GB1595456A - Optical fibre cable jointing - Google Patents

Description

(54) OPTICAL FIBRE CABLE JOINTING (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company of 190 Strand, London, WC2R lDU, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to jointing optical fibre cables, especially for use in high pressure environments, such as for underwater use.

Optical fibres are now well known for use in telecommunications, and the need has arisen for such fibres to be incorporated into cables for use in difficult environments. One such is undersea use, where high pressures are encountered, and where it is desirable to prevent the ingress of water. An object of the invention is to provide an optical fibre cable for such difficult environments.

According to the present invention there is provided a method of making a joint for optical fibre cables each of which has a central strength member surrounded by a plurality of optical fibres each of which is enclosed in an electrically insulating material, an inner sheath and an outer sheath, in which the outer sheath is removed from the ends of the two cables and each said end is fitted into a ferrule with an outwardlyextending flange, in which the optical fibres in each said cable are bared at the ends thereof, in which pairs of fibres, one in each said cable are respectively coupled in an optical coupling member, and in which the two semi-cylindrical coupling members are fitted over the two cable ends and the optical coupling member with the flanges on the ferrules each received in a groove on the inner face of the coupling formed by said two semi-cylindrical members, whereafter the outer sheath is extended over the two semicylindrical members.

An optical fibre cable and a joint between two such cables, the joint embodying the present invention, will now be described with reference to the drawing accompanying the Provisional Specification in which: Fig. 1 is a longitudinal cross section of two cables embodying the invention joined according to the method of invention, while Fig. 2 is a transverse cross section of an optical fibre cable.

Features of the optical fibre cable are claimed separately in Application No.

22936/77, (Serial No. 1595455) from which this application has been divided.

Referring now to the drawing, we will first describe the construction of the cable, which as already mentioned is claimed in Application No. 22 936/77. This cable has a central strength member 1 formed by a metallic wire which is helically grooved, the number of grooves being determined by the number of fibres to be accommodated in the cable. The optical fibres such as 2 of the cable are each insulated, and each one is laid into one of the grooves, and several layers of steel wire 3 are wound round the central member and thus over the central member and over the optical fibres. The function of these wires is to provide the cable with the required strength.

To prevent crushing of the optical fibres by the steel wires, the direction of lay of the first layer of steel wires is opposite to that of the grooved central wire, and hence also opposite to the direction of lay of the optical fibres.

A copper tape 4 is formed around the assembly formed by the strength member with the fibres and the steel-wires, seam welded and drawn down tightly around the steel strands. The functions of the copper tape are (a) to provide the electrically conductive path needed for the supply of electrical power by the regenerators needed along the cables' length and (b) to provide a hermetic seal against the ingress of water or other contaminant.

An insulating layer 5 of a suitable plastics material is extruded around the sheath provided by the copper tape 4, the thickness of the insulating layer being determined by the electrical requirements of the cable. If necessary, the cable can be protected from damage by the application, outside the layer 5, of a final wrapping of steel or another protective coating.

We now consider the techniques for jointing two cables each of which is as described above. The ends of the cables to be jointed are each prepared by removing the plastics insulation to expose the copper covered steel strands 3. Then a tubular metallic ferrule 6 is placed over each prepared end and collapsed over and on to the copper covered steel strands, e.g. by a rotary swaging operation.

The cable ends each with its fitted ferrule are located with their flanges in recesses in a split coupling 7 formed by two substantially semi-cylindrical members of, for instance, metal. This coupling provides the means of transmitting the axial load along the cable, and also provides a pressure resistant chamber in which an optical coupling device 8 is located. This device can take any one of a number of possible forms and hence is not described herein. The optical fibres are joined together within this coupling device 8 which is of course located within the chamber defined by the body of the split coupling.

Note that the ends of the two cables' strength members both project into the chamber just referred to.

The two halves of the split coupling 7 are fastened together with a belly band clip 9 as shown, or by counter-sunk screws which extend through the wall thickness of the coupling.

Finally a plastics sheath 5 is moulded round the joint so as to amalgamate with the cables' plastics sheath and thus form a watertight electrically insulating barrier.

WHAT WE CLAIM IS:- 1. A method of making a joint for optical fibre cables each of which has a central strength member surrounded by a plurality of optical fibres each of which is enclosed in an electrically insulating material, an inner sheath and an outer sheath, in which the outer sheath is removed from the ends of the two cables and each said end is fitted into a ferrule with an outwardly-extending flange, in which the optical fibres in each said cable are bared at the ends thereof, in which pairs of fibres, one in each said cable are respectively coupled in an optical coupling member, and in which two semi-cylindrical coupling members are fitted over the two cable ends and the optical coupling member with the flanges on the ferrules each received in a groove on the inner face of the coupling formed by said two semi-cylindrical members, whereafter the outer sheath is extended over the two semi-cylindrical members.

2. A method of making a joint for optical fibre cables, substantially as described with reference to the drawing accompanying the Provisional Specification.

3. A joint between two optical fibre cables made by the method of claim 1 or 2.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. jointing two cables each of which is as described above. The ends of the cables to be jointed are each prepared by removing the plastics insulation to expose the copper covered steel strands 3. Then a tubular metallic ferrule 6 is placed over each prepared end and collapsed over and on to the copper covered steel strands, e.g. by a rotary swaging operation. The cable ends each with its fitted ferrule are located with their flanges in recesses in a split coupling 7 formed by two substantially semi-cylindrical members of, for instance, metal. This coupling provides the means of transmitting the axial load along the cable, and also provides a pressure resistant chamber in which an optical coupling device 8 is located. This device can take any one of a number of possible forms and hence is not described herein. The optical fibres are joined together within this coupling device 8 which is of course located within the chamber defined by the body of the split coupling. Note that the ends of the two cables' strength members both project into the chamber just referred to. The two halves of the split coupling 7 are fastened together with a belly band clip 9 as shown, or by counter-sunk screws which extend through the wall thickness of the coupling. Finally a plastics sheath 5 is moulded round the joint so as to amalgamate with the cables' plastics sheath and thus form a watertight electrically insulating barrier. WHAT WE CLAIM IS:-

1. A method of making a joint for optical fibre cables each of which has a central strength member surrounded by a plurality of optical fibres each of which is enclosed in an electrically insulating material, an inner sheath and an outer sheath, in which the outer sheath is removed from the ends of the two cables and each said end is fitted into a ferrule with an outwardly-extending flange, in which the optical fibres in each said cable are bared at the ends thereof, in which pairs of fibres, one in each said cable are respectively coupled in an optical coupling member, and in which two semi-cylindrical coupling members are fitted over the two cable ends and the optical coupling member with the flanges on the ferrules each received in a groove on the inner face of the coupling formed by said two semi-cylindrical members, whereafter the outer sheath is extended over the two semi-cylindrical members.

2. A method of making a joint for optical fibre cables, substantially as described with reference to the drawing accompanying the Provisional Specification.

3. A joint between two optical fibre cables made by the method of claim 1 or 2.