Optical fiber unit and optical fiber cable

Abstract

This optical fiber unit (1) comprises: a plurality of optical fibers or a plurality of optical fiber ribbons (10); a water-absorbing fiber (20) that is provided along an aggregate of the plurality of optical fibers or the plurality of optical fiber ribbons; and a plastic film (30) that has a thickness of less than 0.1 mm and covers the periphery of the aggregate of the plurality of optical fibers or the plurality of optical fiber ribbons, and the water-absorbing fiber. The inner surface of the plastic film (30) adheres to the water-absorbing fiber (20), and a portion of the aggregate of the plurality of optical fibers or the plurality of optical fiber ribbons (10) and a portion of the water-absorbing fiber (20) are exposed from the plastic film (30).

Description

Optical fiber unit and optical fiber cable

[0001] The present disclosure relates to an optical fiber unit and an optical fiber cable.

[0002] Patent Document 1 discloses a cable in which intermittently bonded optical fiber ribbons are arranged in a circular unit tube.

[0003] Japanese Patent Application Publication No. 2019-124936

[0004] The optical fiber unit of the present disclosure comprises: a plurality of optical fibers or a plurality of optical fiber ribbons; a water-absorbing fiber arranged along the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons; and a plastic film having a thickness of less than 0.1 mm that covers the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and the water-absorbing fiber, wherein the inner surface of the plastic film is adhered to the water-absorbing fiber, and a portion of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and a portion of the water-absorbing fiber are exposed from the plastic film.

[0005] The optical fiber cable of the present disclosure comprises: a plurality of the optical fiber units; and an outer jacket covering the plurality of the optical fiber units.

[0006] Fig. 1 is a perspective view of an optical fiber unit according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view of the optical fiber unit shown in Fig. 1. Fig. 3 is a schematic diagram of a manufacturing apparatus for manufacturing the optical fiber unit shown in Fig. 1. Fig. 4 is a cross-sectional view of an optical fiber cable including a plurality of optical fiber units shown in Fig. 1. Fig. 5 is a table for explaining the results of characteristic evaluation of the optical fiber unit according to an embodiment of the present disclosure.

[0007] [Problem to be Solved by the Present Disclosure] In an optical fiber unit having a loose tube structure as disclosed in Patent Document 1, the tube may be thinned to achieve high-density packaging of optical fibers. However, if the tube is thinned excessively, the resin coating that forms the tube is likely to run out during extrusion molding. For this reason, a plastic film that covers the periphery of multiple optical fibers or multiple optical fiber ribbons may be provided in the optical fiber unit.

[0008] On the other hand, optical fiber units in which a plastic film is provided to cover the periphery of a plurality of optical fibers or a plurality of optical fiber ribbons have a problem in that the optical fiber unit is difficult to disassemble. Also, in such optical fiber units, if water comes into contact with the outside of the optical fiber unit, the water may not be absorbed by the water-absorbing fibers inside the optical fiber unit, and the water may easily flow along the outside of the optical fiber unit within the optical fiber cable.

[0009] The present invention aims to provide an optical fiber unit and an optical fiber cable that can easily disassemble the optical fiber unit while improving packaging density and manufacturing yield, and that can more effectively prevent water from penetrating into the interior of the optical fiber cable.

[0010] [Effects of the Present Disclosure] According to the present disclosure, it is possible to easily disassemble an optical fiber unit while improving packaging density and manufacturing yield, and to more effectively prevent water from penetrating into the interior of an optical fiber cable.

[0011] (Explanation of Embodiments of the Present Disclosure) First, embodiments of the present disclosure will be listed and described. An optical fiber unit according to an embodiment of the present disclosure comprises: (1) a plurality of optical fibers or a plurality of optical fiber ribbons; a water-absorbent fiber arranged along the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons; and a plastic film having a thickness of less than 0.1 mm and covering the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and the water-absorbent fiber, wherein an inner surface of the plastic film is adhered to the water-absorbent fiber, and a portion of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and a portion of the water-absorbent fiber are exposed from the plastic film.

