CORRESPONDING METHOD

The present invention relates to a connection member for coupling various devices mounted to an optical communications cable, such as an undersea cable. The invention also relates to a method of coupling such members to optical communications cables.

The use of optical cables is fundamental to many communications networks, in particular for providing high speed communications between physically spaced locations. Such cables are often provided to effect communications between different nations or separated populations within the same nation. Many of these are often laid at sea such as in the case of intercontinental cables. Additional smaller range "festoon" systems are provided to link population centres upon the same continental land mass.

Such cable systems normally include various devices positioned along the cable. For long cables, these devices include optical repeaters which amplify and/or regenerate the optical signals- so as to ensure that a clean signal arrives intact at the remote cable end. Other devices include branch units where one cable is divided into two or more cables, and joints where two cables meet and are joined together. It is a difficult task technologically, to install cables containing such devices or indeed to replace or maintain devices already installed in a cable system. In cable laying or recovery operations, these devices are required to withstand very high loads due to the forces produced during these operations. Further devices such as bend limiters are therefore provided, usually coupled to the device to be protected. Bend limiters control these forces since they allow for stress transfer between devices and limit the angle of bend experienced by the cable at the location of the device.

One particular problem that occurs during cable maintenance operations is the placement or replacement of

opto-electronic devices such as an optical cable repeater within a cable. Such devices are normally supplied by manufacturers as sealed units with optical fibre "pig tails" emanating from either end. The pig tails comprise a series of fibres usually within a flexible tube or matrix. These are joined to the corresponding fibres of an optical cable whilst at the same time they require protection from the environment since, unlike a complete optical cable, such pig tails do not contain a load bearing structure such as armouring.

The conventional manner of installing or replacing a repeater is shown in Figure 1. Here, only one end of a repeater 100 is shown. A pig tail of optical fibres 101 exits the end of the repeater and is provided as a helix. A similar pig tail is provided at the opposite end. The pig tail is to be connected to the fibres contained in an optical cable 102, this cable containing the standard armouring and other protection for use undersea. The cable end 102 is terminated with a joint device 103 such as is described in published European patent application EP-A- 0067673, incorporated herein by reference. In addition, a bend limiter 104 (for example as described in published British application GB-A-2142788 , also incorporated herein by reference) is provided upon the cable 102. It should be noted however that the bend limiter 104 can be simply threaded onto the end of the cable 102 even when the joint 103 is attached. This is important since, during a standard connection procedure, the delicate fibres are connected together inside the joint 103 by extending the pig tail as shown by the arrow 105 in Figure 1, to the location of the universal joint 103. This allows sealing and armouring operations to be performed remote from the repeater 100. Following connection at that location, the cable and joint are moved closer to the repeater and the pig tail helix is reformed. The bend limiter is then slid over the joint and mounted to both the joint and the repeater so as to provide for load transfer between the

devices when the cable is returned to the seabed. The delicate pig tail is therefore protected inside the internal bore of the bend limiter.

However, there is now interest in developing much smaller opto-electronic devices for some applications, where the device such as a repeater is substantially of similar diameter to the joint. Practically, this means that a device such as a bend limiter, for protecting the delicate pig tail can no longer be simply slid over the joint in the final stage of the procedure. It is therefore desirable to provide a new kind of connection member that is not size limited in the manner described above.

In accordance with a first aspect of the present invention, we provide a connection member for coupling first and second cable devices mounted to an optical communications cable, the connection member comprising at least first and second parts, the parts being adapted in use to be coupled together around a portion of the communications, cable, and further adapted in use to be coupled to and between the first and second devices.

