GB2194848A - Strain-relief mechanism for fibre-optic terminations - Google Patents

Abstract

A fibre-optic termination for a fibre-optic cable containing one or more optical fibres in which one end of the or each optical fibre (20a, 20b, 20c) extends from the sheathing (18) of the cable and is connected to a respective electro-optical terminator device (22a, 22b, 22c) the or each of which is slidable longitudinally in a respective holder (24a, 24b, 24c) contained in the housing (10) of the fibre-optic termination. The electrical connections (26a, 26b, 26c) to the electro-optical termination devices (22a, 22b, 22c) are flexible so as to allow a longitudinally slidable movement thereof. <IMAGE>

Description

SPECIFICATION Strain-relief mechanism for fibre-optic terminations The present invention relates to optical fibres and is concerned particularly with a means of providing strain relief at the ends of such optical fibres, for the purpose of preventing damage to the fibres during flexing of a cable containing several such fibres.

When an optical fibre, for example of glass or plastics, is contained in a protective sheath, the fibre is frequently allowed to be loose in- side the sheath. This looseness allows the sheath to be bent slightly, without the fibre being bent. Further bending may occur, however, until the fibre touches the sheath, and subsequently exerts pressure on the sheath.

Continued bending will then set up a longitudinal strain in the optical fibre which ultimately may lead to damage to the fibre.

The above-described condition is particularly exacerbated when relatively short lengths of cable, e.g. less then one metre, are bent over relatively large angles, e.g. greater than 45".

Similarly, when a bundle of optical fibres contained within a sheath are bent, some fibres within the bundle may be strained to a greater extent than others, due to variable bend radii.

In addition to creating a breakage hazard in the fibre, damage may also be caused during such bending to the interface between the optical fibre itself and the terminating device to which it is normally attached. The terminating device is typically either a light-emitting diode or a semi-conductor opto-diode, or other such radiation emitting or rsdiation receiving devices.

It is an object of the present invention to provide a means of overcoming the aforegoing deficiencies of the known termination arrangements.

In accordance with the present invention, there is provided a fibre-optic termination for a fibre-optic cable containing one or more optical fibres, wherein one end of the or each optical fibre extends from the sheathing of the cable and is connected to a respective electro-optical terminating device, the or each of which is slidable longitudinally in a holder.

The or each terminating device, which may for example be a radiation-emitting or a radiation-receiving device, is preferably slidably received in a respective holder, the holders being themselves mounted within a common housing.

Preferably, the or each holder is simply a hollow tube of plastics or metal within which the respective terminating device is longitudinally slidable.

The termination device or devices must be connected electrically to electrical terminations of the system in a manner which allows for the movement of the termination device(s).

This can be achieved, for example, by flexible wires or by a sliding contact, such as a rod which slides in a coaxial tube.

By means of the aforegoing arrangement, the establishment of strain within the or each optical fibre contained within a fibre optic cable, when that cable is subjected to bending, can be eliminated or at least considerably reduced.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic longitudinal section through one embodiment of a fibre-optic termination device in accordance with the present invention; and Fig. 2 shows a known fixed termination device.

Referring first to Fig. 1, the illustrated termination device comprises a tubular housing 10 into one end of which there is fitted the tubular flange 12 of an end cap 14. The end cap 14 has a central hole 16 which receives and tightly grips, for example by clamping or by adhesive as shown, the outer sheathing 18 of a length of fibre-optic cable. In the present case the sheathing is shown to be enclosing three individual optical fibres 20a, 20b, 20c, but in practice the sheathing may contain any number of such fibres, including a single fibre.

The cable sheathing 18 is terminated just inwardly of the end cap 14 and the optical fibres 20a, 20b, 20c project therefrom and are connected at their ends to respective terminating electro-optic devices 22a, 22b, 22c, in this case light-emitting diodes (LED). The latter connection can be made, for example, by the use of an adhesive.

As indicated by the arrow in Fig. 1, the strain established in the optical fibre 20b during bending of the cable sheath results from the presence of a longitudinal force F on the end portion of that fibre. Similar forces of greater or lesser magnitude may be experienced by the other optical fibres 20a, 20c.

In order to reduce these forces F to a minimum, each LED 22 is mounted within a respective LED holder 24a, 24b, 24c such that it is able to move within the holder in the direction of the force F. The holders 24 can for example, be plastics or metal tubes in which the LEDs are a sliding fit.

Thus, when the cable is bent, the LEDs can move as necessary so as to eliminate or reduce considerably the stress within the optical fibres and also at the fibre optic/terminating interface.

Electrical connection to the LEDs 22 is maintained by the provision of flexible wires 26a, 26b, 26c between each LED 22 and a respective electrical termination 28a, 28b, 28c mounted within the tubular housing 10 on a printed circuit board 30.

As an alternative to the use of flexible wires 26, the electrical connection between the LEDs and the electrical terminations 28 can be achieved by the use of sliding contacts, for example in the form of conductive rods received in respective coaxial conductive tubes.

Thus, where several optical fibres 20 are housed within a single cable sheath 18, an equal number of electro-optical devices 22 may be housed in an equal number of holders 24 to ailow for the abovedescribed sliding movement. In the illustrated example, where three devices 22 are present, each is allowed to slide independently of the others, thereby to compensate for different bend radii.

The end of the fibre optic opposite to the strain-relieved end may be terminated either in another strain-relieved termination or a fixed termination as shown in Fig. 2 of the present drawings where the ends of the optical fibres are fixed, for example by adhesive or moulding, into a soiid socket or plug member 32.

Claims (7)

1. A fibre-optic termination for fibre-optic cable containing one or more optical fibres, wherein one end of the or each optical fibre extends from the sheathing of the cable and is connected to a respective electro-optical terminating device, which or each of which, is slidable longitudinally in a holder.

2. A fibre-optic termination as claimed in claim 1 wherein the or each terminating device is slidably received in a respective holder.

3. A fibre-optic termination as claimed in claim 2 wherein the or each respective holder is mounted in a common housing.

4. A fibre-optic termination as claimed in any one of claims 1 to 3 wherein the or each holder comprises a hollow tube within which the respective terminating device is longitudinally slidable.

5. A fibre-optic termination as claimed in claim 4 wherein said hollow tube comprises a plastics or metal hollow tube.

6. A fibre-optic termination as claimed in any one of claims 1 to 5 wherein the or each electro-optical terminating device is electrically connected to respective electrical terminations by flexible wires or sliding contacts.

7. A fibre-optic termination substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.