WO1988001395A1

WO1988001395A1 - Joining optical fibres

Info

Publication number: WO1988001395A1
Application number: PCT/GB1987/000574
Authority: WO
Inventors: Alan Alfred Mills
Original assignee: University Of Leicester
Priority date: 1986-08-19
Filing date: 1987-08-17
Publication date: 1988-02-25
Also published as: IL83588A0; AU7789787A; GB8620113D0

Abstract

A method of forming a butt splice between members for carrying optical signals, which comprises bringing the ends of the members into abutment and applying between the ends or applying to at least one of said ends a coupling composition that comprises a liquid having the same or substantially the same refractive index as the members, the liquid having dispersed therein a viscosity increasing agent that also has the same or substantially the same refractive index as the member, the coupling composition being flowable.

Description

Joining Optical Fibres

The present invention relates to the joining of optical signal carriers, for example, it relates primarily, but by no means exclusively, to the splicing of optical fibres, for example silica optical fibres.

It is preferable to use different types of splices in different situations. Permanent joints or splices are required where it is essential to have strong joints of high transmission that will never come apart accidentally, for example, in the construction of a main trunk network. They are best accomplished by autogenous fusion of the fibres end-to-end, with very precise positioning. The technique is commonly called 'welding', and advanced microprocessor-controlled welders are commercially available. However, even the best of these disturb the refractive index function across the splice and weaken the fibre around the splice, due to the rapid heating/cooling cycle. Moreover, the welding equipment is very expensive.

Semi-permanent joints or splices are required, for example, to join optical fibres to the light-emitting diodes and other solid-state devices that act as transmitters and receivers at the ends of the fibre optic network. Such devices tend to be damaged easily by heat, so welding is not suitable, and instead 'optical quality' epoxy cements are currently in use. Such optical couplants are expensive and, as the two components of the cement are mixed by the user, the refractive index inevitably varies from batch to batch. Moreover, although such splices are called "semi-permanent", it is difficult to break and reform them.

"Plug-in" splices, that is to say, demountable or disconnectable splices, will become more and more important as networks of optical fibres approach and branch closer and closer to the end-users. Large numbers of couplings will be made and unmade at the lowest levels, and it will be desirable for the consumer himself to be able to connect different equipment, for example, telephones, videophones, facsimile machines and computers to the network.

It has been proposed to insert the ends of two optical fibre cables to be spliced into a plug and socket respectively of a connector assembly. The plug and socket are then engaged to hold the fibre ends in as close abutment to each other as possible. Such mechanical abutment of confronting surfaces results in appreciable loss of signal intensity and clarity because of the presence of an air film between the ends, and because of the inevitable roughness of the surface. This roughness can be reduced by the use, for example, of a diamond saw, or by polishing the ends when cut. However, these measures are not practical where a large number of splices are to be made under field conditions. Cleavage-fracture initiated at a microscopic nick made with a special device incorporating a tungsten carbide or similar blade is preferable under these circumstances, but there is still signal loss across the splice and degradation of the signal due to reflection at the two interfaces.

Thus the splicing of cables presents particular problems in the laying of fibre optic telephone or other signal cables in situations where copper cables have hitherto been used.

The present invention provides a method of forming a butt splice between members for carrying optical signals, which comprises bringing the ends of the members into abutment and applying between the ends or applying to at least one of said ends a coupling composition that comprises a liquid having the same or substantially the same refractive index as the members to be spliced, the liquid having dispersed therein a viscosity increasing agent that has the same or substantially the same refractive index as the members to be spliced, the coupling composition being flowable.

The present invention also provides the use of a flowable composition that comprises a liquid having the same or substantially the same refractive index as a member for carrying optical signals, the liquid having dispersed therein a viscosity increasing agent that also has the same or substantially the same refractive index as a member for carrying optical signals as a coupling composition for a butt splice between such members.

In a method of the present invention two or more smaller members for carrying optical signals may be butt spliced to a single larger member.

In the method of the present invention, transmission across a splice is so improved that, although it is still desirable that a cut end for a splice should be as near as possible to perpendicular to the axis and as smooth as possible, any deviation from the perpendicular and any roughness is less important than in previously proposed splicing methods.

The coupling composition used in the method of the present invention is flowable (spreadable) . A suitable minimum viscosity at zero shear is 10^ centipoises.

The composition may be in the form of a flowable gel and is preferably thixotropic, that is to say, the composition exhibits a time-dependent decreasing viscosity or shear stress at constant shear rate. When the shearing force is eliminated, the viscosity returns over a period of time to its original "at-rest" value.

