GB1592191A

GB1592191A - Optical cables

Info

Publication number: GB1592191A
Application number: GB2310777A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-07-01

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL CABLES (71) We, BICC Limited, a British Company, of 21 Bloomsbury Street, London WC1B 3QN, do hereby declare the invention, 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 described in and by the following statement: This invention relates to optical cables for the transmission of the ultraviolet, visible and infra-red regions of the electromagnetic spectrum, which regions, for convenience, will hereinafter all be included in the generic term "light", and especially, but not exclusively, to optical cables for use in the communication field adapted for transmission of light having a wavelength within the range 0.8 to 1.3 micrometres.

According to the invention an improved optical cable comprises a bare flexible elongate member of metal or metal alloy having at least one bore extending throughout its length and, loosely housed in the bore or in at least one of the bores of and unsupported with respect to the elongate member, at least one separate optical fibre and/or at least one optical bundle.

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 elements. Each optical fibre of the optical bundle may be used independently as a separate light guide, each with its own modulated light source and detector, or a plurality of optical fibres of a bundle may be used together as a single light guide, with a single light source.

The or each separate optical fibre and/or the or each optical fibre of the optical bundle or bundles may be of circular or non-circular cross-section.

By virtue of being loosely housed in the or a bore in the flexible elongate member of metal or metal alloy, limited relative movement between the or each separate optical fibre and the elongate member and/or between the or each optical bundle and the elongate member can take place when the cable is flexed.

Preferably the or each bore in the flexible elongate member extends substantially pa rallel to the axis of the member.

The or each separate optical fibre and/or optical bundle may be of substantially greater length than the bore of the flexible elongate member in which it is loosely housed but preferably the or each separate optical fibre and/or optical bundle and the bore are of equal or approximately equal lengths.

Two or more separate optical fibres and/ or two or more optical bundles may be secured side-by-side on or within at least one substantially flat flexible support member, the relative cross-sectional sizes of the bore and the supported fibres and/or bundles being such that the flexible support member supporting the fibres and/or bundles is loosely housed in the bore of, and is unsupported with respect to, the elongate member. The substantially flat flexible support member is preferably in the form of at least one tape, for instance of paper or plastics material, glass or of metal or metal alloy. In some circumstances, it is preferred that the or each tape is of a material having a coefficient of thermal expansion approximating to that of the material or materials of the optical fibres. For example, where the optical fibres are of a silica-based material, the or each tape may be of steel.

Where the flexible support member consists of a single tape, the separate optical fibre and/or optical bundles may be secured by adhesive to one surface of the tape; viewed in transverse cross-section the tape may be corrugated so that it has a plurality of troughs extending along its length, in each of some or all of which a separate optical fibre or optical bundle may be secured. Where the flexible support member consists of two tapes, one overlying the other, the separate optical fibres and/or optical bundles may be sandwiched between the two tapes and may be secured by adhesive to at least one of the adjacent surfaces of the tapes; one or each of these two tapes may be transversely corrugated as described above. Where one or each of two tapes is transversely corrugated, the two tapes may be so bonded together that the optical bundles and/or separate optical fibres are secured within the flexible support member so formed but are capable of limited movement within the troughs in which they lie. Where optical fibres and/or bundles are secured within a substantially flat flexible support member, preferably the flexible support member comprises a single tape of plastics material with the separate optical fibres and/or optical bundles wholly or partially embedded in it.

As a means of initially identifying any separate optical fibre and/or optical bundle secured side-by-side on or within at least one substantially flat flexible support member, the support member may carry a longitudinally extending datum mark on its surface and/or at least one of the optical fibres and/or optical bundles may be assymmetrically positioned with respect to the or each other optical fibre and/or optical bundle so that it constitutes a longitudinally extending datum.

The bare flexible elongate member of metal or metal alloy may be of circular or non-circular cross-section. It may be an extruded body of metal or metal alloy having one or more than one bore but preferably the flexible elongate member comprises one or more than one tape of metal or metal alloy folded or otherwise arranged to form a tube. In a preferred embodiment the flexible elongate member is a substantially fluid-tight tube of circular cross-section formed from a single transversely folded tape of metal or metal alloy.

The flexible elongate member may be made of any suitable metal or metal alloy but preferably it is made of aluminium or aluminium alloy or copper or copper alloy.

