GB2156539A

GB2156539A - Manufacture of optical guide assembly

Info

Publication number: GB2156539A
Application number: GB08508293A
Authority: GB
Inventors: David Turner Parr
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1984-03-29
Filing date: 1985-03-29
Publication date: 1985-10-09
Also published as: GB8408155D0; GB8508293D0; GB2156539B

Abstract

An optical guide assembly comprises an optical fibre 11 with a coating 12 loosely housed in a bore of a tube 14, wherein the coating 12 has a grooved outer surface such that, when the leading end of the coated fibre is introduced into an end of the bore of the tube 14 and air or other fluid is continuously injected into the end of the tube at such a pressure as to blow or otherwise carry the coated fibre along the tube 14, turbulence is created in the air or other fluid flowing around the coated fibre to lift it away from the inner surface of the tube, thereby to reduce the friction between the coated fibre and the tube wall. Preferably, the surface of the coating 12 has two helical grooves 13 of opposite lay and/or a plurality of annular grooves at longitudinally spaced positions along its length. <IMAGE>

Description

SPECIFICATION Manufacture of optical guide element This invention relates to the manufacture of an optical guide element of the kind in which at least one flexible optical guide is so loosely housed in a bore extending within and along the length of the element that, when the optical guide element 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 element.

It has been proposed to manufacture an optical fibre element by introducing the leading end of a length of optical fibre into an end of the bore of a preformed tube and by continuously injecting into said end of the tube fluid which will have no deleterious effect on the optical fibre or on the preformed tube and which is at such a pressure that the length of optical fibre is carried long the tube until the length of optical fibre is loosely housed in and throughout the length of the tube.

It is an object of the present invention to provide an improvement in the aforesaid method of manufacturing an optical guide element comprising a preformed tube in which at least one flexible optical guide is loosely housed.

In the improved method according to the invention, the flexible optical guide has an outer peripheral surface of such a shape that turbulence is created in the continuously injected fluid flowing around the flexible optical guide to lift the optical guide from the bottom surface of the tube thereby to reduce the friction between the optical guide and the bottom wall of the tube.

Since the friction is reduced between the flexible optical guide being carried along the tube and the bottom wall of the tube, for substantially the same pressure at which fluid is continuously injected into the tube, a length of tube into which a length of flexible optical guide can be carried is substantially greater than would otherwise be the case for a flexible optical guide of equivalent weight per unit length whose outer surface is not shaped to create turbulence in the injected fluid.

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

Preferably, the flexible optical guide has in its outer peripheral surface n grooves extending helically along the guide, "/2 of the grooves having a left hand lay and "/2 of the grooves having a right hand lay, where n is an even number. Alternatively, or additionally, the flexible optical guide may have in its outer peripheral surface a plurality of annular grooves at longitudinally spaced positions along its length. In both cases, preferably the walls of each groove are smoothly curved.

To reduce further any friction between the flexible optical guide and the wall of the tube as the optical guide is blown along the tube by air or other gas, preferably as the length of 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 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 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 a 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 flexible optical guide along the tube will, of course, depend upon the weight per unit length of the optical guide, the reiative transverse dimensions of the bore of the tube and of the flexible optical guide and the length of the tube into which a length of optical guide is to be blown or otherwise carried but, preferably, the pressure will be at least several times atmospheric pressure.

The flexible optical guide may be a single optical fibre, an optical fibre bundle or an optical fibre element.

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

The invention will be further illustrated by a description, by way of example, of two preferred forms of optical fibre element and of the preferred method of manufacturing a preferred form of optical fibre element with reference the accompanying drawing, in which: Figures 1 and 2, respectfully, are sectional side and end views of a first preferred form of optical fibre element; Figures 3 and 4, respectfully, are sectional side and end views of a second preferred form of optical fibre element, and Figure 5 is a schematic representation of the preferred method of manufacturing the preferred optical fibre element illustrated in Figs. 3 and 4.

The first preferred form of optical fibre element illustrated in Figs. 1 and 2 comprises an optical fibre 1 which has a coating 2 of plastics material in which is formed at longitudinaly spaced positions along the length of the coated fibre, a plurality of annular grooves 3. The optical fibre is loosely housed in the bore of a duct 4.

