GB2179470A

GB2179470A - Optical fibre cables

Info

Publication number: GB2179470A
Application number: GB08614644A
Authority: GB
Inventors: Ronald Yaxley Gill
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1985-08-21
Filing date: 1986-06-16
Publication date: 1987-03-04
Also published as: GB8520906D0; GB8614644D0

Abstract

An optical fibre cable incorporates a ribbon 4 of extruded plastic material within an outer cover 1, the ribbon having a plurality of closed channels 5 disposed side by side and containing one or more optical fibres, the wall of each channel being formed with at least one region 7 of reduced thickness to facilitate penetration of the channel and give access to the fibre or fibres. The external surface of the ribbon may have a groove 8 containing an electrical conductor 9. Alternatively the conductor 9 may be embedded in the channel wall. <IMAGE>

Description

SPECIFICATION Optical fibre cables This invention relates to optical fibre cables, that is to say cables of the kind incorporating one or more optical fibres within a protective cover.

It has been proposed to accommodate the fibres in a plurality of closed channels disposed side by side in a member of extruded plastics material having a generally flattened cross section, commonly called a ribbon, and to enclose the strip in a said protective cover, which may also be formed, at least partly, of an extruded plastics material.

In accordance with the invention in an optical fibre cable of this kind, in which a protective cover has within it at least one ribbon of extruded plastics material formed with a plurality of closed channels disposed side by side and containing one or more optical fibres, the wall of each channel which contains a said fibre or fibres is formed with at least one region of reduced thickness extending longitudinally along the channel thereby forming a line of weakness which facilitates penetration of the wall to give access to the channel.

The presence of a region of reduced thickness in the wall of the ribbon facilitates the formation of a slit in any desired position along a said channel whilst keeping the remainder of the channel, and the other channels, closed. This provides access to the interior of the channel at that position, and facilitates the removal of one or more fibres from the channel, for example for splicing to other fibres, as may be desired.

Thus, access to a channel may in some cases be obtained by tearing along such a line of weakness associated with the channel. If the region of reduced thickness is sufficiently thin, a slit may be formed in the wall by inward pressure immediately adjacent one side of the region.

Preferably, however, each said channel has at least two adjacent lines of weakness so that a complete strip can be readily removed from the ribbon to leave a slot providing access to the channel.

The fibre or fibres are preferably loosely accommodated with the respective channels which may, if desired, contain a water-repellant or water-blocking material, or other material in semi-solid or powdered form.

The cover which accommodates the ribbon is preferably formed in part by a tubular member of extruded plastics material surrounding or having embedded within it one or more elongate strength members of any suitable material in order to prevent any undue stress being placed on the ribbon, or the fibres contained therein, when the cable is subjected to a tensile force.

Preferably, also, the ribbon has a length which is greater than the length of the cover in which it is accommodated. For example it may be of undulating or helically coiled form, or may be twisted, either continuously in one direction, or with the direction of twist periodically reversed.

Between two adjacent channels the wall of the ribbon may have at least one groove formed in its external surface, the groove accommodating an electrical conductor, for example an insulated copper wire.

The mouth of the groove may be deformed following the introduction of the conductor therein to trap the conductor in the groove.

Alternatively one or more conductors may be embedded in the wall of the ribbon.

One cable in accordance with the invention will now be described by way of example with reference to Figs. 1 to 4 of the accompanying schematic drawings, in which Figures 1 and 2 illustrate a transverse section and a longitudinal section respectively of the cable, Figure 3 represents a perspective view of part of a strip element employed in the cable, and Figure 4 represents a transverse section of the element on an enlarged scale.

Referring to the drawings the cable comprises a protective cover 1 in the form of an extruded plastics tube having strength members 3 embedded in the tube wall.

The strength members may be formed of metal wire, high tensile strength plastics or any other suitable material, and may extend either longitudinally along the cover or helically around the cover axis. In some cases the direction of lay of helically extending strength members may be reversed periodically at spaced positions along the cover.

The cover 1 accommodates an extruded plastics ribbon 4 having a pair of closed channels 5 disposed side by side within the ribbon, and each containing a plurality of optical fibres as at 6. The wall of each channel is formed with two grooves 7 on its internal surface at diametrically opposite positions adjacent the respective broader faces of the ribbon, forming regions of reduced wall thickness.

