GB2183060A

GB2183060A - Optical fibre cable

Info

Publication number: GB2183060A
Application number: GB08626772A
Authority: GB
Inventors: Terence Hall; Alan James Peacock
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1985-11-15
Filing date: 1986-11-10
Publication date: 1987-05-28
Also published as: GB8626772D0; GB8528242D0

Abstract

An optical fibre cable has, within an outer sheath 4, a central plastics coated 2 strength member 1 spaced from the inner surface of the sheath 4 by at least one bead 3 extending helically around the coating 2, the fibres 5 also extending helically within the space formed around the coated strength member 1 by the bead or beads 3. The bead(s) 3 may be a separate member which may be bonded to the coating 2 or may be formed as an integral part of the coating 2. Some or all of the optical fibre bundles 5, 6 may be replaced by optical fibre ribbons. <IMAGE>

Description

SPECIFICATION Optical fibre cable This invention relates to optical fibre cables of the type in which a plurality of optical fibres are accommodated in a channel located within an outer sheath, which also accommodates one or more longitudinally extending strength members for preventing or reducing tensile forces on the fibres.

According to the invention such an optical cable comprises, within the outer sheath, a central longitudinally extending strength member having a coating of plastics material, and spaced from the inner surface of the sheath by at least one bead extending helically around the exterior of the coating, the fibres also extending in a helical manner around the coated strength member within said space.

The space thus provides the channel in which the optical fibres are accommodated, the dimensions of which will depend in part on the size of the bead or beads.

The bead or beads may be a separate member, which may be bonded to the plastics coating if desired, or may be formed as an integral part of the coating. The coating is conveniently extruded on to the strength member, which may be metallic or non-metallic, and the bead or beads in such a case may be extruded integrally with the coating.

The optical fibres may be disposed in a plurality of groups, which may either consist of bundles of fibres or fibres bonded together in the form of ribbons, each group of fibres preferably being encapsulated in a protective coating, which may be in the form of an extrudate of resilient foamed plastics material.

Preferably also the space between the coated strength member and the sheath which is not occupied by the groups of optical fibres contains a cushioning material which may also be in the form of a resilient foamed plastics material.

The cushioning material preferably effectively fills the interstices between the groups of fibres themselves, and also between the groups of fibres and the coated strength member and the sheath, so as to restrict or prevent the passage of water along the cable.

In some cases the space may also contain a water blocking powder.

In some cases the cable may incorporate, within the space between the coated strength member and the sheath, a plurality of layers of optical fibre bundles or ribbons, with layers of foamed plastics material or other suitable cushioning material between them.

One cable in accordance with the invention and a modification thereof will now be described by way of example with reference to Figs. 1 and 2 of the accompanying schematic drawing which represent transverse sections through the two different forms of cable.

The cable illustrated in Fig. 1 comprises a central longitudinally extending strength member 1, which may consist of stranded metal wires, Kevlar or other suitable material having a coating 2 of plastics material extruded around it. A helical bead 3 surrounds the plastics coating 2, the bead also being of plastics material, and conveniently being extruded as part of the coating, although in some cases it may be formed- as a separate member bonded to the coating. The assembly is surrounded by an extruded outer sheath 4, the helical bead maintaining the coated strength member centrally within the sheath.

The space between the coated strength member and the sheath contains a plurality, in this case ten, bundles of optical fibres 5 each encapsulated in a coating 6 of foamed plastics material, conveniently extruded around the fibres forming the bundle.

In the manufacture of the cable a layer 7 of foamed plastics or other suitably resilient material is conveniently applied around the coated strength member 1, 2 before the application of the optical fibre bundles 5, 6. A further layer 8 of foamed plastics or other material is then applied over the optical fibre bundles, and the cable core so formed is bound with a suitable tape 9 followed by the extruded outer sheath 4 which may, if desired incorporate a moisture barrier iaminate (not shown).

The layers 7, 8 effectively fill the space between the coated strength member 1, 2 and the sheath 4 not occupied by the optical fibre bundles 5, 6 and serve to provide a water blocked optical cable. If desired a water blocking powder may be applied between the surfaces of the layers 7, 8 to improve the water blocking performance.

In a modification illustrated in part in Fig. 2 the optical fibre bundles 5, 6 may be disposed in a plurality of layers as at 11, 12, 13 with additional layers 14, 15 of foamed plastics or other material placed between the layers of optical fibres, the cable being otherwise constructed in the same manner as that shown in Fig. 1.

In either of the cables illustrated in Fig. 1 or Fig. 2 some or all of the optical fibre bundles may be replaced by optical fibre ribbons.

1. An optical cable, of the type described, comprising, within the outer sheath, a central longitudinally extending strength member having a coating of plastics material, and spaced from the inner surface of the sheath by at least one bead extending helically around the exterior of the coating, the fibres also extending in a helical manner around the coated strength member within said space.