The second preferred form of optical fibre element illustrated in Figs. 3 and 4 comprises an optical fibre 11 having a coating 1 2 of plastics material in the outer peripheral surface of which two grooves 1 3 extend helically along the fibre, one of the grooves having a left hand lay and the other of the grooves having a right hand lay. The walls of each groove are smoothly curved. The coated optical fibre is loosely housed in the bore of a duct 14.

Fig. 5 illustrates diagramatically the apparatus employed in making the optical fibre elements illustrated in Figs. 1 and 2 and in Figs.

3 and 4. This apparatus comprises a tubular coupler 21 which is sealed to the end of a duct D and which has at the end of the coupler remote from the duct a small orifice 22 through which a coated optical fibre F, which is a tight fit in the orifice, can pass from a drum 23 into the coupler. In the side wall of the coupler 21 is a port 24 through which air at a pressure several times atmospheric pressure can be injected.

In using the apparatus illustrated in Fig. 5 to manufacture the optical fibre element shown in Figs. 1 and 2, the coated optical fibre is drawn from the drum 23 through the orifice 22 into the coupler 21 and air is injected through the port 24 into the coupler under a pressure several times atmospheric pressure. The longitudinally spaced, annular grooves 3 in the plastics coating 2 of the fibre 1 create such turbulence in the continuously injected air flowing into the coupler and duct and around the coated fibre that the fibre is lifted from the bottom surface of the duct thereby to reduce friction between the coated fibre and the bottom surface of the duct as the fibre is blown along the duct.

In manufacturing the second preferred form of optical fibre element shown in Figs. 3 and 4, the coated fibre F is fed from the drum 23 through the orifice 22 into the coupler 21 and into the end of the duct 14 and air at a pressure several times that of atmospheric pressure is continuously injected into the coupler through the port 24 and into the duct.

The two grooves 1 3 in the outer peripheral surface of and extending along the length of the plastics coated fibre create turbulence in the continuously injected air flowing around the coated fibre to lift the coated fibre from the bottom surface of the duct thereby to reduce the friction between the coated fibre and the bottom surface of the duct as the coated fibre is blown along the duct.

Claims

1. A method of manufacturing an optical guide element which comprises introducing the leading end of a length of 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 flexible optical guide or on the preformed tube and which is at such a pressure that the length of flexible optical guide is carried along the tube until the length of flexible optical guide is loosely housed in and throughout the length of the tube, wherein the flexible optical guide has an outer peripheral surface of such a shape that turbulence is created in the continuously injected fluid flowing around the flexible optical guide to lift the optical guide from the bottom surface of the tube thereby to reduce the friction between the optical guide and the bottom wall of the tube.

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

3. A method as claimed in Claim 2, wherein, as the length of 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 flexible optical guide has in its outer peripherals surface n grooves extending helically along the guide, n/2 of the grooves having a left hand lay and "/2 of the grooves having a right hand lay, where n is an even number.

5. A method as claimed in any one of the preceeding Claims, wherein the flexible optical guide has in its outer peripheral surface a plurality of annular grooves at longitudinally spaced positions along its length.

6. A method as claimed in Claim 4 or 5, wherein the walls of each groove are smoothly curved.

7. A method as claimed in any one of the preceeding Claims, wherein air or other fluid is continuously injected into said end of the preformed tube to blow or otherwise carry the flexible optical guide along the tube whilst the tube is wound on a drum.

8. A method as claimed in any one of the Claims 1 to 6, wherein the preformed tube is a component of an installed optical cable or is a duct in which a flexible optical guide is to be loosely housed.

9. A method as claimed in any one of the preceding Claims, wherein the fluid is continuously injected into the preformed tube at a pressure several times atmospheric pressure.

10. A method as claimed in any one of the preceeding Claims, wherein the flexible optical guide is a single optical fibre.

11. A method of manufacturing an optical guide element substantially as hereinbefore described with reference to and as shown in Fig. 5 of the accompanying drawing.

1 2. An optical guide element manufactured by the method claimed in any one of the preceeding Claims.