GB1598186A

GB1598186A - Methods and apparatus for preparing the ends of optical fibres for forming fibre couplings

Info

Publication number: GB1598186A
Application number: GB3774277A
Authority: GB
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1977-09-09
Filing date: 1977-09-09
Publication date: 1981-09-16

Description

(54) IMPROVEMENTS IN OR RELATING TO METHODS AND APPARATUS FOR PREPARING THE ENDS OF OPTICAL FIBRES FOR FORMING FIBRE COUPLINGS (71) We, TELEPHONE CABLES LIMITED, of Chequers Lane, Dagenham, Essex RM9 6QA, a British Company, 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:- This invention relates to a method of, and apparatus for, preparing the ends of a plurality of optical fibres prior to coupling the fibres with a corresponding set of fibres in end-to-end relationship, for example by butt joining the fibre ends.

When coupling together two lengths of optical cable each incorporating a plurality of vitreous optical fibre waveguides, the preparation of each cable end includes the steps of removing an end portion of the cable sheath so as to expose end lengths of the fibres, and preparing the free ends of the fibres by a known technique which involves scoring a portion of the vitreous surface of each fibre and breaking the fibre at the scored point, under tension, to give a fibre end surface which is optically flat and free from irregularities, and is substantially orthogonal to the fibre axis. It is required to break the exposed portions of all the individual fibres in the cable to the same length, this being achieved by scoring all the fibres at corresponding points and breaking them under substantially the same tension.

It is an object of the present invention to provide an improved method of, and apparatus for, scoring exposed portions of a plurality of optical fibres and breaking the fibres to the same length while under substantially the same tension, and it is a further object of the invention to carrying out the scoring and breaking operation in such a manner that the fibres can readily be individually matched, in end-to-end relationship, with a corresponding set of fibres which have been prepared in the same way. The invention is also concerned with the provision of apparatus for preparing the ends of two corresponding sets of optical fibres, preparatory to forming a joint between two lengths of optical fibre cable.

According to the invention, a method of preparing the ends of a plurality of vitreous optical fibres, for coupling said fibres to a corresponding set of optical fibres in end-toend relationship, includes the steps of arranging exposed lengths of the fibres in a planar parallel array, supporting the said fibre lengths between first and second retaining means which are spaced apart, subjecting the said fibre lengths between the retaining means to tension individually in sequence, and traversing scoring means across the array at a location between the said first and second retaining means and along a path substantially orthogonal to the longitudinal axes of the said fibre lengths, so that the fibres are scored, to cause breaking thereof, individually in the same sequence as that in which the said lengths are tensioned, the sequential tensioning and scoring of the said fibre lengths being effected in such a manner that all the fibre lengths are scored while under substantially the same tension, that after each fibre is broken the said length of the next fibre in the sequence is tensioned before being contacted by the scoring means, and that all the fibres are scored at the same positions in the respective said lengths so that after all the fibres are broken the thus prepared ends thereof lie on a line orthogonal to the axes of the fibres Preferably the fibres are arranged in the said array in a predetermined order matching that of the corresponding set of fibres to which the fibres of said array are to be coupled, for facilitating the subsequent coupling of the two sets of fibres.

The substantially equal tensioning of the fibre lengths can be effected, for example, by the continuous application of a constant load, of suitable magnitude for ensuring clean breakage of the fibres, to one of the fibre array retaining means. The sequential tensioning of the fibre lengths is preferably effected by causing relative movement between the first and second retaining means to take place in steps as each fibre is broken, while the applied load is kept constant. The arrangements ensuring sequential and substantially equal tensioning of the fibre lengths, in conjunction with the specified relative positioning of the fibre retaining means and the scoring means, result in all the fibres constituting the array being broken to the same length.

Further according to the invention, apparatus for preparing the ends of a plurality of vitreous optical fibres by the method described above includes first and second clamps spaced apart for retaining the fibre array, each of said clamps including a member for supporting the fibres, a clamping member co-operating with said fibre support member to grip the fibres, and means for locking the clamping member in the fibre gripping position, means for applying a substantially equal tensioning load to all the fibre lengths retained between the clamps, means for effecting stepwise movement of one of the clamps in relation to the other clamp in such a manner as to cause sequential tensioning of the said fibre lengths, and, located between the said clamps, a scorer component consisting of a scoring blade and a carrier therefor, the blade carrier being supported by means enabling it to travel in a direction substantially orthogonal to the longitudinal axes of the said fibre lengths so as to cause the blade to traverse the fibre array and score the fibres in sequence.

