GB1559026A

GB1559026A - Optical guides

Info

Publication number: GB1559026A
Application number: GB15271/77A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1977-04-13
Filing date: 1977-04-13
Publication date: 1980-01-09
Also published as: IT7848834A0; JPS581108A; DE2815514C2; NL186040B; FR2387460B2; JPS59112205U; NL186040C; NL7803904A; SE7804109L; FR2387460A2; SE439695B; IT1156163B; DE2815514A1; JPS53128346A

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL GUIDES (71) We, BICC LIMITED, a British Company, of 21 Bloomsbury Street, London WClB 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 guides for the transmission of the ultra-violet, 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 waveguides for use in the communications field adapted for transmission of light having a wavelength within the range 0.8 to 1.3 micrometres.

In the Complete Specification of our Patent No. 1479426 there is described and claimed an optical guide in the form of an optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body, at least one optical bundle as hereinafter defined and/or one or more than one separate optical fibre housed in the bore or in at least one of the bores, and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

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 and/or non-optical fibre may be of circular or non-circular cross-section.

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

The aforesaid patent is a Patent of Addition to our Patent No. 1422147.

The present invention is an improvement in or modification of the optical cable forming the subject of Patent No. 1479426 and provides an optical cable in accordance with said patent in which any optical bundle and/or separate optical fibre can be readily identified.

According to the invention, the improved optical cable comprises an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres secured side-by-side on or within at least one substantially flat flexible support member which is housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

Since the substantially flat flexible support member on or within which the or each optical bundle and/or separate optical fibre is secured is housed loosely in a bore extending lengthwise in the extruded elongate body, limited relative movement between the flexible support member and the extruded elongate body - and hence between the or each optical bundle and/or the or each separate optical fibre and the extruded elongate body - can take place when the cable is flexed.

By virtue of the fact that the position of each optical bundle and/or of each separate optical fibre secured on or within the flexible support member with respect to the other optical bundle or bundles and/or other separate optical fibre and fibres is constant throughout the length of the cable, any optical bundle and/or separate optical fibre can be readily identified at any transverse cross-section of the cable.

Furthermore, since each optical bundle and/or each separate optical fibre is secured on or within a flexible support member. feeding of the optical bundles and/or optical fibres into the bore or bores of the extruded elongate body during manufacture of the cable, and especially when initially introducing the optical bundles and/or optical fibres into the bore or bores, is facilitated.

Where the extruded elongate body has a transverse cross-sectional shape of such a form that the parts of the body on opposite sides of a plane passing through the axis or axes of the bore or bores are substantially indentical, preferably initial identification of the optical bundles and/or optical fibres is further facilitated by providing a longitudinally extending datum mark on the surface of the extruded elongate body.

Preferably, the substantially flat flexible support member is in the form of at least one tape, for instance of paper or plastics material, of 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 optical bundles and/or optical fibres may be secured by adhesive to one surface of the tape; viewed in transverse cross-section the cape may be corrugated so that it has a plurality of troughs extending along its length, in each of some or all of which an optical bundle or separate optical fibre may be secured.

Where the flexible support member consists of two tapes, one overlying the other, the optical bundles and/or separate optical fibres may be sandwiched between the two tapes and secured by adhesive to 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 the optical bundles and/or separate optical fibres are secured side-by-side within at least one flexible support member, preferably theJ are wholly or partially embedded in a single tape of plastics material.

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

Preferably, the or each bore extends substantially parallel to the axis of the extruded elongate body and the or each elongate reinforcing member is substantially parallel to the bore or bores, the axes of the bore or bores and of the reinforcing member or members lying in substantially common plane. Where the optical cable includes two or more elongate reinforcing members, the or each bore or at least two bores may be located between two reinforcing members. The or each bore may lie wholly in the space bounded by two planes located on opposite sides of two reinforcing members and touching both members so that the optical fibres are protected by the reinforcing members against crushing.

