GB2147577A

GB2147577A - Improved fibre cutting apparatus

Info

Publication number: GB2147577A
Application number: GB08424911A
Authority: GB
Inventors: Richard Grigsby
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1983-10-04
Filing date: 1984-10-03
Publication date: 1985-05-15
Also published as: GB8424911D0; GB8326538D0; GB2147577B

Abstract

Optical fibre cleaving apparatus which will reliably produce optical fibres with a flat radially extending face has a cutter 1 with a rectilinear cutting edge which may be fixed in space but is preferably so resiliently mounted as to be constrained to move to a limited extent in a direction normal to the cutting edge; and a table having a curved surface whose axis of curvature is parallel to the cutting edge. A length of optical fibre F can be maintained in tension across the table with its axis normal to the cutting edge and when the table 4 is moved towards the cutting edge to move the tensioned optical fibre into contact with and along the cutting edge, the fibre is scored to such an extent that it breaks to form the required flat radially extending end faces. <IMAGE>

Description

SPECIFICATION Improved fibre cutting apparatus In effecting a joint between two optical fibres, one or each of which may be an element of an optical cable, in order to ensure optimum light coupling efficiency or, in other words, to keep light losses at the joint as low as possible, it is desirable that the neighbouring end faces of the optical fibres be substantially flat and lie in planes radial to the axes of the fibres.

In order to provide an optical fibre with an end face that is both substantially flat and lies in plane radial to the axis of the fibre, it is necessary to break the optical fibre in such a way that the mirror zone, that is the optically smooth surface adjacent to the origin of the fracture, extends across the entire optical fibre. It has been shown that to make a reliable clean mirror zone fracture, the stress distribution across the optical fibre must not be allowed to become zero or negative at any point across the optical fibre.To achieve this end, apparatus and hand tools have been developed for effecting a fracture of an optical fibre by means of which the optical fibre is simultaneously bent over a curved former and placed under tension and a cutting edge, extending transversely of the fibre, is moved towards and transversely across the fibre to score the fibre to a sufficient extent to effect the required fracture. Whilst clean mirror zone fractures can be produced by means of apparatus and hand tools of this kind, we have found that not every fibre fractured using an apparatus or hand tool of this kind has the clean mirror zone fracture desired.

It is an object of the present invention to provide improved apparatus for providing an optical fibre with an end face that is substantially flat and lies in a plane radial to the axis of the fibre, which improved apparatus is substantially more reliable than apparatus hitherto proposed for this purpose and which can be readily used by semi-skilled or unskilled personnel.

According to the invention, the apparatus comprises a rectilinear cutting edge; means for maintaining a length of optical fibre, adjacent but spaced from the cutting edge, in tension with the axis of the fibre substantially normal to said cutting edge; and means for moving the tensioned optical fibre into contact with and along the cutting edge to score the fibre to such an extent that the tensioned fibre breaks to form end faces of the fibre that are substantially flat and lie in planes radial to the axis of the fibre.

The rectilinear cutting edge may be fixed in space but, preferably, it is so resiliently mounted that, when a tensioned optical fibre is moved into contact with the cutting edge, the cutting edge is constrained to move to a limited extent in a direction normal to the cutting edge and to the tensioned optical fibre.

The improved apparatus has the important advantage that, when the fibre is moved into contact with and along the cutting edge, the risk that the score effected in the fibre will not be normal to the axis of the fibre is substantially less than is the case where a cutting edge is moved into contact with and transversely across a tensioned optical fibre fixed in space. Consequently, optical fibres with end faces that are substantially flat and lie in planes radial to the axes of the fibre can be substantially more reliably produced using the improved apparatus than other apparatus for this purpose hitherto proposed and used.

The improved apparatus of the invention may be in the form of a simple and inexpensive hand tool suitable for use in the field or it may be in the form of a more sophisticated instrument for use in the laboratory.

The means for causing a tensioned optical fibre to move into contact with and along the cutting edge preferably comprises a table having a curved surface whose axis of curvature is substantially parallel to the cutting edge and preferably lies in the same plane as the cutting edge, the table being arranged to move towards the cutting edge until the tensioned optical fibre is stretched across the curved surface of the table and, as the tensioned optical fibre contacts the cutting edge, to move in a direction substantially parallel to the cutting edge to cause the cutting edge to effect a score across the fibre to such an extent that the tensioned fibre breaks to form the required end faces.

Any convenient means may be employed to grip an optical fibre at longitudinally spaced positions along the fibre to maintain the opti cal fibre in tension, but, preferably, such gripping means comprises two pairs of jaws, at least one jaw of each pair being adjustable with respect to the other jaw of the pair to grip an optical fibre therebetween.

Preferably, the cutting edge is formed on a diamond but, in some circumstances, it may be formed on a sapphire.

The improved apparatus is especially, but not exclusively, suitable for preparing the ends of optical fibres that are to be fusion spliced.

The invention is further illustrated, by a description, by way of example, of preferred apparatus for providing an optical fibre with an end face that is substantially flat and lies in a plane radial to the axis of the fibre with reference to the accompanying drawings, in which Figure 1(a) and (b) illustrates diagrammatically the basic concept of operation of the apparatus of the invention, and Figure 2 is a transverse cross-sectional view of the preferred hand tool.