The fibre supporting members of the fibre clamps are preferably formed with a plurality of slots or grooves for accommodating the fibres individually, substantially equally spaced apart.

A suitable block or anvil is preferably provided, between the clamps and in the vicinity of the scorer component, for supporting the portions of the fibres to be scored.

This anvil may, if desired, be provided with grooves for accommodating the individual fibres, and/or with a transverse groove, disposed orthogonally to the positions in which the fibre lengths will lie, for receiving the scoring blade.

For the application of a tensioning load to the fibre lengths retained between the clamps, the apparatus preferably includes means for applying a constant load to one of the clamps. In a preferred arrangement for effecting the sequential tensioning of the said fibre lengths, the clamps are initially disposed with their longitudinal axes parallel, so that the fibre lengths retained between the clamps will lie orthogonally to said clamp axes, one of the clamps is arranged to be capable of pivotal movement such that the angle of disposition of the longitudinal axis of the said clamp relative to that of the second clamp can be varied for slackening said fibre lengths, and means are provided for imparting to one of the clamps stepwise movement, suitably in the form of a rotational or sliding motion, in such a direction that the slackened fibre lengths are tensioned in turn, a step in such movement taking place as each fibre is broken and being halted by tensioning of the next fibre length in the sequence. The tensioning load may be applied to the clamp which undergoes the pivotal movement, and such movement may be effected by the initial application of the load.

Preferably one of the clamps is arranged to undergo both the pivotal movement and the stepwise movement described above, the fibre tensioning load also being applied to this clamp, while the other clamp is held stationary: the two clamps in such an arrangement will hereinafter be referred to as the "movable clamp" and the "fixed clamp" respectively. Thus the movable clamp may be pivotally supported on a carrier which is disposed with its longitudinal axis parallel to that of the fixed clamp, and which is capable of stepwise rotational or sliding movement in a direction away from the fixed clamp. In operation of such an arrangement, with the array of fibre lengths held in position between the clamps the movable clamp is initially pivoted into an oblique position towards the fixed clamp on the application of a load which causes tensioning of the first fibre length in the sequence, the remaining fibre lengths in the array being slackened as a result of the oblique positioning of the movable clamp. The first fibre is then scored until it breaks, the movable clamp carrier is caused to move away from the fixed clamp so as to tension the second fibre length, which is then scored to breaking, and this procedure is repeated, while the applied load is maintained constant, until all the fibres have been broken. The initial operation of the load applying means may be arranged to cause an initial movement of the movable clamp carrier which results in pivoting of the clamp on the carrier and in the application of the load to the movable clamp, and the load applying means may also be arranged to effect the further stepwise movements of the said clamp carrier, for example the clamp carrier may be mounted on a spring-loaded rotatable shaft, rotation of which is effected by virtue of the force of the spring, which also provides the fibre tensioning load.

In an alternative arrangement, the fibre tensioning load may be applied to one clamp, causing the above-described pivotal movement thereof, whilst the other clamp is arranged to undergo the stepwise movements for sequential tensioning of the fibre lengths.

To facilitate the formation of a joint between two lengths of optical fibre cable, instead of employing a single apparatus in accordance with the invention for preparing the ends of the fibres of each cable separately, a duplicated form of the apparatus is preferably employed. Thus a suitable apparatus in accordance with the invention for the end preparation of two corresponding sets of optical fibres includes two pairs of fibre-retaining clamps, one pair for each set of fibres, and associated with each pair of clamps means for applying a fibre tensioning load to one of the clamps and means for effecting stepwise movement of one of the clamps; preferably the two pairs of clamps are so arranged that a single scorer component can be employed in the same position for scoring both sets of fibres. In addition, this form of apparatus is preferably so constructed that a fibre jointing arrangement can be accommodated, in conjunction therewith, in such a position that each set of fibres can be retained in one of the clamps while the joint is made: this ensures that the two sets of fibres are correctly matched, provided that the fibres are initially arranged in corresponding order in the two pairs of clamps.