Preferably, as is described and claimed in our Patent No. 1480206, where the optical cable includes two separate reinforcing members embedded in the extruded elongate body and arranged on opposite sides of and substantially parallel to the bore with their axes and the axis of the bore lying in a substantially common plane, the transverse cross-section of the extruded elongate body is such that, over that part of the cable extending between planes substantially perpendicular to said common plane and passing through the axes of the reinforcing members, the width of the body is substantially less than the width of the body measured in said perpendicular planes.

The or each bore may be of any transverse cross-sectional shape but preferably the cross-sectional shape of the or each bore is of an elongate form with the or each flexible support member so housed loosely in the bore that the axes of the optical bundles and/or separate optical fibres lie in a plane or planes that is or are parallel or approximately parallel to the major transverse dimension of the bore.

The or each reinforcing member is of such a material and of such a cross-sectional area having regard to the material or materials and cross-sectional area of the optical bundle or bundles and/or of the separate optical fibre or fibres that the strain otherwise imparted to the or each optical fibre when the cable is stressed in such a way as to tend to subject the or any optical fibre to a tensile force is eliminated or reduced at least to a substantial extent by the reinforcing member or members.

The or each elongate reinforcing member may be a single solid element or, with a view to making the optical cable as flexible as possible, the or each reinforcing member may comprise a plurality of elements stranded together. The or each element is preferably of steel, carbon fibre or any other suitable material having the necessary Young's Modulus.

The optical cable of the present invention may include any one or more of the optional features of the optical cables described and claimed in the Complete Specifications of our Patents Nos. 1479426 and 1480206.

The invention is further illustrated, by way of example, by the accompanying drawing which shows diagrammatic transverse cross-sectional views of six optical fibre arrays for incorporation in an optical cable and of two preferred forms of optical cable.

The optical fibre arrays shown in Figure 1 to 6 are drawn on a greatly enlarged scale to clarify their structure. The array shown in Figure 1 comprises a flexible tape 1 of plastics material which has secured by adhesive to one of its major surfaces four optical fibres 2 which are spaced apart and extend substantially parallel to the axis of the tape. In the array shown in Figure 2 four optical fibres 12 are sandwiched between and secured by adhesive to the adjacent surfaces of two flexible tapes 11, 13 of plastics material. The array shown in Figure 3 comprises a flexible plastics tape 21 which, viewed in transverse crosssection, is so corrugated that it has a plurality of troughs 24 extending along its length in each of which an optical fibre 22 is secured by adhesive. The array shown in Figure 4 differs from that shown in Figure 3 in that optical fibres 32 secured by adhesive in the troughs 34 of a flexible corrugated plastics tape 31 are also secured by adhesive to a major surface of a flexible plastics tape 33 which effectively closes the troughs 34 and is secure by adhesive to the peaks 35 defining the troughs. In the array shown in Figure 5, optical fibres 42 are sandwiched between, and secured by adhesive in the troughs 44, 48 or, two flexible corrugated plastics tapes 41, 47 whose peaks 45, 49 are secured together by adhesive. The array shown in Figure 6 comprises a plastics tape 51 in which four optical fibres 52 extending side-by-side are wholly embedded.

The optical cables shown in Figures 7 and 8 are drawn on a smaller scale than the optical fibre arrays shown in Figures 1 to 6.

The optical cable shown in Figure 7 comprises an extruded plastics elongate body 61 of dum-bell shaped cross-section in which two steel reinforcing wires 62 are embedded on opposite sides of the two bores 63, each of an elongate transverse cross-section, the axes of the bores and reinforcing wires lying in a common plane.

Loosely housed in each bore 62 is an optical fibre array 64 similar to that illustrated in Figure 3. The external surface of the body 61 carries a longitudinally extending rib 65 to provide for ready identification of any optical fibre of the arrays 64.

