AU601487B2 - Optical cable - Google Patents

Description

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'i V; COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-1969 t COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED "OPTICAL CABLE" -ci The following statement is a full description of this invention, including the best method of performing it known to us:o 1 I :-11 llll~-- -9 C R~SZsl

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This invention relates to an optical cable whose core contains a compressible contrel element around which at least one optical wave guide is stranded.

Such a cable is known and includes a stranded layer of optical waveguides alternating with compressible filler members which surrounds a compressible central element. When the jacket is stretched, the optical waveguides can assume a smaller centre-circle diameter, thus compensating for the change in length. In doing so, however, they must take up the forces necessary to compress the central element.

An object of the present invention is to provide an opr tical cable in which, when the cable is subjected to changes in length, the optical waveguides have to absorb virtually no forces.

According to the invention there is provided an optical cable whose core contains a compressible central element cc around which at least one optical waveguide is stranded, Sc wherein the compressible central element includes a braid of n e-4 in -ers' b(& substantially non tonilo /threads or yarns surrounding a cushion member.

An embodiment of the invention will now be described with reference to the accompanying drawing, in which: •Fig. 1 shows the layers at one end of the cable in accordance with the invention, and Fig. 2 is a cross section through the cable of Fig. 1.

Further embodiments are contained in the following description.

The cable shown in the figures includes a central ele- Sn 4Pt- e ns'%Ile ment consisting of a core member 1, which is on-tran; and resistant to axial compression, a compressible cushion mem- 2 it U ber 2 concentrically surrounding the core member 1, and a braid 3 of ncn tcnsil threads or yarns surrounding the cussion member 2.

Stranded around the central member is a layer of alternating optical waveguides 4 and buffer members 5. This layer is surrounded by a covering 6.

The covering 6 is surrounded by a non-tensile cable jacket consisting of a net tape 7 and a plastic layer 8 extruded over the net tape 7, which is finished with a moisture-absorbing adhesive. The net tape 7 contains lengthwise aramid and crosswise polyester threads. In aet rial cables, the plastic layer is preferably made of HDPE.

O t During the extrusion of the plastic layer 8, it is bonded to the net tape 7. In other embodiments of the cable, other t C cable jackets may be applied over the covering 6.

The core member 1 is made of glass-fibre or aramid- S fibre-reinforced plastic or a liquid-crystal polymer, for rexample. It may be omitted if the cable jacket is of suit- 4 e able construction. The cushion member 2 is made of microib cellular rubber, cured or uncured soft poly-urethane foam, special polyester yarn or flock yarn, for example. The braid 3 preferably consists of glass or aramid yarns.

When the cable is subjected to a tensile load, which results in an elengation of the cable, the hose-like braid 3 also becomes longer, so that its diameter decreases; as a result, the cushion member 2 is compressed. The pitch of the braid 3 is greater than the stranding pitch of the optical waveguides 4, so that the tensile forces act virtually only on the braid 3. The optical wave-guides 4 can thus as- Ssume a smaller centre-circle diameter without any appreci- 3 iYr" able forces acting on them. Only the buffer members which are stranded with the optical waveguides 4, are compressed. The buffer members 5 are preferably made of flock yarn, which is very easily compressible.

In another embodiment of the cable, the buffer members are omitted. Theoretically the smallest possible centrecircle diameter of the optical waveguides is reached when the optical waveguides touch.

The covering 6 is either a wrap of several layers of plastic film, such as a polyester film and an over-lying polyethylene film, or a thin-walled extruded plastic tube in e t which a longitudinal fibre tape of polyester fleece or t r swelling fleece is disposed.

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Claims (11)

1. An optical cable whose core contains a compressibl central element around which at least one optical waveguide is stranded, wherein the compressible central element in- cludes a braid of substantially inextensible threads or yarns surrounding a cushion member, whereby, when the cable is subjected to a tensile load the braid contracts radially to compress the central element.

2. An optical cable as claimed in claim 1, wherein the braid contains substantially inextensible glass and/or plas- tic threads, particularly aramid yarns.

3. An optical cable as claimed in claim 1 or 2, wherein the compressible central element includes a core member which is substantially inextensible and resistant to axial compression.

4. An optical cable as claimed in any one of the pre- ceding claims, including a substantially inextensible jacket comprising a substantially inextensible longitudinal net tape and a plastic covering extruded over the net tape.

An optical cable as claimed in claim 4, wherein the net tape comprises lengthwise aramid and/or glass threads and plastic cross-threads.

6. An optical cable as claimed in claim 4 or 5, wherein the net tape is finished with an adhesive.

7. An optical cable as claimed in claim 6, wherein the adhesive has moisture--absorbing properties.

8. An optical cable as claimed in any one of claims 1 to 7 wherein the braid consists of a first set of threads or yarns wound in a first direction around the cushion member 1- and a second set of threads or yarns wound in the opposite direction around the cushion member.

9. An optical cable as claimed in claim 8 wherein the pitch of the windings of the threads or yarns of the braid is greater than the pitch of the stranding of the optical waveguide or waveguides.

An optical cable as claimed in any one of claims 1 oL0o to 9 wherein there are two or more optical waveguides and S wherein compressible buffer members are stranded between ad- jacent optical waveguides.

11. An optical cable substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings. DATED THIS TWENTY-SIXTH DAY OF JUNE 1990 ALCATEL N.V. DTXJ K 6 L *b