GB2157019A

GB2157019A - Manufacture of optical cable

Info

Publication number: GB2157019A
Application number: GB08508294A
Authority: GB
Inventors: Stephen Peter Driskel
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1984-03-29
Filing date: 1985-03-29
Publication date: 1985-10-16
Also published as: GB2157019B; GB8408156D0; GB8508294D0

Abstract

An optical cable having loosely housed in a bore of a tube 8 a resiliently set undulating flexible optical guide 1 is manufactured by introducing the leading end of the undulating guide into an end of the bore of the tube and continuously injecting air into the end of the tube at such a pressure that the undulating guide is blown along the tube until it extends along the whole length of the tube. The air flows around the undulating guide and against the trailing faces of the undulations to carry the guide along, and to lift it off the lower surface of, the tube. <IMAGE>

Description

SPECIFICATION Manufacture of optical cable This invention relates to the manufacture of optical cable of the kind in which a flexible optical guide is so loosely housed in a bore extending within and along the length of the cable that, when the optical cable is bent or flexed whilst it is being manufactured or installed or whilst it is in service, the optical guide can move transversely and longitudinally within the bore with respect to the cable.

It is an object of the present invention to provide an improved method of manufacturing an optical cable which has loosely housed in a bore extending within and along the length of the cable a flexible optical guide which is resiliently set in such a form that it follows a path of smoothly curved undulations, the axes of curvature of the undulations lying parallel to one another and substantially normal to the longitudinal axis of the optical guide.

In the improved method according to the invention, the leading end of a length of resiliently set undulating flexible optical guide is introduced into an end of the bore of a preformed tube and fluid which will have no deleterious effect on the optical guide or on the tube is continuously injected into said end of the tube at such a pressure that the length of undulating flexible optical guide is carried along the tube until the length of undulating flexible optical guide is loosely housed in and throughout substantially the whole length of the tube.

The fluid continuously injected under pressure into the bore flows around the undulating flexible optical guide and against the trailing faces of the smoothly curved undulations to carry the flexible optical guide along, and to lift the flexible optical guide of the lower surface of, the tube.

The fluid employed to carry the length of undulating flexible optical guide along the tube may be in liquid or semi-liquid form and may constitute a component of the finished cable by substantially filling the tube but, preferably, the fluid employed is air or other gas which blows the length of undulating flexible optical guide along the tube.

To reduce friction between the undulating flexible optical guide and the internal surface of the bore of the tube as the optical guide is blown along the tube by air or other gas, preferably as the length of undulating flexible optical guide travels from the source of its supply to said end of the tube it is dusted with French chalk, talc or other lubricating powder which will have no deleterious effect on the optical guide.

The improved method of manufacture as hereinbefore described may be effected either in the factory or on site. That is to say, in the factory the tube into which the resiliently set undulating flexible optical guide is blown or otherwise carried by the continuously injected air or other fluid may be a tube of metal or non-metal which may or may not be wound on a drum and which, after the undulating flexible optical guide has been blown or otherwise carried into the tube, may or may not be assembled with one or more than one other cable component and/or may or may not be sheathed to form an optical cable; or, on site, the tube may be a component of an installed optical cable or may be a duct in which an undulating flexible optical guide is to be loosely housed.

The pressure at which air or other fluid is continuously injected into the bore of the tube to blow or otherwise carry the undulating flexible optical guide along the tube will, of course, depend upon the weight per unit length of the optical guide, the relative transverse dimensions of the bore of the tube and of the undulating flexible optical guide and the length of the tube into which a length of undulating flexible optical guide is to be blown or otherwise carried but, preferably, the pressure will be at least several times atmospheric pressure.

Where the tube is of excessive length or in other circumstances, the amplitude and pitch of the smoothly curved undulations may be arranged to provide trailing faces on the undulations that are so inclined to the longitudinal axis of the optical guide as to increase the distance which the undulating flexible guide can be blown or otherwise carried along the tube for a given pressure of the injected air or other fluid.

Preferably, the resiliently set undulating flexible optical guide is an undulating optical fibre ribbon as described in the specification of our co-pending British Patent Application No: 8415490 or it is an undulating optical fibre element comprising a flexible tube in which at least one optical fibre is loosely housed as described in the specification of our co-pending British Patent Application No: 8506468.

The invention also includes an optical cable manufactured by the improved method hereinbefore described.

The invention is further illustrated by a description, by way of example, of the preferred method of manufacturing an optical cable which has loosely housed in a bore extending within and along the length of the cable a flexible resiliently set undulating optical fibre ribbon structure, with reference to the accompanying drawing which shows a schematic representation of the method.

Referring to the drawing, an optical fibre ribbon structure 1 comprising eight optical fibres arranged side by side between two resilient metal wires, the axes of the optical fibres and of the metal wires lying in a substantially common plane and the optical fibres and metal wires being wholly embedded in a body of plastics material, is caused to travel in the direction of its length through a device 2 which effects a resilient set in the metal wires in such a form that the optical fibre ribbon structure follows a path of smoothly curved undulations, the axes of curvature of the undulations lying parallel to one another and substantially normal to the longitudinal axis of the ribbon structure. Down-stream of the device 2, the undulating optical fibre ribbon structure passes through an applicator 3 wherein the ribbon structure is dusted with talc and, from the applicator, the undulating optical fibre ribbon structure passes into one limb 5 of a Y-coupler 4 which is inserted in one end of a preformed tube 8 and into the other limb 6 of which air is injected at a pressure several times that of the atmosphere.

The Y-shaped coupler 4 is provided with an exhaust valve 7. The air continuously injected through the limb 6 into the Y-shaped coupler 4 blows the undulating flexible optical fibre ribbon structure along the tube 8 until the length of undulating flexible optical fibre ribbon structure is loosely housed in and throughout substantially the whole length of the tube.

Claims

1. A method of manufacturing an optical cable which has loosely housed in a bore extending within and along the length of the cable a flexible optical guide which is resiliently set in such a form that it follows a path of smoothly curved undulations, the axes of the curvature of the undulations lying parallel to one another and substantially normal to the longitudinal axis of the optical guide, which method comprises introducing the leading end of a length of resilient undulating flexible optical guide into an end of the bore of a preformed tube and continuously injecting into said end of the tube fluid which will have no deleterious effect on the optical guide or on the tube and which is at such a pressure that the length of undulating flexible optical guide is carried along the tube until the length of undulating flexible optical guide is loosely housed in and throughout substantially the whole length of the tube.

2. A method as claimed in Claim 1, wherein the fluid which is continuously injected into said end of the tube is air or other gas which blows the length of undulating flexible optical guide along the tube.

3. A method as claimed in Claim 2, wherein, as the length of undulating flexible optical guide travels from the source of its supply to said end of the tube, it is dusted with French chalk, talc or other lubricating powder which will have no deleterious effect on the optical guide

4. A method as claimed in any one of the preceeding Claims, wherein the tube is a component of an installed optical cable or is a duct in which an undulating flexible optical guide is to be loosely housed.

5. A method as claimed in any one of Claims 1 to 3, wherein the steps of introducing a length of resiliently set undulating flexible optical guide into an end of the tube and continuously injecting fluid under pressure into said end of the tube are effected with the tube wound on a drum.

6. A method as claimed in any one of the preceeding claims, wherein the fluid is continuously injected into the tube at a pressure at least several times atmospheric pressure.

7. A method of manufacturing an optical cable substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

8. An optical cable manufactured by the method claimed in any one of the preceeding