For operation, the apparatus of the invention, and in particular the cable jointing form of apparatus described in the preceding paragraph, is most conveniently disposed so that the fibre array or arrays lie substantially horizontally during the tensioning and cutting procedure. However, for joining cable lengths in some locations, it might be necessary for the apparatus to be disposed vertically or at an inclination, and in such cases it may be desirable to make some modifications to the apparatus for ensuring that the fibre tensioning loads applied to the two pairs of clamps are kept constant and are substantially equal.

A specific form of apparatus in accordance with the invention for the end preparation of two corresponding sets of optical fibre waveguides, and the method of operation of the apparatus, together with its use in conjunction with fibre jointing means in the forma bon of a joint between two lengths of optical fibre cable, will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a perspective view of the fibre tensioning and scoring apparatus, Figure 2 is a plan view of a part of the apparatus of Figure 1, with an array of fibres in position and in the condition prevailing at the commencement of the fibre tensioning and scoring procedure, Figure 3 is a side elevation of the scorer unit included in the apparatus of Figure 1, and Figure 4 is a perspective view of a fibre jointing unit for use in conjunction with the apparatus of Figure 1.

Like parts in the different figures of the drawings are indicated by the same reference numerals.

As shown in Figure 1, the fibre tensioning and scoring apparatus, which is designed for the end preparation of two sets of seven fibres each, preparatory to joining the fibres, is supported on a framework consisting of a base plate 1, and front plate 2 and back plate 3 connected together by cross pieces 4. Fibre array retaining clamps 5, 6, 7, 8, and a fibre scoring arrangement including the scorer unit 9, extend from the front of the front plate, above the base plate, and the arrangements for applying fibre tensioning loads to the two sets of fibres, and for effecting stepwise relative movements between the clamps retaining each set of fibres, are located in the spaces between the front and back plates. For operation of the apparatus, the base plate is normally disposed horizontally. The fibre retaining clamps are sufficiently raised above the base plate to enable a fibre jointing unit to be accommodated beneath them, supported on the base plate; guides 10 are provided on the base plate for locating the fibre jointing unit.

The arrangement of fibre retaining clamps consists of movable clamps 5 and 8 and fixed clamps 6 and 7, the two fixed clamps, together with the fibre scoring arranement located between them, constituting a central unit disposed between the movable clamps.

Clamps 5 and 7 are employed for holding a first set of fibres of sequential tensioning and scoring thereof; and clamps 6 and 8 are employed for holding a second set of fibres for the performance of the same operations on the latter. Each of the clamps includes an elongated U-section fibre support member 11 formed with two opposing sets of seven slots 12, for accommodating the seven fibres individually, and a clamping bar 13 pivoted on the fibre support member 11, at 14, so that the said bar can be held vertically, as shown in the cases of clamps 6 and 8 in Figure 1, or lowered into the trough 15 between the two sets of slots, as shown in clamps 5 and 7 in Figure 1, for clamping the fibres in position.

Each clamp also includes a locking disc 16, carried on the forward end of the fibre support member, for locking the clamping bar in the clamping position; each of the discs 16 is formed with a spiral groove on its inner surface (not shown in the drawings), providing a cam surface which co-operates with a pin 17 on the free end of the clamping bar 13; the pin is inserted into the groove in the disc when the clamping bar is lowered, and on rotation of the disc the said cam surface travels over the pin, thus forcing the clamping bar downwards into the trough 15.

Rubber strips 18 are attached to the undersides of the clamping bars 13, to bear upon the fibres in the trough.

Each of the movable clamps 5 and 8 is pivotally supported on a rotatable carrier 19.

The pivots are not visible in the drawings, but the position of the pivot 20 of clamp 8 is indicated by a broken circle in Figure 2.

Each of these pivots is subjected to some restraint by a spring, one end of which is attached to the pivot pin, and the other end of which is held against the side of the carrier, as shown at 21 in Figure 1. The pivotal movements of these clamps towards the central unit are limited by abutment of respective arms 22, 23, attached to the sides of the clamps, against the adjacent sides of -the clamp carriers: arm 22 of lamp 5 is shown in Figure 1, and arm 23 of clamp 8 is shown in Figure 2; stops 24 (Figure 1) and 25 (Figure 2) are provided to prevent pivoting of the respective clamps in the opposite direction, away from the central unit. (Movements of the movable clamps and other moving parts towards and away from the central unit will hereinafter be referred to as "forward" and "backward" movements respectively).

