JP2020071263A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable of a small diameter having no bending directionality.SOLUTION: An optical fiber cable 1 provided herein has one tension member 3 disposed roughly at the center thereof. A plurality of optical fiber units 9 is disposed around the tension member 3. Each optical fiber unit 9 is obtained by twisting a plurality of optical fiber ribbons 9a together and forming a bundle by wrapping the ribbons with a bundling member not shown in the figure. An outer periphery of the plurality of optical fiber units 9 is wrapped with a wrapping tape 11. Further, a tear string 5 is provided as necessary, and an outer periphery of the wrapping tape 11 is covered with a sheath 13. The sheath 13 of the optical fiber cable 1 of the present invention should exhibit a shrinkage rate of 5.1% or less when kept at 70°C. This reduces the effect on the optical fiber units 9 as shrinkage of the sheath 13 is small even in usage environments.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical fiber cable that accommodates a plurality of optical fiber cores.

  Since the amount of information transmitted in one optical fiber cable increases with the increase in the amount of information in recent years, it is desired to store the optical fibers in the optical fiber cable at a high density and increase the number of optical fiber storage cores. ing. On the other hand, various optical fiber cables have been proposed.

  As such an optical fiber cable, for example, an optical fiber cable in which a tension member is embedded in the center and a plurality of grooves are formed on the outer peripheral surface and a plurality of optical fibers are accommodated in each groove is proposed. Has been done. (For example, patent document 1).

  Further, there is proposed an optical fiber cable in which a jacket is provided on the outer circumference of a plurality of optical fiber units, and a tension member is embedded in the jacket (for example, Patent Document 2).

JP, 2014-212511, A JP, 2016-206350, A

  However, in the slot type optical fiber cable, it is difficult to make the optical fiber cable thin due to the sectional area occupied by the slots.

  Further, when the tension member is arranged in the jacket without using the slots, it is also difficult to make the optical fiber cable thin because the thickness of the jacket needs to be equal to or larger than the outer diameter of the tension member. .. Further, since the tension member is not arranged at the center of the optical fiber cable, the bending of the optical fiber cable is directional.

  The present invention has been made in view of such a problem, and an object thereof is to provide an optical fiber cable having a small diameter without bending directionality of the optical fiber cable.

  To achieve the above-mentioned object, the present invention comprises a tension member, a plurality of optical fiber units arranged on the outer circumference of the tension member, and a jacket provided on the outer circumference of the optical fiber unit. The fiber unit is an optical fiber cable in which a plurality of optical fiber core wires are bundled and configured, and the shrinkage rate of the jacket at 70 ° C. is 5.1% or less.

  It is desirable that the outer cover has a thickness of 2.0 mm or less.

  It is desirable that the resin constituting the outer cover be linear low-density polyethylene or low-density polyethylene.

  According to the present invention, since the tension member is not embedded in the jacket but is arranged in the cable core, it is not necessary to unnecessarily increase the thickness of the jacket, and it is possible to reduce the diameter of the cable. .. For example, the thickness of the outer cover can be 2.0 mm or less.

  Further, since the tension member is arranged substantially at the center of the optical fiber cable, the bending direction of the optical fiber cable is not restricted to a specific direction, and the degree of freedom in handling is high.

  On the other hand, since the tension member and the jacket are not integrated, it is not possible to suppress shrinkage of the jacket under the use environment, and there is a concern that transmission loss may increase. By suppressing the shrinkage ratio to 5.1% or less, it is possible to suppress an increase in loss of the optical fiber.

  Such shrinkage can be obtained by optimizing the cooling conditions after extruding the jacket, but in particular, if the resin constituting the jacket is linear low-density polyethylene or low-density polyethylene, The shrinkage rate of the jacket at 70 ° C. can be reliably suppressed to 5.1% or less.

  According to the present invention, it is possible to provide an optical fiber cable having a small diameter without bending directionality of the optical fiber cable.

Sectional drawing which shows the optical fiber cable 1. The figure which shows the optical fiber tape cable core 9a.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an optical fiber cable 1. The optical fiber cable 1 is mainly composed of a tension member 3, an optical fiber unit 9, a press winding 11, an outer jacket 13 and the like.

  One tension member 3 is arranged substantially at the center of the optical fiber cable 1. For the tension member 3, for example, steel wire or FRP can be applied. The outer circumference of the tension member 3 may be coated with resin.

  A plurality of optical fiber units 9 are arranged on the outer circumference of the tension member 3. In the illustrated example, four optical fiber units 9 are arranged in a twisted state. The optical fiber unit 9 is composed of a plurality of optical fiber core wires. In the illustrated example, the optical fiber unit 9 is composed of a plurality of optical fiber ribbons 9a.

  FIG. 2 is a schematic view showing the optical fiber ribbon core wire 9a. The optical fiber tape core wire 9a is configured by bonding a plurality of optical fiber element wires 17 in parallel. Adjacent optical fiber wires 17 are bonded by the bonding portion 15 intermittently with a predetermined interval in the longitudinal direction of the optical fiber wires 17. The adhesive portions 15 are arranged in a zigzag pattern in the longitudinal direction of the optical fiber ribbon core wire 9a.