[0012] In this way, the assembly of multiple optical fibers or multiple optical fiber ribbons is covered with a thin plastic film having a thickness of less than 0.1 mm, thereby improving the packaging density of the optical fibers. Furthermore, since the plastic film is wrapped around the water-absorbing fiber so as to adhere to it, the occurrence of molding defects is suppressed compared to when a thin film tube is formed around multiple optical fibers or multiple optical fiber ribbons by extrusion molding, and the manufacturing yield of the optical fiber unit can be improved.

[0013] In addition, since a portion of the aggregate of multiple optical fibers or multiple optical fiber ribbons is exposed from the plastic film, the optical fiber unit can be easily disassembled. Furthermore, since a portion of the water-absorbing fiber is exposed from the plastic film, even if the outside of the optical fiber unit comes into contact with water, the water-absorbing fiber can absorb the water, and water can be more effectively prevented from penetrating into the optical fiber cable.

[0014] (2) In the optical fiber unit of (1) above, the plastic film may be wound longitudinally along the longitudinal direction of the plurality of optical fibers or the plurality of optical fiber ribbons.

[0015] With this configuration, an optical fiber unit in which a portion of the aggregate of multiple optical fibers or multiple optical fiber ribbons and a portion of the water-absorbing fiber are exposed from the plastic film can be manufactured by a relatively easy method. Furthermore, compared to when the plastic film is wound spirally, the length manufactured per unit time can be longer, thereby improving production efficiency.

[0016] (3) In the optical fiber unit of (1) or (2) above, the plastic film may cover an area of ​​30% to 70% of the outer circumference of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons.

[0017] If more than 70% of the outer circumference of the assembly of optical fibers or optical fiber ribbons is covered with a plastic film, the dismantling and waterproofing properties of the optical fiber unit will be reduced, whereas if less than 30% of the outer circumference of the assembly of optical fibers or optical fiber ribbons is covered with a plastic film, the adhesive strength of the plastic film to the water-absorbing fiber will be reduced.

[0018] Therefore, as described above, by configuring the optical fiber unit so that 30% to 70% of the outer periphery of the assembly of multiple optical fibers or multiple optical fiber ribbons is covered with a plastic film, the disassembly and waterproofing properties of the optical fiber unit can be improved, and the adhesive strength of the plastic film to the water-absorbing fiber can be sufficiently ensured.

[0019] (4) In any of the optical fiber units (1) to (3) above, the inner surface of the plastic film may be coated with a first adhesive having a melting point of 120°C or less, and the water-absorbing fiber may contain a second adhesive.

[0020] The optical fibers or optical fiber ribbons do not contain adhesive. Furthermore, the optical fibers or optical fiber ribbons have a coating resin that has a high melting point and contains a release agent such as silicone. Therefore, it is difficult to bond the optical fiber ribbons to the plastic film.

[0021] In contrast, as described above, by containing adhesive in both the plastic film and the water-absorbing fiber, the optical fiber unit can be heated and cooled while wrapped in the plastic film, thereby bonding the water-absorbing fiber and the plastic film with sufficient adhesive strength, while reducing the adhesive strength between the optical fiber or optical fiber ribbon and the plastic film, thereby ensuring the disassembly of the optical fiber unit.

[0022] An optical fiber cable according to an embodiment of the present disclosure includes: (5) a plurality of optical fiber units according to any one of (1) to (4) above; and an outer jacket covering the plurality of optical fiber units.

[0023] As described above, since the assembly of a plurality of optical fibers or a plurality of optical fiber ribbons is covered with a thin plastic film having a thickness of less than 0.1 mm, the packaging density of the optical fibers can be improved. Furthermore, since the plastic film is wrapped around the water-absorbing fiber so as to adhere to the water-absorbing fiber, the occurrence of molding defects can be suppressed compared to when a thin film tube is formed around a plurality of optical fibers or a plurality of optical fiber ribbons by extrusion molding, and the manufacturing yield of the optical fiber unit can be improved.