Each movable clamp carrier is mounted for rotation on a shaft 26, 27 running in ball bearings 28, 29 mounted in apertures in the front plate 2 and back plate 3 respectively.

Spacer members 30, 31 are carried on the shafts, for spacing the clamp carriers from the front plate. Means for effecting stepwise rotational movements of the clamp carriers 19 and simultaneously applying fibre tensioning loads to the movable clamps consist of levers 32, 33 supported in blocks 34, 35 which are mounted respectively on the portions of the shafts 26, 27 located behind the front plate, and springs 36, 37 carried on the respective shafts, between the lever blocks 34, 35 and the back plate, the respective ends of each said spring being attached to the lever block and the back plate: one of these springs, 37, is shown in Figure 2, an end only of spring 36 being visible in Figure 1.

Notched brackets 38, 39 are mounted on the back plate for retaining the levers 32, 33 in an inoperative position when the apparatus is At in use or when the movable clamps 5 and 8 are required to be held stationary in the mid-position shown in Figure 1, and the levers are pivoted in their respective blocks' for movement between the said position in the notches and the free position for operation of the clamps 5 and 8, in which position the levers are shown in Figure 1. A loop spring 40 is attached to each lever and to its supporting block, to hold the lever in each of said positions as required. Stops 41, 43 (Figure 1) and 42, 44 (Figure 2) are mounted on the front plate, for holding the levers 32, 33 respectively in desired forward and backward positions.

The central unit comprises the fixed fibre clamps 6 and 7, mounted on a platform 45, and the fibre scoring and breaking arrangement which consists of an anvil 46 mounted on the platform 45 between the fixed clamps and, disposed above the anvil, the scorer unit 9 (to be described in detail below) slidably mounted on a pair of rods 47 supported between front and rear buffers 48, 49. The whole central unit is hinged in a block 50 adjacent the back plate, so that this unit can be raised from the position shown in Figure 1, and in addition the assembly of scorer unit 9, slide rods 47 and front buffer 48 is pivoted in the rear buffer 49 so that this assembly can be raised independently, leaving the fixed clamps in the position shown.

Referring now to Figure 3, the scorer unit consists of a metal box-like carrier 51 with two opposite open sides and a cover plate 52, having a pair of cylindrical channels 53 through the base in which the rods 47 are a sliding fit and, in the centre of the rear side of the base, a slot 54 through which the blade arm 55 extends. The blade arm is pivoted at 56, the pivot being mounted between the channels 53, and is attached to a spring 57 supported from a member 58 in an aperture 59 in the front face of the carrier, and a scoring blade 60 is attached to the lower edge of the blade arm. A screw 61 is inserted through a second aperture 62 in the front of the carrier, to act as a stop limiting the movement of the blade arm towards the front of the carrier and hence limiting the descent of the blade below the base of the carrier.

The fibre jointing unit, shown in Figure 4, for use in conjunction with the fibre tensioning and scoring apparatus shown in Figure 1 consists of a base plate 63 supporting a cable clamp 64 at each end, and a fibre jointing plate 65 supported centrally on the base plate. The fibre jointing plate is formed with seven V-shaped grooves 66, of suitable dimensions for accommodating the optical fibres, continued at each end into V-shaped slots 67, which are formed in slightly thickened sections of the plate. The V-shaped grooves 66 are precision machined to such dimensions that both sides of a groove will make tangential contact with a fibre lying therein, and the fibre will stand slightly proud of the surface of the plate on each side of the groove: such accurate dimensioning of the grooves ensures accurate alignment of the butting ends of the fibres when the fibre joints are made, so that optical losses in the joints, in operation of the cable, are minimised. The slots 67 are provided to facilitate insertion of the fibres into the grooves 66.

The scoring blade 60 is suitable formed of tungsten carbide, and all other parts of the apparatus described above are composed of metal, suitable types of steel preferably being used for the construction of the clamp carrier shafts 30, 31, levers 32, 33, the pins 17 on the clamping bars 13, the slide rods 47, the scoring blade arm 55, the brackets 38, 39, lever stops 41, 42, 43 and 44, movable clamp stop arms 22, 23, and the various pivots, while the remaining parts may suitably be formed of an aluminium alloy.

