GB2040062A

GB2040062A - Optical fibre terminations

Info

Publication number: GB2040062A
Application number: GB7902576A
Authority: GB
Original assignee: GREEN PRECISION IND Ltd LEE; LEE GREEN PRECISION INDUSTRIES Ltd
Current assignee: GREEN PRECISION IND Ltd LEE; LEE GREEN PRECISION INDUSTRIES Ltd
Priority date: 1979-01-24
Filing date: 1979-01-24
Publication date: 1980-08-20

Abstract

A termination for an optical fibre 14 comprises a ferrule 6 having a bore 40 in which is mounted a plastics conical clamping member 50, fibre 14 extending through a bore 54 in the clamping member 50 to terminate at the end of ferrule bore 40. Clamping member 50 has a slot (Figure 2, not shown) communicated with bore 54 along a helical interface to prevent fibre 14 escaping into the slot. The forcing of clamping member 50 into bore 40, bore 40 having a conical surface 44 coacting with the clamping member, serves to clamp the fibre 14 centrally of the ferrule accurately, without the use of potting resin. <IMAGE>

Description

SPECIFICATION Optical fibre terminations This invention relates to terminations for optical fibres.

A problem with terminating optical fibres is that of maintaining an acceptable level of lighttransmission at the termination. In particular it is difficult accurately ly to locate the end of the fibre so as to align the fibre end with an element which is to receive light transmitted from the end of the fibre or which is to transmit light to the end of the fibre. Such element is commonly an end of a further optical fibre, which further increases the problem of accurate alignment.

The common way of terminating an optical fibre is to secure the fibre end in a ferrule by potting with a suitable casting resin, the fibre end extending into a bore in an end of the ferrule. The end of the ferrule is thereafter polished to present a polished fibre end for maximum transmissivity at the termination.

Diameters of optical fibres currently range from 1 mm to 0.05 mm in various steps of size, with a size tolerance of + 5% of diameter for silica fibres to + 10% of diameter for polymer fibres.

High precision machining techniques will give a positional tolerance of 0.03 mm of the bore in the ferrule end.

As a result of these tolerance, it is difficult accurately to locate a fibre. If however it were possible to accurately locate the fibre end centrally of the bore in the ferrule, a considerable improvement would be achieved in the accurate location of the fibre end, thus improving the performance of a fibre end connector.

It has been proposed in British Patent Specification No. 1,478,134 to terminate a fibre and accurately to locate the fibre end in a ferrule, the ferrule having a body with a cylindrical internal bore registering with an aperture in an end of the ferrule, a right circular compressible cylindrical body being positioned in the bottom of the bore and being compressed in that position by a piston sliding in the bore. The optical fibre extends through the piston and compressed member into the aperture in the end of the ferrule. The compressed member serves accurately to locate the member relative to the aperture in the end of the ferrule. The fibre end is fixed in position by a potting resin within the aperture in the ferrule end and surrounding the fibre end.

Such an arrangement has disadvantages, among which may be mentioned the necessity of employing a potting resin to secure the fibre in the ferrule and in addition the relatively large number of parts required to locate the fibre end.

It is an object of the present invention accurately to locate an optical fibre in an end connector therefor whilst avoiding the use of a potting resin to secure the fibre.

The present invention provides a termination for an optical fibre comprising a ferrule having a bore, the bore having art a free end of the ferrule a diameter greater than the maximum anticipated diameter of the fibre end, taking into account tolerances in diamter of the fibre, a clamping member having a bore through which said fibre extends, said clamping member having a slot or slots extending along its length, said slot or slots communicating with said bore of said clamping member at an interface following a non-linear path, and the external surface of said clamping member cooperating with the internal surface of a widened portion of said ferrule bore whereby the forcing of said clamping member into said widened portion serves to clamp said fibre centrally of said ferrule bore.

The slot or slots of said clamping member permit the clamping member to clamp the fibre when the clamping member is forced into the ferrule. Since as a practical matter the width of the slot will normally be greater than the diameter of the bore in the clamping member (as a result of the inherent minimum size limitation in a slot-cutting instrument), it is important that the interface of the slot or slots with the bore does not follow a straight line, since otherwise the fibre may escape from the bore into the slot. With current manufacturing processes, the smallest practical width of slot is 0.25 mm whereas the fibre may be only 0.1 mm. in diameter.

Preferably for simplicity in manufacture, the interface follows a helix along the bore, but other arrangements may be envisaged for example a step-wise path or a sinuous path in one segment of the bore.

The termination in accordance with the invention avoids the use of a potting resin.

The clamping member preferably has a part conical external surface cooperating with a part conical surface of said widened bore portion so as to provide an efficient clamping action when the clamping member is forced into the bore widened portion.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure 1 is a sectional view of an end connector for an optical fibre in accordance with the invention; and Figure 2 is an enlarged perspective view of a clamping and positioning member of Figure 1.

