GB1583276A

GB1583276A - Optical cables

Info

Publication number: GB1583276A
Application number: GB2046277A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1978-05-16
Filing date: 1978-05-16
Publication date: 1981-01-21

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL CABLES (71) We, BIce 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 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 present invention an optical cable comprises a plurality of separately formed cable elements wound helically in one or more than one layer around an elongate central core and, surrounding the plurality of cable elements, an outer protective sheath, wherein each of the cable elements comprises an extruded elongate body of rubber or plastics material that has a transverse cross-section approximating to a sector of an annulus and wherein each of some or all of the cable elements has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side by side with the bore, at least one elongate reinforcing member.

Preferably the axes of the bore or bores and of the reinforcing member or members of each of said cable elements lie along the circumferential surface of an imaginary cylinder of circular cross-section whose axis lies along the longitudinal axis of the cable.

Said cable elements may be of substantially identical construction and, for example, each may include a single bore loosely housing at least one separate optical fibre and/or at least one optical bundle and two elongate reinforcing members, one on each side of the bore, or each may include a single elongate reinforcing member and, on each side of the reinforcing member, a bore loosely housing at least one separate optical fibre and/or at least one optical bundle. In all cases, preferably in each of said cable elements the diameter of the or each reinforcing member may be greater than the largest transverse dimension of the or each bore.

The or each bore of each of said cable elements may be lined by at least one tape of metal or metal alloy.

By the expression "optical bundle" is meant a group of optical fibres or a group of fibres including at least one optical fibre and at least one non-optical reinforcing fibre or reinforcing elongate element. Each optical fibre of the optical bundle may be used independently as a separate light guide, each with its own modulated light source and a detector, or a plurality of optical fibres of a bundle may be used together as a single light guide.

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

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

The or each elongate reinforcing member d each of said cable elements will be of such a material and of such a cross-sectional area having regard to the material or materials and cross-sectional area of the separate optical fibre or fibres and/or the optical bundle or bundles of the cable element that the strain otherwise imparted to the or each optical fibre of the cable element when the optical cable is stressed in such a way as to tend to subject the or any optical fibre of the cable element to a tensile force is eliminated or reduced at least to a substantial extent by the reinforcing member or mem bers. Thus, the protection afforded the separate optical fibre or fibres and/or optical bundle or bundles of a cable element by its associated reinforcing member or members against strain when the optical cable is stressed is independent of the other cable elements.

Where the plurality of cable elements are helically wound in two or more layers around the elongate central core, preferably the directions of lay of adjacent layers are of opposite hand.

Where some only of the plurality of cable elements comprise an extruded elongate body of rubber or plastics material having, throughout its length, a bore in which at least one separate optical fibre and/or at least one optical bundle is loosely housed, at least one of the other cable elements may comprise an extruded elongate body of rubber or plastics material which has a transverse cross-section approximating to a sector of an annulus and in which is embedded one or more than one elongate electric conductor.

The elongate central core around which the plurality of cable elements are helically wound may take any convenient form. In one embodiment it may comprise one or more than one elongate reinforcing member and/or one or more than one elongate insulated electric conductor. In another embodiment the elongate central core may consist of a single tube of rubber or plastics material which is of substantially circular cross-section and in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle. In yet another embodiment the elongate central core may comprise two or more cable elements each comprising an extruded body of rubber or plastics material that has a transverse cross-section approximating to a sector of a circle and that has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side-by-side with the bore, at least one elongate reinforcing member. In still another embodiment the elongate central core may comprise a single tube which is of substantially circular cross-section and which loosely houses at least one extruded elongate body of rubber or plastics material that has a bore in which is loosely housed a separate optical fibre and/or optical bundle and, embedded in the body alongside the bore, at least one reinforcing member.

The outer protective sheath is preferably an extruded body of rubber or plastics material and, to bind the plurality of helically wound cable elements together prior to and during extrusion of the sheath, preferably at least one layer of helically wound tape of insulating material is applied directly over the layer or outermost layer of cable elements.

In some circumstances, at least one stranded layer of armouring wires may be provided under or over the outer protective sheath.

Alternatively, a reinforcing wall comprising at least one layer comprising one or more than one elongate element of reinforcing material may be wholly or partially embedded in or may surround the outer protective sheath.