In operation of the apparatus described above with reference to the drawings, for the end preparation and joining of corresponding set of seven optical fibres in two lengths of cable, the fibre jointing unit shown in Figure 4 is first placed in position on the base plate of the apparatus of Figure 1, and is located by the guides 10 so that the jointing plate 65 lies directly below the anvil 46 with the grooves 66 aligned with the slots 12 of the clamps. End portions of the two cable lengths to be coupled are inserted into the respective cable clamps 64, and the portions of the cable sheath overlying the base plate 63 are removed to expose appropriate lengths of the fibres, the free lengths of the fibres being sufficient to provide some slack for facilitating manipulation of the fibres in the subsequent operations.

The assembly of scorer unit 9, slide rods 47 and buffer 48 is raised by pivoting at 49, the clamping bars 13 of all the clamps are raised, and the movable clamps 5 and 8 are tilted forwards (that is to say, towards the fixed clamps), suitably through an angle of about 30 to the vertical, by rotation of the clamp carriers 19 by means of the respective levers 32, 33, which are moved forward of the stops 41 and 42 and held against the forward edges of said stops. The two sets of optical fibres are then threaded through the slots 12 of the respective movable clamps, care being taken to ensure that both sets of fibres are arranged in the same order, and the fibres are clamped in position in these clamps by lowering and locking the clamping bars 13 as described above, the lengths of the fibres lying forward of the clamps 5 and 8 respectively being sufficient to extend beyond the fixed clamps 7 and 6 respectively. The forward tilting of the movable clamps, prior to clamping of the fibres therein, ensures that there shall be some slack in the portions of each set of fibres between a movable clamp and a cable clamp, which slack will be required for effecting the subsequent fibre jointing operation.

One of the levers 32, 33 is returned to the upright position and placed in the notch in the appropriate bracket 38 or 39, so that the associated movable clamp is held stationary in the horizontal position, while the fibres clamped therein are threaded through the slots 12 of the two fixed clamps and clamped in the farther of the fixed clamps. The scorer unit assembly is then lowered into the operating position shown in Figure 1. The apparatus is thus ready for effecting the end preparation of the first set of fibres; while this operation is being carried out, the second movable clamp, with the second set of fibres clamped therein but otherwise free, is retained in the forward tilted position, the free ends of the fibres lying loosely below the central unit of the apparatus.

The commencement of the sequential fibre tensioning operation in respect of one set of fibres is illustrated in Figure 2, which shows fixed clamp 6 and the corresponding movable clamp 8 with the means for applying the fibre tensioning load to, and effecting stepwise movements of, the latter clamp. The components located between the two clamps shown, namely the other fixed clamp and the fibre scoring and breaking arrangement as shown in Figure 1, have been omitted from Figure 2 for clarity. To initiate the fibre tensioning procedure, the lever 33 is released from the bracket 39 and moves backwards towards the stop 44 by virtue of the force of the spring 37, thus causing backward rotation of the clamp carrier 19 and applying a load thereto, which load causes tensioning of the fibres in sequence. Simultaneously with the said movement of the lever, the clamp 8 is pivoted forwards by the resulting tensioning of the first fibre 71 of the array between the clamps, the pivoting movement of the clamp 8 being limited by abutment of the arm 23 against the carrier 19; the tensioning of the fibre also prevents further rotation of the clamp carrier, and hence halts the backward movement of the lever. The clamp 8 is thus in the position shown in Figure 2, with fibre length 71 tensioned and the remaining fibre lengths 72 to 77 inclusive slackened to a degree increasing from 72 to 77. The scorer unit is then pushed along the slide rods 47 until the blade 60 scores the fibre 71 in the centre of the portion of the fibre lying on the anvil 46, causing the fibre to break at this point.

Braking of the first fibre 71 releases the clamp 8 so that the carrier 19 rotates further backward under the force of the spring 37 until stopped by the resulting tensioning of the second fibre 72. This fibre is then scored and broken, the clamp carrier 19 rotates backward until fibre 73 is tensioned, and the sequence of operations is continued in this manner until all the fibres have been broken at corresponding points. It will be apparent that stepwise rotational movement of the movable clamp carrier takes place automatically as each fibre is broken, to effect tensioning of the next fibre in the array: the fibre tensioning load is constant, since it is determined by the strength of the spring 37.

