GB1583520A

GB1583520A - Optical cables

Info

Publication number: GB1583520A
Application number: GB2023277A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1978-05-12
Filing date: 1978-05-12
Publication date: 1981-01-28

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL CABLES (71) We, BICC LIMITED, a British Company, of 21 Bloomsbury Street, London WClB 3QN, do hereby declare the inven tion, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly des cribed in and by the following statement : This invention relates to optical cables for the transmission of the ultra-violet, visible and infra-red regions of the electro magnetic spectrum, which regions for con venience, will hereafter all be included in the generic term 'light', and especially, but not exclusively, to optical cables for use in the communication field adapted for trans mission of light having a wavelength within the range of 0.8 to 1.3 micrometres.

In one form of optical cable that has been proposed one or more than one separ ate optical fibre and/or one or more than one optical bundle is or are loosely housed in a bore of a tube or other extruded elon gate body of rubber or plastics material the arrangement being such that when the cable is flexed limited relative movement can take place between the or each separate optical fibre and/or between the or each optical bundle and the tube or other ex truded elongate body.

By the expression 'optical bundle' is meant a group of optical fibres or a group of fibres including one or more optical fibres and one or more non-optical reinforcing fibres or other reinforcing elongate ele ments.

In some circumstances during manufac ture of the aforesaid form of optical cable, there is a risk that wrinkling or kinking, and perhaps fracture, of the optical -fibre or of some of the fibres may occur and this risk is substantially increased where the op tical cable is to include separate optical fibres. Wrinkling or kinking of an optical fibre is undesirable as it causes an increase in attenuation; fracture of an optical fibre cannot be tolerated.

It is an object of the present invention to provide a method of manufacturing an optical cable in which the risk of wrinkling or kinking of optical fibres during manufacture is substantially reduced.

According to the invention the method comprises causing at least one tape of metal or metal alloy to travel in the direction of its length; folding the advancing tape or tapes transversely or otherwise arranging the tape or tapes in such a way that adjacent longitudinal edges of the tape or tapes butt or overlap form a tube; feeding into the tube as it is being formed at least one separate optical fibre and/or at least one optical bundle, the relative crosssectional sizes of the tube and the optical fibre or fibres and/or the optical bundle or bundles being such that the optical fibre or fibres and/or the optical bundle or bundles is or are loostly housed in the tube; and extruding around the tube so formed an elongate body of rubber or plastics material which bonds to the outer surface of the tube.

Preferably, the or each tape of metal or metal alloy has a layer of rubber or plastics material on at least one of its major surfaces and the or each tape is so transversely folded or otherwise arranged that the layer of rubber or plastics material of the or each is outermost so that, when the elongate body of rubber or plastics material is extruded around the tube, a firm bond is achieved between the materials of the layer on the or each tape and the elongate body.

The or each tape may also have a layer of rubber or plastics material on its inwardlyfacing surface so that the tube formed there- from will have a lining of rubber or plastics material.

By virtue of the fact that the extruded elongate body is bonded to an underlying metal tube, three important advantages are obtained. Firstly, the tube serves to prevent substantial longitudinal shrinkage of the extruded elongate body whilst it is cooling which might otherwise cause an optical fibre or fibres loosely housed in the bore of, the elongate body to wrinkle or kink and perhaps fracture. Secondly, the risk that.

an optical fibre or bundle will stick to the internal surface of the extruded elongate body is eliminated. Thirdly, feeding of an optical fibre and/or optical bundle into the tube as it is being formed substantially facilitates manufacture of the optical cable.

Yet another advantage is that the tube of metal or metal alloy constitutes a circumferentially continuous moisture - proof barrier.

Preferably, the tube is formed by causing a single tape to advance in a direction substantially parallel to the direction of travel of the advancing optical fibre or fibres and/or optical bundle or bundles and folding the tape transversely so that its longitudinal edges butt.

Where the optical cable is to include two or more separate optical fibres and/or two or more optical bundles, the optical fibres and/or optical bundles may be secured side-by-side on or within at least one substantially flat tape or other flexible support member of metallic or non-metallic material, the tape-supported fibres and/or bundles being fed into the tube as it is being formed and the relative crosssectional sizes of the tube and the tapesupported fibres and/or bundles being such that the tape supporting the fibres and/or bundles is loosely housed in the tube.

Usually, but not necessarily, the or each optical fibre will have a protective coating of enamel, lacquer or other suitable hardened material.

To facilitate feeding of the or each separate optical fibre and/or optical bundle into the tube, preferably the leading end of the optical fibre and/or bundle, or of the tape supporting the optical fibres and/ or bundles, is lightly bonded to the inside surface of the tube by a suitable adhesive.