[0024] In addition, since a portion of the assembly of multiple optical fibers or multiple optical fiber ribbons is exposed from the plastic film, the optical fiber unit can be easily disassembled. Furthermore, since a portion of the water-absorbing fiber is exposed from the plastic film, even if the outside of the optical fiber unit comes into contact with water, the water-absorbing fiber can absorb the water, and water can be more effectively prevented from being transmitted into the optical fiber cable, which is an assembly of optical fiber units.

[0025] (Details of the embodiments of the present disclosure) Specific examples of the optical fiber unit and optical fiber cable of the present disclosure will be described below 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.

[0026] [Configuration of Optical Fiber Unit] Fig. 1 is a perspective view of an optical fiber unit 1 according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view of the optical fiber unit 1 shown in Fig. 1. As shown in Figs. 1 and 2, the optical fiber unit 1 includes a plurality of optical fiber ribbons 10, a water-absorbent fiber 20 arranged along the assembly of the optical fiber ribbons 10, and a plastic film 30 that covers the assembly of the optical fiber ribbons 10 and the water-absorbent fiber 20.

[0027] In this example, 12 optical fiber ribbons 10 are twisted together in a bundled state to form an assembly of optical fiber ribbons 10. Each optical fiber ribbon 10 includes a plurality of optical fiber core wires (an example of optical fibers) 11. The optical fiber ribbon 10 in this example includes 12 optical fiber core wires 11. The optical fiber unit 1 includes 144 optical fiber core wires 11. The plurality of optical fiber core wires 11 that make up the optical fiber ribbon 10 are, for example, intermittently connected to adjacent optical fiber core wires 11 along the longitudinal direction of the optical fiber unit 1. The plurality of optical fiber core wires 11 are bundled so that the aggregate cross-sectional outer shape is approximately circular.

[0028] The water-absorbent fiber 20 is, for example, wound spirally around the outer periphery of the assembly of optical fiber ribbons 10. More specifically, as shown in Fig. 2, the water-absorbent fiber 20 includes water-absorbent powder 21 and a binder (second adhesive) 22 for fixing the water-absorbent powder 21. The water-absorbent powder 21 contained in the water-absorbent fiber 20 absorbs water that has entered the inside of the optical fiber unit 1 and prevents the water from seeping into the optical fiber unit 1 in the longitudinal direction.

[0029] The plastic film 30 is, for example, wound lengthwise along the longitudinal direction of the assembly of optical fiber ribbons 10. More specifically, the plastic film 30 is, for example, a colored resin film having a thickness of less than 0.1 mm. The plastic film 30 includes an adhesive resin (first adhesive) 32 coated on a part or all of the inner surface of the plastic film 30.

[0030] The adhesive resin 32 is, for example, a thin film formed from a polyester adhesive material, and has a melting point of 120° C. or less. In the optical fiber unit 1, the adhesive resin 32 adheres to the water-absorbent fibers 20, thereby maintaining the state in which the plastic film 30 covers the assembly of optical fiber ribbons 10 and the periphery of the water-absorbent fibers 20.

[0031] As described above, the plurality of optical fiber ribbons 10 are covered with the thin plastic film 30 having a thickness of less than 0.1 mm, which can improve the packaging density of the optical fiber cores 11. Furthermore, since the plastic film 30 is wrapped around the water-absorbing fiber 20 so as to adhere to it, the occurrence of molding defects is suppressed compared to when a thin film tube is formed around the plurality of optical fiber ribbons 10 by extrusion molding, and the manufacturing yield of the optical fiber unit 1 can be improved.

[0032] Furthermore, a portion of the assembly of optical fiber ribbons 10 and a portion of the water-absorbent fibers 20 are exposed from the plastic film 30. Specifically, the plastic film 30 covers an area of ​​30% to 70% of the outer periphery of the assembly of optical fiber ribbons 10. Of the portion of the assembly of optical fiber ribbons 10 and the water-absorbent fibers 20, the portions exposed from the plastic film 30 are, for example, linear along the longitudinal direction of the optical fiber unit 1.

[0033] [Method of Manufacturing Optical Fiber Unit] Next, a description will be given of a method of manufacturing the optical fiber unit 1. Fig. 3 is a schematic diagram of a manufacturing apparatus for manufacturing the optical fiber unit 1 shown in Fig. 1 .

