GB2205970A

GB2205970A - Optical cable joint assemblies

Info

Publication number: GB2205970A
Application number: GB08812640A
Authority: GB
Inventors: Edward Thompson Lloyd
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1987-06-19
Filing date: 1988-05-27
Publication date: 1988-12-21
Anticipated expiration: 2008-05-27
Also published as: GB8812640D0; GB8714389D0; GB2205970B; DK301888A; DK301888D0

Abstract

An optical cable joint assembly, especially for submarine cables having a tubular sheath 2 containing the optical fibres 13 surrounded by an annular tensile layer 4, incorporates a pair of attachment means 5-8 each connectable to the tensile layer 4 at an end of a respective cable, and a coupling means 15 securable to both of the attachment means to secure them and hence the cables to each other, each attachment means having a recess for the passage of fibres 13 emerging from the respective cable sheath, and the wall of each recess having an opening 12 to enable the fibres to be brought out, prior to mechanical connection of the cables by the coupling means, for subsequent connection to each other. The wires of the tensile layer 4 and/or the inner surface of ferrule 6 may be coated with a gritty substance e.g. silicon carbide. The coupling means 15 may have right- and left-handed threaded regions. <IMAGE>

Description

Joint Assemblies This invention relates to a joint assembly for forming a connection between optical fibre cables of the kind in which a tubular sheath accomnodates the optical fibre or fibres, and is surrounded by an annular layer, resistant to tensile loads, the invention relating especially to a joint assembly for submarine cables of this kind.

An object of the invention is to provide a joint assembly suitable for connecting such cables, which has advantages over existing forms of cable joints used for such a purpose.

According to the invention a joint assembly for forming a connection between two optical fibre cables of the kind referred to, comprises a pair of attachment means each connectable to the tensile layer at the end of a respective one of the cables, and a coupling means securable to both of the attachment means so as to secure the latter, and hence the cables, to each other, each attachment means having a recess for the passage of the fibre or fibres emerging from the sheath of the respective cable, and the wall of each recess being apertured to enable the ends of the fibre or fibres to emerge therefrom for connection to the fibre or fibres of the other cable.

Such a joint assembly simplifies the operation of joining the cables because the fibres of both cables can be brought out and secured temporarily away from the connection position prior to the mechanical connection of the cables, the mechanical connection of the two cables being carried out subsequently, followed by the splicing and location of the fibres around the coupling means. In the completed joint assembly the tensile load is transmitted through the joint between the annular tensile layers of the cables through the various members of the assembly.

The parts forming the mechanical connection between the tensile layers can also provide a passage for an electric current where this is required.

Preferably the coupling means comprises a member having right- and left-hand threaded regions at opposite ends which are capable of co-operating with right- and left-hand threaded regions of the respective attachment means, the screwing of the member to both attachment means having the effect of drawing them towards each other.

Preferably the attachment means are shaped so as to interengage and prevent relative rotation, as by the provision of at least one tongue on one of the attachment means engageable with a co-operating groove in the other.

Preferably also, the joint assembly incorporates an annular organiser tray, arranged to surround the coupling member and carrying flanges around which excess lengths of fibres can be looped, the use of excess lengths of fibres facilitating the splicing of the fibres away from the imnediate vicinity of the joint.

Conveniently the tensile layer of each cable is provided by a series of wires, for example of steel, coiled helically around the tubular sheath which, in the case of a submarine cable, is preferably of metal, such as lead.

Each attachment means conveniently comprises a rigid tapered insert which is introduced between the sheath and the tensile layer of the respective cable, a ferrule swaged down on to the layer over the insert, and a recessed joining member which provides the said enclosure and carries the right- or left-hand thread, as appropriate, and which is attachable to the ferrule. For this purpose the ferrule is preferably provided with a radially directed flange at the end adjacent the joining member, and the latter is provided with an external thread on to which a union member surrounding the ferrule is screwed so as to clamp the joining member against the end surface of the flange. Means, such as pegs fitting into respective sockets in the flange and joining member, may be provided for preventing rotation of the joining member relative to the ferrule.

A sleeve resistant to hydrostatic pressure conveniently surrounds the elements of the joint assembly, so as to provide an enclosure for the fibre ends, the ends of the sleeve preferably extending over the respective union member, with seals* such as "O-ring" seals, being provided between the union members and the internal surface of the sleeve. A moisture repellent or a desiccant, such as silica gel or a molecular sieve, may be provided within the enclosure if desired. To complete the joint assembly an electrically insulating moisture impervious layer is applied over the sleeve and adjacent ends of the cable sheaths. The material forming the layer can be applied using any convenient technique.