Referring to Fig. 1, in its simplest form the apparatus of the invention comprises a cutting blade 1 which has a rectilinear cutting edge and which is fixed in space; a pair of clamping jaws 2, 2' and a pair of clamping jaws 3, 3' for maintaining a length of optical fibre F, adjacent but spaced from the cutting edge, in tension with the axis of the fibre normal to the cutting edge, tension being maintained in the optical fibre by movement of the pair of clamping jaws 3, 3' away from the cutting blade 1 in the direction of arrow A as the jaws clamp the fibre; and a table 4 which has a curved surface whose axis of curvature is parallel to and lies in the same plane as the cutting edge.The table 4 is arranged to move towards the cutting edge until the tensioned optical fibre F is stretched across the curved surface of the table and, as the tensioned optical fibre contacts the cutting edge, to move in a direction parallel to the cutting edge to cause the cutting edge to effect a score across the fibre to such an extent that the tensioned fibre breaks to form, on each portion of optical fibre, an end face that is substantially flat and lies in a plane radial to the axis of the fibre.

The hand tool shown in Fig. 2 comprises an elongate tubular member 11 of substantially rectangular cross-section at one end of which is mounted a cutting blade assembly 1 2.

Pivotally mounted near the other end and within the tubular member 11 is an elongate member 14 which supports at the end adjacent the cutting blade assembly 1 2 a table 1 5. Pivotal movement of the elongate means ber 14 to cause the anvil 1 5 to move towards the cutting blade assembly 1 2 is effected by means of a spring loaded button 1 6 against the action of a coil spring (not shown) which maintains the table spaced from the cutting blade assembly.

The cutting blade assembly 1 2 includes a cutting blade 1 7 having a rectilinear cutting edge extending substantially parallel to the length of the hand tool, which cutting blade is resiliently mounted on a spring loaded piston 18 slidable in a cylinder 19.

The table 1 5 has a curved surface whose axis of curvature is parallel to and lies in the same plane as the rectilinear cutting edge of the cutting blade 1 7.

Transversely spaced on opposite sides of the cutting blade assembly 1 2 are jaws 21 and 22 of two pairs of resiliently supported jaws 21, 21' and 22, 22', the jaws 21' and 22' being carried by the elongate member 14 and transversely spaced on opposite sides of the table 15.Each of the jaws 21, 21' and 22, 22' has a surface that is convexly curved in planes normal to the rectilinear cutting edge of the cutting blade 1 7. The jaws 22, 22' are so resiliently mounted and are so shaped that, when the jaws move towards one another to grip an optical fibre between them, the parts of the jaws in contact with the fibre tend to move away from the table 1 5 and from the other pair of jaws 21, 21' thereby exerting a tensile force on the fibre in a direction substantially normal to the rectilinear cutting edge of the cutting blade 1 7.

in use, a length of optical fibre F is introduced transversely cf the cutting blade 1 7 between the pairs of jaws 21, 21' and 22.

22' and the button 1 6 is depressed to cause the elongate member 14 to pivot against the action of the coil spring (not shown) initially to cause the pairs of clamping jaws to grip the optical fibre and. by transverse movement of the jaws 22, 22' to maintain the length of optical fibre in tension with its axis normal to the rectilinear cutting edge of the cutting blade, As further pivotal movement of the elongate member 1 4 is effected, the table moves towards and in a direction parallel to the cutting edge to bring the tensioned optical fibre F stretched across the curved surface of the table into contact with the rectilinear cutting edge of the cutting blade which is constrained to move to a limited extent against the action of its associated coil spring 20 in a direction normal to the cutting edge and to the tensioned optical fibre, a score being effected across the fibre to such an extent that the tensioned fibre breaks to form, on each portion of the optical fibre, an end face that is flat and lies in a plane radial to the axis of the fibres

Claims

1. Apparatus for providing an optical fibre with an end face that is substantially flat and lies in a plane radial to the axis of the fibre, which apparatus comprises a rectilinear cutting edge; means for maintaining a length of optical fibre, adjacent but spaced from the cutting edge, in tension with the axis of the fibre substantially normal to said cutting edge; and means for moving the tensioned optical fibre into contact with and along the cutting edge to score the fibre to such an extent that the tensioned fibre breaks to form end faces of the fibre that are substantially flat and lie in planes radial to the axis of the fibre.

2. Apparatus as claimed in Claim 1, wherein the rectilinear cutting edge is so resiliently mounted that, when a tensioned optical fibre is moved into contact with the cutting edge, the cutting edge is constrained to move to a limited extent in a direction normal to the cutting edge and to the tensioned optical fibre.

3. Apparatus as claimed in Claim 1 or 2, wherein the means for causing a tensioned optical fibre to move into contact with and along the cutting edge comprises a table having a curved surface whose axis of curvature is substantially parallel to the cutting edge, the table being arranged to move towards the cutting edge until the tensioned optical fibre is stretched across the curved surface of the table and, as the tensioned optical fibre contacts the cutting edge, in a direction substantially parallel to the cutting edge to cause the cutting edge to effect a score across the fibre to such an extent that the tensioned fibre breaks to form the required end faces.

4. Apparatus as claimed in Claim 3, wherein the axis of curvature of the curved surface of the curved table lies in the same plane as the cutting edge.

5. Apparatus as claimed in any one of the preceding Claims, wherein the means for maintaining a length of optical fibre in tension with the axis of the fibre substantially normal to the cutting edge comprises two pairs of jaws, one on each side of the cutting edge, at least one jaw of each pair being adjustable with respect to the other jaw of the pair to grip an optical fibre therebetween.

6. Apparatus as claimed in any one of the preceding Claims, wherein the cutting edge is formed on a diamond.

7. Apparatus as claimed in any one of the preceding Claims, wherein the apparatus is in the form of a hand tool.

8. Apparatus for providing an optical fibre with an end face that is substantially flat and lies in a plane radial to the axis of the fibre, which apparatus is substantially as hereinbefore, described with reference to and as shown in Fig. 2 of the accompanying drawings.