[0034] First, the optical fiber ribbons 10 are unwound from each of a plurality of supply bobbins around which the optical fiber ribbons 10 are wound, and the optical fiber ribbons 10 from each supply bobbin are twisted together to form an assembly. Then, the water-absorbing fiber 20 is wound spirally around the outer periphery of the assembly of optical fiber ribbons 10. Hereinafter, the assembly of optical fiber ribbons 10 and the water-absorbing fiber 20 before being covered with the plastic film 30 will be referred to as the "optical fiber ribbon unit 1A."

[0035] Next, the optical fiber ribbon unit 1A is sent to the film forming section 110. The film forming section 110 is supplied with the optical fiber ribbon unit 1A and the plastic film 30 coated with the adhesive resin 32.

[0036] The plastic film 30 is unwound from the bobbin 130 and sent to the film forming section 110. The film forming section 110 winds the plastic film 30 so as to cover a portion of the optical fiber ribbon unit 1A. At this time, the plastic film 30 is wound lengthwise along the longitudinal direction of the optical fiber ribbon unit 1A.

[0037] The plastic film 30 may be wound in a spiral shape. However, when the plastic film 30 is wound vertically, it is possible to manufacture, by a relatively easy method, an optical fiber unit 1 in which a portion of the assembly of optical fiber ribbons 10 and a portion of the water-absorbing fibers 20 are exposed from the plastic film 30. Furthermore, compared to when the plastic film 30 is wound in a spiral shape, the length of the optical fiber unit 1 manufactured per unit time can be increased, thereby improving production efficiency.

[0038] Next, the optical fiber ribbon unit 1A, with the plastic film 30 wrapped around it, is sent to the heat welding unit 120. The optical fiber ribbon unit 1A sent to the heat welding unit 120 is heated to a temperature equal to or higher than the melting point of the adhesive resin 32. As a result, the adhesive resin 32 melts.

[0039] Then, when the optical fiber ribbon unit 1A passes through the heat welding part 120 and is cooled to a temperature below the melting point of the adhesive resin 32, the adhesive resin 32 solidifies. This allows the plastic film 30 coated with the adhesive resin 32 to be adhered to the optical fiber ribbon unit 1A, as exemplified in FIG. 2 .

[0040] As described above, the water-absorbing fiber 20 contains a binder 22 for fixing the water-absorbing powder 21. Meanwhile, the optical fiber ribbon 10 has a coating resin such as an ultraviolet-curable acrylate resin. This coating resin has a high melting point. Furthermore, this coating resin does not contain an adhesive, but contains a release agent such as silicone.

[0041] Therefore, when the optical fiber ribbon unit 1A is heated with the plastic film 30 wrapped around it, the water-absorbing fiber 20 is easily bonded to the plastic film 30, while the optical fiber ribbon 10 is less easily bonded to the plastic film 30 than the water-absorbing fiber 20.

[0042] This allows the water-absorbing fiber 20 and the plastic film 30 to be bonded with sufficient adhesive strength to prevent the optical fiber ribbon unit 1A from coming apart, while reducing the adhesive strength between the optical fiber ribbons 10 and the plastic film 30, thereby manufacturing an optical fiber unit 1 that is easy to disassemble. Note that it is desirable that the plastic film 30 is configured so as not to deform due to heat at temperatures equal to or higher than the melting point of the adhesive resin 32.

[0043] [Optical fiber cable] Fig. 4 is a cross-sectional view of an optical fiber cable 50 including a plurality of optical fiber units 1 shown in Fig. 1. The optical fiber cable 50 includes a plurality of optical fiber units 1, a cable jacket 51 that covers the plurality of optical fiber units 1, a tension member 52, a water-absorbing tape 53, and a tear string 54.

[0044] The tension member 52 is made of, for example, fiber reinforced plastic (FRP) and aramid fiber. The tension member 52 prevents excessive tension from being applied to the optical fiber core 11 inside the optical fiber cable 50. In the example shown in Fig. 4, one tension member 52 is disposed at the center of the optical fiber cable 50 in a cross-sectional view, but the position and number of tension members 52 are not limited.

