GB2170921A

GB2170921A - Optical cables

Info

Publication number: GB2170921A
Application number: GB08524321A
Authority: GB
Inventors: Raymond Sydney Ashpole; Terence Alexander Ketteringham
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1985-02-08
Filing date: 1985-10-02
Publication date: 1986-08-13
Also published as: GB8503244D0; GB8524321D0

Abstract

An optical cable comprises a central strength member 6 surrounded by a plurality of longitudinally-extending flexible strips 2 bent to form open channels, at least one of which accommodates one or more optical fibres 7, and a cover 9 which surrounds the strips and closes the mouths of the channels. The channels may incorporate a water blocking and/or a hydrogen absorbing material. <IMAGE>

Description

SPECIFICATION Optical cables This invention relates to optical cables of the type where one or more optical fibres are loosely accommodated within channels extending longitudinally along the cable and to a method of manufacturing such cables.

According to the invention an optical cable comprises a plurality of flexible strips extending longitudinally along the cable, each strip being curved across at least part of its width so as to form an open longitudinally-extending channel, at least one optical fibre loosely enclosed within at least one of the channels, a central strength member extending longitudinally between the strips which are arranged around it with the open side of the channel facing outwards, and a cover member surrounding the strips and closing off the channels.

In a preferred embodiment, the strips are arranged so that the walls of each channel contact the walls of the adjacent channels and conveniently the walls which are in contact are biassed against each other due to the resilience of the strip so as to give the cable rigidity. The strips are preferably tapes made of either paper or plastics, and must, of course, be sufficiently stiff to provide support for the cover member. The cover member is conveniently a flexible tape, for example, of Mylar, (i.e. polyethyleneterephthalate polyester film), wrapped around the channels in a helical fashion.

The central strength member may be made of steel or impregnated glass or Kevlar and the strips may be bonded thereto using an adhesive. Water blocking and/or hydrogen absorbing media can be incorporated in the channels and sheaths may be applied around the cover member if desired.

One embodiment of a cable according to the invention will now be more fully described with reference to the drawings of which: Figure 1 shows in diagrammatic form the steps required for making a cable according to the invention; and Figure 2 shows a cross-sectional view through such a cable.

The cable 1 is made by passing six tapes 2 made of thermoplastics material, such as Mylar, although only two are shown in Fig. 1, to a die 3 where the tapes 2 are formed into channels. As is shown in Fig. 1, the tapes 2 are fed via rollers 4 and are heated by directing hot air at them, as shown by arrows 5, so as to make them easier to bend.

A central strength member 6, made of stranded steel wires, is fed between the tapes 2 into the die 3 and optical fibres 7 are fed via rollers 8 on the outside of the tapes 2 so as to be positioned in the channels when they are formed in the die 3.

When the tapes 2 reach the die 3, they are curved transversely so as to form longitudinal channels as best shown in Fig. 2. The channels are arranged around the central strength member 6 with their open sides outermost.

Their walls are in contact with the adjacent wall, and, due to the resilience of the plastics material, they are biassed against each other so as to give rigidity to the complete cable.

Any desired number of optical fibres 7 may be provided within each channel, although only one per channel is shown in Fig. 2. The fibres 7 are fed into the die 3 at a controlled rate so that they are loose within the channels so that any stresses on the complete cable are not transferred to the fibres.

Immediately the channels are formed, with the optical fibres 7 within them, a Mylar tape 9 is wrapped around the channels so as to enclose them and keep the fibres within their respective channels. A plastics sheath 10 is then extruded around the tape 9 to further protect the cable, and the wrapped cable is twisted so as to make the channels have a helical twist along the cable, which can be reversed at intervals if desired.

It will be appreciated that the channels may have a water blocking and/or a hydrogen absorbing medium incorporated in them in any desired manner and that the channels, of which there can be any desired number, can be bonded both to each other and to the central strength member.

The above method of cable production is quite fast and the speed is mainly limited by the speed of the tape wrapping operation.

However, a great advantage, is that it can be stopped at any time to allow splicing of the tapes, strength member or optical fibres, and thus continuous cables can readily be produced.

1. An optical cable comprising a plurality of flexible strips extending longitudinally along the cable, each strip being curved across at least part of its width so as to form an open longitudinally-extending channel, at least one optical fibre loosely enclosed within at least one of the channels, a central strength member extending longitudinally between the strips which are arranged around it with the open side of the channel facing outwards, and a cover member surrounding the strips and closing off the channels.