Referring to the drawings, an end connector for an optical fibre is shown as comprising three main parts, namely an end piece 2, a body piece 4, and a ferrule 6, for locating and securing the end of an optical fibre. An optical fibre cable 8 is shown as having an outer plastics sheath 10, an inner layer of fibrous material 12 serving to protect silica optical fibre 14 which has an inner plastics sheath 16. The sheaths 10, 16 and material 12 are cut offto expose the end of fibre element 14 for inserting into ferrule 6.

Body piece 4 of the end connector comprises a cylindrical end portion 20 having internal threads 22 and longitudinal slots 24for clamping outer sheath 10 of cable 8 by means of an external sleeve member (not shown) threaded onto threads 25. A screw thread 26 is adapted to receive an internally screw threaded portion 28 of end piece 2 to secure end piece 2 to body portion 4. Body piece 4 has an internally screw threaded bore 30 cooperating with an abutment face 32 disposed in a radial plane for receiving ferrule 6, ferrule 6 having an outer thread 33 engaging with threaded bore 30.

End piece 2 has a shroud 34 extending beyond the end of ferrule 6 and being journalled as at 36 for rotation. Shroud 34 has an internal screw thread 38 for connection to an end connector (not shown) for a further optical fibre.

Ferrule 6 has an internal bore 40 at its free end 42 having a diameter not significantly greater than that of opticle fibre 14 (say 0.1 mm.) and equal to the maximum anticipated diameter of fibre 14 taking into account a diameter tolerance of about +5% in the fibre diameter, i.e., the diameter of bore 40 is about 0.105 mm. In any event, bore 40 should not be so great as to permit insertion of a fibre having a diameter the "next step up" from 0.10 mm. namely 0.15 mm. Bore 40 widens in a region spaced about 0.25 mm. from free end 42 to provide a part conical surface 44, the bore then continuing to the other end of ferrule 6 and providing a cylindrical surface 48.

A plastics clamping member 50 (more clearly shown in Figure 2) is provided inserted into ferrule 6 and having a part conical outer surface 52 cooperating with the part conical inner surface 44.

Member 50 has a bore 54 of a diameter matching that of fibre 14 into which fibre 14 is inserted.

Member 50 is formed with a slot 56 which is cut into the member 50. Slot 56 extends along the length of member 50 in a helical manner and communicates with bore 54, whereby the interface 58 between bore 54 and slot 56 follows a helical path along bore 56.

This configuration prevents fibre 14 escaping from bore 54 into slot 56.

Member 50 is forced into ferrule 6 and the cooperating part conical surfaces 44, 52 serve as a result of the presence of slot 56 to force member 50 to clamp optical fibre 14 within ferrule 6 and to locate the end of fibre 14 accurately centrally of bore 14. It will be observed the end 59 of member 50 engages abutment face 32 to maintain the clamping action.

When ferrule 6 is secured within body piece 4, the free end of ferrule 6 and the end of fibre 14 are polished to increase the transmissivity of the fibre end. End piece 2 may thereafter by located on body piece 4.

it may thus be seen there is provided a simple and effective method of securing and accurately locating or positioning an end of an optical fibre in an end connector. The need for a potting resin for securing the fibre end is avoided and the number of component parts of the end connector can be reduced as compared with known arrangements. Modifications and alternative configurations are envisaged without departing from the scope of the invention; thus for example, different types of body pieces and end pieces may be employed not having the particular configuration described.

Claims

1. Atermination for an optical fibre comprising a ferrule having a bore, the bore having at a free end of the ferrule a diametergreaterthan the maximum anticipated diameter of the fibre end, taking into account tolerances in diameter of the fibre, a clamping member having a bore through which said fibre extends, said clamping member having a slot or slots extending along its length, said slot or slots communicating wth said bore at an interface following a non-linear path, and the external surface of said clamping member cooperating with the internal surface of a widened portion of said ferrule bore whereby the forcing of said clamping member into said widened portion serves to clamp said fibre centrally of said ferrule bore.

2. Atermination as claimed in Claim 1 wherein said clamping member has a conical external surface portion cooperating with a complementary conical internal surface portion of said widened bore portion.

3. Atermination as claimed in Claim 1 or 2, wherein said interface of said slot or slots and said bore follows a helical path along said bore.

4. Atermination as claimed in any preceding claim wherein the clamping member is formed of plastics.

5. A termination for an optical fibre as claimed in Claim 1 and substantially as described with reference to the accompanying drawings.

6. Atermination as claimed in any preceding claim incorporated in an optical fibre end connector, said connector being adapted to make a coaxial connection with a similar end connector fitted with a similar optical fibre termination.

7. Atermination as claimed in any of Claims 1 to 5 incorporated in an optical fibre end connection substantially as described with reference to the accompanying drawings.