The optical cable shown in Figure 8 comprises an extruded plastics elongate body 71 of dumb-bell shaped cross-section in which two steel reinforcing wires 72 are embedded on opposite sides of a single bore 73 of elongate transverse cross-section, the axes of the bore and reinforcing wires lying in a common plane. Loosely housed in the bore 73 is an optical fibre array 74 similar to that illustrated in Figure 1. To provide for ready identification of any optical fibre of the array 74, the external surface of the body 71 carries a longitudinally extending rib 75.

WHAT WE CLAIM IS: 1. An optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres secured side-by-side on or within at least one substantially flat flexible support member which is housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

2. An optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres secured by adhesive side-by-side to one surface of a flexible tape which is housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

3. An optical cable is claimed in Claim 2, wherein, viewed in transverse cross-section, the tape is corrugated so that it has a plurality of troughs extending along its length and an optical bundle or optical fibre is secured in each of some or all of said troughs.

4. An optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres sandwiched between and secured by adhesive side-by-side to the adjacent surfaces of two flexible tapes which are housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

5. An optical cable as claimed in Claim 4,

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. stranded together. The or each element is preferably of steel, carbon fibre or any other suitable material having the necessary Young's Modulus. The optical cable of the present invention may include any one or more of the optional features of the optical cables described and claimed in the Complete Specifications of our Patents Nos. 1479426 and 1480206. The invention is further illustrated, by way of example, by the accompanying drawing which shows diagrammatic transverse cross-sectional views of six optical fibre arrays for incorporation in an optical cable and of two preferred forms of optical cable. The optical fibre arrays shown in Figure 1 to 6 are drawn on a greatly enlarged scale to clarify their structure. The array shown in Figure 1 comprises a flexible tape 1 of plastics material which has secured by adhesive to one of its major surfaces four optical fibres 2 which are spaced apart and extend substantially parallel to the axis of the tape. In the array shown in Figure 2 four optical fibres 12 are sandwiched between and secured by adhesive to the adjacent surfaces of two flexible tapes 11, 13 of plastics material. The array shown in Figure 3 comprises a flexible plastics tape 21 which, viewed in transverse crosssection, is so corrugated that it has a plurality of troughs 24 extending along its length in each of which an optical fibre 22 is secured by adhesive. The array shown in Figure 4 differs from that shown in Figure 3 in that optical fibres 32 secured by adhesive in the troughs 34 of a flexible corrugated plastics tape 31 are also secured by adhesive to a major surface of a flexible plastics tape 33 which effectively closes the troughs 34 and is secure by adhesive to the peaks 35 defining the troughs. In the array shown in Figure 5, optical fibres 42 are sandwiched between, and secured by adhesive in the troughs 44, 48 or, two flexible corrugated plastics tapes 41, 47 whose peaks 45, 49 are secured together by adhesive. The array shown in Figure 6 comprises a plastics tape 51 in which four optical fibres 52 extending side-by-side are wholly embedded. The optical cables shown in Figures 7 and 8 are drawn on a smaller scale than the optical fibre arrays shown in Figures 1 to 6. The optical cable shown in Figure 7 comprises an extruded plastics elongate body 61 of dum-bell shaped cross-section in which two steel reinforcing wires 62 are embedded on opposite sides of the two bores 63, each of an elongate transverse cross-section, the axes of the bores and reinforcing wires lying in a common plane. Loosely housed in each bore 62 is an optical fibre array 64 similar to that illustrated in Figure 3. The external surface of the body 61 carries a longitudinally extending rib 65 to provide for ready identification of any optical fibre of the arrays 64. The optical cable shown in Figure 8 comprises an extruded plastics elongate body 71 of dumb-bell shaped cross-section in which two steel reinforcing wires 72 are embedded on opposite sides of a single bore 73 of elongate transverse cross-section, the axes of the bore and reinforcing wires lying in a common plane. Loosely housed in the bore 73 is an optical fibre array 74 similar to that illustrated in Figure 1. To provide for ready identification of any optical fibre of the array 74, the external surface of the body 71 carries a longitudinally extending rib 75. WHAT WE CLAIM IS:

1. An optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres secured side-by-side on or within at least one substantially flat flexible support member which is housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

5. An optical cable as claimed in Claim 4,

wherein, viewed in transverse cross-section, one or each of said two tapes is corrugated so that it has a plurality of troughs extending along its length and an optical bundle or optical fibre is secured in each of some or all of said troughs.