  In addition, in the illustrated example, an example in which the optical fiber tape 17 is composed of twelve optical fiber strands 17 is shown, but the present invention is not limited to this. Applicable. In addition, the length and the interval of the adhesive portion 15 are not limited to the illustrated example.

  The optical fiber unit 9 is configured by twisting a plurality of optical fiber ribbons 9a and winding a bundle member (not shown) to form a bundle. A plurality of the optical fiber units 9 thus obtained are further bundled and arranged on the outer circumference of the tension member 3.

  A press winding 11 is wound around the outer circumference of the plurality of optical fiber units 9. Further, the tear cord 5 is arranged as necessary, and the outer circumference of the press winding 11 is covered with the outer cover 13. That is, the jacket 13 is provided on the outer circumference of the plurality of optical fiber units 9 via the press winding 11.

  The optical fiber unit 9 is only wound around a bundle member and is not inserted into a tube or the like. That is, the optical fiber units 9 are separated from each other only by the spirally wound tape-shaped bundle member. Further, the tape-shaped press winding 11 wound around the outer circumference of the optical fiber unit 9 comes into contact with the jacket 13.

  Here, the inventors have found that when the optical fiber cable 1 having the structure as shown in FIG. 1 is manufactured by the conventional method, the loss increase of each optical fiber core wire becomes large under the use environment. The inventors paid attention to the shrinkage amount of the jacket 13 as the cause.

  For example, a conventional slot-type optical fiber cable is covered so that the outer periphery of a slot wound with a presser winding is closely attached to the outer cover. Therefore, even if the jacket tries to shrink, the shrinkage of the jacket is suppressed by the slot having a high elastic modulus. Therefore, it is considered that the influence of the shrinkage of the jacket transmitted to the optical fiber unit hardly occurs.

  On the other hand, in the slotless type optical fiber cable, a tension member is embedded inside the jacket. Therefore, even if the outer jacket tries to contract, the contraction of the outer jacket is suppressed by the tension member integrated with the outer jacket. Therefore, it is considered that the influence of the shrinkage of the jacket transmitted to the optical fiber unit hardly occurs.

  However, in the structure such as the optical fiber cable 1 which is the slotless type and in which the tension member 3 is not arranged inside the jacket 13, the jacket 13 contracts under the use environment, and the jacket 13 contracts. The optical fiber unit 9 (each optical fiber ribbon 9a) is directly affected by the above. Therefore, it is considered that a force is applied to the optical fiber ribbon 9a, which leads to an increase in loss.

  Therefore, in the optical fiber cable 1 according to the present invention, the shrinkage rate of the jacket 13 when kept at 70 ° C. is set to 5.1% or less. By doing so, the amount of shrinkage of the jacket 13 is small even in the environment of use, so that the influence on the optical fiber unit 9 is small. As a result, it is possible to suppress an increase in loss of the optical fiber core wire.

  Next, a method for manufacturing the optical fiber cable 1 will be described. First, a plurality of optical fiber ribbons 9a are twisted together, and one or more bundle members are wound around it to manufacture the optical fiber unit 9.

  After that, a plurality of optical fiber units 9 are twisted around the outer circumference of the tension member 3, and a press winding 11 is wound around the outer circumference. Further, the optical fiber cable 1 is manufactured by extruding and covering the outer circumference of the press winding 11 with the jacket 13.

  Here, by controlling the air-cooling time of the optical fiber cable 1 from the combination of the air-cooling section distance after extrusion molding of the jacket 13 and the manufacturing linear velocity, the shrinkage rate of the jacket 13 at 70 ° C. can be controlled. .. For example, if the temperature of the jacket 13 becomes sufficiently low before being rapidly cooled by water cooling with a sufficient air-cooling time, the processing strain at the time of extrusion is relaxed and then the jacket 13 is cooled. The amount of shrinkage of the jacket 13 can be suppressed.

  However, if the production linear velocity of the optical fiber cable 1 is reduced too much, the production efficiency will deteriorate. Further, if the air-cooling section distance is made too long while the production linear velocity is increased, the jacket 13 is deformed during that period and the production line becomes long.

  In order to set the shrinkage ratio at 70 ° C to 5.1% or less, for example, the temperature of the jacket 13 immediately before entering water cooling is preferably 150 ° C or less, and more preferably 80 ° C or less. .. If the resin constituting the jacket 13 is linear low-density polyethylene or low-density polyethylene, it is excellent in manufacturability and it is not necessary to raise the extrusion temperature excessively. For example, the shrinkage rate at 70 ° C. can be suppressed by extruding the jacket 13 at an extrusion temperature of about 200 ° C., and then performing air cooling to reduce the temperature to 150 ° C. or less or 80 ° C. or less and then water cooling.

  Further, in the present embodiment, since the tension member is not embedded in the outer cover 13, it is not necessary to make the thickness of the outer cover 13 equal to or larger than the outer diameter of the tension member. Further, in order to shorten the air-cooling time of the jacket 13, it is desirable that the jacket 13 has a small thickness. For example, the jacket 13 has a thickness of 2.0 mm or less.