In the case of submarine cables provided with an outer armoured layer, the joint assembly is conveniently also provided with a rigid, pressure resistant outer sleeve coaxially surrounding the enclosure sleeve to provide mechanical protection, in addition to providing a mechanical connection between the armoured layers of the cables by means of suitable clamps.

The electrically insulating moisture impervious material is then preferably provided between the enclosure sleeve and the outer sleeve in order to insulate the outer tube and hence the armoured layer from the electrical current path between the tensile layers.

The insulating material is preferably one which becomes solid after its introduction, and may be a thermoplastic material such as polyethylene or a hardenable resin.

One joint assembly in accordance with the invention for use in connecting together two optical fibre submarine cables of the kind referred to will now be described, by way of example only, with reference to Figures 1 and 2 of the accompanying schematic drawings, in which Figure 1 represents an axial section through the cable joint in diagrammatic form, one half of the joint being shown completely, the other half, which is shown only in part, being a mirror image of the first, and Figure 2 illustrates a perspective view of part of the joint assembly.

Each cable comprises a polyethylene sheath 1 and an inner metal sheath 2, between which is located an annular layer resistant to tensile loads and formed by a series of closely adjacent helically coiled steel wires 4. The end of the polyethylene sheath 1 is cut away to reveal the wires 4 of this tensile layer and the Inner sheath 2, and a tapered insert 5 is introduced between protruding ends of the sheath 2 and wires 4 as shown. A tubular ferrule 6, previously located around the wires 4, is screwed on to the insert and is swaged down on to the wires so as to grip the wires firmly between itself and the insert. The gripping action may be enhanced, if desired, by coating the wires 4 and/or the inner surface of the ferrule 6 with a gritty substance such as silicon carbide.The tensile strength of the joint may be further enhanced by the addition of an epoxy compound between the ferrule and the insert.

The outer end of each ferrule 6 is provided with a radially directed flange 7 against which is secured the recessed end of a co-operating joint member 8 by means of a union nut 9 which screws on to the threaded external surface of the member 8 so as to clamp it against the end surface of the flange 7. Pins 11, which engage within recesses in the abutting ends of the ferrule 6 and joint member 8, prevent relative rotation of these elements.

The walls of joint members 8 are provided with openings 12 through which the ends of optical fibres 13, emerging from the end of the inner sheath 2, can pass as shown.

In one method of making the mechanical connection between the two cables, as is illustrated in Figure 1, the opposite end of each joint member 8 carries a threaded stub 14, these having a rightand left-hand thread respectively, and the joint members are secured to each other by a tubular coupling member 15 internally threaded with right- and left-hand threads at opposite ends. One of the joint members 8, in this case the left-hand threaded member, is provided with a tongue 16 arranged to locate within a co-operating groove 17 in the other member, and thereby serving to prevent relative rotation of the members.In another method of making the mechanical connection between the two cables - avoiding the use of left hand threads - the opposite end of each member 8 has a flange provided with a number of holes situated coaxially in a regular fashion, these holes accept bolts or set screws permitting both members 8 to be drawn towards and locked to each other, at the same time also preventing relative rotation of the members. However it will readily be appreciated that other coupling arrangements performing the same function would be suitable for such a purpose.

In forming a joint between two cables, each cable end is prepared by removing appropriate lengths of the surrounding layers, leaving a sufficient length of fibre ends, and the attachment means, comprising the insert 5, ferrule 6, joint member 8 and union nut 9, is secured thereto as previously described, the protruding ends of the fibres 13 being threaded through the opening 12 during this process. It will thus be seen that threading of the fibres through the openings 12 can be carried out separately at the two cable ends before the latter are brought together. The fibre ends of both cables are then secured temporarily away from the jointing position, while the joint members 8 are secured together by the coupling member 15.

The fibres 13 of the two cables can then be spliced together as at 18, while the cables are mechanically secured together by the joint assembly, using any suitable splicing technique, there being sufficient excess length of fibres to enable the fibres to be spliced at any convenient location away from the immediate joint area. This excess length of fibres can then be looped around a tubular flanged organiser tray 19 fitted around the coupling member 15, as illustrated more clearly in Figure 2.

It is important that the fibres should not be subjected to bend radii less than, say, 40mum and the flanged organiser tray 19 shown in Figure 2 ensures that this requirement can be net.

