GB1586373A

GB1586373A - Optical fibre cable

Info

Publication number: GB1586373A
Application number: GB5687/78A
Authority: GB
Original assignee: AEG Telefunken Kabelwerke AG
Current assignee: Kabel Rheydt AG
Priority date: 1977-02-25
Filing date: 1978-02-13
Publication date: 1981-03-18
Also published as: IT1092811B; FR2382016B1; DE2708878B2; DE2708878A1; FI780325A; JPS6044642B2; FR2382016A1; JPS53106143A; FI74823B; FI74823C; IT7820522A0; NL7801130A; DE2708878C3

Description

(54) OPTICAL FIBRE CABLE (71) We, AEG-TELEFUNKEN Kabelwerke Aktiengesellschaft, Rheydt, of Monchengladbach, Federal Republic of Germany, a German body corporate, 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: The invention relates to optical fibre cable made from a sturdy tube with an optical fibre or fibre group lying therein.

Fibres made of a material which is suited to transmitting light in the infra-red, visible, ultraviolet range or in a part of these ranges of the electromagnetic spectrum are understood as optical fibres in the present context. The optical fibres can be surrounded by a protective casing in order to protect their surfaces. In the first instance, optical fibres of this type serve to transmit information.

Optical fibres are very vulnerable mechanically. Therefore, they are arranged in protective casings either individually or several at a time for further processing, laying and installation. These arrangements of optical fibres are called optical fibre cables in the present context. They can serve either directly or only after applying appropriate external casings as transmission lines. But they can so be twisted together as optical twisting elements and thus can form the core of a multi fibre optical cable. During twisting, the twisted elements are subjected to high bending and tension loads. Even when laying and assembling the cable later, bending and tension loading occur which act on the photoconductor arrangement. Thus the optical fibres contained in the cable can be damaged or limited in their quality of transmission.

It is known to arrange these fibres loosely in tube-like casings absorbing the mechanical loads in order to keep bending and tension loads arising during twisting of the photoconductor arrangements away from the optical fibres. The optical fibres lie in the tube-like casings and are freely movable. This type of photo-conductor arrangement is known from German Offenlegungsschrift No. 25 56 861. A disadvantage of this known optical fibre cable lies in the fact that it must be wound on to a drum after manufacture. When winding it on to the drum, the optical fibres do not however remain at the centre point of the tube but lie inside the tube against the wall which is closest to the centre point of the drum. If this cable is now extended for twisting, the fibres are shorter than the tube and therefore are stretched and this often leads to breakage of the fibres.

The present invention seeks to provide an optical fibre cable which retains the advantages of a loose casing for the optical fibres in which casing the optical fibres are reliably protected from tension and compressionloads in which winding on to the drum after manufacture does not lead to differences in length between the tube casing and the optical fibres. The photoconductor arrangement should be capable of being wound on to the drum after manufacture and being extended again without danger of breakage.

According to the invention, there is provided an optical fibre cable comprising a tube and optical fibre cable comprising a tube and an optical fibre element in the tube, the optical fibre element following a helical path about the centre of the tube and being supported so as not to touch the tube wall.

In preferred manner, one or more strands made of cushioning material and wound helically round the optical fibre or fibre group can be provided as the support element. The support elements or strands may comprise fibrous material. It has been proved that woollen threads are very good for this purpose. The optical fibres of a fibre group may be arranged in the photoconductor arrangement in accordance with the invention in untwisted manner.

In order to manufacture the photoconductor arrangement in accordance with the invention, a support thread may be spitally wound round the optical fibre or fibre group, this thread comprising wool, for example, and the tube may then be extruded around this arrangement. The optical fibre with the wool thread twisted round it may be introduced into a longitudinally cut tube which is then closed again or closes itself. This method of insertion of strands into tubes is described in our West German OLS No. 26 51 725. It is in fact known to provide helical spacers in electrical coaxial cables which keep the internal conductor on the axis of the external conductor. With the photoconductor arrangement in accordance with the invention, the optical fibres do not lie in a coaxial position however but are wound slightly eccentrically round the tube axis. The very rigid connection of the external conductor to the internal conductor caused by the spacers in coaxial cables does not permit any conclusions to be drawn as to the advantages of the design proposed in accordance with the invention, in which design, the optical fibre may be supported by a fibrous woollen helix and may be positioned freely about the tube axis and may thus be particularly suited to a photoconductor arrangement.