[0045] A plurality of optical fiber units 1 are provided around the tension member 52. The water-absorbing tape 53 is arranged to cover the plurality of optical fiber units 1. By providing the optical fiber cable 50 with the water-absorbing tape 53, the waterproofness of the optical fiber cable 50 is improved.

[0046] The cable jacket 51 is configured to cover the plurality of optical fiber units 1 and the water-absorbing tape 53. The cable jacket 51 is made of a hard material such as high-density polyethylene. The hard material is, for example, a resin material with a Young's modulus of 800 MPa or more and 1200 MPa or less.

[0047] The tear cord 54 is provided on the outside of the water-absorbing tape 53 so as to be embedded in the cable jacket 51. The cable jacket 51 can be torn by pulling the tear cord 54.

[0048] 5 is a table illustrating the results of characteristic evaluation of the optical fiber unit 1 according to the embodiment of the present disclosure. Here, six samples, sample S1 to sample S6, were manufactured as samples of the optical fiber unit 1. By varying the manufacturing conditions for each sample, the disassembly property and waterproof property of the optical fiber unit 1 were verified.

[0049] (Description of Samples) Sample S1 has a configuration in which the number of coated optical fibers 11 included in the assembly of optical fiber ribbons 10 is 144, no water-absorbent fibers 20 are included, and the plastic film 30 covers the entire circumference of the assembly of optical fiber ribbons 10. In such sample S1, the plastic films 30 are partially overlapped and bonded to each other around the outer periphery of the assembly of optical fiber ribbons 10, thereby maintaining a state in which the plastic film 30 covers the entire circumference of the assembly of optical fiber ribbons 10. Sample S2 has the same configuration as sample S1, except that it includes two 2000 denier water-absorbent fibers 20.

[0050] 1 and 2 , in which a portion of the assembly of optical fiber ribbons 10 and a portion of the water-absorbing fibers 20 are exposed from the plastic film 30. Specifically, in sample S3, the assembly of optical fiber ribbons 10 contains 144 optical fiber cores 11, two 2000 denier water-absorbing fibers 20, and the plastic film 30 covers 70% of the assembly of optical fiber ribbons 10.

[0051] Sample S4 has the same configuration as sample S3 except that the plastic film 30 covers 60% of the aggregate of optical fiber ribbons 10. Sample S5 has the same configuration as sample S3 except that the plastic film 30 covers 50% of the aggregate of optical fiber ribbons 10. Sample S6 has the same configuration as sample S3 except that the plastic film 30 covers 30% of the aggregate of optical fiber ribbons 10.

[0052] (Dismantling Ease) The evaluators measured the time required to manually dismantle the plastic film 30 for each of the samples S1 to S6, thereby evaluating the dismantling ease of each sample.

[0053] If the time required to dismantle a sample was shorter than the lower limit of a predetermined range, the evaluator rated the dismantling ability of the sample as "A." If the time required to dismantle a sample was within the predetermined range, the evaluator rated the dismantling ability of the sample as "B." If the time required to dismantle a sample was longer than the upper limit of the predetermined range, the evaluator rated the dismantling ability of the sample as "C." The evaluator also performed the dismantling ability evaluation for each sample multiple times.

[0054] In samples S1 and S2, it took time to disassemble the overlapping portions of the plastic film 30, and the disassembly evaluation was "B" or "C." In sample S3, it took time to peel off the adhesion between the plastic film 30 and the water-absorbent fiber 20, and all of the disassembly evaluations were "B." In sample S4, disassembly was easy, and the disassembly evaluation was "A" or "B." In samples S4 and S5, disassembly was even easier, and all of the disassembly evaluations were "A."

[0055] From the above evaluation results, it was confirmed that the lower the proportion of the aggregate of optical fiber ribbons 10 covered by the plastic film 30, the more easily the optical fiber unit 1 can be dismantled.

[0056] (Waterproofing Properties) For each of samples S1 to S6, the evaluator brought the outside of one longitudinal end of the sample into contact with water, and after 24 hours, measured the length of water running inside the sample (the running water length). Specifically, a hose was connected to the end of each sample, and water was poured into the hose. At this time, the height between the center of the sample and the top surface of the poured water was set to 1 m. In this state, the sample was left at room temperature for 24 hours. Thereafter, the sample was removed from the hose, and the length of water immersion in the sample was measured as the running water length.