  As described above, according to the present embodiment, since it is the slotless type, the slot does not increase the outer diameter of the optical fiber cable. Further, since the tension member 3 is not embedded in the outer cover 13, the outer cover 13 can be made thin and the optical fiber cable can be made thin. Further, since one tension member 3 is provided in the approximate center of the optical fiber cable 1, there is no directionality of bending of the optical fiber cable 1.

  Further, since the shrinkage rate of the jacket 13 at 70 ° C., which is the operating temperature of the optical fiber cable 1, is small, the jacket 13 that the optical fiber unit 9 receives even if the jacket 13 and the tension member 3 are not integrated. It is possible to reduce the influence of the contraction of. Therefore, it is possible to suppress an increase in transmission loss of each optical fiber core wire.

  Various optical fiber cables were made by changing the shrinkage ratio of the jacket, and the increase in transmission loss during the heat cycle test was evaluated. The cross-sectional structure of the optical fiber cable is generally the same as that shown in FIG.

  Twelve optical fiber strands having a diameter of 200 μm were intermittently adhered to each other to prepare intermittent optical fiber ribbons as shown in FIG. In addition, 12 optical fiber tape cores were twisted together and a 2 mm wide plastic tape was wound to form a 144-fiber optical fiber unit.

  As the tension member, a glass FRP having a diameter of 2.0 mm and having a diameter of 2.5 mm coated with low density polyethylene was used. Four optical fiber units having 144 cores were twisted around the tension member at a pitch of 300 mm. A water absorbent non-woven fabric was wound around the outer circumference of the twisted optical fiber unit, and an outer cover was extruded and covered thereon to form a 576-fiber optical fiber cable. The material of the outer cover was linear low-density polyethylene, and the thickness of the outer cover was 1.7 mm.

  The optical fiber cable having the outer cover extruded and coated was cooled to room temperature through a water tank kept at about 18 ° C. after passing through an air-cooled section at a constant distance. The shrinkage rate of the jacket when kept at 70 ° C. was controlled by controlling the air cooling time from the combination of the distance of the air cooling section after extrusion of the jacket and the production linear velocity.

  The manufactured optical fiber cable was cut out by 1 m, and the components other than the jacket, such as the internal optical fiber unit and the tension member, were pulled out from the jacket and removed to obtain a jacket piece. The jacket piece was kept for 6 hours in a constant temperature bath kept at 70 ° C, and after taking out from the constant temperature bath, the length after cooling to room temperature was compared with the initial length of 1 m, and the shrinkage rate of the outer sheath was calculated. I calculated.

  As a result, it is better to lengthen the air-cooling time after extrusion and cool it in the water tank after the temperature of the jacket has sufficiently decreased, because the processing strain during extrusion is relaxed and then cooled The result was suppressed.

  Next, 1000 m of each optical fiber cable in which the shrinkage factor of the jacket is changed by changing the air cooling conditions is prepared, and each temperature is set at -30 ° C to 70 ° C, which is a general operating environment temperature of the optical fiber cable. The heat cycle test was performed for 3 cycles with the holding time at 6 hours. With respect to the transmission loss (wavelength 1550 nm) at room temperature measured in advance, an increase in loss at each temperature was confirmed. The results are shown in Table 1.

  The increase in loss in the lower part of Table 1 is “×” when it exceeds 0.15 dB / km, and “◯” when it is 0.15 dB / km or less, and is 0.10 dB / km or less Was designated as "◎".

  In Examples 1 to 3, since the air-cooling time was extended as compared with the conventional case, the shrinkage rate of the jacket at 70 ° C. was 5.1% or less, and the loss increase during heat cycle was 0.15 dB / km or less. In particular, in Examples 1 and 2 in which the shrinkage rate of the jacket at 70 ° C. was 2.8% or less, the loss increase during the heat cycle was 0.10 dB / km or less, which was a very good result.

  On the other hand, in Comparative Examples 1 and 2 which had a general air cooling time, the shrinkage rate of the jacket at 70 ° C. exceeded 5.1%. In addition, since the tension member and the jacket are not integrated, the jacket, which has been left with processing strain at the time of high temperature, contracts by wrapping the optical fiber core wire inside the jacket, resulting in a large loss. It is considered that an increase was seen.

  Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not affected by the above-described embodiments. It is obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and naturally, these are also within the technical scope of the present invention. It is understood that it belongs.

1 ... Optical fiber cable 3 ... Tension member 5 ... Tear string 9 ... Optical fiber unit 9a .... Optical fiber ribbon 11 .... … Adhesive part 17 ………… Optical fiber strand

Claims (3)

Tension members,
A plurality of optical fiber units arranged on the outer periphery of the tension member,
An outer cover provided on the outer periphery of the optical fiber unit,
Equipped with,
The optical fiber unit is configured by bundling a plurality of optical fiber core wires,
An optical fiber cable characterized in that the shrinkage rate of the jacket at 70 ° C. is 5.1% or less.   The optical fiber cable according to claim 1, wherein the thickness of the jacket is 2.0 mm or less.   The optical fiber cable according to claim 1 or 2, wherein the resin forming the jacket is linear low-density polyethylene or low-density polyethylene.

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