2. An optical cable according to Claim 1 wherein the bead or each said bead is constituted by a separate member.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical fibre cable This invention relates to optical fibre cables of the type in which a plurality of optical fibres are accommodated in a channel located within an outer sheath, which also accommodates one or more longitudinally extending strength members for preventing or reducing tensile forces on the fibres. According to the invention such an optical cable comprises, within the outer sheath, a central longitudinally extending strength member having a coating of plastics material, and spaced from the inner surface of the sheath by at least one bead extending helically around the exterior of the coating, the fibres also extending in a helical manner around the coated strength member within said space. The space thus provides the channel in which the optical fibres are accommodated, the dimensions of which will depend in part on the size of the bead or beads. The bead or beads may be a separate member, which may be bonded to the plastics coating if desired, or may be formed as an integral part of the coating. The coating is conveniently extruded on to the strength member, which may be metallic or non-metallic, and the bead or beads in such a case may be extruded integrally with the coating. The optical fibres may be disposed in a plurality of groups, which may either consist of bundles of fibres or fibres bonded together in the form of ribbons, each group of fibres preferably being encapsulated in a protective coating, which may be in the form of an extrudate of resilient foamed plastics material. Preferably also the space between the coated strength member and the sheath which is not occupied by the groups of optical fibres contains a cushioning material which may also be in the form of a resilient foamed plastics material. The cushioning material preferably effectively fills the interstices between the groups of fibres themselves, and also between the groups of fibres and the coated strength member and the sheath, so as to restrict or prevent the passage of water along the cable. In some cases the space may also contain a water blocking powder. In some cases the cable may incorporate, within the space between the coated strength member and the sheath, a plurality of layers of optical fibre bundles or ribbons, with layers of foamed plastics material or other suitable cushioning material between them. One cable in accordance with the invention and a modification thereof will now be described by way of example with reference to Figs. 1 and 2 of the accompanying schematic drawing which represent transverse sections through the two different forms of cable. The cable illustrated in Fig. 1 comprises a central longitudinally extending strength member 1, which may consist of stranded metal wires, Kevlar or other suitable material having a coating 2 of plastics material extruded around it. A helical bead 3 surrounds the plastics coating 2, the bead also being of plastics material, and conveniently being extruded as part of the coating, although in some cases it may be formed- as a separate member bonded to the coating. The assembly is surrounded by an extruded outer sheath 4, the helical bead maintaining the coated strength member centrally within the sheath. The space between the coated strength member and the sheath contains a plurality, in this case ten, bundles of optical fibres 5 each encapsulated in a coating 6 of foamed plastics material, conveniently extruded around the fibres forming the bundle. In the manufacture of the cable a layer 7 of foamed plastics or other suitably resilient material is conveniently applied around the coated strength member 1, 2 before the application of the optical fibre bundles 5, 6. A further layer 8 of foamed plastics or other material is then applied over the optical fibre bundles, and the cable core so formed is bound with a suitable tape 9 followed by the extruded outer sheath 4 which may, if desired incorporate a moisture barrier iaminate (not shown). The layers 7, 8 effectively fill the space between the coated strength member 1, 2 and the sheath 4 not occupied by the optical fibre bundles 5, 6 and serve to provide a water blocked optical cable. If desired a water blocking powder may be applied between the surfaces of the layers 7, 8 to improve the water blocking performance. In a modification illustrated in part in Fig. 2 the optical fibre bundles 5, 6 may be disposed in a plurality of layers as at 11, 12, 13 with additional layers 14, 15 of foamed plastics or other material placed between the layers of optical fibres, the cable being otherwise constructed in the same manner as that shown in Fig. 1. In either of the cables illustrated in Fig. 1 or Fig. 2 some or all of the optical fibre bundles may be replaced by optical fibre ribbons. CLAIMS

3. An optical cable according to Claim 2 wherein each said member is bonded to the plastics coating.

4. An optical cable according to Claim 1 wherein the bead of each such bead are formed as an integral part of the coating.

5. An optical cable according to Claim 4 wherein the coating is extruded onto the strength member.

6. An optical cable according to any of Claims 1 to 5 wherein the strength member is metallic.

7. An optical cable according to any of Claims 1 to 5 wherein the strength member is non-metallic.

8. An optical cable according to any preceding claim wherein the optical fibres are disposed in a plurality of groups.

9. An optical cable according to Claim 8 wherein each group of fibres is encapsulated in a protective coating.

10. An optical cable according to Claim 9 wherein the protective coating is in the form of an extrudate of a resilient foamed plastics material.

11. An optical cable according to Claim 8 wherein one or more of the groups of fibres consist of bundles of fibres.

12. An optical cable according to Claim 8 wherein on or more of the groups of fibres consist of fibres bonded together in the form of a ribbon.

13. An optical cable according to any of Claims 8 to 12 wherein the space between the coated strength member and the sheath which is not occupied by the groups of optical fibres contains a cushioning material.

14. An optical cable according to Claim 13 wherein the cushioning material is in the form of a resilient foamed plastics material.

15. An optical cable according to Claim 13 or 14 wherein the space also contains a water blocking powder.

16. An optical cable according to any of Claims 8 to 15 incorporating within the space between the coated strength member and the sheath, a plurality of layers of optical fibre bundles or ribbons, with layers of foamed plastics material or other suitable cushioning material between them.

17. An optical cable substantially as herein described with reference to Fig. 1 or Fig. 2 of the accompanying drawing.