JPH05224105A - Optical fiber cable - Google Patents

Abstract

PURPOSE:To prevent the degradation in the transmission characteristic and long-term reliability of the optical fiber cable by relieving the stresses and strains generated in optical fibers when the optical fiber cable is bent. CONSTITUTION:Optical fiber units 13 are constituted by housing the optical fibers or ribbons 3 of coated optical fibers within substantially U-shaped plastic spacers 12. The bottoms of plastic spacers 12 are directed toward a tension member 6 at the center of the cable and the plural optical fiber units 13 are gathered and disposed around the tension member 6. The plastic spacers 12 have projections 17 on one, side of the surfaces thereof in contact with each other and have flat surfaces 18 on which the projections 17 can glide on the opposite side thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable and, more particularly, to an optical fiber cable having a structure in which a bending portion of the cable does not cause distortion in the optical fiber due to external stress.

[0002]

2. Description of the Related Art In an optical fiber cable, how to reduce the contact external force applied to the optical fiber accommodated in the optical fiber from a cable component adjacent to the optical fiber to prevent stress strain from occurring in the optical fiber. It is an important issue to be solved.

In order to deal with such a problem, the present applicant has previously proposed an optical fiber cable according to Japanese Patent Laid-Open No. 55-45087. This optical fiber cable has a structure as shown in FIG. 5, and a desired number of optical fibers 2 or optical fiber ribbons 3 are provided inside a plastic spacer 1 extruded in a sheath 5 in a U-shaped cross section. It has an optical fiber unit 4 containing A plurality of the optical fiber units 4 are arranged around the tension member 6 at the center of the cable, and the bottom portions 7 of the plastic spacers 1 are gathered and arranged toward the tension member 6 described above, and the presser winding 8 is provided on the bottom portion 7. And the sheath 5 are sequentially applied to complete the optical fiber cable.

Polyethylene, polyester, polyvinyl chloride or the like is used as the material of the above-mentioned plastic spacer 1. Particularly, in order to realize a large strength, a plastic material reinforced by containing glass fiber (commonly known as FR
It is also possible to use P). The optical fiber cable shown in FIG. 5 protects the optical fiber 2 and the optical fiber tape core wire 3 housed therein from lateral pressure due to the high strength of the plastic spacer 1, and keeps its transmission characteristics stable. It is easy to handle. However, the optical fiber cable having this optical fiber unit structure also has a problem to be improved when it is bent into a U shape as shown in FIG.

That is, when the optical fiber cable 9 is bent into a U shape as shown in FIG.
With the boundary as the boundary, the compressive stress is in the direction of arrow A on the side closer to the center of curvature, and the tensile stress is in the direction of arrow B on the side farther from the center of curvature 11. Therefore, in an optical fiber cable having a structure in which a plurality of optical fiber units 4 are twisted together, the optical fiber unit 4 in the cable is the dotted line C in FIG.
As indicated by, the tensile stress and the compressive stress are alternately received in the longitudinal direction, lateral pressure acts on the optical fiber 2 and the optical fiber tape core wire 3, and the transmission characteristics deteriorate.

[0006]

Conventionally, in the optical fiber cable of this type, the friction between the optical fiber units 4 or between the optical fiber unit 4 and the tension member 6, and between the optical fiber unit 4 and the presser winding 8 is large, and the above-mentioned problems occur. The extension strain and the compression strain generated in the optical fiber unit 4 by the tensile stress and the compression stress of the above are not offset or relaxed to each other. Therefore, when bending stress is applied to the optical fiber cable during and after the laying work of the optical fiber cable, the strain generated in the optical fiber unit 4 and the optical fiber 2 or the optical fiber tape core wire 3 accommodated in the unit is generated. Becomes larger,
There is a problem that the transmission characteristics and long-term reliability are adversely affected.

An object of the present invention is to provide an optical fiber cable which solves the above-mentioned drawbacks.

[0008]

According to the present invention, a predetermined number of optical fibers or optical fiber ribbons are housed inside a plastic spacer having a substantially U-shaped cross section, and a plurality of plastic spacers are accommodated. In an optical fiber cable that is assembled and arranged with the bottom part of the cable facing the tension member at the center of the cable, at least one of the contact surfaces of the above-mentioned plastic spacers or the plastic spacer and other cable components is a facing surface. Is characterized by having a protrusion that slidably contacts with.

Of the contact surfaces of the plastic spacers described above, it is preferable to have a projection on one side and a flat surface on the other side.

Further, a protrusion may be provided on the contact surface with the tension member, which is the bottom of the plastic spacer.