In addition, the external surface of the ribbon 4 has a groove 8 formed along the central part of each of its two broader faces, between the two channels 5, each groove containing an insulated electrical conductor 9, the mouths 11 of the grooves 8 being of narrower width than the diameters of the insulated conductors so as to trap the conductors within the grooves.

The presence of the grooves 7, 8 results in two regions of reduced wall thickness associated with both sides of each of the two channels 5. This enables a strip of the wall over one or both of the two channels 5, on one or other side of the ribbon, as may be desired, to be readily torn back to expose the fibres 6 in the channel, as in Fig. 3, which shows strips 12 being torn baek over both channels.

In the manufacture of the ribbon, the mouths of the external grooves 8 are initially made sufficiently wide, as at 13 in Fig. 4, to allow the insertion of the conductors, and the ribbon material adjacent the mouths of the grooves is subsequently deformed under heat and applied pressure to partially close the groove mouths and thereby trap the conductors in the grooves. Fig. 4 shows one such conductor 9 already trapped as described.

The ribbon 4 is conveniently of undulating form within the cover 1 as shown in Fig. 2 in order to prevent undue stress being placed on the ribbon, and hence the fibres contained therein, when the cable is stretched to a limited degree under a tensile load, the fibres preferably lying approximately along the neutral axis of the ribbon.

In a modification the ribbon 4 may be coiled into helical form or it may be twisted about its axis, either continuously in one direction or in an oscillating manner.

In a further modification the insulated conductors 9, instead of being located in grooves, may be embedded in the wall of ribbon.

It will be appreciated that, although the embodiment described has only two channels 5, it could be formed with three or more such channels.

The outer cover 1 may have an inner lining, for example of metal foil, possibly with a plastic coating in one or each surface, acting as a moisture barrier, and may be surrounded by an outer sheath. Other modifications are clearly practicable.

Claims

1. An optical fibre cable, of the kind referred to in which a protective cover has within it at least one ribbon of extruded plastics material formed with a plurality of closed channels disposed side by side and containing one or more optical fibres, the wall of each channel which contains a said fibre or fibres is formed with at least one region of reduced thickness extending longitudinally along the channel thereby forming a line of weakness which facilitates penetration of the wall to give access to the channel.

2. An optical fibre cable according to Claim 1, wherein access to a channel is obtained by tearing along a line of weakness associated with the channel.

3. An optical fibre cable according to Claim 1, wherein the region of reduced thickness is sufficiently thin to enable a slit to be formed in the wall by inward pressure immediately adjacent one side of the region.

4. An optical fibre cable according to Claim 1, 2 or 3, wherein each said channel has at least two adjacent lines of weakness so that a complete strip can be readily removed from the ribbon to leave a slot providing access to the channel.

5. An optical fibre cable according to any preceding claim, wherein the fibre or fibres are loosely accommodated within the respective channels.

6. An optical fibre cable according to Claim 5, wherein said channels contain a water-repellant or water-blocking material, or other material in semi-solid or powdered form.

7. An optical fibre cable according to Claim 1, wherein the cover which accommodates the ribbon is formed in part by a tubular member of extruded plastics material surrounding or having embedded within it one or more elongate strength members capable of preventing any undue stress being placed on the ribbon, or the fibres contained therein, when the cable is subjected to a tensile force.

8. An optical fibre cable according to Claim 7, wherein the ribbon has a length which is greater than the length of the cover in which it is accommodated.

9. An optical fibre cable according to Claim 8, wherein the ribbon is of undulating or helically coiled form, or twisted, either continuously in one direction, or with the direction of twist periodically reversed.

10. An optical fibre cable according to any preceding claim, wherein between two adjacent channels the wall of the ribbon has at least one groove formed in its external surface, the groove accommodating an electrical conductor.

11. An optical fibre cable according to Claim 11, wherein the electrical conductor is an insulated copper wire.

12. An optical fibre cable according to Claim 10 or 11, wherein the mouth of the groove is deformed so as to trap the conductor in the groove.

13. An optical fibre cable according to any preceding claim, wherein one or more conductors are embedded in the wall of the ribbon.

14. An optical fibre cable substantially as herein described with reference to Figs. 1 to 4 of the accompanying drawing.