The elongate element or elongate elements of reinforcing material may be wound helically about the outer protective sheath or they may extend lengthwise of, and preferably substantially parallel to, the axis of the cable. Where the reinforcing elongate element or elongate elements of the reinforcing wall are wound helically about the outer protective sheath, preferably the reinforcing wall comprises at least two layers of elongate elements or reinforcing material wound helically about the sheath, the directions of lay of adjacent layers being of opposite hand. The helically wound elongate elements of adjacent layers may be interwoven to form a braided sleeve of reinforcing material and in this case the braided sleeve may be partially or wholly embedded in the outer protective sheath.

Alternative to or additional to the reinforcing wall, the outer protective sheath may be surrounded by an oversheath of an extruded rubber or plastics material having a low friction coefficient, such as nylon, and, in this case, preferably the outer protective sheath and oversheath are separated by a moisture barrier in the form of a continuous layer of tape or metal or metal alloy, one or each surface of the tape preferably carrying a layer of rubber or plastics material which is bonded to the outer protective sheath or oversheath, as the case may be. Where an oversheath is provided, a reinforcing wall may be embedded in the oversheath.

Preferably, each of some or all of a plurality of elongate elements of reinforcing material embedded at spaced positions around the outer protective sheath or the oversheath and extending substantially lengthwise of the cable has, in the element, undulations, preferably radially extending undulations, that serve to improve the mechanical bonding of the element within the sheath and the flexibility of the cable.

The elongate elements of reinforcing material having undulations therein may each comprise a single wire or a plurality of wires stranded together, the wire or strand being crimped at spaced positions along its length to form undulations but, with a view to maintaining the weight of the cable as low as possible, preferably each of these elongate elements comprises a bunch of - compacted yams of glass fibre or other inorganic reinforcing material.

Where the undulating elongate reinforcing elements are bunches of compacted yarns of glass fibre or other inorganic reinforcing material, preferably these yarns are not preimpregnated with an agent for bonding to the material of the oversheath and preferably, also, there is substantially no air in the interstices between the elementary filaments of the bunch. Each bunch may consist of elements of glass fibre or of other inorganic material of the same kind and/or thickness or it may consist of a combination of elements of different kinds from one another, for example, single or double yarns and/or of different thicknesses from one another.

The layer or layers of helically wound cable elements may be surrounded by one or more than one stranded layer of insulated electric conductors. Preferably the or each layer of insulated conductors will be under the outer protective sheath but, where an oversheath is provided, the or each layer of insulated conductors may lie between the outer protective sheath and the oversheath.

The invention is further illustrated by a description, by way of example, of a preferred optical cable with reference to the accompanying drawing which shows a diagrammatic transverse cross-sectional view of the cable, drawn on an enlarged scale.

Referring to the drawing, the optical cable comprises a plurality of separately formed cable elements 11 helically wound in a single layer around an elongate central core 1 and, surrounding the layer of cable elements, an outer protective sheath 21.

The central core 1 comprises two pairs of insulated electric conductors 2 and 3, each pair having the same length of pair twist. If desired, one pair of conductors 2 may be a video pair and the pair of conductors 3 may be an audio pair. Each insulated conductor 2 comprises a copper core of diameter 0.9 mm and a polyethylene insulating covering of 0.55 mm radial thickness; each insulated conductor 3 comprises a copper core of diameter 0.5 mm and a polyethylene insulating covering of 0.4 mm radial thickness.

Each cable element 11 comprises an elongate extruded body 12 of polyethylene having a transverse cross-section approximating to a sector of an annulus. The layer of cable elements 11 has an internal diameter of 4.0 mm and external diameter of 12.0 mm. Each extruded body 12 has embedded in the body and extending throughout its length a steel reinforcing wire 14 and, on each side of the wire, is a bore 15 in which is loosely housed an optical fibre 16. The axes of the wires 14 and bores 15 lie along the circumferential surface of an imaginary cylinder of circular cross-section whose axis lies along the longitudinal axis of the cable.

Each wire 14 has a diameter of 1.3 mm, each bore 15 has a diameter of 1.0 mm and each optical fibre has a diameter of 62.5cm. The cable elements 11 are bound together by a helically lapped paper tape 17.

The outer protective sheath 21 is an extruded body of polyethylene. Embedded in the sheath 21 at circumferentially spaced positions is a plurality of elongate reinforcing members 22 each comprising a bunch of compacted yarns of glass fibre having, in the brunch, radially extending undulations that serve to improve the mechanical bonding of the bunch within the sheath 21 and the flexibility of the cable.