[0011]

When the optical fiber cable is bent, a compressive stress acts on the side closer to the center of curvature and a tensile stress acts on the far side from the neutral line of the cable. In this case, the frictional force between the plastic spacers or between the plastic spacers and the tension member is small, and the plurality of twisted plastic spacers slide in the sheath so as to relieve the compressive stress and the tensile stress.

[0012]

EXAMPLE An example of an optical fiber cable according to the present invention will be described below with reference to FIG.

FIG. 1 is a sectional view of an optical fiber cable according to a first embodiment of the present invention, in which a desired number of optical fiber ribbons 3 are accommodated inside a plastic spacer 12 having a substantially U-shaped cross section. To form the optical fiber unit 13. The plastic spacer 12 has a bottom 1
4 are arranged and gathered toward the tension member 6 at the center of the cable, and a press winding 15 is applied on the tension member 6 to fix each spacer, and a sheath 16 is further applied thereon.

A plurality of protrusions 17 are provided on one side of the contact surface between the aforementioned plastic spacers 12 and a flat surface 18 is provided on the other side. By using the combination of the protrusion 17 and the flat surface 18 for the contact surface in this way, the contact area becomes small and the plastic spacers 12 easily slide together. If the contact area is made smaller, the plastic spacers 12 will be more likely to slide. Therefore, in order to increase the sliding efficiency, the width of the protrusions 17 may be reduced and the number of the protrusions 17 may be reduced, but it is also necessary to balance the strength. As shown in FIG. 2, when the contact surfaces of the plastic spacers 12 are divided into five inward and outward directions, the results of the test by the inventors of the present invention show that the widths of the two protrusions 17 are A ₁ , A ₂ , and the middle thereof. When the width of the part is B and the width of the inner and outer ends is C ₁ C ₂ ,
_{A 1: A 2: B:} C 1: C 2 = 1: 1: 1: 0.5:
It has been confirmed that when provided in a dimensional relationship of 0.5, the configuration has an optimum size having both sliding performance and strength.

FIG. 3 is a cross-sectional view of the optical fiber cable according to the second embodiment, showing the bottom portion 14 of the plastic spacer 12,
That is, a plurality of protrusions 17 are provided on the contact surface with the tension member 6.
Is provided. Further, a plurality of protrusions 17 are provided on the contact surface between the plastic spacers 12 as in the first embodiment. Therefore, according to the second embodiment, the plastic spacer 12 and the tension member 6 slide more smoothly. It should be noted that the present invention is not limited to the above-described embodiment, and the contact area between the plastic spacers 12 and the contact area between the plastic spacers and the cable component such as the tension member 6 are reduced through the protrusions. If so, the design can be changed appropriately. For example, the cross-sectional shape of the protrusion 17 is also arbitrary, and the parallel protrusion may be configured as a spiral special protrusion.

[0016]

As described above, according to the present invention,
In an optical fiber cable with a structure in which optical fiber units are twisted together, when this cable is bent, the optical fiber units and the optical fiber unit and the tension member slide smoothly, and the extension strain and compression acting on the optical fiber unit The strain is easily alleviated, and the strain generated in the optical fiber can be reduced, whereby the transmission characteristics and the long-term reliability can be prevented from lowering.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical fiber cable according to a first embodiment of the present invention.

FIG. 2 is a partial view of the plastic spacer of FIG.

FIG. 3 is a sectional view of an optical fiber cable according to the second embodiment as well.

FIG. 4 is an explanatory diagram showing stress acting on a bent portion of an optical fiber cable.

FIG. 5 is a cross-sectional view of a conventional optical fiber cable.

[Explanation of symbols]

6 ... tension member, 12 ... plastic spacer,
13 ... Optical fiber unit, 14 ... Bottom part, 17 ... Protrusion,
18 ... Flat surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroaki Sano 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Wataru Katsurajima 1-taya, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Ki Industry Co., Ltd. Yokohama Works (72) Inventor Shigeru Tanaka 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Ki Industries Co., Ltd. Yokohama Works (72) Inventor Shigeru Tomita 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A plastic fiber spacer having a substantially U-shaped cross-section and a predetermined number of optical fibers or optical fiber ribbons inside the plastic spacer to form an optical fiber unit. An optical fiber cable in which the bottom portion of the optical fiber cable is assembled and arranged so as to face the tension member at the center of the cable. At least one side of the contact surfaces between the plastic spacers or between the plastic spacers and the other cable components, and an opposing surface, An optical fiber cable having a protrusion that slidably contacts. 2. The optical fiber cable according to claim 1, wherein one of the contact surfaces of the plastic spacers has a protrusion and the other has a flat surface. 3. The optical fiber cable according to claim 1, wherein a protrusion is provided on a contact surface with a tension member which is a bottom portion of the plastic spacer.