In a coupling composition used in the method of the present invention, the viscosity increasing agent is generally solid.

As indicated above, in a coupling composition for use in the present invention both the components have the same or substantially the same refractive index as the optical fibres to be spliced i.e. they are "index matched". Fused silica, a material much used in the manufacture of optical fibres, has a refractive o index of ")^ = 1.458, so the components of the coupling composition should have a refractive index of the same or substantially the same value, for example, from

1.450 to 1.466, for example, from 1.453 to 1.463 preferably from 1.456 to 1.460, and most preferably

1.458.

For use with optical fibres of or comprising fused silica, the viscosity increasing agent preferably is fumed silica or comprises fumed silica. "Fumed silica" is very finely divided (smoke size) vitreous silicon dioxide prepared generally by the flame hydrolysis of silicon tetrachloride. It has substantially the same refractive index as the fused silica used for optical fibres. Moreover, it is suitable for increasing the viscosity of a liquid in such a way as to give a thixotropic system.

Fumed silica may be modified by the incorporation of one or more other glass-forming oxides, for example, germanium and phosphorus oxides, by mixing their volatile chlorides with the SiCl4 at the flame hydrolysis stage. The resulting "smoke" particles have a different refractive index from that of fumed silica alone and may be of use in joining optical fibres having a refractive index other than that of fused silica.

Fumed silica (whether consisting of silica alone or comprising one or more other components) is hydrophilic when it comes directly from the.furnace, and binds strongly with water and other polar molecules. Hydrophobic fumed silica is made by treatment of the corresponding hydrophilic material with a reactive silane, for example, dimethyl- dichlorosilane. Both hydrophilic and hydrophobic grades of fumed silica are available commercially, for example, as "Aerόsil" (Wacker-Chemie GmbH) and as "Cab- O-Sil" (Cabot Corporation). ("Aerosil" and "Cab-O-Sil" are Trade Marks.) Hydrophobic or hydrophilic fumed silica may be used in the present invention, the former being preferred in certain compositions if immersion in liquid water is a possibility.

The liquid component of the coupling composition must have a refractive index the same or substantially the same as that of the members to be spliced, and should be transparent in the wavelengths of transmitted signals. Examples of liquids suitable for use in compositions for splicing fused silica fibres are saturated aliphatic hydrocarbons, polycyclic hydrocarbons, silicones, polyethylene glycols, and fluorocarbons, either alone or in admixture.

The material commonly known as "liquid paraffin" ay be used as a liquid component. It is prepared from the lubricating oil fraction of natural petroleum by treatment with powerful reagents, for example, fuming sulphuric acid and/or by catalytic hydrogenation, followed by vacuum distillation. Being a mixture of many homologous aliphatic hydrocarbons, the material is liquid at temperatures at which the individual components would be solids. There are available grades of liquid paraffin that have refractive indexes varying from about 1.46 to 1.48.

The refractive index of a hydrocarbon or a hydrocarbon blend that is too high or too low may be brought to the desired value by blending with another saturated aliphatic hydrocarbon, for example, it may be lowered by blending with a saturated hydrocarbon of lower molecular weight, for example, hexadecane (cetane) o of 25= 1.4345. Alternatively, and more cheaply, a commercially available lower boiling point saturated hydrocarbon mixture prepared by purification of the diesel oil fraction (refractive index about 1.42) may be used to lower the refractive index. To raise the refractive index decahydronaphthalene (refractive index about 1.48) or tetrahydronaphthalene (refractive index about 1.55) may be used.

The silicone liquids known as methylphenylpoly- siloxanes have refractive indices in the range of

1.41 - 1.51. They may be blended to give any chosen value in this range. The silicone available commercially as Dow-Corning 553 has a refractive index of 1.458.

Certain polyethylene glycols (PEGs) have suitable refractive indices, and may be blended appropriately, for example, polyethylene glycol 200 has a refractive index of l-ϊ459 -and polyethylene glycol 400 has a refractive index of 1.465. However, PEGS are hygroscopic and water-miscible and so are generally less suitable than aliphatic hydrocarbons or silicones.

Fluorocarbons of appropriate refractive indices may be used as the liquid component.

