GB2274175A

GB2274175A - Submarine optical cable joint

Info

Publication number: GB2274175A
Application number: GB9300358A
Authority: GB
Inventors: David John Lickman; James Noel Power; Michael William Sharpe; Charles Jeremy Brown; Steven Craig Beech; Ian Mark Boardman
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1993-01-09
Filing date: 1993-01-09
Publication date: 1994-07-13
Also published as: GB9300358D0

Abstract

A joint for an optical fibre cable 100, 101 having a central optical fibre package 10 and a surrounding strength member 12, comprises first and second bulkhead members 16 each incorporating clamping means 18, 20 for clamping the bulkhead member to the strength member 12 of a respective cable end, whereby the bulkhead member forms a collar on the cable, and a pair of longitudinally split half shells adapted to fit together to form a housing (30) for the joint, the half shells being shaped when secured together to engage at each end the bulkhead members whereby the tensile load in the jointed cable is transferred from the strength member of one cable end via the bulkhead, the housing and the other bulkhead to the strength member of the other cable end. <IMAGE>

Description

CABLE JOINT This invention relates to cable joints for lightweight submarine optical fibre cables.

In a known method of jointing such cables a rigid cylindrical housing is first parked, together with a one bulkhead arrangement over one of the cable ends to be joined. A second bulkhead arrangement is parked over the other cable end to be joined. The cable ends are prepared by stripping back the outer layers to expose the wire strength members and then the inner components of the cable, down to the optical fibres. The bulkheads are then affixed to the prepared cable ends and are linked together, the prepared cable ends being long enough to allow the fibre joints to be made easily.After the fibre joints are made the bulkheads are secured in the ends of the housing. (This brief description omits many intermediate steps required in the preparation of the cable ends and the process of marking the fibre joints.) Such a jointing procedure is fully described in British patent publication GB 2 233 782A.

However, handling and assembling such a rigid cylindrical housing is difficult and requires special tools and procedures.

It is an object of the present invention to provide a simple compact and easily assembled joint arrangement for a lightweight submarine optical fibre cable with wire strength members or other cables of a similar construction.

According to the present invention there is provided a joint for an optical fibre cable having a central optical fibre package and a surrounding strength member, the joint comprising first and second bulkhead members each incorporating clamping means for clamping the bulkhead member to the strength member of a respective cable end, whereby the bulkhead member forms a collar on the cable, and a pair of longitudinally split half shells adapted to fit together to form a housing for optical fibre joints, the half shells being shaped when secured together to engage at each end the bulkhead members whereby the tensile load in the jointed cable is transferred from the strength member of one cable end via the bulkhead, the housing and the other bulkhead to the strength member of the other cable end.

In a preferred embodiment of the invention the bulkhead members each comprise a cylindrical body member having an enlarged bore portion, the clamping means comprising a first ferrule member having an internally tapered bore located within the enlarged bore portion, a second ferrule member having a complementary externally tapered surface whereby cable strength member wires are splayed and secured between the co-operating tapered surfaces, and means for securing the ferrule member in the bulkhead bore to apply longitudinal compression of the ferrule members to clamp the strength members.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which.

Fig. la illustrates an external view of a cable joint housing; Fig. lb illustrates a longitudinal cross section of the housing of Fig. la; Fig. 2 illustrates a cross section of a bulkhead assembly; Fig. 3 is an internal view of the housing of Fig. 1 showing an arrangement of optical fibre joints within the housing.

Referring to the drawings, the joint to be made is between two cable ends 100,101 each of which comprises a central optical fibre package 10 contained within a steel C-section tube surrounded by helical lay steel wires 12 forming a strength member. This is followed by a welded copper hydrogen barrier, an inner extruded polyethylene sheath 14 and, for some applications, either a layer of armour wires or steel tape armour covered by an outer sheath of polyethylene.

