GB1594007A - Methods and apparatus for preparing the ends of optical fibres for forming fibre couplings - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO METHODS AND APPARATUS FOR PREPARING THE ENDS OF OPTICAL FIBRES FOR FORMING FIBRE COUPLINGS (71) We, THE GENERAL ELECTRIC COMPANY LIMITED, of 1 Stanhope Gate, London W1A 1EH, 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 an end of a vitreous optical fibre prior to coupling the fibre either to a similar fibre in end-to-end relationship, or to another form of optical waveguide, or to a device co-operating with the fibre.

When it is desired to join two vitreous optical fibres together in end-to-end relationship, for example when coupling two lengths of optical fibre cable together, the fibres to be joined are each required to be prepared by breaking off an end portion of the fibre in such a manner that the new end surface of the fibre is substantially wholly optically flat and free from irregularities, and is substantially orthogonal to the longitudinal axis of the fibres. Similar end preparation of a fibre is required prior to coupling the fibre to any other form of optical waveguide or to a device such as a light source or a photo-detector. The breaking of the fibre is usually achieved by scoring the vitreous surface of the fibre at one point, over a portion of its circumference, while the fibre is subjected to longitudinal tension sufficient to cause it to break at the scored point.

It is necessary to exercise careful control over the conditions under which the scoring and breaking of the fibre are carried out, in order to ensure that a clean break giving an optically flat fracture surface, is obtained; in particular, the magnitude of the tensioning load applied to the fibre is somewhat critical. If local stresses in the fibre are too high, the fracture face will include a hackle zone, that is to say an area of forked fracture. It has been proposed to control the stress distribution across the cross-section of the fibre, in order to avoid the production of a hackle zone, by tensioning the fibre while it is bent over a curved former; however, when this method is employed, it is necessary to ensure that the applied tensioning load is higher than a certain minimum, the value of which depends upon the curvature of the former, in order to overcome the compressive stress in the region of the concave side of the curved fibre and hence prevent the formation of a compression lip extending from the fracture face in this region.

It is an object of the present invention to provide an improved method of, and apparatus for, breaking a vitreous optical fibre to form a prepared fibre end for coupling to another fibre end or other device.

According ot the invention, a method of preparing an end of a vitreous optical fibre, prior to coupling said fibre to a second optical fibre in end-to-end relationship or to another device, includes the steps of supporting a length of said fibre on a plane surface, applying to said supported length of fibre a first longitudinally tensioning load of magnitude sufficient to render said length of fibre straight and taut, but insufficient to cause breaking of the fibre on scoring, then scoring the fibre at a point in the said supported length thereof while the application of said first load is maintained and, subsequently to said scoring step, applying to said supported length of the fibre a second longitudinally tensioning load of increased magnitude to cause the fibre to break at the scored point.

The first tensioning step for rendering the fibre straight and taut will hereinafter be referred to as "light" tensioning, and the load applied for effecting such light tensioning will be referred to as the "light" load.

The second, increased, tensioning load will be referred to herein as the "breaking" load.

Supporting the fibre on a plane surface for the scoring and breaking operations is advantageous in that it eliminates any compressive stresses in the fibre and hence prevents the possibility of the formation of a compression lip on breaking of the fibre.

The need to ensure that the breaking load applied is above a given minimum is thus avoided.

The scoring of a fibre produces local stresses in the fibre, due to the pressure of the scoring blade used, so if the fibre is scored while it is subjected to a sufficiently high tensioning load to cause breaking, the increased local stresses resulting from the scoring may be sufficient to produce a hackle zone on the fracture face. Hence the method of the invention, in which the breaking load is not applied until after the fibre has been scored, has the additional advantage that such uncontrolled increased local stresses are avoided, so that a breaking load of known, predetermined magnitude can be applied over the whole of the cross-section of the fibre; thus the production of a hackle zone can readily be prevented. The maximum breaking load permissible for avoiding the production of a hackle zone depends on the diameter of the vitreous fibre (excluding any protective resin coating on the fibre): for example, in the case of a silica fibre of diameter 120 microns, the braking load should not exceed 220 grams. It follows that the notch scored in the fibre must be of sufficient depth to ensure that the fibre will break under an applied tensioning load not exceeding the permissible maximum.

Apparatus in accordance with the invention for preparing an end of a vitreous optical fibre by the method described above includes an anvil with a plane upper surface, a pair of clamps, located one on each side of said anvil, for gripping an optical fibre so that a length thereof between the clamps is held in contact with said plane surface, means for applying a first load to at least one of the clamps for effecting light tensioning of the fibre, a scoring blade and carrier therefor, located above the anvil, means for causing the blade to travel over the anvil in a direction orthogonal to the longitudinal axis of the fibre, so as to score the fibre, and means for applying a second load to at least one of the clamps for further tensioning the fibre sufficiently to cause the fibre to break at the scored point.

The successive light fibre tensioning and further fibre tensioning steps are suitably effected by means causing relative movement between the clamps to take place in two stages, respectively in conjunction with the application of the said first and second loads to the clamp or clamps. Preferably one of the clamps remains stationary, and the second clamp is arranged to be moveable in a direction away from the stationary clamp, for example by pivoting, and is carried by or attached to a member or members through which the respective loads are applied to said second clamp on movement thereof, and thence to the said length of fibre. If desired, a single load applying means may be provided, and arranged to apply both the first and second loads by progressive action; alternatively, two separate load applying means may be provided, for the application of the first and second loads respectively. The load applying means may consist of a spring or springs, means being provided for effecting relative movement between the clamps for example by causing the moveable clamp carrier or member or members attached to the moveable clamp to move, under the force of the spring or springs.

An arrangement is preferably included, in association with the scoring blade carrier, for causing the blade, as it travels over the anvil, to be first lowered so that it will score the fibre, with a sawing action, to the required depth, then raised out of contact with the fibre, and finally, after breaking of the fibre, to be returned to its initial position without again touching the prepared end of the fibre.

The apparatus is preferably so arranged that the sequence of steps consisting of gripping the optical fibre in the clamps, lightly tensioning the fibre, scoring the fibre, and applying the breaking load to the fibre, can be carried out in rapid succession as a result of a continuous manual operation of suitable actuating means. A manually operated tool of this kind, in accordance with the invention, will now be described by way of example with reference to the drawings accompanying the Provisional Specification, in which Figure 1 is a plan view of the arrangement for supporting, tensioning and breaking a fibre, Figure 2 is a plan view of the mechanism for actuating the arrangement shown in Figure 1, Figure 3 is a front elevation of parts shown in Figures 1 and 2, and Figure 4 is a side elevation of parts shown in Figure 1 and 2, viewed in the direction indicated by arrows IV in Figures 1 and 2.

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

The components of the apparatus of the example are mounted on a base plate 1: Figure 1 shows the upper surface of the base plate and the components mounted thereon, and Figure 2 shows the under surface of the base plate and the components mounted thereon. The upper and lower portions of the apparatus are covered respectively by top and bottom cover plates 2, 3, which are screwed on to pillars 4,5; the cover plates are omitted from Figures 1 and 2, so that the operative components of the apparatus are exposed to view.

The arrangement shown in Figure 1, and partly also in Figure 3 and 4, consists essentially of an anvil 6, fixed to the base plate, for supporting an optical fibre, clamps 7 and 8 for gripping the fibre, clamp 7 being fixed to the base plate and clamp 8 being pivotally mounted on th base plate, springs 9 and 10 respectively providing a light fibre tensioning load and a fibre breaking load, an arm 11 for carrying a fibre scoring blade (not shown) and support means for the blade arm, and means for causing the clamp components to engage and for simultaneously causing pivotal movement of the clamp 8 away from the anvil, applying the said loads in succession to said clamp, and causing the blade arm to travel forward over the anvil and to lower the blade on to the fibre. Handles 12 are connected to the actuating mechanism mounted on the under side of the base plate 1 and shown in Figure 2.

The anvil 6 consists of a rectangular block with a plane upper surface 13 with raised portions 14 and 15 at the front end, the central portion 15 lying only 1-2 mm above the surafce 13; a groove 16 is formed in the centre of the top of the anvil, extending along the whole of the surface 13 and through the central raised portion 15, and a channel 17 (Figure 3) is formed in the base of the anvil, again extending along the whole length thereof.

Each of the clamps 7, 8, consists of a front block 18 integral with the base 19 a block 20 slidably mounted on the base 19 and attached to a rod 21 with head 22, which rod is arranged to slide through a hole in a block 23, 24, also integral with the base 19 in each case, and carries a compression spring 25 located between block 20 and blocks 23, 24 respectively.

The mating surfaces of blocks 18 and 20 are covered with pads 26 of resilient material, suitably natural or synthetic rubber.

The base 19 of clamp 7 is fixed to the base plate 1, so that this clamp remains stationary in operation of the apparatus.

The base 19 of clamp 8 has an integral rearwardly extending arm 27, which is pivoted in the block 24, on a pivot extending through the base plate 1, and is formed with a recess 28 at its rear end and a cam surface, including an elongated recess 29, on the inside edge. A second arm 30 is located below, and parallel to, the arm 27, is also pivoted on the block 24, and has a cam surface including a recess 31 on the inside. The arm 30 carries a pillar 32, against which the recessed rear end of arm 27 abuts, and the light tensioning spring 9, in the form of a length of resilient wire, is connected between the pillar 32 and a screw 33 carried by the arm 27. A tension spring 10, for providing the fibre breaking load, is connected between a screw 34 carried by an arm 30 and a pillar 35 fixed to the base plate 1. The arms 27 and 30 will hereinafter be referred to respectively as the "light load arm" and the "breaking load arm".

The blade arm 11 carries a pair of blade clips in the form of strips of spring steel, 36, which are attached to the sides of the arm and are connected together by a screw 37 co-operating with a tapped bush 38. For use of the apparatus a fibre scoring blade, preferably formed of diamond particles bonded in a phenolic resin, and supported in a suitable mount, is inserted between the front ends of the clips and gripped in position by operation of the screw (the blade and blade mount are not shown in the drawings). The assembly of blade arm and blade clips has a cam surfaced recess 39 on the under side (Figure 4).

The blade arm 11 is pivotally mounted in a block 40 and passes through, with clearance, a notch 42 in a bar 41 which is screwed to the block 40, and is further supported in notch 44 in a plate 43 which is screwed to the back of the anvil 6, the blade arm being urged downwards into the notch 44 by a hoop spring 45 lying in a slot 46 in the top of the blade arm the ends of the spring being inserted into holes in the block 40. The clamp rod heads 22 abut against the rear surface of the bar 41, the ends of which have recesses 47 (visible in Figure 3) to permit the bar 41 to travel along the rods 21 without coming into contact with them.

The block 40 is mounted on a bar 48 which is arranged to slide forward through the channel 17 in the anvil 6, thus carrying the blade arm forward over the anvil. The rear end of the sliding bar 48 carries a head 49 having a tapered end 50 arranged to cooperate with the cam surfaced recesses 29 and 31 in the load arms 27 and 30.

The assembly of block 40 and sliding bar 48 is mounted on a pin 51 (shown in Figure 4) which passes through a slot 52 in the base plate 1, as shown in Figure 2, this slot being of sufficient length to permit forward movement of the said assembly, and hence of the blade arm, over a required distance. As shown in Figures 2 and 4, the handles 12 are pivotally mounted on the base plate 1 at 53, and are connected to the pin 51 by linkages 54 and 55 mounted on pivots 56. The handles are also connected together by a strong steel tension spring 57 mounted on pillars 58 carried by the handles, which spring returns the handles to the rest position (in which they are shown) when they are released after use. The pivot on which the block 24, with clamp 8 and light load arm 27, and the breaking load arm 30 are mounted is shown at 59 in Figures 2 and 4.

Materials employed for the construction of the apparatus, in addition to those mentioned above, suitably consist of mild steel for the slide bar 48 and head 49, block 40, bar 41, plate 43, linkages 54, 55 slide assembly pin 51, clamp springs 25, return spring pillars 58, clamp pivot 59, linkage pivots 56, handles pivot 53 and washers 60, silver steel for the clamp rods 21 and heads 22, blade arm pivot 61 (Figure 4), and load spring pillars 32, 35, a suitable type of steel for the various screws, nuts and washers, brass for the bush 38, piano wire for the springs 9, 10 and 45, and aluminium alloy for the remaining parts. The handles 12 may be covered with grips 62, suitably of natural or synthetic rubber, as shown in Figure 1.

For operation of the apparatus described above with reference to the drawings, a fibre scoring blade is inserted between the blade arm clips as described, and an optical fibre is laid between the blocks 18 and 20 of the clamps 7 and 8 and across the top of the anvil 6 adjacent to the raised portions 14 and 15 of the anvil, the end portion of the fibre which is to be broken off being held in the fixed clamp 7. The handles 12 are then manually closed together in a fairly slow, continuous movement so that as a result of the action of the handles, through the linkages 54 and 55, on the pin 51, the slide bar 48 slides forward through the channel 17. This forward movement of the bar 48, together with the components carried thereby, namely the head 49, block 40, bar 41 and blade arm 11, causes the following sequence of operations to take place: Firstly, the forward movement of bar 41, releasing the backward pressure on the heads 22 of rods 21, allows the clamp blocks 20 to slide forward under the force of the compression springs 25, so that the fibre is gripped between the pads 26 of blocks 18 and 20 of both clamps; as the bar 41 continues to move forward it disengages from the heads 22. The next stage in the forward movement of bar 48 brings the point 50 of head 49 to the recess 29 in the cam surface on the light load arm 27 allowing the light load spring 9 to drive the clamp 8 away from the anvil 6 by pivoting of the arm 27, until the fibre is pulled taut: thus a light tension is applied to the fibre, sufficient only to ensure that the fibre is straight and free from slack.

At the same time the blade arm 11 is carried forward and, on further forward movement of the bar 48, while the light load on clamp 8 is maintained, the recess 39 in the blade arm passes through the notch 44 in plate 43. The front portion of the blade arm is thus brought downward by the action of the spring 45 and is simultaneously carried forward over the fibre, so that the blade saws a notch in the fibre. The raised portions 14 and 15 of the anvil prevent the fibre from being pushed forward by the blade: it will be apparent that the central raised portion 15 of the anvil must be lower than the portions 14 in order to accommodate the front portion of the blade arm as it passes over the fibre.

The groove 16 is provided to ensure that the blade will not touch the anvil.

During the final stage in the forward movement of bar 48 the recess 39 in the blade arm passes forward of the plate 43, and as the portion of the blade arm immediately behind this recess engages with the notch 44 the blade is raised out of contact with the fibre. At the same time the point of head 49 is brought to the recess 31 in the breaking load arm 30, causing pivoting of this arm under the force of breaking load spring 10. Thus the pillar 32 is again brought into engagement with the light load arm 27 (which had previously been taken out of engagement with the said pillar by the initial pivoting move ment), so that the arms 27 and 30 continue to pivot together and the full breaking load is applied to the fibre via the clamp 8, causing the fibre to break at the notched point: the breaking of the fibre takes place after the blade has been raised as aforesaid.

On release of the handles, after the fibre breaks, the slide bar 48 is moved backwards to its original position by the action of the return spring 57 and linkages 54 and 55, so that the blade arm is withdrawn: since, on breaking of the fibre, the portion thereof held in clamp 8 springs away from the other portion by virtue of the position of clamp 8 at an increased distance from the anvil, on withdrawal of the blade arm the blade does not touch the prepared end of the said portion of the fibre held in clamp 8; the fibre portion held in clamp 7 is discarded. Simultaneously with the withdrawal of the blade arm, the load arms 27 and 30 are returned to their initial positions by engagement with the slide arm head 49 as it moves backwards, and the sliding clamp blocks 20 are returned to their initial positions by the action of bar 41 abutting against the heads 22 of rods 21.

In a specific example, the tool described above with reference to the drawings, with a spring 10 designed to give a maximum breaking load of 220 grams, has been used for breaking 120 microns diameter optical fibres consisting of silica suitably doped to give a step or graded refractive index profile across the cross-section of the fibre, and having a protective coating composed of several layers, each 3 to 5 microns thick, of polyurethane resin loaded with carbon powder in the inner layers and titania powder in the outer layers, the overall diameter of the coated fibre being 150 microns.

It is not necessary to remove this protective coating before breaking the fibre.

WHAT WE CLAIM IS: - 1. A method of preparing an end of a vitreous optical fibre, prior to coupling said fibre to a second optical fibre in endto-end relationship or to another device, which method includes the steps of supporting a length of said fibre on a plane surface, applying to said supported length of fibre a first longitudinally tensioning load of magnitude sufficient to render said length of fibre straight and taut but insufficient to cause breaking of the fibre on scoring, then scoring the fibre at a point in the said supported length thereof while the application of said first load is maintained and, subsequently to said scoring step, applying to said supported length of the fibre a second longitudinally tensioning load of increased magnitude to cause the fibre to break at the scored point.

2. Apparatus for preparing an end of a vitreous optical fibre by the method according to Claim 1, which apparatus includes an anvil with a plane upper surface, a pair of clamps, located one on each side of said anvil, for gripping an optical fibre so that a length thereof between the clamps is held in contact with said plane surface, means for applying a first load to at least one of the clamps for effecting light tensioning (as hereinbefore defined) of the fibre, a scoring blade and carrier therefor, located above the anvil, means for causing the blade to travel over the anvil in a direction orthogonal to the longitudinal axis of The fibre, so as to score the fibre, and means for applying a second load to at least one of the clamps for further tensioning the fibre sufficiently to cause the fibre to break at the scored point.

3. Apparatus according to Claim 2, wherein means are included for causing relative movement between the said clamps to take place in two stages, respectively in conjunction with the application of the said first and second loads, for effecting the successive light fibre tensioning and further fibre tensioning steps.

4. Apparatus according to Claim 3, wherein one of the said clamps is arranged to remain stationary, and the second clamp is arranged to be movable in a direction away from the stationary clamp and is carried by or attached to a member or members through which the respective loads are applied to said second clamp on movement thereof, and thence to the said length of fibre.

5. Apparatus according to Claim 2, 3 or 4, wherein a single load applying means is provided, and is arranged to apply both the first and second loads by progressive action.

6. Apparatus according to Claim 2, 3 or 4, wherein two separate load applying means are provided, for the application of the first and second loads respectively.

7. Apparatus according to any of the preceding Claims 3 to 6, wherein the load applying means consists of a spring or springs, and wherein means are provided for effecting relative movement between the clamps under the force of the spring or springs.

8. Apparatus according to any of the preceding Claims 2 to 7, which includes an arrangement, in association with the scoring blade carrier, for causing the blade, as it travels over the anvil, to be first lowered so that it will score the fibre, with a sawing action, to a required depth, then raised out of contact with the fibre, and finally, after breaking of the fibre, returned to its initial position without again touching the prepared end of the fibre.

9. Apparatus according to any of the preceding Claims 2 to 8, which includes manually operable actuating means, and which is so arranged that the sequence of steps consisting of gripping the optical fibre in the clamps, lightly tensioning the fibre, scoring the fibre, and applying the breaking load to the fibre, can be carried out in rapid succession as a result of a continuous operation of said actuating means.

10. Apparatus according to Claim 2, substantially as shown in, and as hereinbefore described with reference to, the drawings accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. give a step or graded refractive index profile across the cross-section of the fibre, and having a protective coating composed of several layers, each 3 to 5 microns thick, of polyurethane resin loaded with carbon powder in the inner layers and titania powder in the outer layers, the overall diameter of the coated fibre being 150 microns. It is not necessary to remove this protective coating before breaking the fibre. WHAT WE CLAIM IS: -

1. A method of preparing an end of a vitreous optical fibre, prior to coupling said fibre to a second optical fibre in endto-end relationship or to another device, which method includes the steps of supporting a length of said fibre on a plane surface, applying to said supported length of fibre a first longitudinally tensioning load of magnitude sufficient to render said length of fibre straight and taut but insufficient to cause breaking of the fibre on scoring, then scoring the fibre at a point in the said supported length thereof while the application of said first load is maintained and, subsequently to said scoring step, applying to said supported length of the fibre a second longitudinally tensioning load of increased magnitude to cause the fibre to break at the scored point.

2. Apparatus for preparing an end of a vitreous optical fibre by the method according to Claim 1, which apparatus includes an anvil with a plane upper surface, a pair of clamps, located one on each side of said anvil, for gripping an optical fibre so that a length thereof between the clamps is held in contact with said plane surface, means for applying a first load to at least one of the clamps for effecting light tensioning (as hereinbefore defined) of the fibre, a scoring blade and carrier therefor, located above the anvil, means for causing the blade to travel over the anvil in a direction orthogonal to the longitudinal axis of The fibre, so as to score the fibre, and means for applying a second load to at least one of the clamps for further tensioning the fibre sufficiently to cause the fibre to break at the scored point.

3. Apparatus according to Claim 2, wherein means are included for causing relative movement between the said clamps to take place in two stages, respectively in conjunction with the application of the said first and second loads, for effecting the successive light fibre tensioning and further fibre tensioning steps.

4. Apparatus according to Claim 3, wherein one of the said clamps is arranged to remain stationary, and the second clamp is arranged to be movable in a direction away from the stationary clamp and is carried by or attached to a member or members through which the respective loads are applied to said second clamp on movement thereof, and thence to the said length of fibre.

5. Apparatus according to Claim 2, 3 or 4, wherein a single load applying means is provided, and is arranged to apply both the first and second loads by progressive action.

6. Apparatus according to Claim 2, 3 or 4, wherein two separate load applying means are provided, for the application of the first and second loads respectively.

7. Apparatus according to any of the preceding Claims 3 to 6, wherein the load applying means consists of a spring or springs, and wherein means are provided for effecting relative movement between the clamps under the force of the spring or springs.

8. Apparatus according to any of the preceding Claims 2 to 7, which includes an arrangement, in association with the scoring blade carrier, for causing the blade, as it travels over the anvil, to be first lowered so that it will score the fibre, with a sawing action, to a required depth, then raised out of contact with the fibre, and finally, after breaking of the fibre, returned to its initial position without again touching the prepared end of the fibre.

9. Apparatus according to any of the preceding Claims 2 to 8, which includes manually operable actuating means, and which is so arranged that the sequence of steps consisting of gripping the optical fibre in the clamps, lightly tensioning the fibre, scoring the fibre, and applying the breaking load to the fibre, can be carried out in rapid succession as a result of a continuous operation of said actuating means.

10. Apparatus according to Claim 2, substantially as shown in, and as hereinbefore described with reference to, the drawings accompanying the Provisional Specification.