With a view to preventing mechanical damage to the surface of any optical fibre arising from abrasion with another optical fibre or other fibre loosely housed in the or a bore in the flexible elongate member when flexing of the optical cable occurs, the interstices between the separate optical fibre or fibres and/or the optical bundle or bundles and the wall of the bore may be filled throughout the length of the cable with a greasy filling medium which will permit relative sliding movement between the separate optical fibre or fibres and/or optical bundle or bundles and the flexible elongate member. Preferably, the filling medium employed consists of, or comprises as a major constituent, petroleum jelly.

The or each optical fibre may have a continuous abrasion-resistant coating of a hardened material or may have a continuous coating of a suitable buffer material, which material may be a hardened or soft material.

The bore or at least one of the bores of the flexible elongate member may house loosely one or more than one insulated elongate electric conductor.

The invention further includes a method of manufacturing an improved optical cable as hereinbefore described, which method comprises forming a bare flexible elongate member of metal or metal alloy having at least one bore extending throughout its length and, as the flexible elongate member is being formed, feeding into the bore or at least one of the bores, at least one separate optical fibre and/or at least one optical bundle, the relative cross-sectional sizes of the bore and the optical fibre or fibres and/or the optical bundle or bundles being such that the fibre or fibres and/or the bundle or bundle is or are loosely housed in the bore of, and is or are unsupported with respect to, the elongate member.

The bare flexible elongate member may be formed by extrusion but preferably it is formed by 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 the tape or tapes form a tube; and sealing adjacent longitudinally extending edges of the tape or tapes to make the tube substantially fluid-tight.

Preferably the tape or tapes is or are so transversely folded or otherwise arranged that adjacent longitudinal edges of the tape or tapes butt or overlap and are secured together, for example by welding.

Feeding of an optical fibre and/or optical bundle into the tube as it is being formed from a tape or tapes substantially facilitates manufacture of the optical cable. Preferably the tube is formed by transversely folding a single advancing tape of metal or metal alloy so that its longitudinal edges butt or overlap, and welding or otherwise securing the edges together. In some circumstances, to enhance the flexibility of the cable, the or each tape may have transversely extending corrugations and the or each tape may be formed with transversely extending corrugations as it is advancing towards the means by which it is transversely folded to form a tube.

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 tape or other flexible support member of metallic or non-metallic material, the tape-supported fibres and/or bundles being fed into the or a bore as the flexible elongate member is being formed and the relative crosssectional sizes of the bore and the tapesupported fibres and/or bundles being such that the tape supporting the fibres and/or bundles is loosely housed in the bore of, and is unsupported with respect to, the elongate member.

To facilitate feeding of the or each separate optical fibre and/or optical bundle into a tube being formed from a tape or tapes, preferably the leading end of the 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 or a bore of the flexible elongate member 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 said bore during manufactue of the flexible elongate member, where the member is formed from a tape or tapes preferably at the die or other means by which the member is formed.

The invention is further illustrated by a description, by way of example, of a preferred optical cable and its method of manufacture and of six forms of optical fibre element that may be used in an optical cable according to the invention with reference to the accompanying drawings, in which: Figure I is a transverse cross-sectional view of the preferred optical cable; Figure 2 is a diagrammatic representation of its method of manufacture, and Figures 3 to 8 are transverse crosssectional views of the six forms of optical fibre element drawn on a greatly enlarged scale.

Referring to Figure 1, the optical cable comprises a bare flexible copper tube 3 having a bore 2 in which is loosely housed an optical fibre 1 which is unsupported with respect to the tube. The tube 3 comprises a transversely folded copper tape 4 whose longitudinally extending edges are secured together at a welded butt joint 5. The tube 3 has dn internal diameter of 1.0 mm and an external diameter of 1.5 mm the optical fibre 1 has a diameter of 130 m.

In manufacturing the optical cable shown in Figure 1, as will be seen on referring to Figure 2 the copper tape 4 is fed from a supply reel 6 over a guide pulley 7 to a tube forming die 9 where the tape is transversely folded to form the tube 3 and the optical fibre 1 is fed from a supply (not shown) over a guide pulley 8 into the tube 3 as it is formed in the tube-forming die. To facilitate feeding of the optical fibre 1 into the tube 3, the leading end of the fibre is lightly bonded to the inside surface of the tube by a suitable adhesive. On emerging from the tube forming die 9, the transversely folded tape 4 with the longitudinally extending edges of the tape butting passes under a welding head 10 where the butting edges were welded together.

If desired, in travelling from the supply reel 6 to the guide pulley, the tape 4 may passing through a corrugating device (not shown) which forms transversely extending corrugations in the tape so that when the tape is transversely folded to form a tube, the tube is circumferentially corrugated throughout its length.