When the last fibre 77 has been broken, the clamp 8 is released completely, and the clamp carrier rotates backwards until stopped by abutment of the lever 33 against the stop 44. The clamp 8 is retained in this position, still holding the fibres, while the fibres of the second cable length are prepared in the same way.

On completion of the above-described end preparation of the first set of fibres, the scorer unit assembly is raised, the unwanted portions of the first set of fibres are removed from the fixed clamp 6, and then the lever 32 is operated to rotate the movable clamp 5 into the horizontal position and to hold it in that position while the second set of fibres is clamped in the fixed clamp 7. The fibre tensioning, scoring and breaking procedure described above is then repeated for the second set of fibres, using the movable clamp 5 and lever 32. It will of course be understood that the order in which the two sets of fibres are treated is immaterial, the procedure described above, using movable clamp 8 first and movable clamp 5 second, being by way of example.

For joining the prepared ends of the two sets of fibres, the whole central unit comprising the fixed clamps and the fibre scoring and breaking arrangement is hinged upwards so that the jointing plate 65 is rendered accessible, and the movable clamps 5 and 8 are rotated forwards until stopped by abutment of the levers 32 and 33 against the forward edges of the stops 41 and 42 respectively, so that the fibre ends are brought down to the jointing plate. The fibre ends are inserted into the respective sets of V-shaped slots 67 in the jointing plate, and thus led into the Vgrooves 66, each set of fibres being maintained in the correct order so that the two sets are individually matched. The fibre ends are brought into abutment in the grooves 66 and are held together by virtue of the resilience of the fibres. A quick setting epoxy resin adhesive, or other suitable adhesive, having a refractive index matching that of the optical waveguide material of the fibres, may then be applied over the portions of the fibres in the grooves 66, to cause the butted fibre ends to adhere together and the fibres to adhere to the jointing plate; alternatively, the adhesive may be applied to the plate before the fibre ends are inserted into the grooves. Before the adhesive has set a cover plate (not shown) is placed over the jointing plate and the joined fibre ends, to ensure that the fibres are pressed down into the grooves. The fibre tensioning and scoring apparatus is finally removed, the jointing unit being retained in the cable installation.

In the apparatus shown in Figure 1, the anvil 46 has a curved upper surface, and the movable clamps 5 and 8 are disposed at a slightly lower level than the central unit, in order to accommodate the inclination of the fibres resulting from their conforming to the said curved surface. If desired, however, the upper surface of the anvil could be planar, and in that case all the clamps would be disposed at the same level with respect to the base plate. Further if desired, the upper surface of the anvil may have grooves aligned with the slots 12 in the clamps, for accommodating the fibres, and/or a central transverse groove may be provided in said surface for receiving the scoring blade. It will be understood that the relative positions of the movable clamps 5, 8 and the anvil and scorer unit must be so adjusted as to ensure that the two sets of prepared fibre ends, which initially lie in the same position on the anvil, will meet in abutting relationshi

