JPS60177311A - Optical fiber cable - Google Patents

Abstract

PURPOSE:To reduce the strain of an optical fiber when tensile force and flexural force operate on a cable by stranding plural units around a tensile strength body which has a sufficiently large external diameter at specific intervals while inverting the stranding direction periodically. CONSTITUTION:A unit 2 is constituted by stranding, for example, six optical fiber cores 8 around a reinforcing material 7 in one direction and also covering the outside with a buffer layer 9. Each optical fiber core 8 is formed by coating an optical fiber 10 with a silicone resin coating 101 and a plastic coating 11. This unit 2 is stranded around the tensile strength body 1 which has the much larger diameter than the unit 2 clockwise, counterclockwise, clockwise... alternately at specific intervals. Consequently, even when tensile strength and flexural force operate on the cable, the strain of the optical fiber 10 is reduced to hold stable transmission characteristics.

Description

[Detailed description of the invention] The present invention relates to an optical fiber cable for optical communication.

Generally, optical fibers are more sensitive to internal stress (strain) than copper wires. For example, if a tensile force or bending force exceeding a certain value is applied, the fiber will break after a certain period of time, and even if it does not break, it will break. Transmission characteristics deteriorate significantly. Furthermore, if the optical fiber has surface scratches, it will break early due to internal stress (strain) caused by a slight external force.

Conventionally, thin (for example, 0.9 mm diameter) optical fiber core wires are twisted on the outer surface of a reinforcing material with a small outer diameter (for example, 1 mm), and the twisting direction is periodically reversed at appropriate length intervals. The structure is based on 1975-12075.
No. 5 was proposed as No. 5, and even when tensile force or bending is applied to the optical fiber cable, internal stress (
Measures have been taken to prevent distortion from occurring.

However, in order to inversely twist extremely thin optical fibers onto the outer surface of a reinforcing material with a small outer diameter as described above, it is necessary to repeatedly invert parts of the twisting device, which is extremely difficult. The problem is that the optical fiber itself is more likely to be damaged during processing, and the optical fiber is forced to be bent in an inverted shape to a small radius of curvature, resulting in large internal stress (strain) remaining in the optical fiber. This poses a problem in that the transmission characteristics may deteriorate or there is a high probability that a part of the optical fiber will break within a short period of time after the optical fiber cable is installed. Furthermore, even if reverse twisting is performed along the outer surface of the reinforcing material, which has a small outer diameter, the frictional resistance with the optical fiber core is large, and there is a problem that there is little margin for expansion and contraction of the entire optical fiber core. .

The present invention solves these conventional problems and makes it difficult for distortion to occur in the optical fiber itself when tensile force or bending force is applied to the optical fiber cable, thereby maintaining stable transmission characteristics. , has excellent durability, can be easily processed without damaging the surface of the optical fiber during processing, can be easily taken out without causing distortion to the optical fiber during terminal processing, and can easily perform highly reliable terminal processing. The purpose is to make it possible. Therefore, the feature of the present invention is that a plurality of optical fiber cores are twisted in one direction around a reinforcing material, and a buffer layer is coated on the outside.
- and a tensile strength member having an outer diameter sufficiently larger than the outer diameter of the unit, and a plurality of the units are twisted around the tensile strength member by periodically reversing the twisting direction at predetermined intervals. It lies in the point where it comes together.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows a concrete example of the optical fiber cable according to the present invention in cross section, in which a tensile strength member 1 having a sufficiently large outer diameter is arranged at the center, and four units 2 are arranged around it. . . . and seven intervening strings 3 . . . are arranged at equal pitches around the circumference, and are bound with two narrow tapes, and from the outside, a presser such as non-woven fabric or embossed tape is attached. It is covered with a winding layer 12, a longitudinal layer 19 of plastic laminated metal tape, a sheath 4, etc. As this tensile strength member 1, for example, one having a steel stranded wire 5 in the center, which is integrally covered with a plastic layer 6 such as polyethylene, is used. The intervening string 3 is a so-called dummy unit, which is made of a plastic string such as polyethylene. Note that the dummy unit does not necessarily have to be provided.

As shown in FIGS. 2 and 3, the unit 2 is constructed by twisting, for example, six optical fiber cores 8 around the reinforcing material 7 in one direction (left-handed twist in the figure) and It is constructed by covering the outside with a buffer layer 9 such as polypropylene yarn.The reinforcing material 7 is made of twisted steel wire or a single wire, and the optical fiber core 8 is made of an optical fiber 10 coated with a silicone resin wave 101 and plastic. It is possible to freely select graded index type, stethoscope index type, and various other types.

Next, FIG. 4 is a diagram depicting one unit 2 and tensile strength member 1 as a representative example for explaining the twisted state of the optical fiber cable already described in FIG. As is not obvious, the unit 2 is visibly entwined around the tensile strength member 1, and twisted together with the twisting direction periodically reversed at predetermined intervals P. Hence, the inversion pinch. is twice this interval P, and the relationship Q=2P holds true. That is, the rotation is alternately reversed at fixed intervals P, such as clockwise rotation, counterclockwise rotation m=clockwise rotation, counterclockwise rotation, and so on.

