is two or more. Although not particularly limited, the total number N of optical fibers 51 included in the optical fiber ribbon 50B is preferably 48 or more and 144 or less (48≦N≦144), and more preferably 60 or more and 108 or less (60≦N≦108). Furthermore, a continuous fixed optical fiber ribbon may be used as the sub-tape fiber 55.

[0091] In addition, in the above-described embodiments, a type of cable in which all optical fibers are accommodated in a single accommodation space (center tube type, slotless type) has been given as an example of an optical fiber cable, but the optical fiber cable may be of other types. For example, the optical fiber cable may be of a slotted type, in which case, the individual spaces surrounded by the grooves of the slotted rod and the protective layer can be considered as accommodation spaces. Alternatively, the optical fiber cable may be of a loose tube type, in which case, the internal space of each tube can be considered as accommodation spaces. However, an optical fiber cable of a type in which all optical fibers are accommodated in a single accommodation space (center tube type, slotless type), as in the above-described embodiments, can achieve greater effectiveness than a slotted type or loose tube type optical fiber cable.

[0092] Examples and comparative examples of this embodiment will be described below. In the following examples and comparative examples, optical fiber cables were fabricated and the transmission characteristics of the optical fiber cables were evaluated. Note that the present invention is not limited to these examples.

[0093] In Example 1, an optical fiber cable was fabricated as shown in Fig. 1, which included 12 optical fiber units. Each optical fiber unit was made up of an optical fiber ribbon with 72 fibers. Therefore, the optical fiber cable of Example 1 included 864 optical fibers.

[0094] For the optical fiber cable of Example 1, a digital microscope (VHX-60000 manufactured by Keyence Corporation) was used to measure the fiber density ρ for all unit spaces in the vertical cross section. At this time, a cross section perpendicular to the longitudinal direction of the optical fiber cable was cut out, and epoxy resin was filled into the optical fiber cable in a state where no radial force of the optical fiber cable was applied to the cross section, thereby preventing the optical fiber cable from deforming. Then, the above-mentioned average value x was calculated using this fiber density ρ. １ ~x ４ , standard deviation σ １ ~σ ４, and the coefficient of variation CV １ ~CV ４ The results are shown in Table 1 below. The area of ​​the accommodation space for the optical fiber cable of Example 1 is 68.3 mm ２ It was.

[0095]

[0096] <Comparative Example 1> In Comparative Example 1, an optical fiber cable was produced having the same configuration as in Example 1, except that a constrained unit was used as the optical fiber unit. However, the optical fiber unit used was made by bundling six optical fiber ribbons, each having 12 optical fibers, with a bundling material. For the optical fiber cable of Comparative Example 1, the above-mentioned average value x １ ~x ４ , standard deviation σ １ ~σ ４ , and the coefficient of variation CV １ ~CV ４ The results are shown in Table 1. The area of ​​the accommodation space for the optical fiber cable of Comparative Example 1 is 68.8 mm ２ This was almost the same as in Example 1.

[0097] <Evaluation of Transmission Characteristics> The transmission characteristics were evaluated for Example 1 and Comparative Example 1. In this evaluation of transmission characteristics, the optical fiber cables of Example 1 and Comparative Example 1 were subjected to two temperature cycles in the range of -40°C to +70°C in accordance with the "Temperature cycling" provisions of "Telcordia Technologies Generic Requirements GR-20-CORE, issue 4, July 2013," and the maximum loss variation at a measurement wavelength of 1.55 μm was measured. In this transmission characteristic evaluation, if the maximum loss variation was 0.15 dB / km or less, the results were evaluated as good and given an "A." If the maximum loss variation exceeded 0.15 dB / km, the results were evaluated as unsatisfactory and given a "B." The results are shown in Table 1 above.

[0098] In Example 1, the first coefficient of variation CV １The second coefficient of variation CV was less than 0.10, and the maximum loss variation in the transmission characteristic evaluation was 0.15 dB / km or less. ２ is 0.10 or less, and the third coefficient of variation CV ３ is 0.30 or less, and the fourth coefficient of variation CV ４ In contrast, in Comparative Example 1, the first coefficient of variation CV １ The second coefficient of variation CV was 0.20 or more, and the maximum loss variation in the transmission characteristic evaluation exceeded 0.15 dB / km. ２ is greater than 0.15, and the third coefficient of variation CV ３ is greater than 0.30, and the fourth coefficient of variation CV ４ was greater than 0.20.