[0057] If the water travel length inside the sample was 2.5 m or less, the evaluator rated the waterproofing properties of the sample as "A." If the water travel length inside the sample was longer than 2.5 m and less than 3.0 m, the evaluator rated the waterproofing properties of the sample as "B." If the water travel length inside the sample was longer than 3.0 m, the evaluator rated the waterproofing properties of the sample as "C." The evaluator also evaluated the waterproofing properties of each sample multiple times.

[0058] For sample S1, the shortest value of the water travel length was longer than 3.0 m, so all the waterproofing properties were evaluated as "C." For sample S2, the shortest value of the water travel length was longer than 2.5 m, and the longest value was 2.9 m, so all the waterproofing properties were evaluated as "B."

[0059] For sample S3, the longest water travel length was 2.5 m, so all waterproofing properties were evaluated as "A." For sample S4, the longest water travel length was 2.0 m, so all waterproofing properties were evaluated as "A." For sample S5, the longest water travel length was 1.9 m, so all waterproofing properties were evaluated as "A." For sample S6, the longest water travel length was 1.6 m, so all waterproofing properties were evaluated as "A."

[0060] From the above evaluation results, it was confirmed that the lower the proportion of the plastic film 30 covering the assembly of optical fiber ribbons 10, the more water can be absorbed by the water-absorbing fiber 20, and the more effectively water can be prevented from being transmitted to the assembly of optical fiber unit 1.

[0061] Furthermore, as described above, since the water-absorbent fibers 20 are wound spirally around the outer periphery of the assembly of optical fiber ribbons 10, the water-absorbent fibers 20 are more likely to be exposed to the outside of the plastic film 30 than when the water-absorbent fibers 20 are straight. This further improves the waterproof performance of the optical fiber unit 1.

[0062] The optical fiber unit 1 may be configured to include a plurality of single-core optical fibers 11 instead of the optical fiber ribbon 10. Even in such an optical fiber unit 1, if a portion of the aggregate of the optical fiber fibers 11 and a portion of the water-absorbing fiber 20 are exposed from the plastic film 30, the disassembly and waterproofing of the optical fiber unit 1 can be improved.

[0063] Although the present disclosure has been described above based on specific embodiments, the present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0064] REFERENCE SIGNS LIST 1 Optical fiber unit 1A Optical fiber ribbon unit 10 Optical fiber ribbon 11 Optical fiber core 20 Water-absorbing fiber 21 Water-absorbing powder 22 Binder 30 Plastic film 32 Adhesive resin 50 Optical fiber cable 51 Cable jacket 52 Tension member 53 Water-absorbing tape 54 Tear string 110 Film forming section 120 Heat-sealed section 130 Bobbin

Claims

1. A fiber optic unit comprising: a plurality of optical fibers or a plurality of optical fiber ribbons; water-absorbing fibers arranged along the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons; and a plastic film having a thickness of less than 0.1 mm and covering the periphery of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and the water-absorbing fibers, wherein the inner surface of the plastic film adheres to the water-absorbing fibers, and a part of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons and a part of the water-absorbing fibers are exposed from the plastic film.

2. The fiber optic unit according to claim 1, wherein the plastic film is wound longitudinally along the longitudinal direction of the plurality of optical fibers or the plurality of optical fiber ribbons.

3. The fiber optic unit according to claim 1 or claim 2, wherein 30% or more and 70% or less of the outer periphery of the plurality of optical fibers or the assembly of the plurality of optical fiber ribbons is covered by the plastic film.

4. The fiber optic unit according to any one of claims 1 to 3, wherein the inner surface of the plastic film is coated with a first adhesive having a melting point of 120°C or less, and the water-absorbing fibers contain a second adhesive.

5. An optical fiber cable comprising: a plurality of fiber optic units according to any one of claims 1 to 4; and a jacket covering the plurality of fiber optic units.

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