WHAT WE CLAIM IS: 1. An optical cable comprising a plurality of separately formed cable elements wound helically in one or more than one layer around an elongate central core and, surrounding the plurality of cable elements, an outer protective sheath, wherein each of the cable elements comprises an extruded elongate body of rubber or plastics material that has a transverse cross-section approximating to a sector of an annulus and wherein each of some or all of the cable elements has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side by side with the bore, at least one elongate reinforcing member.

2. An optical cable comprising a plurality of separately formed cable elements wound helically in one or more than one layer around an elongate central core and, surrounding the plurality of cable elements, an outer protective sheath, wherein each of the cable elements comprises an extruded elongate body of rubber or plastics material that has a transverse cross-section approximating to a sector of an annulus and wherein each of some or all of the cable elements has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side by side with the bore, at least one elongate reinforcing member, the axes of the bore or bores and of the reinforcing member or members of each of said cable elements lying along the circumferential surface of an imaginary cylinder of circular cross-section whose axis lies along the longitudinal axis of the cable.

3. An optical cable as claimed in Claim 1 or 2, wherein the cable elements are of substantially identical construction.

4. An optical cable as claimed in any one of the preceding Claims, wherein each of some or all of the cable elements includes a

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of - compacted yams of glass fibre or other inorganic reinforcing material. Where the undulating elongate reinforcing elements are bunches of compacted yarns of glass fibre or other inorganic reinforcing material, preferably these yarns are not preimpregnated with an agent for bonding to the material of the oversheath and preferably, also, there is substantially no air in the interstices between the elementary filaments of the bunch. Each bunch may consist of elements of glass fibre or of other inorganic material of the same kind and/or thickness or it may consist of a combination of elements of different kinds from one another, for example, single or double yarns and/or of different thicknesses from one another. The layer or layers of helically wound cable elements may be surrounded by one or more than one stranded layer of insulated electric conductors. Preferably the or each layer of insulated conductors will be under the outer protective sheath but, where an oversheath is provided, the or each layer of insulated conductors may lie between the outer protective sheath and the oversheath. The invention is further illustrated by a description, by way of example, of a preferred optical cable with reference to the accompanying drawing which shows a diagrammatic transverse cross-sectional view of the cable, drawn on an enlarged scale. Referring to the drawing, the optical cable comprises a plurality of separately formed cable elements 11 helically wound in a single layer around an elongate central core 1 and, surrounding the layer of cable elements, an outer protective sheath 21. The central core 1 comprises two pairs of insulated electric conductors 2 and 3, each pair having the same length of pair twist. If desired, one pair of conductors 2 may be a video pair and the pair of conductors 3 may be an audio pair. Each insulated conductor 2 comprises a copper core of diameter 0.9 mm and a polyethylene insulating covering of 0.55 mm radial thickness; each insulated conductor 3 comprises a copper core of diameter 0.5 mm and a polyethylene insulating covering of 0.4 mm radial thickness. Each cable element 11 comprises an elongate extruded body 12 of polyethylene having a transverse cross-section approximating to a sector of an annulus. The layer of cable elements 11 has an internal diameter of 4.0 mm and external diameter of 12.0 mm. Each extruded body 12 has embedded in the body and extending throughout its length a steel reinforcing wire 14 and, on each side of the wire, is a bore 15 in which is loosely housed an optical fibre 16. The axes of the wires 14 and bores 15 lie along the circumferential surface of an imaginary cylinder of circular cross-section whose axis lies along the longitudinal axis of the cable. Each wire 14 has a diameter of 1.3 mm, each bore 15 has a diameter of 1.0 mm and each optical fibre has a diameter of 62.5cm. The cable elements 11 are bound together by a helically lapped paper tape 17. The outer protective sheath 21 is an extruded body of polyethylene. Embedded in the sheath 21 at circumferentially spaced positions is a plurality of elongate reinforcing members 22 each comprising a bunch of compacted yarns of glass fibre having, in the brunch, radially extending undulations that serve to improve the mechanical bonding of the bunch within the sheath 21 and the flexibility of the cable. WHAT WE CLAIM IS:

1. An optical cable comprising a plurality of separately formed cable elements wound helically in one or more than one layer around an elongate central core and, surrounding the plurality of cable elements, an outer protective sheath, wherein each of the cable elements comprises an extruded elongate body of rubber or plastics material that has a transverse cross-section approximating to a sector of an annulus and wherein each of some or all of the cable elements has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side by side with the bore, at least one elongate reinforcing member.

single bore loosely housing at least one separate optical fibre and/or at least one optical bundle and two elongate reinforcing members, one on each side of the bore.