The aliphatic hydrocarbon/fumed silica and silicone/fumed silica coupling compositions of the invention have the following advantages: They are a. transparent from the UV to the IR, that is to say, from 350 to 1600 n , especially around 800-850 n , where most data transmission is currently conducted; b. not liable to darkening or yellowing with oxidation or exposure to the signal-carrying radiation; c. not liable to hardening or polymerization on exposure to signal-carrying radiation; d. of high boiling point and low freezing point; e. inert, non-toxic, non-corrosive, odourless; f. insoluble in water, and non-hygroscopic.

The silicone/silica coupling compositions are more expensive than the hydrocarbon/silica compositions but are more resistant to liquid water.

A coupling composition of the invention may be produced by admixing the various components. It is generally advantageous for the mixing to be carried out under conditions of heat and/or partial vacuum to reduce the risk of the entrainment of small air bubbles. These bubbles may otherwise cause an opalescent appearance in the product. It may be advantageous to filter the resulting mixture to remove occasional agglomerations of fumed silica. which exceed colloidal dimensions.

A composition of suitable viscosity may be achieved by using a ratio of fumed silica: liquid, for example, liquid paraffin or silicone, in the range of 5-10 : 100 by weight.

It is being proposed to manufacture optical fibres having a graded refractive index varying, generally decreasing, along the radius from the centre of the fibre. This is achieved by incorporating other materials with the silica. Such materials include, for example, germanium dioxide, phosphorus pentoxide and phosphorus fluorides. It is generally adequate to provide a coupling composition having the same or substantially the same refractive index as the silica core of the fibre, but if desired a coupling composition of different refractive index may be used, for example, having a co-fumed silica as described above as the viscosity increasing agent.

In a method of forming a butt splice between members for carrying optical signals according to the present invention, the splice is preferably held by retaining means. Such means may be a simple sleeve, or it may comprise a conventional optical fibre joining device, for example, of the plug and socket type.

A conventional device may be modified for use according to the method of the present invention by the provision of means for supplying a coupling composition according to the present invention to the interface between the ends of the two members to be joined. A reservoir containing the coupling composition may be in connection with the interface, and the composition may be applied to the interface by direct or indirect action, for example, by squeezing a flexible reservoir by direct or indirect manual pressure. Coupling composition may be forced from a rigid reservoir by pressure, for example, by the action of a piston.

It is advantageous if the device is in plug and socket form, that is to say, the device has two mating parts, each of which is capable of holding a member for carrying an optical signal, for example, an optical fibre having a free end, the two parts of the device being adapted to interlock in such a manner that the ends are brought into and maintained in abuntment. One or both parts of the device is or are provided with means for supplying coupling composition to the interface between the end faces or to one or both end faces.

A device of the invention may be suitable for producing a permanent splice but it is often advantageous if the splice is disconnectable or demountable. The reservoir of coupling compound may then be used to replace or replenish the coupling compound at the interface whenever a new splice is made.

The invention further provides a pack which comprises 1) a device for forming a butt splice between members for carrying optical signals including optical fibres, which comprises means for holding the abutting ends of the members, and which also comprises 2) a coupling compound of the invention, for example, contained within a tube, for example, a tube having a nozzle for the application of the coupling compound.

The present invention further provides a device for use in forming a butt splice between members for carrying optical signals, which comprises resilient members having one or more channels each for carrying one of said members and also having one or more holes parallel to the channel(s) and each suitable for the insertion of a screw or bolt. The resilient member is of a resiliently deformable material for example, natural or synthetic rubber, polyethylene or PTFE (polytetrafluoroethylene) . The screws to be used are preferably tapering screws. It is preferable to use several screws arranged around the or each optical fibre channel or channels, for example, at least four, for example, eight screws, preferably arranged equidistantly from the optical fibre channel or channels.

In use, the or each member for carrying an optical signal is inserted through a channel of the resilient member. If desired, either before or after insertion the end is cleaved cleanly at right angles to the axis. The member is then withdrawn a short way within the channel until it is substantially flush with the end of the resilient member. The screws are then tightened substantially uniformly.

The alignment of each member in its channel may be adjusted by differential tightening and loosening of screws in the screw holes. Very fine adjustments may be achieved in this manner. The adjustment may be followed, for example, with the aid of a "plug-on" accessory (based on a simple microscope with cross hair graticule viewing a "socket" stage) .

In a further embodiment, a resilient member of the invention is held by a rigid member. This arrangement reduces the disturbance to the alignment of the or each member for carrying optical signals within its channel in the resilient means when the resilient member is moved. The rigid member may be conical in shape.