(The detailed constituents of the cable are not shown in the drawings.) Each cable end is first prepared by stripping the outer sheath or armouring, inner sheath 14 and strength member wires 12 to expose the optical fibre package 10 for sufficient length to allow the fibre joint(s) to be made. A typical optical fibre package 10 may consist, for example, of six optical cables each composed of eight fibres in a ribbon construction, the six ribbons being stacked together. The outer sheath, armouring and inner sheath are further stripped back to expose a short length of the steel wire strength members. A bulkhead 16 is placed over the exposed strength member wires 12. Likewise a first ferrule member 18 is placed over the strength member such that the ferrule lies within an enlarged bore portion of the bulkhead 16.The strength member wires 12 are then splayed and a second ferrule 20 is placed over the core package 10 so that the splayed wires 12 are gripped between the complementary conical tapers of the two ferrules. A split collet 22 may then be placed over the core package 10 and finally a retaining nut 24 is screwed into the bulkhead member 16 to apply compression to both the collet 22 and the ferrules 18 and 20. To aid the secure retention of the strength member wires 12 the complementary tapered surfaces of the two ferrules 18, 20 may be coated with a carbide grit material. The two cable ends, each with its bulkhead affixed in place, are laid in one half 30a of a longitudinally split housing 30, the bulkheads fitting within recesses 32a, 32b respectively. The ends of the optical fibre packages having been suitably prepared the fibres 40 are joined 42 or spliced in known fashion.The lengths of the exposed fibre 40 are sufficiently long to allow trimming back and re-jointing in the event that the initial jointing is deemed to be faulty. As a result it will be appreciated that usually there will be an excess length of exposed fibre i.e. there will be slack in the jointed fibre, which has to be accommodated within the housing. As bare optical fibres are comparatively flexible it is sufficient to coil 44 the jointed fibres or ribbons within the housing interior, provided that due care is taken not to bend the fibres below the minimum bend radius permitted. Fig. 3 shows the disposition of the jointed fibres within the housing interior. The housing interior is, in this case, modified by the inclusion of guides or spacers 34 to ensure the smooth transition from straight to bent fibres. Once the joints have been completed and the fibres adequately coiled the other half of the split housing 30 is put in place and the two halves are secured together by transverse bolts (not shown) through bolt holes 36. The housing may, if required, be provided with means for injection of a potting compound in known fashion. Finally a previously loosely fitted heat shrinkable sleeve 38 is pulled over the housing and heated to form a tight sealing cover to the housing. In practice the heat shrinkable cover may be in three pieces, two end pieces 38a, 38b being fitted first and a third central piece 38c being fitted to overlap the two end pieces. This three-piece construction enables the considerable difference in diameters of the housing 30 and the cable 100, 101 to be accommodated within the limited shrinkage range of conventional heat shrink materials.

Claims

CLAIMS:

1. A joint for an optical fibre cable having a central optical fibre package and a surrounding strength member, the joint comprising first and second bulkhead members each incorporating clamping means for clamping the bulkhead member to the strength member of a respective cable end, whereby the bulkhead member forms a collar on the cable, and a pair of longitudinally split half shells adapted to fit together to form a housing for optical fibre joints, the half shells being shaped when secured together to engage at each end the bulkhead members whereby the tensile load in the jointed cable is transferred from the strength member of one cable end via the bulkhead, the housing and the other bulkhead to the strength member of the other cable end.

2. A joint for an optical fibre cable according to claim 1 wherein the assembled joint is encased overall within a heat shrinkable sleeving.

3. A joint for an optical fibre cable according to claim 1 or 2 wherein excess lengths of optical fibre are lossely coiled within the housing after being jointed.

4. A joint for an optical fibre cable according to claim 1, 2 or 3 wherein the bulkhead members each comprise a cylindrical body member having an enlarged bore portion, the clamping means comprising a first ferrule member having an internally tapered bore located within the enlarged bore portion, a second ferrule member having a complementary externally tapered surface whereby cable strength member wires are splayed and secured between the co-operating tapered surfaces, and means for securing the ferrule member in the bulkhead bore to apply longitudinal compression of the ferrule members to clamp the strength members.

5. A joint for an optical fibre cable substantially as described with reference to the accompanying drawings.