Instead of the optical fibre 1, the bore 2 of the copper tube 3 of the optical cable shown in Figure 1 may loosely house any one of the optical fibre elements shown in Figures 3 to 8, the optical fibre elements being drawn on a greatly enlarged scale to clarify their structure. The optical fibre element shown in Figure 3 comprises a flexible tape 12 of plastics material which has secured by adhesive to one of its major surfaces four optical fibres 11 which are spaced apart and extend substantially parallel to the axis of the tape.

In the optical fibre element shown in Figure 4, four optical fibres 21 are sandwiched between and secured by adhesive to the adjacent surfaces of two flexible tapes 22, 23 of plastics material. The tape 23 has a longitudinally extending rib 27 to provide for ready identification of any optical fibre 21. The optical fibre element shown in Figure 5 comprises a flexible plastics tape 32 which, viewed in transverse cross-section, is so corrugated that it has a plurality of troughs 34 extending along its length in each of which an optical fibre 31 is secured by adhesive. The optical fibre element shown in Figure 6 comprises a corrugated flexible plastics tape 42 which has a plurality of troughs 44 extending along its length, the troughs being closed by a flat plastics tape 43 which is bonded to the peaks 45. Optical fibres 41 are secured by adhesive in the troughs 44. In the optical fibre element shown in Figure 7, optical fibres 51 are sandwiched between, and secured by adhesive in the troughs 54, 58 of, two flexible corrugated plastics tapes 52, 53 whose peaks 55, 59 are secured together by adhesive. To provide for ready identification of any optical fibre 51, the tape 53 has a longitudinally extending rib 57. The optical fibre element shown in Figure 8 comprises a plastics tape 62 in which four optical fibres 61 extending side-by-side are wholly embedded. The tape 62 has a longitudinally extending rib 67 to provide for ready identification of any optical fibre 61.

In the Complete Specification of our co-pending Patent Application No 30474/77 (Serial No 1592192) there is described and claimed a coaxial cable comprising inner and outer electric conductors radially spaced apart and electrically insulated from one another, wherein the inner conductor has extending throughout its length at least one bore in which at least one separate optical fibre and/or at least one optical bundle is or are loosely housed.

WHAT WE CLAIM IS: 1. An optical cable comprising a bare flexible elongate member of metal or metal alloy having at least one bore extending throughout its length and, loosely housed in the bore or in at least one of the bores of and unsupported with respect to the elongate member, at least one separate optical fibre and/or at least one optical bundle.

2. An optical cable as claimed in Claim 1, wherein the or each bore extends substantially parallel to the axis of the flexible elongate member.

3,. An optical cable as claimed in Claim 1 or 2, wherein the flexible elongate member is of circular cross-section.

4. An optical cable as claimed in any one of the preceding Claims, wherein the bare flexible elongate member is an extruded body of metal or metal alloy having one or more than one bore.

5. An optical cable as claimed in any one of Claims 1 to 3, wherein the bare flexible elongate member comprises one or more than one tape of metal or metal alloy folded or otherwise arranged to form a tube.

6. An optical cable comprising a bare substantially fluid-tight flexible tube of substantially circular cross-section formed by transversely folding a single longitudinally extending tape of metal or metal alloy so that its edges abut or overlap and, loosely housed in the bore of and unsupported with respect to the tube, at least one separate optical fibre and/or at least one optical bundle.

7. An optical cable as claimed in Claim 5 or 6, wherein the flexible tube is circumferentially corrugated.

8. An optical cable as claimed in any one of the preceding Claims, wherein the flexible elongate member or flexible tube is made of aluminium or aluminium alloy or of copper or copper alloy.

9. An optical cable as claimed in any one of the preceding Claims, wherein two or more separate optical fibres and/or two or more optical bundles are secured side-byside on or within at least one substantially flat flexible support member, the relative cross-sectional sizes of the bore and the supported fibres and/or bundles being such that the flexible support member supporting the fibres and/or bundles is loosely housed in the bore of, and is unsupported with respct to, the elongate member or tube.

10. An optical cable as claimed in Claim 9, wherein the substantially flat flexible support member is a flexible tape to one surface of which said separate optical fibres and/or optical bundles are secured by adhesive.

11. An optical cable as claimed in Claim 10, wherein, viewed in transverse crosssection, the tape is corrugated so that it has a plurality of troughs extending along its length and an optical fibre or optical bundle is secured in each of some or all of said troughs.