The use of such a connection member having at least two parts presents a radical change from the use of devices such as bend limiters in the past. The parts are brought together during installation so as to accommodate the portion of the cable between the devices. The coupling of the parts along with their coupling to the first and second devices therefore provides a protective environment for the cable portion and whilst allowing stress transfer across the resultant assembly. As will be appreciated, such a connection member can be used upon any part of an optical cable and is therefore not necessarily only limited to accommodating pig tails. Therefore the first and/or the second device may comprise a joint, a repeater, a coupler, a filter, a branch or a bend limiter. Each device may also be a compound device comprising two or more of the aforementioned devices, such as a joint and a bend limiter. The first and second

devices may therefore comprise bend limiters or, the first device may comprise a bend limiter coupled to a joint and the second device may comprise a bend limiter coupled to a repeater. The parts are typically arranged such that, once coupled, they define a bore within them in which the portion of the cable is accommodated. The bore is preferably of sufficient dimensions so as to accommodate a coiled optical fibre pig tail. Although such a member may take a number of forms, preferably it is provided as a cylinder. In this case, the first and second parts may be substantially semi-cylinders . The parts can be coupled together by any suitable means, such as bolts. Such means are also preferably releasable. Three or more parts may be used where necessary, depending upon the nature of the cable portion to be accommodated and the devices to which the parts are coupled.

Although a connection member according to the first aspect of the present invention may be used with conventional opto-electronic components such as large repeaters, it finds particular advantage in new smaller opto-electronic devices such as repeaters, which have dimensions approximately similar to those of other devices such as joints. Preferably, therefore the diameter of the member is substantially equal to or less than that of the first and/or second devices .

One major advantage of using connection members and devices of approximately the same size, is that, provided this size is small enough, the assembly as a whole may be passed through standard cable laying equipment such as ploughs. In the past such assemblies have had to be handled and buried separately. The ability to pass such assemblies through standard cable handling apparatus provides a great advantage in that expensive burial operations with remotely operated vehicles are no longer needed in this case. Although the invention is applicable to land based cable systems, preferably the connection

member is adapted for use in an underwater and/or buried environment .

The connection member provides for a new method of coupling optical cables and in accordance with a second aspect of the present invention, we provide a method of coupling first and second optical communications cables, the cables having respective first and second optical cable devices, the method comprising: - a) connecting a portion of the first optical cable from the first device to the second device; b) coupling the at least first and second parts of a connection member according to the first aspect of the invention together about the said portion of the first optical cable; and, c) coupling the said at least first and second parts of the connection member to the first and second devices.

It should be noted that steps (b) and (c) can be performed in any order or indeed at the same time . In some cases, each of the parts is connected to each of the first and second devices, whereas in other cases one part is connected to one device, and the other to the other device.

Prior to step (a) , the method preferably further comprises providing the portion of the first cable as a pig tail and extending this to allow attachment to the second device during step (a) . Achieving such separations by extension is important since step (a) preferably further comprises mounting a protection material to the second device, such as by armouring and sealing the device within a polymer coating. Before either coupling step, the first and second devices are typically brought together following the connection of the portion of the first cable to the second cable, such that the portion is caused to adopt a helical conformation prior to coupling of the parts and devices. This may be achieved with a mandrel. The method also further comprises the production of a larger assembly by repeating the method so as to couple a common first device to connection members upon either side

of the first device, and to further couple each of these connection members to respective second devices. This produces a first device such as a repeater, flanked by two connection members, these being further flanked by respective second devices. Each of these devices may also comprise additional devices such as bend limiters.

Therefore in accordance with a third aspect of the present invention an optical communications cable assembly comprises a common first device, two connection members according to the first aspect of the invention, and two second devices. The first device for each of the connection members preferably comprises a repeater, a filter, coupler and so on, and the second devices each comprise respective joints. When assembled, one end of each connection member is coupled to the first device upon opposing sides and each other end is coupled to one of the second devices .

One or more of these first and second devices may further comprise one or more bend limiters. For example the common repeater of the first device may be provided with bend limiters upon either side.

With the use of a number of bend limiters, the full assembly preferably comprises :- a) a joint for coupling to a first optical cable; b) a bend limiter; c) a connection member; d) a bend limiter; e) an opto-electronic device; f) a bend limiter; g) a connection member; h) a bend limiter; i) a joint for coupling to a second optical cable . In accordance with a fourth aspect of the present invention we provide an optical communications cable assembly comprising a first device, a second device and a

connection member according to the first aspect of the invention, wherein the first and second devices each comprise a combined opto-electronic device and joint, such that, when assembled, opposing ends of the connection member are coupled to the first and second devices.

