GB2215081A

GB2215081A - Optical fibre cable

Info

Publication number: GB2215081A
Application number: GB8803162A
Authority: GB
Inventors: Stuart Robert Barnes; Ian Houghton; Andrew Thomas Summers
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1988-02-11
Filing date: 1988-02-11
Publication date: 1989-09-13
Anticipated expiration: 2008-02-11
Also published as: GB8803162D0; GB2215081B

Abstract

A communications cable comprises a strength member 1 and a plurality of packages 2 stranded around the strength member 1 and each package including optical fibres 7 each package being usable individually as a cable. Each package may comprise a tubular member reinforced with tensile strength elements 4 with the fibres packaged as ribbons inside the substantially rectangular compartment 5 of strain member tubes 3. 8 is a paper tape and 9 an extended plastic sheath. <IMAGE>

Description

OPTICAL FIBRE CABLE WITH HIGH FIBRE COUNT.

This invention relates to an optical fibre cable capable of incorporating a large number of optical fibres.

British Patent specification No. 1487464 describes a loose tube optical fibre cable in which the fibres are individually tubed, or a plurality of such fibres are contained in a tube, and these tubes fibres are laid up around a central strength member and subsequently encased in a sheath.

The loose tube arrangement enables the fibres to be easily handled during the manufacturing process.

According to the present invention there is provided a communication cable comprising a strength member and a plurality of packages each including optical fibres and each useable individually as a cable.

In a preferred embodiment each package comprises a tube having a logitudinal compartment of generally rectangular cross section and containing a stack of ribbon elements, each ribbon element containing a plurality of fibres. Preferably each tube has means reinforcing it, such as wires or high tensile plastics filaments embedded therein.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings in which Figure 1 shows a cross section of a high fibre count cable according to an embodiment of the present invention, Figure 2 shows schematically a technique for making the cable, and Figure 3 shows schematically the technique for making each package of the cable.

Referring to Figure 1 of the drawings the cable comprises a central stranded-wire strength member 1.

Around the strength member 1 are six packages such as 2 each having a strain member tube 3 which in this embodiment is reinforced by tensile strength elements 4.

Each tube has a logitudinal compartment 5 of generally rectangular cross section containing a stack 6 of ribbons such as 7. Each ribbon 7 incorporates a plurality of fibres and there could be as many as twelve fibres per ribbon.

These ribbon elemetns are in this embodiment not glued together or otherwise held together but are loosely floating within the compartment 5.

The length of the ribbon elements 7 is similar to the length of the strain member tube 3 although there may be a slight excess length. However with improved fibre strength now envisaged, particularly with modern fibre encapsulation materials, an excess length of fibre within the strain member tube may not be necessary.

The compartment 5 is preferably filled with a water blocking material such as Hyvis, Rheogel, or peroleum jelly.

Around the strain member tubes is wrapped a paper tape 8 and a plastic sheath 9 is extruded over the tape 8. In manufacturing the cable described, tne strength member 1 would be fed through a stranding machine, and this is shown in Figure 2. The centraL strength number 1 is drawn from a drum 1A through a stranding machine 2B from which packages 2 are drawn from drums such as 2A. The strength member 1 with the stranded packages 2 around it then passes through a tubing stage 8B in which a paper tape 8 is drawn from a reel 8A and formed as a tube around the packages 2.

Alternatively the tape could be wrapped helically around the packages 2.

The sub-assembly then enters an extrusion head 9A and the plastics sheath 9 is extruded over the tape 8 and the finished cable wound onto a storage drum 10.

Although not shown in Figure 2 there would be a water blocking injection station to ensure that the interstices 11 (see Figure 1) are filled with water blocking compound. This could be achieved by wiping the packages 2 with water blocking compound before they enter the stranding machine and/or after they leave the stranding machine. This is indicated generally by the reference numerals 12 in Figure 2.

Referring now to Figure 3 the packages are manufactured by feeding ribbon elements 6 from storage reels such as 6A through a tapered guide 30 so that they are lying in close side-by-side relationship.

This relationship is maintained through guide rollers 31 where the ribbons enter an extrusion head 32.

This extrusion head extrudes a tubular package having the configuration of the strain member 3 shown in Figure 1 and also the tensile strength elements 4 are fed into the extrusion head from storage reels such as 4A so that these tensile strength elements 4 become embedded in the strain member tube 3.

The resulting package 2 is wound onto a storage drum 2A.

The cable described has the advantage of providing a very high fibre count. For example each package is shown in the preferred embodiment as containing thirty-two fibres and with six such packages, and that provides a fibre count of just under two hundred. The main advantage of the cable in use, is that the individual packages 2 can be used as cables in their own right. Thus the cable can be laid over a distance of one or two km, for example, and then the individual packages can be released from the cable and taken a distance of lOOm or more to the subscriber's premises, the tensile and bending stresses on each package being borne substantially by its own strain member tube. In this way it is possible to provide a cable which provides both the function of a long distance cable and those of a relatively short cable.

The cable can be drawn into ducts or with suitable armouring which is not shown in Figure 1 could be buried in the ground.

The optical fibre ribbon elements are preferably manufactured in accordance with teaching of our published patent specification No. 2181271.

Claims

CLAIMS.

1. A communications cable comprising a tensile strength member and a plurality of packages each including optical fibres and each usable individually as a cable.

2. A cable as claimed in claim 1, wherein each packages comprises a strain member tube containing at least one ribbon optical fibre element.

3. A calbe as claimed in claim 2, wherein each strain member tube incorporates tensile strength elements embedded therein.

4. A cable as claimed in claim 2 or 3, wherein each strain member tube has a rectangular cross section conpartment containing said ribbon elements.

5. A cable as claimed in any preceding claim comprising a central strength member, said plurality of packages being stranded around said strength member and an outer protective plastic sheath extruded over said packages.

6. A calbe as claimed in any preceding claim wherein the interstices of the cable contain a water blocking gel-like material.

7. A cable substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

8. A method of manufacturing a communications cable comprising providing a strength member and stranding around the strength member a plurality of packages each including optical fibres and each usable individually as a cable, and providing means around the packages to hold them to the strength member.

9. A method as claimed in claim 8 wherein each package comprises a cylindrical tube having a central compartment having a substantially rectangular cross section, and wherein said tube is extruded at the same time as optical fibres are introduced into the central compartment of the tube.

10. A method of manufacturing an optical fibre cable substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.