Where it is desired to fill the interstices in the tube with a greasy filling medium, for instance petroleum jelly, to reduce the risk that the or any optical fibre may be scratched, scored or otherwise damaged as a result of sliding contact with another optical fibre or other component of the cable when the cable is flexed, the greasy filling medium may be introduced into the tube during manufacture of the cable, preferably at the die or other means by which the tube is formed.

The or each tape forming the tube may be of any suitable metal or metal alloy but preferably it is of aluminium or aluminium alloy or copper or copper alloy. In some circumstances, to enhance the flexibility of the cable, the tube may have transversely extending corrugations and the or each tape may be formed with transversely extending corrugations as it is advancing towards the die or other means by which it is transversely folded, or otherwise arranged to form a tube.

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

The invention is further illustrated by a description, by way of example, of the preferred method of manufacturing an optical cable with reference to the accompanying drawing, in which: Figure 1 is a schematic representation of the preferred method and Figure 2 is a transverse cross-sectional view of an optical cable manufactured by the method shown in Figure 1, drawn on an enlarged scale.

Referring to Figure 1, an enamel-coated optical fibre 1 under a controlled tension and an aluminium tape 2 from a supply reel 4 are fed, respectively, over guide pulleys 5 and 6 to a tube-forming die 7, where the tape is folded transversely around the optical fibre in such a way that the longitudinal edges of the tape butt and that a coating 3 of plastics material (Figure 2) on one of its major surfaces forms an outer plastics coating of the tube 8 so formed.

To facilitate initial feeding of the optical fibre 1 into the tube 8, the leading end of the optical fibre may have been lightly bonded to the adjacent leading end of the tape 2 so that the fibre will pass smoothly into the tube as it is being formed. On emerging from the die 7, the tube 8 passes to an extruder where a sheath 10 of plastics material is extruded around the tube, the plastics material of the sheath bonding firmly with the plastics coating 3 on the outer surface of the tube.

As will be seen on referring to Figure 2, the optical cable manufactured by the method described with reference to Figure 1 comprises an optical fibre 1 loosely housed in a composite tubular body comprising the aluminium tube 8 formed by the transversely folded tape 2 and the plastics sheathl0 bonded firmly to the plastics coating 3 on the outer surface of the tube 8.

WHAT WE CLAIM IS: - 1. A method of manufacturing an optical cable which comprises causing at least one tape of metal or metal alloy to travel in the direction of its length; folding the advancing tape or tapes transversely or otherwise arranging the tape or tapes in such a way that adjacent longitudinal edges of the tape or tapes butt or overlap form a tube; feeding into the tube as it is being formed at least one separate fibre and/or at least on optical bundle, the relative cross-sectional sizes of the tube and the optical fibre or fibres and/or the optical bundle or bundles being such that the optical fibre or fibres and/or the optical bundle or bundles is or are loosely housed in the tube; and extruding around the tube

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. body is eliminated. Thirdly, feeding of an optical fibre and/or optical bundle into the tube as it is being formed substantially facilitates manufacture of the optical cable. Yet another advantage is that the tube of metal or metal alloy constitutes a circumferentially continuous moisture - proof barrier. Preferably, the tube is formed by causing a single tape to advance in a direction substantially parallel to the direction of travel of the advancing optical fibre or fibres and/or optical bundle or bundles and folding the tape transversely so that its longitudinal edges butt. Where the optical cable is to include two or more separate optical fibres and/or two or more optical bundles, the optical fibres and/or optical bundles may be secured side-by-side on or within at least one substantially flat tape or other flexible support member of metallic or non-metallic material, the tape-supported fibres and/or bundles being fed into the tube as it is being formed and the relative crosssectional sizes of the tube and the tapesupported fibres and/or bundles being such that the tape supporting the fibres and/or bundles is loosely housed in the tube. Usually, but not necessarily, the or each optical fibre will have a protective coating of enamel, lacquer or other suitable hardened material. To facilitate feeding of the or each separate optical fibre and/or optical bundle into the tube, preferably the leading end of the optical fibre and/or bundle, or of the tape supporting the optical fibres and/ or bundles, is lightly bonded to the inside surface of the tube by a suitable adhesive. Where it is desired to fill the interstices in the tube with a greasy filling medium, for instance petroleum jelly, to reduce the risk that the or any optical fibre may be scratched, scored or otherwise damaged as a result of sliding contact with another optical fibre or other component of the cable when the cable is flexed, the greasy filling medium may be introduced into the tube during manufacture of the cable, preferably at the die or other means by which the tube is formed. The or each tape forming the tube may be of any suitable metal or metal alloy but preferably it is of aluminium or aluminium alloy or copper or copper alloy. In some circumstances, to enhance the flexibility of the cable, the tube may have transversely extending corrugations and the or each tape may be formed with transversely extending corrugations as it is advancing towards the die or other means by which it is transversely folded, or otherwise arranged to form a tube. The invention also includes an optical cable made by the method hereinbefore described. The invention is further illustrated by a description, by way of example, of the preferred method of manufacturing an optical cable with reference to the accompanying drawing, in which: Figure 1 is a schematic representation of the preferred method and Figure 2 is a transverse cross-sectional view of an optical cable manufactured by the method shown in Figure 1, drawn on an enlarged scale. Referring to Figure 1, an enamel-coated optical fibre 1 under a controlled tension and an aluminium tape 2 from a supply reel 4 are fed, respectively, over guide pulleys 5 and 6 to a tube-forming die 7, where the tape is folded transversely around the optical fibre in such a way that the longitudinal edges of the tape butt and that a coating 3 of plastics material (Figure 2) on one of its major surfaces forms an outer plastics coating of the tube 8 so formed. To facilitate initial feeding of the optical fibre 1 into the tube 8, the leading end of the optical fibre may have been lightly bonded to the adjacent leading end of the tape 2 so that the fibre will pass smoothly into the tube as it is being formed. On emerging from the die 7, the tube 8 passes to an extruder where a sheath 10 of plastics material is extruded around the tube, the plastics material of the sheath bonding firmly with the plastics coating 3 on the outer surface of the tube. As will be seen on referring to Figure 2, the optical cable manufactured by the method described with reference to Figure 1 comprises an optical fibre 1 loosely housed in a composite tubular body comprising the aluminium tube 8 formed by the transversely folded tape 2 and the plastics sheathl0 bonded firmly to the plastics coating 3 on the outer surface of the tube 8. WHAT WE CLAIM IS: -