[0099] 1... Optical fiber cable 5... Storage space 6, 6A to 6C... Unit space 10... Optical fiber assembly 11... Inner unit layer 12... Outer unit layer 20, 20A to 20E, 30, 30A, 40, 40A... Optical fiber unit 201A to 201E... Boundary 202... Convex portion 203... Concave portion θ １ ~θ ３ ...bending angle 50, 50B...optical fiber ribbon 501...trajectory 502, 503...end portion 51...optical fiber 52...first connecting portion 55...sub-tape 56...second connecting portion 60...first inclusion 70...second inclusion 80...pressure winding 80a...inner surface 81...pressure winding tape 90...sheath 91...internal space 100...tensile member

Claims

1. An optical fiber cable comprising a plurality of optical fiber ribbons and a protective layer having a storage space for storing the plurality of optical fiber ribbons, wherein, in a vertical cross section perpendicular to the longitudinal direction of the optical fiber cable, the storage space is divided into unit spaces of 1 mm square, and a fiber density ρ of the optical fiber in the unit space is measured, and a first coefficient of variation CV １ An optical fiber cable that satisfies the following formula (1). １ = σ １ / x １ <0.20 ... (1) However, in the above formula (1), x １ is the average value of the fiber density ρ for all the unit spaces excluding the unit space containing the protective layer, and σ １ is the standard deviation of the fiber density ρ for all the unit spaces except the unit space containing the protective layer.

2. The optical fiber cable according to claim 1, wherein the fiber density ρ for all the unit spaces excluding the unit space including the protective layer satisfies the following formula (2): 11 fibers / mm ２ ≦ρ≦17 cores / mm ２ … (2) 3. The optical fiber cable according to claim 1 or 2, wherein the first coefficient of variation CV １ An optical fiber cable that satisfies the following formula (3). １ <0.10 … (3) 4. An optical fiber cable according to any one of claims 1 to 3, wherein the optical fiber cable has an inclusion other than the optical fiber in the accommodation space, and a second coefficient of variation CV ２ An optical fiber cable that satisfies the following formula (4). ２ = σ ２ / x ２ ≦0.15 (4) In the above formula (4), x ２ is the average value of the fiber density ρ for the unit space including the inclusion, and σ ２ is the standard deviation of the fiber density ρ for the unit space including the inclusion 5. The optical fiber cable according to claim 4, wherein the second coefficient of variation CV ２ An optical fiber cable that satisfies the following formula (5). ２ ≦0.10 … (5) 6. The optical fiber cable according to any one of claims 1 to 5, wherein the third coefficient of variation CV ３ An optical fiber cable that satisfies the following formula (6). ３ = σ ３ / x ３ ≦0.30 (6) In the above formula (6), x ３ is the average value of the fiber density ρ for a unit space including the protective layer, and σ ３ is the standard deviation of the fiber density ρ for a unit space including the protective layer.

7. The optical fiber cable according to any one of claims 1 to 6, wherein the fourth coefficient of variation CV ４ An optical fiber cable that satisfies the following formula (7). ４ = σ ４ / x ４ ≦0.20 (7) In the above formula (7), x ４ is the average value of the fiber density ρ over all the unit spaces, and σ ４ is the standard deviation of the fiber density ρ over all the unit spaces.

8. An optical fiber cable as claimed in any one of claims 1 to 7, comprising a plurality of optical fiber units each including the optical fiber ribbon, the plurality of optical fiber units including three or more optical fiber units gathered around an imaginary point in the vertical cross section, the three or more optical fiber units including: a first optical fiber unit having a first boundary bent at a first bending angle around the imaginary point; and a second optical fiber unit having a second boundary bent at a second bending angle around the imaginary point, the first bending angle being an acute angle, and the second bending angle being an obtuse angle.

9. The optical fiber cable according to claim 8, wherein the first bend angle is 45° or less.

10. An optical fiber cable as claimed in claim 8 or 9, wherein the portion bent at the first bending angle at the first boundary is a portion where the trajectory of the optical fiber ribbon core wire provided in the first optical fiber unit bends.

11. An optical fiber cable as described in any one of claims 1 to 10, wherein the optical fiber cable comprises third and fourth optical fiber units each having the optical fiber ribbon core wire and adjacent to each other in the vertical cross section, a third boundary of the third optical fiber unit having a convex portion protruding toward the fourth optical fiber unit, and a fourth boundary of the fourth optical fiber unit having a concave portion into which the convex portion is recessed.

12. An optical fiber cable as claimed in any one of claims 1 to 11, comprising a plurality of optical fiber units each including the optical fiber ribbon, and the plurality of optical fiber units are open-type optical fiber units that are not constrained by a bundling material.

13. An optical fiber cable as claimed in any one of claims 1 to 12, wherein the optical fiber ribbon comprises a plurality of sub-tape core wires, each of which comprises two or more optical fibers, and the plurality of sub-tape core wires are intermittently connected in the longitudinal direction of the optical fiber ribbon core wire.

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