Claims

**WARNING** start of CLMS field may overlap end of DESC **. stopped by abutment of the lever 33 against the stop 44. The clamp 8 is retained in this position, still holding the fibres, while the fibres of the second cable length are prepared in the same way. On completion of the above-described end preparation of the first set of fibres, the scorer unit assembly is raised, the unwanted portions of the first set of fibres are removed from the fixed clamp 6, and then the lever 32 is operated to rotate the movable clamp 5 into the horizontal position and to hold it in that position while the second set of fibres is clamped in the fixed clamp 7. The fibre tensioning, scoring and breaking procedure described above is then repeated for the second set of fibres, using the movable clamp 5 and lever 32. It will of course be understood that the order in which the two sets of fibres are treated is immaterial, the procedure described above, using movable clamp 8 first and movable clamp 5 second, being by way of example. For joining the prepared ends of the two sets of fibres, the whole central unit comprising the fixed clamps and the fibre scoring and breaking arrangement is hinged upwards so that the jointing plate 65 is rendered accessible, and the movable clamps 5 and 8 are rotated forwards until stopped by abutment of the levers 32 and 33 against the forward edges of the stops 41 and 42 respectively, so that the fibre ends are brought down to the jointing plate. The fibre ends are inserted into the respective sets of V-shaped slots 67 in the jointing plate, and thus led into the Vgrooves 66, each set of fibres being maintained in the correct order so that the two sets are individually matched. The fibre ends are brought into abutment in the grooves 66 and are held together by virtue of the resilience of the fibres. A quick setting epoxy resin adhesive, or other suitable adhesive, having a refractive index matching that of the optical waveguide material of the fibres, may then be applied over the portions of the fibres in the grooves 66, to cause the butted fibre ends to adhere together and the fibres to adhere to the jointing plate; alternatively, the adhesive may be applied to the plate before the fibre ends are inserted into the grooves. Before the adhesive has set a cover plate (not shown) is placed over the jointing plate and the joined fibre ends, to ensure that the fibres are pressed down into the grooves. The fibre tensioning and scoring apparatus is finally removed, the jointing unit being retained in the cable installation. In the apparatus shown in Figure 1, the anvil 46 has a curved upper surface, and the movable clamps 5 and 8 are disposed at a slightly lower level than the central unit, in order to accommodate the inclination of the fibres resulting from their conforming to the said curved surface. If desired, however, the upper surface of the anvil could be planar, and in that case all the clamps would be disposed at the same level with respect to the base plate. Further if desired, the upper surface of the anvil may have grooves aligned with the slots 12 in the clamps, for accommodating the fibres, and/or a central transverse groove may be provided in said surface for receiving the scoring blade. It will be understood that the relative positions of the movable clamps 5, 8 and the anvil and scorer unit must be so adjusted as to ensure that the two sets of prepared fibre ends, which initially lie in the same position on the anvil, will meet in abutting relationship when lowered into the grooves of thejointing plate. It will further be understood that the fibre tensioning load must be of a suitable magnitude for ensuring that the fibres break cleanly, to give a substantially wholly opti cally flat end surface orthogonal to the fibre axis; the maximum permissible load for obtaining this result depends upon the diameter of the fibre: for example, for a vitreous silica fibre of diameter 120 microns (excluding any protective resin coating), a load not exceeding 220 grams is employed. Furthermore, when the optical fibres have a protective resin coating, as is usual, the position of, and the load on, the scoring blade must be so adjusted as to ensure that scoring is effected to a sufficient depth to cut through the resin coating and score the vitreous surface of the fibre. WHAT WE CLAIM IS:

1. A method of preparing the ends of a plurality of vitreous optical fibres, for coupling said fibres to a corresponding set of optical fibres in end-to-end relationship, which includes the steps of arranging exposed lengths of the fibres in a planar parallel array, supporting the said fibre lengths between first and second retaining means which are spaced apart, subjecting the said fibre lengths between the retaining means to tension individually in sequence, and traversing scoring means across the array at a location between the said first and second retaining means and along a path substantially orthogonal to the longitudinal axes of the fibre lengths, so that the fibres are scored, to cause breaking thereof; individually in the same sequence as that in which the said lengths are tensioned, the sequential tensioning and scoring of the said fibre lengths being effected in such a manner that all the fibre lengths are scored while under substantially the same tension, that after each fibre is broken the said length of the next fibre in the sequence is tensioned before being contacted by the scoring means, and that all the fibres are scored in the same positions in the respective said lengths so that

after all the fibres are broken the thus prepared ends thereof lie on a line orthogonal to the axes of the fibres.

2. A method according to Claim 1, wherein the said lengths of the fibres are arranged in said array in a predetermined order matching that of the said corresponding set of optical fibres to which the fibres of said array are to be coupled.

3. A method according to Claim 1 to 2, wherein the sequential and substantially equal tensioning of the fibre lengths in said array is effected by causing relative movement between the first and second fibre array retaining means to take place in steps while a constant load is applied continuously to one of the said retaining means.

4. Apparatus for preparing the ends of a plurality of vitreous optical fibres by the method according to Claim 1, which includes first and second clamps spaced apart for retaining the said fibre array, each of said clamps including a member for supporting the fibres, a clamping member co-operating with said fibre support member to grip the fibres, and means for locking the clamping member in the fibre gripping position, means for applying a substantially equal tensioning load to all the fibre lengths retained between the clamps, means for effecting stepwise movement of one of the clamps in relation to the other clamp in such a manner as to cause sequential tensioning of the said fibre lengths, and, located between the said clamps, a scorer component consisting of a scoring blade ànd a carrier therefor, the blade carrier being supported by means enabling it to travel in a direction substantially orthogonal to the longitudinal axes of the said fibre lengths so as to cause the blade to traverse the fibre array and score the fibres in sequence.