This aspect is concerned with the use of a combined opto-electronic device and joint. The opto-electronic part of the combined device may be a repeater, or another device such as a filter, a coupler or a branch. In some cases the one or more devices may further comprise one or more bend limiters. Preferably the assembly comprises :- a) a combined joint-amplifier for coupling to a first optical cable; b) a bend limiter; c) a connection member; d) a bend limiter; and e) a combined joint-amplifier for coupling to a second optical cable.

Further connection members and combined joint- amplifiers may be inserted into the assembly. Typically, the combined join-amplifier (s) is a UJ-amplifier . The joint-amplifier may be a two fibre-pair amplifier although such an amplifier may also accommodate the passage or "pass-through" of further fibre pairs for amplification in another similar device or devices. Not all of the amplifier fibre pair capability need be used in some cases. For example a twelve fibre cable can be amplified using three connected joint-amplifiers each using a four fibre device or two such joint-amplifiers each with an eight fibre device (and with four individual amplifiers in the second device being inactive) .

Some examples of connection members, assemblies and associated methods according to the invention are now described with reference to the accompanying drawings, in which: -

Figure 1 shows a prior art method of connecting a joint and a repeater;

Figure 2 shows an example connection member according to the invention;

Figure 3 shows an example repeater assembly according to the invention; Figure 4 shows an enlarged central view of the assembly;

Figure 5 is a flow diagram showing an example method of constructing the assembly according to the invention;

Figure 6 shows the components arranged schematically after step 202 in Figure 5;

Figure 7 shows the arrangement after step 205 in Figure 5 ; and

Figure 8 shows an arrangement using UJ-amplifiers .

Figure 2 shows an example of a connection member according to the invention generally indicated at 1. This has two parts, 2, 3. The parts may be made from any suitable material such as stainless steel, alloy steel or titanium.

Each of the parts 2, 3 has complimentary surfaces 4 which are engineered such that, once the parts are fitted together, the surfaces 4 from the two parts contact thereby forming a complete cylinder. In order to attach the parts 2, 3, a number of bolts 5 are provided each of which passes through a corresponding hole 6 from the part 2 into a corresponding hole 7 in part 3. A central bore 8 is provided as the inside of the cylindrical connection member 1. For maintenance and replacement purposes the parts 2, 3 are arranged to be releasably coupled using the bolts. At either end of the parts 2, 3 a circumferential groove 9 is provided to allow coupling of the member to a corresponding surface (protrusion) upon first and second devices (described below) to which the member is coupled during use . It will be appreciated that, the use of complimentary grooves and protrusions (such as a ridge) upon the parts 2, 3 and upon the corresponding devices provides for

simultaneous coupling of not only the part 2 to the part 3 but also of the parts to the respective devices. Alternatively, additional attachment means, such as bolts can be used to secure the parts to the devices, one such bolt is schematically indicated at 10. Although a single groove 9 is shown in Figure 2, preferably "multiple" grooves are provided by arranging a continuous helical groove in a similar manner to a screw thread. Of course separate multiple grooves could also be used. Figure 3 shows an example of the use of two such connection members 1 in a repeater assembly. A first device in the form of a repeater is indicated at 20 in the centre of Figure 3. It will be appreciated however that any opto-electronic cable device such as a filter or coupler could be used in this example. This repeater is broadly similar in function to those known in the art although it is significantly smaller in dimensions and it will be noted that the external form of the repeater 20 is similar to that of the two joints 21, 22 also shown in Figure 3. In this example, the joints 21, 22 take the form of any suitable joints known in the art such as the Universal Joint available from Global Marine Systems Limited. The purpose of the joints is to allow the repeater 20 to be connected to first and second optical communication cables 23 and 24.