An inner sleeve 21, resistant to hydrostatic pressure, which has been previously threaded on to one of the cable ends, is slid over the assembly, and held in position by circlips 22, ZO-ringw seals as at 23 being provided to seal the enclosure containing the fibre ends against moisture penetration. A suitable desiccant may be previously introduced into the enclosure if desired.

An outer protective sleeve 24 provides mechanical protection and, in addition, provides a mechanical connection between armoured layers 25 surrounding the polyethylene sheaths 1 of the cables, the sleeve 24 being clamped to the armoured layers 25 by a suitable clamping means, for example as Indicated at 26.

A solidifiable insulating material 27, which may comprise polyethylene or a hardenable resin, can be introduced into the sleeve 24 so as to surround the inner sleeve 21 and the adjacent ends of the polyethylene cable sheaths 1, so as to insulate the outer sleeve 24 from the current path provided by the jointing assembly elements between the tensile layer wires 4, the material also helping to reduce penetration of moisture. Additional "0-ring" seals (not shown) may also be provided between various elements of the joint assembly for this latter purpose. Where the cables are not provided with outer armour layers 25, the outer protective sleeve 24 can be omitted. In such a case an insulating moisture impervious layer is applied over the inner sleeve 21 and over the ends of the polyethylene sheaths 1 of the cables in order to insulate the current path from the surrounding water.

Claims

1. A joint assembly for forming a connection between two optical fibre cables of the kind in which a tubular sheath accommodates the optical fibre or fibres, and is surrounded by an annular layer resistant to tensile loads, comprising a pair of attachment means each connectable to the tensile layer at the end of a respective one of the cables, and a coupling means securable to both of the attachment means so as to secure the latter, and hence the cables, to each other, each attachment means having a recess for the passage of the fibre or fibres emerging from the sheath of the respective cable, and the wall of each recess being apertured to enable the ends of the fibre or fibres to emerge therefrom for connection to the fibre or fibres of the other cable.

2. A joint assembly according to Claim 1 wherein the coupling means comprises a member having right- and left-hand threaded regions at opposite ends which are capable of co-operating with right- and left-hand threaded regions of the respective attachment means, the screwing of the member to both attachment means having the effect of drawing them towards each other.

3. A joint assembly according to Claim 2 wherein the attachment means are shaped so as to interengage and prevent relative rotation, as by the provision of at least one tongue on one of the attachment means engageable with a co-operating groove in the other.

4. A joint assembly according to Claim 1, 2 or 3 wherein the joint assembly incorporates an annular organiser tray, arranged to surround the coupling means and carrying flanges around which excess lengths of fibres can be looped.

5. A joint assembly according to any preceding Claim wherein the tensile layer of each cable is provided by a series of wires, coiled helically around the tubular sheath.

6. A joint assembly according to Claim 5 wherein the tubular sheath is formed of metal.

7. A joint assembly according to Claim 6 wherein the tubular sheath is formed of lead, and the tensile layer Is provided by steel wires.

8. A joint assembly according to Claim 2 wherein each attachment means comprises a rigid tapered insert which is introduced between the sheath and the tensile layer of the respective cable, a ferrule swaged down on to the layer over the insert, and a. recessed joining member which provides the said enclosure and carries the right- or left-hand thread, as appropriate, and which is attachable to the ferrule.

9. A joint assembly according to Claim 8 wherein the ferrule is provided with a radially directed flange at the end adjacent the joining member, and the latter is provided with an external thread on to which a union member surrounding the ferrule is screwed so as to clamp the joining member against the end surface of the flange.

10. A joint assembly according to any preceding Claim wherein a sleeve resistant to hydrostatic pressure surrounds the elements of the joint assembly, so as to provide an enclosure for the fibre ends, the ends of the sleeve extending over at least part of the respective attachment means, seals being provided between the attachment means and the internal surface of the sleeve.

11. A joint assembly according to Claim 10 wherein a moisture repellent and/or a desiccant and/or a molecular sieve material is/are provided within the said enclosure.

12. A joint assembly according to Claim 10 or 11 provided with a rigid, pressure resistant outer sleeve coaxially surrounding the enclosure sleeve to provide mechanical protection, the outer sleeve being clamped to the armoured layers to provide a mechanical connection between them.

13. A joint assembly according to Claim 10 wherein an electrically insulating moisture impervious layer surrounds the sleeve and adjacent ends of the cable sheaths the insulating material comprising a thermoplastics material or a hardenable resin.

14. A joint assembly substantially as shown in and as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.