5. Apparatus according to Claim 4, wherein the fibre supporting members of the clamps are formed with a plurality of slots or grooves for accommodating the fibres individually, substantially equally spaced apart.

6. Apparatus according to Claim 4 or 5 which includes an anvil located between the clamps and in the vicinity of the scorer component, for supporting the portions of the fibres to be scored.

7. Apparatus according to Claim 6, wherein the said anvil is provided with grooves for accommodating the individual fibres.

8. Apparatus according to Claim 6 or 7 wherein the said anvil is provided with a groove, disposed orthogonally to the positions in which the said fibre lengths will lie, for receiving the scoring blade.

9. Apparatus according to any of the preceding Claims 4 to 8, which includes means for applying a constant fibre tensioning load to one of the clamps.

10. Apparatus according to Claim 9, wherein the clamps are initially disposed with their longitudinal axes parallel, so that said fibre lengths retained between the clamps will lie orthogonally to said clamp axes, one of the clamps is arranged to be capable of pivotal movement such that the angle of disposition of the longitudinal axis thereof relative to the longitudinal axis of the second clamp can be varied, whereby the fibre lengths so retained will be slackened, and means are provided for imparting to one of the clamps stepwise movement in such a direction that the slackened fibre lengths will be tensioned in turn, under the application of said load, a step in such movement taking place as each fibre is broken and being halted by tensioning of the next fibre in the sequence.

11. Apparatus according to Claim 10, wherein the fibre tensioning load is arranged to be applied to the clamp which undergoes the said pivotal movement, such movement being effected by the initial application of the load.

12. Apparatus according to Claim 10, wherein the first clamp is arranged to undergo both said pivotal movement and said stepwise movement, and the fibre tensioning load is also arranged to be applied to the first clamp, while the second clamp is held stationary.

13. Apparatus according to Claim 12, wherein the said first clamp is pivotally supported on a carrier which is disposed with its longitudinal axis parallel to that of the second clamp, and which carrier is capable of stepwise rotational or sliding movement in a direction away from the second clamp.

14. Apparatus according to Claim 13, wherein the initial operation of the load applying means is arranged to cause an initial movement of the said clamp carrier, which movement results in pivoting of the first clamp on the carrier and in the application of said load to the first clamp, and wherein the load applying means is also arranged to effect the further stepwise movements of the carrier.

15. Apparatus according to Claim 11, wherein the fibre tensioning load is arranged to be applied to the first clamp, causing said pivotal movement thereof; and the second clamp is arranged to undergo said stepwise movement for sequential tensioning of the fibres.

16. Apparatus for preparing the ends of each of two corresponding sets of optical fibres, preparatory to forming a joint between two lengths of optical fibre cable, which consists of a duplicated form of the apparatus according to any of the preceding Claims 4 to 15, including two pairs of fibreretaining clamps, one pair for each set of fibres, and associated with each pair of clamps means for applying a fibre tensioning load to one of the clamps and means for effecting stepwise movement of one of the clamps for sequential tensioning of the fibres.

17. Apparatus according to Claim 16, wherein the said two pairs of clamps are so arranged that a single scorer component can be employed in the same position for scoring both sets of fibres.

18. Apparatus according to Claim 16 or 17, which is so constructed that a fibre jointing arrangement can be accommodated in conjunction therewith, in such a position that each set of fibres can be retained in one of the clamps while the joint is made.

19. Apparatus according to Claim 16, for the end preparation of two corresponding sets of optical fibres, substantially as shown in, and as hereinbefore described with reference to, Figures 1, 2 and 3 of the drawings accompanying the Provisional Specification.

20. A method according to Claim 1, for preparing the ends of each of two corresponding sets of optical fibres incorporated in two lengths of optical fibre cable, and of forming a joint between said sets of fibres, employing the apparatus according to Claim 19 and carried out substantially as hereinbefore described with reference to the drawings accompanying the Provisional Specification.