12. An optical cable as claimed in Caim 9, wherein the substantially flat flexible support member is a pair of flexible tapes between which said separate optical fibres and/or optical bundles are sandwiched and to the adjacent surfaces of which the optical fibres and/or optical bundles are secured by adhesive.

13. An optical cable as claimed in Claim 12, wherein, viewed in transverse crosssection, one or each of said two tapes is corrugated so that it has a plurality of troughs extending along its length and an optical fibre of optical bundle is secured in each of some or all of said troughs.

14. An optical cable as claimed in Claim 9, wherein the substantially flat flexible support member comprises two overlying flexible tapes which are bonded together, one or each of which tapes, viewed in transverse cross-section, being so corrugated that it has a plurality of troughs extending along its length in each of some or all of which a separate optical fibre and/or optical bundle is housed and wherein the separate optical fibres and/or optical bundles are secured within the flexible support member but are capable of limited movement within the troughs in which they lie.

15. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of a metal or metal alloy.

16. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of paper or plastics material.

17. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of a material having a coefficient of thermal expansion approximating to that of the material or materials of the optical fibres secured to the tape.

18. An optical cable as claimed in Claim 17, wherein the optical fibres are of a silica-based material and the or each tape is of steel.

19. An optical cable as claimed in Claim 9, wherein the substantially flat flexible

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Claims

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62 has a longitudinally extending rib 67 to provide for ready identification of any optical fibre 61.

In the Complete Specification of our co-pending Patent Application No 30474/77 (Serial No 1592192) there is described and claimed a coaxial cable comprising inner and outer electric conductors radially spaced apart and electrically insulated from one another, wherein the inner conductor has extending throughout its length at least one bore in which at least one separate optical fibre and/or at least one optical bundle is or are loosely housed.

WHAT WE CLAIM IS: 1. An optical cable comprising a bare flexible elongate member of metal or metal alloy having at least one bore extending throughout its length and, loosely housed in the bore or in at least one of the bores of and unsupported with respect to the elongate member, at least one separate optical fibre and/or at least one optical bundle.
2. An optical cable as claimed in Claim 1, wherein the or each bore extends substantially parallel to the axis of the flexible elongate member.
3,. An optical cable as claimed in Claim 1 or 2, wherein the flexible elongate member is of circular cross-section.
4. An optical cable as claimed in any one of the preceding Claims, wherein the bare flexible elongate member is an extruded body of metal or metal alloy having one or more than one bore.
5. An optical cable as claimed in any one of Claims 1 to 3, wherein the bare flexible elongate member comprises one or more than one tape of metal or metal alloy folded or otherwise arranged to form a tube.
6. An optical cable comprising a bare substantially fluid-tight flexible tube of substantially circular cross-section formed by transversely folding a single longitudinally extending tape of metal or metal alloy so that its edges abut or overlap and, loosely housed in the bore of and unsupported with respect to the tube, at least one separate optical fibre and/or at least one optical bundle.
7. An optical cable as claimed in Claim 5 or 6, wherein the flexible tube is circumferentially corrugated.
8. An optical cable as claimed in any one of the preceding Claims, wherein the flexible elongate member or flexible tube is made of aluminium or aluminium alloy or of copper or copper alloy.
9. An optical cable as claimed in any one of the preceding Claims, wherein two or more separate optical fibres and/or two or more optical bundles are secured side-byside on or within at least one substantially flat flexible support member, the relative cross-sectional sizes of the bore and the supported fibres and/or bundles being such that the flexible support member supporting the fibres and/or bundles is loosely housed in the bore of, and is unsupported with respct to, the elongate member or tube.
10. An optical cable as claimed in Claim 9, wherein the substantially flat flexible support member is a flexible tape to one surface of which said separate optical fibres and/or optical bundles are secured by adhesive.
11. An optical cable as claimed in Claim 10, wherein, viewed in transverse crosssection, the tape is corrugated so that it has a plurality of troughs extending along its length and an optical fibre or optical bundle is secured in each of some or all of said troughs.
12. An optical cable as claimed in Caim 9, wherein the substantially flat flexible support member is a pair of flexible tapes between which said separate optical fibres and/or optical bundles are sandwiched and to the adjacent surfaces of which the optical fibres and/or optical bundles are secured by adhesive.
13. An optical cable as claimed in Claim 12, wherein, viewed in transverse crosssection, one or each of said two tapes is corrugated so that it has a plurality of troughs extending along its length and an optical fibre of optical bundle is secured in each of some or all of said troughs.
14. An optical cable as claimed in Claim 9, wherein the substantially flat flexible support member comprises two overlying flexible tapes which are bonded together, one or each of which tapes, viewed in transverse cross-section, being so corrugated that it has a plurality of troughs extending along its length in each of some or all of which a separate optical fibre and/or optical bundle is housed and wherein the separate optical fibres and/or optical bundles are secured within the flexible support member but are capable of limited movement within the troughs in which they lie.
15. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of a metal or metal alloy.
16. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of paper or plastics material.
17. An optical cable as claimed in any one of Claims 10 to 14, wherein the or each tape is of a material having a coefficient of thermal expansion approximating to that of the material or materials of the optical fibres secured to the tape.
18. An optical cable as claimed in Claim 17, wherein the optical fibres are of a silica-based material and the or each tape is of steel.
19. An optical cable as claimed in Claim 9, wherein the substantially flat flexible