A further embodiment of the invention provides a device for forming a butt splice between two resilient members for carrying optical signals which comprises two resilient members of the invention and means for holding the two members in butt splice configuration. The device may further comprise a rigid member holding each resilient means.

The butt splice-holding means may be provided on the resilient members themselves or, when rigid members are present, on the rigid members. Such holding means are for example, mating screw threads.

Alternatively, external holding means may be provided. This may hold the resilient members or the rigid member if present. Such external holding means may be, for example, a sleeve or body fitting over the splice and holding the two components in place. Such external holding means may be formed _iι situ over the splice or may slide over the splice or be in two or more interlocking parts. Such parts may have been produced along the axis of the sleeve or body or across the axis. They may be held together by a permanent fastening means, for example, by adhesive, or by an openable fastening means, for example, clips, mating screw threads or bayonet fastenings.

In a preferred embodiment the resilient means are held by respective rigid members that are themselves held by external holding means. This enables the two resilient members to be brought into alignment with one another with the minimum disturbance within the channel to the or each member for carrying optical signals, and to be held in such alignment.

It is generally preferable for the butt splice holding means to have a disconnectable fastening. This enables the butt splice to be dismounted and reconnected, for example, form a different connection in analogy to a plug and socket connection for electrical systems.

An external holding means may also comprise means for attaching the device to a solid support.

A device according to the invention preferably also comprises means for supplying coupling composition according to the present invention to the interface between the abutting ends of the members to be spliced or to one or both ends.

The coupling composition supplying means (reservoir) is, for example, a chamber in connection with one or each of the channels for the members to be spliced, or in connection with the interface between the two members to be spliced. The reservoir is capable of supplying coupling composition to the interface between the two members by direct or indirect action, for example, it may be flexible, comprise a piston or be arranged such that fastening the device causes the coupling composition to be forced out.

In use, one of the members to be spliced is inserted through a channel of one of the resilient means, which is itself held by a rigid member. If desired, either before or after insertion the end of the member is cleaved cleanly. The member is then withdrawn a short way within the channel until it is flush with the end of the resilient means. The screws are then tightened substantially uniformly. This is repeated for each other optical member to be spliced.

The alignment of each member in its channel in its respective resilient means is generally adjusted at this stage, preferably with the aid of a "plug-on" accessory (based on a simple microscope with cross hair graticule viewing a "socket" stage) and/or by finding optimum transmission, for example, using a special meter or simply by following the response of the apparatus connected to be connected by the joint. The adjustment may be achieved by differential loosening and tightening of the screws in the resilient means.

The two resilient members, held in their respective rigid members to minimise disturbance to the alignment of the optical members, are then brought together and held tightly by an external holding means. The alignment of the optical members within their respective channels and across the splice can be adjusted further using the adjusting screws. In this case the adjustments may be tested using a special meter or by following the response of the apparatus to be connected.

The coupling composition may be applied to the end of one or both of the holding means before they are brought together, or it may be applied from the reservoir after the two parts have been brought together and held in place by the external holding means. The device may be arranged such that pressure exerted by the external holding means forces coupling composition into the interface between the ends of the members.

If desired, adhesive or other sealing means may be applied to the sheath of the optical member at the point where it leaves the device retain it in position and to hinder tampering, and if desired the screws may be sealed in. This maintains the alignment of the optical member in the resilient means when a splice is disconnected and a new connection is made.

A device may be dismantled by removing the external holding means and gently pulling out the two rigid members with their inner resilient members. One or more of the optical members may be removed by unscrewing the screws in the appropriate resilient members and pulling out the optical fibre which may be replaced by a different optical member.

Alternatively and more usually, for example, to connect a different device to an input signal member, the external holding means may be disconnected and the unit (optical member carrying input signal resilient means and rigid member) connected to the corresponding unit for the device in question, in direct analogy to putting the plug of a different electrical device into an electrical socket.

In the case where the holding means are integral with the rigid members or the resilient members, the device may be disconnected and a new connection formed analogously.

When a new connection is made, it should be ensured that coupling composition is present at the interface between the two abutting optical members. The composition may be applied manually or from a reservoir when present.

The device of the invention enables "plug and socket" connections to be made and also by the provision of adjusting screws in a resilient material enables the alignment of the member to be spliced to be adjusted simply but effectively.

Instead of just one channel in each resilient means two or more channels may be provided to enable two or more splices to be formed. Moreover, if two or more smaller members are to be butt spliced to a larger member channels of an appropriate number and size are provided. Adjustment of alignment may be carried out using the screws in the resilient means as described above.