6. An optical cable as claimed in Claim 1, wherein the or each 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 an optical bundle and/or separate optical fibre is housed and wherein the optical bundles and/or separate optical fibres are secured within the flexible support member but are capable of limited movement within the troughs in which they lie.

7. An optical cable as claimed in any one of Claims 2 to 6, wherein the or each tape is of a metal or metal alloy.

8. An optical cable as claimed in any one of Claims 2 to 6, wherein the or each tape is of paper or plastics material.

9. An optical cable as claimed in any one of Claims 2 to 6, 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.

10. An optical cable as claimed in Claim 9, wherein the optical fibres are of a silicabased material and the or each tape is of steel.

11. An optical cable comprising an extruded elongate body of rubber or plastics material having at least one bore extending lengthwise in the body; two or more optical bundles as hereinbefore defined and/or separate optical fibres wholly or partially embedded side-by-side in a flexible tape of plastics material housed loosely in the bore or in at least one of the bores; and, embedded in said extruded elongate body and arranged side-by-side with said bore or bores, at least one separate elongate reinforcing member.

12. An optical cable as claimed in any one of the preceding Claims, wherein the surface of the extruded elongate body carries a longitudinally extending datum mark for facilitating initial identification of the optical bundles and/or optical fibres.

13. An optical cable as claimed in any one of the preceding Claims, wherein the flexible support member or at least one of the flexible support members carries a longitudinally extending datum mark and/or at least one of the optical bundles and/or optical fibres is assymmetrically positioned with respect to the or each other optical bundle and/or optical fibre so that it constitutes a longitudinally extending datum.

14. An optical cable as claimed in any one of the preceding Claims, wherein the cross-sectional shape of the or each bore is of an elongate form with the or each flexible tape or other flexible support member so loosely housed in the bore that the axes of the optical bundles and/or separate optical fibres lie in a plane or planes that is or are parallel or approximately parallel to the major transverse dimension of the bore.

15. An optical cable as claimed in any one of the preceding Claims, wherein the or each bore extends substantially parallel to the axis of the extruded elongate body and the or each elongate reinforcing member is substantially parallel to the bore or bores, the axes of the bore or bores and of the reinforcing member or members lying in a substantially common plane.

16. An optical cable as claimed in Claim 15 in which the optical cable includes two or more elongate reinforcing members, the or each bore or at least two bores being located between two reinforcing members.

17. An optical cable as claimed in Claim 16, wherein the or each bore lies wholly in the space bounded by two planes located on opposite sides of two reinforcing members and touching both members.

18. An optical cable as claimed in Claim 16 or 17 in which the optical cable includes two elongate reinforcing members, wherein the transverse cross-section of the extruded elongate body is such that, over that part of the cable extending between planes substantially perpendicular to said common plane and passing through the axes of the reinforcing members, the width of the body is substantially less than the width of the body measured in said perpendicular planes.

19. An optical cable as claimed in any one of the preceding Claims, wherein the or each reinforcing member comprises a plurality of elements stranded together;

20. An optical cable as claimed in Claim 1, wherein the bore or at least one of the bores loosely houses an optical fibre array substantially as hereinbefore described with reference to and as shown in any one of Figures 1 to 6 of the accompanying drawing.

21. An optical cable substantially as hereinbefore described with reference to and as shown in Figure 7 or 8 of the accompanying drawing.