In practice, the repeater unit 20 is provided as a hermetically sealed unit such that the electronics inside are protected and remain undisturbed. However, at either end of this unit a "pig tail" is provided comprising a series of fibres arranged either in a "loose tube" format or held within a matrix. This is encased in a coaxial soft copper tube surrounded by a polyethylene layer. Whilst the housing of the repeater 20 is designed to withstand the load forces within the cable, the pig tails are relatively delicate and it is important that no significant loads are transferred to them either during installation, recovery, maintenance or use.

To either side of the repeater 20, are coupled bend limiters 25, 26. These have a similar function to the known bend limiters described earlier. However, in this case, the bend limiters are not tapered and are merely adapted to restrict the degree of bending permitted between the devices attached to their ends . It should be noted here that the reason for the lack of tapering is because the two devices to which they are coupled are of approximately the same diameter. The second devices to which each of the bend limiters 25, 26 are coupled, are the connection members 1 as described above in association with Figure 2. It is within the bores 8 of these members 1, that the majority of the pig tail lengths reside during use. The pig tails are necessary primarily to provide the sufficient slack within the fibres to allow them to be attached during installation or replacement operations.

Each of the connection members 1 is coupled on either side to bend limiters, namely those already described, and additional bend limiters 27, 28. These bend limiters 27, 28 are in turn each coupled to the joints 21, 22 mentioned above. Further bend limiters 29, 30 respectively are then used to couple the joints to the cables 23, 24.

In practice, the assembly according to this example is about 4.6 metres in length with the bend limiters having a safe working load of about 25 tonnes. The forces are transmitted between the cables 23 and 24 through the housing of each of the components mentioned above. As is indicated in Figure 3, each of the components has an approximately similar diameter. In fact, advantageously, the main housing of the repeater 20 is actually the same component as that used in the joints 21, 22.

Despite the small size of the housing (140mm diameter for the armour case in this example) four transmitters for two fibres pairs (two each way) are accommodated within the repeater housing 20 and a particularly suitable application for this example of the invention is in a festoon type

communication system, which may have a length of around 1500 kilometres.

Further details of the central part of the assembly shown in Figure 3 , are indicated in Figure 4. On the left of Figure 4, the connection member 1 is indicated in its assembled position whereas the second connection member indicated centrally within Figure 4, shows the component semicylindrical parts 2 and 3. The pig tail 35 from the repeater 20 is also shown in a coiled configuration within the connection member 1.

It should be noted that the portion of the cable from which the pig tail is formed extends within the assembly from the repeater 20 in Figure 4 to the joint 22. Similarly, the second pig tail from the repeater 20 extends to the second joint 21 within a corresponding bore.

When a known Universal Joint (UJ) is used to connect two optical cables together, two cable specific ferrules are used upon either side to couple the cables to the UJ. These are housed primarily within the end-pieces of the universal joint so as to transfer loads from the load bearing cable armour across the external housing of the universal joint. Since the bend limiters 26, 28 and the connection member 1 in Figure 4 transfer the loads between the repeater 20 and the universal joint 22 in Figure 4, it will be appreciated that a conventional ferule is not required on the repeater sides of each of the joints 21, 22. Accordingly, a "dummy" ferrule is provided on the repeater 20 side of the Universal Joints 21 and 22 to provide a suitable interface with the Universal Joint but which is not load bearing.

One important problem with the use of reduced diameter bend limiters is that, due to their strength and bending requirements, they contain insufficient internal bores for accommodating the required amount of coiled pig tail fibres. Practically, the connection member according to the invention is therefore necessary in such a case to provide a compact protected region in which the excess pig

tail length can be accommodated following coupling of the fibres from the repeater 20 to the UJs 21, 22. In this example it should also be noted that the connection members are not water tight, although water seals could be provided.

A method of connecting optical communication cables using connection members according to the invention is now described in association with Figures 5 to 7.

With reference to Figure 5, a repeater 20 is provided at step 200, in the form described earlier, this repeater being a hermetically sealed unit with "pig tails" extending upon either side. The pig tails may be either initially coiled or elongate.