Although alignment of an optical member in its channel in a resilient member can be adjusted in situ, it is an advantage of the present invention that a device having an optical signal input can be supplied by a manufacturer with one component of a plug and socket type of joining means of the invention, especially a resilient member held in a rigid member, fitted to the device, the optical member having been aligned in its channel by the manufacturer. The device is then ready for connection to a corresponding component at the user end of an optical signal network, in direct analogy to the plugs and sockets now standard on telephone equipment.

There will now be described an example of the method according to the invention, involving the preparation of an optical coupling composition suitable for use therewith.

Examples

I. Two lengths of silica optical fibre of the grade used for the transmission of telephone signals were to be spliced according to the invention. A retaining sleeve was secured in place over the end of one length, so as to leave a short section projecting. The optical fibre was then cleaved squarely by scribing with a commercially available device. A quantity of hydrocarbon-based or silicone-based coupling composition produced as described below was then placed upon the cleaved end, and the assembly inserted in a mating socket secured to the smoothly cleaved end of the second length of optical fibre. The coupling composition was thereby squeezed into a thin film promoting optical continuity between the cut ends of the two optical fibre cables.

If it is desired at a later date to disconnect the splice then this is achieved simply by unclamping the sleeve member and withdrawing the cable end, since the coupling composition retains its gel-like consistency.

II. Hydrocarbon-based coupling compositions

Coupling compositions were produced as follows:- A quantity of liquid paraffin (also known as white oil and available commercially in a highly purified condition) . was placed in a mixing container having means for partial evacuation. The specific gravity is within the range of 0.83 to 0.86 and its refractive o index,^⁵ = 1.467.

The refractive index of fused silica i.e. the o optical fibres, has a value*). _D25 ⁼ 1.458, and o therefore a quantity of hexadecane ( }- 25 = 1.434) was blended (about 25% by weight) into the liquid paraffin (about 75% by weight) to give an oil having of

Fumed silica was then taken for mixing with the oil to thicken it to the consistency of a gel. The fumed silica was selected from the range marketed under the Trade Mark "Cab-O-Sil" and is identified as "M-5". The fumed silica and the oil were used in a weight ratio 7.5:100 and were preheated and then mixed at 120°C under sub-atmospheric conditions to prevent any tendency to opalescence due to minute occluded bubbles.

The resulting mixture is a transparent, stable, gel-like compound with the same refractive index and dispersive power as fused silica. It is colourless and does not become yellow with time. It has a low freezing point and a high enough effective boiling point ( 250°C) to avoid contamination problems- or loss by evaporation. It is non-toxic and odourless.

The compound is sufficiently water-resistant to remain unaffected under normal conditions in air, but increased resistance to liquid water is obtained by use of silicone-treated hydrophobic fumed silica Cab-O-Sil TS - 720.

III. Silicone-based Coupling Compositions

A methylphenylpolysiloxane available commercially as Dow-Corning 556 and having a refractive index o J_D = 1.458 was mixed with fumed silica (Cab-O-Sil M5) in a weight ratio of 7:100 under conditions as described above for the production of coupling composition A.

The resulting mixture is a colourless transparent, stable gel-like substance having the same refractive index as fused silica. It is non-toxic and odourless.

It is resistant to liquid water.

IV. Radiation Absorption by Coupling Composition

Neither the hydrocarbon-based coupling composition II described above nor the silicone-based coupling composition III described above showed any significant adsorption within the range of from 350 to 1600 nm. (The visible range is from 400 to 750 nm and the range generally used at present for data transmission is 800 - 850 nm.)

^v- Loss Across Splice

Transmission across a splice produced as described in I above using a) the hydrocarbon based coupling composition II and using b) the silicone-based coupling composition III was measured. The loss ratio was only

0.07 dB.

An optical fibre joining device constructed in accordance with the present invention will now be described, by way of- example only, with reference to the accompanying drawing, which is a view in partial cross-section.

Device 100 consists of two parts (A and B) .

There are provided two rigid members 1 each having the form of a tapered cone with an annular flange 2. Within each rigid member 1 is a resilient member 3, of rubber. Within each resilient member 3 are provided eight holes 4 into each of which fits a tapering screw 5. Each screw 5 is provided with a slot 6 for a screwdriver. Hexagonal holes for an Allen key may be provided as an alternative. Threaded plugs 7 hold the respective members 3 in place. Each plug 7 has a slot 8 for tightening the plug 7 in place.