1. A method of manufacturing an optical cable which comprises causing at least one tape of metal or metal alloy to travel in the direction of its length; folding the advancing tape or tapes transversely or otherwise arranging the tape or tapes in such a way that adjacent longitudinal edges of the tape or tapes butt or overlap form a tube; feeding into the tube as it is being formed at least one separate fibre and/or at least on optical bundle, the relative cross-sectional sizes of the tube and the optical fibre or fibres and/or the optical bundle or bundles being such that the optical fibre or fibres and/or the optical bundle or bundles is or are loosely housed in the tube; and extruding around the tube

so formed an elongate body of rubber or plastics material which bonds to the outer surface of the tube.

2. A method of manufacturing an optical cable which comprises causing at least one tape of metal or metal alloy having a layer of rubber or plastics material on at least one of its major surfaces to travel in the direction of its length; folding the advancing tape or tapes transversely or otherwise arranging the tape or tapes in such a way that adjacent longitudinal edges of the tape or tapes butt or overlap form a tube having an outermost layer of rubber or plastics material; feeding into the tube as it is being formed at least one separate optical fibre and/or at least one optical bundle, the relative cross-sectional sizes of the tube and the optical fibre or fibres and/or the optical bundle of bundles being such that the fibre or fibres and/or the optical bundle or bundles is or are loosely housed in the tube; and extruding around the tube so formed an elongate body of rubber or plastics materials which bonds to the layer of rubber or plastics material on the outside of the tube.

3. A method as claimed in Claim 1 or 2, wherein a single tape advancing in a direction substantially parallel to the direction of travel of the advancing optical fibre or fibres and/or optical bundle or bundles is folded transversely so that its longitudinal edges butt.

4. A method as claimed in any one of the preceding Claims, wherein the or each tape has a layer of rubber or plastics material on its inwardly-facing surface so that the tube formed therefrom has a lining of rubber or plastics material.

5. A method as claimed in any one of the preceding Claims, wherein at least two separate optical fibres and/or optical bundles are secured side-by-side on or within at least one substantially flat tape or other flexible support member of metallic or non-metallic material, the tape-supported fibres and/or bundles being fed into the tube as it is being formed and the relative cross-sectional sizes of the tube and the tape-supported fibres and/or bundles being such that the tape supporting the fibres and/or bundles is loosely housed in the tube.

6. A method as claimed in any one of the preceding Claims, wherein the leading end of the or each optical fibre and/or bundle, or of the tape supporting the optical fibres and/or bundles, is lightly bonded to the inside surface of the tube by a suitable adhesive.

7. A method as claimed in any one of the preceding Claims, wherein a greasy filling medium is introduced into the tube during manufacture of the cable at the die or other means by which the tube is formed.

8. A method as claimed in any one of the preceding Claims, wherein the or each tape is formed with transversely extending corrugations as it is advancing towards the die or other means by which it is transversely folded or otherwise arranged to form a tube.

9. A method as claimed in any one of the preceding Claims, wherein the or each tape is of aluminium or aluminium alloy or of copper or copper alloy.

10. A method of manufacturing an optical cable substantially as hereinbefore described with reference to the accompanying drawing.

11. An optical cable when manufactured by the method claimed in any one of the preceding Claims.