5. An optical cable as claimed in any one of Claims 1 to 3, wherein each of some or all of the cable elements includes a single elongate reinforcing member and, on each side of the reinforcing member, a bore loosely housing at least one separate optical fibre and / or at least one optical bundle.

6. An optical cable as claimed in any one of the preceding Claims, wherein, in each of said cable elements, the diameter of the or each reinforcing member is greater than the largest transverse dimension of the or each bore.

7. An optical cable as claimed in any one of the preceding Claims, wherein the or each bore of each of said cable elements is lined by at least one tape of metal or metal alloy.

8. An optical cable as claimed in any one of the preceding Claims, wherein, in each of said cable elements, 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.

9. An optical cable as claimed in any one of the preceding Claims in which the plurality of cable elements are helically wound in two or more layers around the elongate central core, wherein the directions of lay of adjacent layers are of opposite hand.

10. An optical cable as claimed in any one of the preceding Claims in which some only of the plurality of cable elements comprise an extruded elongate body of rubber or plastics material having, throughout its length, a bore in which at least one separate optical fibre and/or at least one optical bundle is loosely housed, wherein at least one of the other cable elements comprises an extruded elongate body of rubber or plastics material which has a transverse cross-section approximating to a sector of an annulus and in which is embedded one or more than one elongate electric conductor.

11. An optical cable as claimed in any one of the preceding Claims, wherein the elongate central core consists of or includes at least one elongate reinforcing member.

12. An optical cable as claimed in any one of the preceding Claims, wherein the elongate central core consists of or includes at least one elongate insulated electric conductor.

13. An optical cable as claimed in any one of Claims 1 to 10, wherein the elongate central core is a single tube of rubber or plastics material which is of substantially circular cross-section and in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle.

14. An optical cable as claimed in any one of Claims 1 to 10, wherein the elongate central core comprises two or more cable elements each comprising an extruded body of rubber or plastics material that has a transverse cross-section approximating to a sector of a circle and that has, extending throughout its length, at least one bore in which is or are loosely housed at least one separate optical fibre and/or at least one optical bundle and, embedded in the body side-by-side with the bore, at least one elongate reinforcing member.

15. An optical cable as claimed in any one of Claims 1 to 10, wherein the elongate central core is a single tube, which is of substantially circular cross-section and which loosely houses at least one extruded elongate body of rubber or plastics material that has a bore in which is loosely housed a separate optical fibre and/or optical bundle and, embedded in the body alongside the bore, at least one reinforcing member.

16. An optical cable as claimed in any one of the preceding Claims, wherein at least one stranded layer of insulated electric conductors surrounds the layer or layers of helically wound cable elements.

17. An optical cable as claimed in any one of the preceding Claims, wherein the outer protective sheath is an extruded body of rubber or plastics material.

18. An optical cable as claimed in any one of the preceding Claims, wherein an oversheath of an extruded rubber or plastics material having a low friction coefficient surrounds the outer protective sheath.

19. An optical cable as claimed in Claim 1S, wherein the outer protective sheath and oversheath are separated by a moisture barrier in the form of a continuous layer of tape of metal or metal alloy, one or each surface of the tape carrying a layer of rubber or plastics material which is bonded to the outer protective sheath or oversheath, as the case may be.

20. An optical cable as claimed in any one of the preceding Claims, wherein at least one stranded layer of armouring wires underlies or overlies the outer protective sheath.

21. An optical cable as claimed in any one of Claims 1 to 19, wherein a reinforcing wall comprising at least one layer comprising one or more than one elongate element of reinforcing material is wholly or partially embedded in or surrounds the outer protective sheath or in the oversheath.

22. An optical cable as claimed in Claim 21, wherein each of some or all of a plurality of elongate elements embedded at spaced positions around the outer protective sheath or oversheath and extending lengthwise of the cable has, in the element, undulations that serve to improve the mechanical bonding of the element within the sheath and the flexibility of the cable.

23. An optical cable substantially as hereinbefore described with reference to and as shown in the accompanying drawing.