A reservoir 9 for coupling compound 10 is formed between the two rigid members 1 and the two resilient members 3. The reservoir -9 is in connection by means of duct 11 with channels 12 through, which optical fibres 13 pass. Channels 12 and screw holes 4 are parellel with each other.

The two halves of the device 100 are held together by the screw caps 14 and body 15 of an external holding means. There is also provided a back nut 16 whereby the device 100 can be attached to a panel 17.

If the device 100 is not to be attached to a panel or other rigid body, then the back nut may be dispensed with and the body 13 need then have ,no projections.

Adhesive 16 is provided at the point where the optical fibre 13,emerges from the device 100. This prevents tampering, adds security and holds the fibres firmly in place. Alternatively or in addition the screws 8 may be sealed in or the ends of the device between the caps 12 may be sealed.

The rigid members 1 each has a flat surface 17 to prevent rotation of the member with respect to the body 13.

The device 100 may be provided in assembled form or in kit form. For use of an assembled device the screws 8 are. loosened but preferably are not removed.

One of the optical fibres 13 is inserted through the channel 12 of one of the resilient members 3 and the end is cleaved cleanly at right angles to the axis of the fibre. The fibre is then withdrawn a short way within the channel 12 until it is flush with the end edge of the member 3. The screws 8 are then tightened first uniformly, but then, to achieve as good an alignment as possible, the screws are adjusted differentialy, preferably while checking the alignment with the aid of a "plug-on" accessory (based on a simple microscope with cross hair graticule viewing a "socket" stage) and/or by finding optimum transmission across the joint, for example, using a special meter or simply by following the response of the apparatus to be connected to the network by the joint.

The two members 3 are then brought together and held tightly using the screw caps 12.

Coupling composition 10 may be applied manually to the end of one of .the members 3 before it is fixed to the other, or it may be applied from the reservoir 12 after the two parts have been fixed together.

The device 100 is then fixed on to a panel using the body 15 and the back nut 16.

Claims

1. A method of forming a butt splice between members for carrying optical signals, which comprises bringing the ends of the members into abutment and applying between the ends or applying to at least one of said ends a coupling composition that comprises a liquid having the same or substantially the same refractive index as the members, the liquid having dispersed therein a viscosity increasing agent that also has the same or substantially the same refractive index as the . member, the coupling composition- being flowable.

2. A method as claimed in claim 1 wherein the coupling composition is thixotropic. \

3. A method as claimed in claim 1 or claim 2 , wherein* the viscosity increasing agent is fumed silica or comprises fumed silica.

4. A method as claimed in claim 3, wherein the viscosity increasing agent is silica that has been co-fumed with one or more glass-forming oxides.

5. A method as claimed in any one of claims 1 to 4, wherein the liquid is a saturated aliphatic hydrocarbon, a polycyclic hydrocarbon, a silicone, a polyethylene glycol or a mixture of two or more thereof .

6. A method as claimed in any one of claims 1 to 4, wherein the liquid is liquid paraffin, liquid paraffin admixed with one or more hydrocarbons selected from hexadecane, decahydronaphthalene, tetrahydronaphthalene and diesel oil fractions; a methylphenylpolysiloxane, or a mixture of two or more methylphenylpolysiloxanes.

7. use of a flowable composition that comprises a liquid having the same or substantially the same refractive index as member for carrying optical signals, the liquid having dispersed therein a viscosity increasing agent that also has the same or substantially the same refractive index as a member for carrying optical signals, as a coupling composition for a butt splice between such members for carrying optical signals.

8. A device for use in forming a butt splice between members for carrying optical signals, which comprises a resiliently deformable member having one or more channels each for carrying one of said members and also having one or more holes parallel to the channel(s) and each suitable for the insertion of a screw or bolt; the resilient member preferably being held by a rigid member.

9. A device for forming a butt splice between, members for carrying optical signals including optical fibres, which comprises (i) two members each of a resilient material and having one or more channels each for carrying one of said members, and one or more holes parallel to the channel(s) and each member preferably being held by a rigid member, each suitable' for the insertion of a screw or bolt, and (ii) means for retaining the two members so their channels are substantially in alignment.

10. A coupling composition suitable for use in forming a butt splice between members for carrying optical signals, which comprises a liquid having the same or substantially the same refractive index as the members, the liquid having dispersed therein a viscosity increasing agent that also has the same or substantially the same refractive index as the members, the coupling composition being flowable.