2. An optical cable according to Claim 1, wherein the strips are arranged so that the walls of each channel contact the walls of the adjacent channels, with the walls which are in contact biassed against each other due to the resilience of the strips so as to give the cable rigidity.

3. An optical cable according to Claim 2, wherein the strips are tapes made from either paper or plastics, and are sufficiently stiff to

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical cables This invention relates to optical cables of the type where one or more optical fibres are loosely accommodated within channels extending longitudinally along the cable and to a method of manufacturing such cables. According to the invention an optical cable comprises a plurality of flexible strips extending longitudinally along the cable, each strip being curved across at least part of its width so as to form an open longitudinally-extending channel, at least one optical fibre loosely enclosed within at least one of the channels, a central strength member extending longitudinally between the strips which are arranged around it with the open side of the channel facing outwards, and a cover member surrounding the strips and closing off the channels. In a preferred embodiment, the strips are arranged so that the walls of each channel contact the walls of the adjacent channels and conveniently the walls which are in contact are biassed against each other due to the resilience of the strip so as to give the cable rigidity. The strips are preferably tapes made of either paper or plastics, and must, of course, be sufficiently stiff to provide support for the cover member. The cover member is conveniently a flexible tape, for example, of Mylar, (i.e. polyethyleneterephthalate polyester film), wrapped around the channels in a helical fashion. The central strength member may be made of steel or impregnated glass or Kevlar and the strips may be bonded thereto using an adhesive. Water blocking and/or hydrogen absorbing media can be incorporated in the channels and sheaths may be applied around the cover member if desired. One embodiment of a cable according to the invention will now be more fully described with reference to the drawings of which: Figure 1 shows in diagrammatic form the steps required for making a cable according to the invention; and Figure 2 shows a cross-sectional view through such a cable. The cable 1 is made by passing six tapes 2 made of thermoplastics material, such as Mylar, although only two are shown in Fig. 1, to a die 3 where the tapes 2 are formed into channels. As is shown in Fig. 1, the tapes 2 are fed via rollers 4 and are heated by directing hot air at them, as shown by arrows 5, so as to make them easier to bend. A central strength member 6, made of stranded steel wires, is fed between the tapes 2 into the die 3 and optical fibres 7 are fed via rollers 8 on the outside of the tapes 2 so as to be positioned in the channels when they are formed in the die 3. When the tapes 2 reach the die 3, they are curved transversely so as to form longitudinal channels as best shown in Fig. 2. The channels are arranged around the central strength member 6 with their open sides outermost. Their walls are in contact with the adjacent wall, and, due to the resilience of the plastics material, they are biassed against each other so as to give rigidity to the complete cable. Any desired number of optical fibres 7 may be provided within each channel, although only one per channel is shown in Fig. 2. The fibres 7 are fed into the die 3 at a controlled rate so that they are loose within the channels so that any stresses on the complete cable are not transferred to the fibres. Immediately the channels are formed, with the optical fibres 7 within them, a Mylar tape 9 is wrapped around the channels so as to enclose them and keep the fibres within their respective channels. A plastics sheath 10 is then extruded around the tape 9 to further protect the cable, and the wrapped cable is twisted so as to make the channels have a helical twist along the cable, which can be reversed at intervals if desired. It will be appreciated that the channels may have a water blocking and/or a hydrogen absorbing medium incorporated in them in any desired manner and that the channels, of which there can be any desired number, can be bonded both to each other and to the central strength member. The above method of cable production is quite fast and the speed is mainly limited by the speed of the tape wrapping operation. However, a great advantage, is that it can be stopped at any time to allow splicing of the tapes, strength member or optical fibres, and thus continuous cables can readily be produced. CLAIMS

3. An optical cable according to Claim 2, wherein the strips are tapes made from either paper or plastics, and are sufficiently stiff to provide support for the cover member.

4. An optical cable according to Claim 1, wherein the cover member is a flexible tape wrapped around the channels in a helical fashion.

5. An optical cable according to Claim 4, wherein the flexible tape is a polyethyleneterephthalate polyester film.

6. An optical cable according to Claim 1, wherein the central strength member is made of steel or impregnated glass or Kevlar and the strips are bonded thereto by means of an adhesive.

7. An optical cable according to any preceding Claim, wherein the one or more channels incorporate water blocking and/or hydrogen absorbing media.

8. An optical cable according to any preceding claim, wherein one or more sheaths are applied around the cover member.

9. An optical cable substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawing.