GB2158750A - Lapping jig for optical fibres - Google Patents

Abstract

In a lapping jig 20 for polishing optical fibre 11, the optical fibre 11 within probe 10 is held in contact with an abrasive 13 at a pressure determined by weights 18 in the body 17 of the jig 20. The abrasive surface 13 and support surface 15 are completely separated preventing contamination of the abrasive by debris from the wear of supports 26. The body 17 of the jig 20 holding the fibre 11 is moveable with respect to the abrasive 13 while maintaining the attitude and pressure between the optical fibre 11 and abrasive 13. <IMAGE>

Description

SPECIFICATION Lapping jig This invention relates to a lapping jig for micro polishing the end of an optical fibre which is held in a probe or ferrule.

Lapping jigs are known, many of which rely largely on the skill of the operator for the best results. In the prior art, one such lapping jig which is commonly used uses a "ring lap". The probe is held by the "ring lap" both of which bear directly on the abrasive media face for polishing the fibre end or probe.

The disadvantage is that the jig in this case degrades, and particles of the parent material contaminate the lapping film. In the case of ferrule optical fibre connectors, the material contaminates and damages the optical face of the fibre, and the jig itself wears and this has to be regularly checked since wear on the ring lap faces will directly influence the mating action of the two opposed conical connector probes for this particular case; in fact wear on the ring lap surface will have the effect of separating two opposed mated connector probes.

The present invention is intended to be simple to use, the lapping jig requiring minimum operator skill. Further, the lapping jig of the present invention requires only the probe end to be in contact with the lapping film, and hence overcomes the above mentioned disadvantages associated with "ring laps" and reduces connector losses.

A further advantage of the present invention is that no tools are required for fitting the connector parts into the lapping jig.

According to the present invention there is provided a lapping jig for polishing an optical fibre at a pre-set angle, the fibre being held in a probe or ferrule, this jig comprising: a flat surfaced member for receiving a layer of abrasive; holding means to secure the probe and the optical fibre in contact with the layer of abrasive; and, means to vary the pressure exterted by the optical fibre upon the layer of abrasive, the holding means for the probe end of the optical fibre being moveable relative to the flat surface while the optical fibre is kept at the pre-set angle relative to the flat surface member during this movement.

Preferably, the means to vary the pressure is provided by varying the weight of a co-axially mounted body on the jig.

An embodiment of the present invention will now be des- cribed, by way of example only, with reference to the accompanying drawings wherein: Figure 1 shows in section a known ring lap jig; Figure 2 shows in section a lapping jig embodiment of the present invention; Figure 3 shows an example of a suitable rotary motion of the lapping jig of Figure 2 for polishing the probe end of an optical fibre; Figure 4 shows a perspective view of a precision sleeve being inserted into a split ball bushing in the main body of the lapping jig of Figure 2; Figure 5 shows a chamber of the lapping jig holding removable weights; Figure 6 shows the lapping jig of Figure 2 set at an angle for enabling specific angles to be achieved on probe or fibre ends; and, Figure 7(a) to (d) shows star, T and Y couplers using angled lapped fibres.

Referring to the drawings, Figure 1 shows a known type of lapping jig 1. An optical fibre is held in a probe or ferrule 4 which forms part of an optical fibre connector 2 for telecommunications or data transmission. The lapping jig 1 and probe end 4 stand on a layer of abrasive lapping film 3 on a flat base 5. When the lapping jig 1 is moved over the film 3 so as to lap the probe end 4, however, debris forms from wear of the lapping jig 1 on the film 3, spoiling the polished end of the fibre and probe end 4. The lapping jig 1 wears in the area 6, resulting in a need for frequent replacement of the lapping jig 1.

Figure 2 shows a lapping jig 20 embodying the present invention. An optical fibre 11 is held in a probe or ferrule 10 which forms part of an optical connector 12. The lapping jig 20 securely holds the fibre 11 and probe 10 against a layer of lapping film 13 mounted on an optically flat surface 14 raised above the base plate 15 on which the lapping jig 20 stands. The lapping jig 20 is moved around the base plate 15 so as to cause lapping of the fibre 11 and probe end 10. The primary alignment of the probe 10 is by means of a close fitting tungsten carbide bush 16. Tungsten carbide is a stable and hard material and has been chosen since the jig may be used on production work, but softer materials could be used.

The pressure of the probe 10 on the film 13 is variable. The jig 20 has dead weight cylinder 17 having a chamber 18 for adding or subtracting lead shot which gives the variation required.

Figure 5 shows the dead weight cylinder 17, the weight of which is adjustable by loading lead shot or similar into the chambers concealed under screw caps 50.

Advantageously a detent plunger 19 is provided on the dead weight cylinder 17 which acts as a clutch giving position location through infinitely variable angular positions when locking the dead weight cylinder 17 to a precision ground tubular shaft 21 of the lapping jig 20.

This action ensures that linear ball bearings 23 do not always locate in the same place so that their tracks are different which would otherwise tend to form wear grooves in the shaft 21.

A linear re-circulating ball bushing 22 is used for accuracy and minimum friction which would otherwise cause 'sticking' of the precision shaft 21 carrying the connector 12 assembly.

Alternatively a plastics lined thin walled metal bush or one piece linear/rotary bearings could be used having low coefficients of friction, and good wear characteristics.

Advantageously, the lapping jig 20 is mounted on a collar 24 which has three legs 26 each having an anti-friction end. The three legged equistable mounting offers minimum friction resistance to motion and can be adjusted to compensate for wear.

The advent of abrasive diamond coated lapping films in various diamond grit sizes down to 0.25 lim has made the lapping process easier and free from liquid slurries which would otherwise be employed.

Usually only a few minutes lapping is required to produce an adequately flat, optically acceptable, end for probes. At first, a relatively course film (3um) is used to lap the optical fibre 11, then progressively finer films are used until the required finish is achieved. The optical fibre 11 is adequately washed to prevent contamination of films and sufficient lapping oil is used.

The lapping jig 20 is provided with an small '0' ring 27 for preventing the ingress of lapping fluid; an '0' ring 28 to secure the lapping film 13 on the flat surface 14; and, an 'O' ring 29 to act as a shock absorber.

Advantageously for sustained long life and continuous production a split ball bushing 41 is employed as shown in Figure 4 and is adjustable using adjustable screws 40 to take up any wear on the precision shaft 21.

Figure 6 shows the lapping jig 20 of Figure 2, but with the collar 24 of the jig 20 set at an angle to the horizontal by adjusting the length of each leg 26 on the collar 24. The use of the three ajustable legs on the collar give sufficient equistable action during hand operation.

It should be noted that the dead weight cylinder 17 itself always locates in the same angular position relative to the lapping jig collar 24 by reason of a nylon peg 25 and the slot in the dead weight cylinder 17.

Thus by adjusting the length of the legs 26, and tilting the angle of the shaft 21, the end of the fibre 11 and probe 10 can be lapped at any specific angle.

For end preparation of most connectors the probe ends are normal to the axis of the fibre, although if desired the mounting could be adjusted to form a lapped end probe at an angle to the central axis of the fibre as shown in Figure 7a, in which 70 represents the core of the fibre and 71 represents the core cladding.

Angled ends can be used for star couplers 'T'couplers and beam splitting arrangements.

Examples of the ways in which angled end fibres could be used as shown in Figures 7(b) to (d).

Although it is preferred that the abrasive film will be diamond impregnated it is envisaged that this could be replaced by softer lapping papers, films, elastomers or textured surfaces which could be po sitioned on the surface 14 and various slurries and grinding compounds. Suitable holding means could be used for the preparation of samples of other optical material, metalurgic materials or the like.

Claims (5)

1. A lapping jig for polishing an optical fibre at a pre- set angle, the fibre being held in a probe or ferrule, this jig comprising; a flat surfaced member for receiving a layer of abrasive; holding means to secure the probe end of the optical fibre in contact with the layer of abrasive; and, means to vary the pressure exterted by the optical fibre upon the layer of abrasive, the holding means being movable relative to the flat surface while the optical fibre is kept at the pre-set angle relative to the flat surface member during this movement.

2. A jig, as claimed in claim 1, including a dead weight cylinder having a chamber so weights can be added, providing thus said means to vary the pressure exerted by the optical fibre.

3. A jig as claimed in claim 1 or 2 preceding including an equistable mounting with anti-friction legs.

4. A jig as claimed in claim 3, wherein the mounting is adjustable allowing the optical fibre to be tilted to a predetermined angle with respect to the layer of abrasive.

5. A lapping jig, constructed, adapted and arranged to perform, substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings, figures 2 to 7.