At step 201, a pig tail 35 from one side of the repeater 20 is threaded through the internal bore of a bend limiter (such as bend limiter 26 in Figure 4) . The bend limiter is coupled to the repeater 20 during this step.

At step 202, the pig tail end is passed through the bore of a second bend limiter although at this stage this second bend limiter is free to move along the pig tail. The status of the assembly after step 202 is shown in Figure 6. An arrow 36 denotes the freedom of movement of bend limiter 28 along the cable portion.

At step 203 it is ensured that the pig tail is extended such that the end of the pig tail is remote from the repeater 20. If the pig tail is supplied as a helix, then the helix is extended during this step. A typical distance for this is between 1 and 2 metres. The ends of the fibres within the pig tail are then attached to corresponding fibres from the optical communication cable

24, this being achieved within the joint 22 as shown in Figure 4. The joint is then assembled and sealed with polyethylene .

At step 204, the second bend limiter 28 is coupled to the joint 22 and additional armouring and injection moulding operations are performed to seal the combined joint 22 and bend limiter 28 to form a compound device.

It is the elongate nature of the pig tail that provides sufficient distance between the repeater 20 and joint 22 so as to allow the sealing and armouring operations to be performed. However, it is desirable that the overall length of the assembly is minimised in the completed assembly to reduce stresses within it and allow it to be passed through cable handling equipment. Therefore at step 205 the joint 22 and the repeater 20 are brought closer together by forming or reforming the pig tail in a helix in the section between the bend limiters 26 and 28.

This can be achieved in a number of ways, for example the length of the pig tail may be wound around a mandrel so as to generate a helix having a radius at least equal to the minimum bend radius for the pig tail. The pig tail in helical form is shown in Figure 4.

During step 205, the final coupling spatial separation of the bend limiters 26 and 28 is achieved such that the connection member 1 may be positioned so as to fill the gap remaining between the two bend limiters (containing the helical pig tail 35) . At step 206 the parts 2 and 3 are brought together in this region from either side of the exposed portion of the coiled pig tail. In doing so, the grooved ends of each of the parts 2, 3 mesh with corresponding surfaces in each of the bend limiters 26, 28. The four bolts are tightened so as to couple the parts 2, 3 together and to simultaneously couple the connection member as a whole to each of the bend limiters 26, 28. This coupling step is shown in Figure 7. The procedure for connecting one half of the assembly has been described above. The second half of the assembly can be similarly generated in this way and this is performed at step 207 in Figure 5. It should also be noted that armouring is performed at the two extreme ends of the assembly.

A further example of the invention is now described. In the earlier example small amplifiers were used having

two fibre pairs (4 fibres in total) and were of similar dimensions to the universal joint (UJ) device. In the present example a combined UJ and amplifier device is provided, denoted a UJ-amplifier . This has a similar diameter and couplings as a conventional UJ for compatibility and handling purposes, although in this case it is extended along its axial length and a two fibre pair amplifier is incorporated within the housing. In this case because of the combined joint and amplifier in a single device, the total number of devices in the cable can be reduced.

In this example however, the requirements of the cable operator are for there to be four fibre pairs. Since the UJ-amplifier can only accommodate two fibre pairs for reasons of space within the housing, this problem is solved by coupling two such UJ-amplifiers along the cable, with the fibre pairs of one amplifier simply passing through the body of the second, and vice versa.

The complete assembly is shown in Figure 8. Here since the UJ-amplifiers 70 have a combined function, only one connection member 1 is required. The bend limiters 25 ' , 26 ' , 27 ' , 28 ' provide the bend limiting and force transfer functions in an analogous manner to their non- primed referenced counterparts in Figure 3. The method of coupling the whole assembly together is analogous to Figure 5 with appropriate modifications and remembering that the two amplifiers 70 each have four fibre pair pigtails on either side, only two of which are connected internally to the amplifier. Note that, in an alternative example, the bend limiters 25' and 26' may be removed and the connection member 1 then provides direct coupling between the UJ- amplifiers 70.