FIG. 5 shows an example of a method for manufacturing such an optical fiber cable, in which Unisol l-2 is fed out from the supply bobbin 13, and tensile strength material is fed out from another Zaburi bobbin 14. 1 is sent out and passed through the batten 15 and the die 16. Reference numeral 17 denotes a torsion catcher, which is of the caterpillar type or three-point roll type, which does not hinder the feeding of the wire in the advancing direction but can prevent twisting. Reverse twisting can be performed by rotating the torsion + + so'j-ya 17 alternately four times as indicated by arrows A and B in FIG.

Reference numerals 19 and 19 are binders or tapes that rotate in opposite directions, and when the torsion catcher 17 turns the binder around, it immediately presses and wraps it to fix it. Then, it is wound onto the winding bobbin 18.

In the manufacturing method shown in Fig. 5, since it is necessary to give twist to the cable, it is preferable to use a material that is easy to twist but has a large tensile strength as the tensile strength member l, such as a collection of FRP strings covered with polyethylene. You can also use

Note that the method for manufacturing this cable is not limited to the one shown in FIG. 5, and various methods may be employed.

For example, it is preferable to use a reversal twisting device in which a fixed batten and a rotating batten that is periodically reversed are provided.

Therefore, FIG. 6 shows a 24-core optical fiber cable manufactured by the manufacturing method shown in FIG.
The unit 2 has an outer diameter of 41 TllTl, the outer diameter of the tensile strength member 1 is 10 mm, the torsional pinch of the unit is 80 cm, the twisting pitch at which the unit 2 is entangled with the tensile strength member 1 is 40 cm, and the reversal pitch Q. is 1
For the case of 20cc, the tension (kg) applied externally to the entire optical fiber cable and the optical fiber 10
... shows the relationship with the amount of strain (%), and the straight line E shows the state before implementation of the present invention in which units 2 ... are twisted together with the direction reversed periodically. On the other hand, the straight line G shows the case where the units (inverted) are tied around the tensile strength member in one direction with a twisting pinch of 40 clTl (Unit 2 and tensile strength member 1 are the same as in the example) ) is shown below. From FIG. 6, it can be seen that by reverse twisting as in the present invention, the amount of distortion of the optical fiber itself can be significantly reduced.

The following conditions can be adopted as the optical fiber gear pull according to the present invention. That is, the cable outer diameter is 15 mm to 80 mm.
In this case, it is desirable to set the twisting pitch to 10 cm to 300 cm and the reversal pitch Q to 20 cm to 1000 cm, and particularly preferably to set the reversal pitch Q to 30 cm to 60 Crrl.

In the case of the manufacturing method shown in FIG. 5, the twisting pitch of the unit 2 is preferably 50 cm or more. If a small twist pitch smaller than this is given to the unit 2, a large residual stress will be generated in the optical fiber IO, leading to a decrease in performance.

As described above, in the present invention, since a plurality of optical fiber core wires 8 are twisted together in one direction around the reinforcing material 7,
When the thin reinforcing material 7 and the thin core wire 8 are combined together, no unreasonable distortion occurs, stable transmission characteristics are maintained, and the core wire 8 is not twisted in the opposite direction, so the surface during processing is There is no risk of scratches, and alignment is easy. The tensile strength member 1 has an outer diameter sufficiently larger than the optical fiber 10 itself, and a plurality of units 2 are arranged around the tensile strength member 1.
... are twisted by periodically reversing the twisting direction at predetermined intervals P, manufacturing is easy, and when tensile force or bending force is applied to the cable, distortion of the optical fiber 10 itself is significantly reduced. This has the advantage that durability is greatly improved, cable breakage accidents can be prevented after cable installation, stable transmission characteristics are maintained at all times, and in particular, optical loss increases due to distortion are small. Also, in order to invert unit 2, optical fiber I
O itself is not strongly pressed against the tensile strength member 1,
No compressive stress (strain) remains, and stable and good transmission characteristics can be obtained. Furthermore, since the unit 2 has the buffer layer 9, is twisted around the tensile strength member 1 having a sufficiently large outer diameter, and is in a reverse position, the frictional resistance between the unit 2 and the tensile strength member 1 when the cable is expanded or contracted is also reduced. It is small and has a lot of room for expansion and contraction. Because this margin is large, when terminating the cable, it can be easily taken out without adding distortion to the optical fiber 10, and it has the great effect of easily performing highly reliable terminating. have

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view showing an example of a unit, FIG. 3 is a perspective view of the same unit, and FIG. 4 is an optical fiber according to the present invention. A front view representatively showing only one unit in order to explain the single state in one embodiment of the cable, FIG. 5 is a simplified diagram showing an example of the manufacturing method, and FIG. FIG. 3 is a diagram showing the characteristics of the invention. ■...Tensile strength body, 2...Unit, 7...Reinforcement material, 8...Optical fiber core wire, 9...Buffer layer, K...
1 pitch, P...predetermined interval, Q...inverted pitch. Patent applicant: Dainichi Nippon Electric Cable Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] ■A unit consisting of a plurality of optical fibers twisted together in one direction around a reinforcing material and a buffer layer coated on the outside, and a unit with an outer diameter sufficiently larger than the outer diameter of the unit. 1. An optical fiber cable comprising a tensile strength member, and a plurality of the units described above are twisted together at predetermined intervals with the twist direction periodically reversed.