support member is a flexible tape of plastics material in which said separate optical fibres and/or optical bundles are wholly or partially embedded.
20. A flexible stranded body as claimed in any one of Claims 9 to 19, wherein the flexible support member carries a longitudinally extending datum mark and/or at least one of the optical fibres and/or optical bundles is assymmetrically positioned with respect to the or each other optical fibre and/or optical bundles so that it constitutes a longitudinally extending datum.
21. An optical cable as claimed in any one of the preceding Claims, wherein the interstices between the separate optical fibre or fibres and/or the optical bundle or bundles and the wall of the bore are filled throughout the length of the cable with a greasy filling medium.
22. An optical cable as claimed in Claim 21, wherein the filling medium consists of, or comprises as a major constituent, petroleum jelly.
23. An optical cable as claimed in any one of the preceding Claims, wherein the or each optical fibre has a continuous abrasionresistant coating of a hardened material or a continuous coating of a buffer material.
24. An optical cable as claimed in any one of the preceding Claims, wherein the or each separate optical fibre and/or optical bundle and the bore in which it is loosely housed are of equal or approximately equal lengths.
25. An optical cable as claimed in any one of the preceding Claims, wherein the bore or at least one of the bores of the flexible elongate member houses loosely one or more than one insulated elongate electric conductor.
26. A method of manufacturing an optical cable which comprises forming a bare flexible elongate member of metal or metal alloy having at least one bore extending throughout its length and, as the flexible elongate member is being formed, feeding into the bore or at least one of the bores, at least one separate optical fibre and/or at least one optical bundle, the relative crosssectional sizes of the bore and the optical fibre or fibres and/or the optical bundle or bundles being such that the fibre or fibres and/or the bundle or bundles is or are loosely housed in the bore of, and is or are unsupported with respect to, the elongate member.
27. A method as claimed in Claim 26, wherein the bare flexible elongate member is formed by extrusion.
28. 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 the tape or tapes form a flexible tube, and sealing adjacent longitudinally extending edges of the tape or tapes to make the tube substantially fluid-tight; and, as the flexible tube is being formed, feeding into its bore at least one separate optical fibre and/or at least one optical bundle, the relative cross-sectional sizes of the bore and the optical fibre or fibres and/or the optical bundle or bundles being such that the fibre or fibres and/or the bundle or bundles is or are loosely housed in the bore of, and is or are unsupported with respect to, the tube.
29. A method as claimed in Claim 28, wherein the flexible tube is formed by transversely folding a single advancing tape so that its longitudinal edges butt or overlp and welding or otherwise securing the edges together.
30. A method as claimed in Claim 28 or 29, wherein the or each tape is formed with transversely extending corrugations as it is advancing towards the means by which it is transversely folded to form a tube.
31. A method as claimed in any one of Claims 26 to 30, wherein two or more separate optical fibres and/or optical bundles being fed into the bore are secured side-by-side on or within at least one tape or other flexible support member.
32. A method as claimed in any one of the preceding Claims, wherein the leading end of the fibre and/or bundle or of the flexible support member supporting the optical fibres and/or bundles, is lightly bonded to the inside surface of the tube by a suitable adhesive.
33 A method of manufacturing an optical cable substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
34. An optical cable substantially as hereinbefore described with reference to and is shown in Figure 1 of the accompanying drawings.
35. An optical cable as claimed in Claim 1 having loosely housed in the bore or at least one of the bores an optical fibre element substantially as hereinbefore described with reference to and is shown in any one of Figures 3 to 8 of the accompanying drawings.