The invention offers the advantage that the optical fibres are not freely movable in the tube but are kept in a line which rotates helically about the tube axis by a predetermined eccentricity. As a result, the optical fibres are prevented from abutting a wall of the tube during winding up on to the drum and are prevented from leading to differences in length which can lead to breakage of the optical fibres when the photoconductor arrangement is extended. The advantages of the loose arrangement of the optical fibres are retained, however, since the support elements provided do not restrict the mobility of the fibres in the tube. The low bearing force of the support elements on the fibres permits relative movement in the longitudinal direction with regard to the arrangement. When a radial pressure arises on the tube, the fibres have sufficient room to deflect. The arrangement in accordance with the invention permits processing of optical fibres without a casing.

An example of embodiment of the invention is shown in the drawings. It shows a view and four sections at different points through the photoconductor arrangement.

The optical fibre or fibre group is designated 2. A woollen thread 3 winds helically round the optical fibre the thread supporting the fibre at a spacing from the inner wall of the tube 1 and giving it a path which is wound slightly eccentrically and spirally round the tube axis 4. The four cross-section A to D show the eccentric position of the optical fibres in four different positions. It can be seen that the optical fibre rotates round the tube axis in a longitudinal direction with a small radius.

WHAT WE CLAIM IS; 1. An optical fibre cable comprising a tube and an optical fibre element in the tube, the optical fibre element following a helical path about the centre of the tube and being supported so as not to touch the tube wall.

2. A cable according to Claim 1, wherein the optical fibre element is a single optical fibre.

3. A cable according to Claim 1, wherein the optical fibre element is a group of optical fibres.

4. A cable according to Claim 1 or 3, wherein the optical fibre or fibre group is kept in its position wound helically round the tube axis by support elements made from a cushioning material.

5. A cable according to Claim 4, wherein a strand wound helically round the optical fibre or fibre group and made of cushioning material is provided as the support element.

6. A cable according to Claim 4 or 5, wherein the support elements or the strand comprise fibrous material.

7. A cable according to Claim 6, wherein the strand is a woollen thread.

8. A photoconductor arrangement according to Claim 3 or any claim apparent directly or indirectly thereto, wherein the optical fibres of a fibre group are not twisted together.

9. An optical fibre cable substantially as described herein with reference to the drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. for this purpose. The optical fibres of a fibre group may be arranged in the photoconductor arrangement in accordance with the invention in untwisted manner. In order to manufacture the photoconductor arrangement in accordance with the invention, a support thread may be spitally wound round the optical fibre or fibre group, this thread comprising wool, for example, and the tube may then be extruded around this arrangement. The optical fibre with the wool thread twisted round it may be introduced into a longitudinally cut tube which is then closed again or closes itself. This method of insertion of strands into tubes is described in our West German OLS No. 26 51 725. It is in fact known to provide helical spacers in electrical coaxial cables which keep the internal conductor on the axis of the external conductor. With the photoconductor arrangement in accordance with the invention, the optical fibres do not lie in a coaxial position however but are wound slightly eccentrically round the tube axis. The very rigid connection of the external conductor to the internal conductor caused by the spacers in coaxial cables does not permit any conclusions to be drawn as to the advantages of the design proposed in accordance with the invention, in which design, the optical fibre may be supported by a fibrous woollen helix and may be positioned freely about the tube axis and may thus be particularly suited to a photoconductor arrangement. The invention offers the advantage that the optical fibres are not freely movable in the tube but are kept in a line which rotates helically about the tube axis by a predetermined eccentricity. As a result, the optical fibres are prevented from abutting a wall of the tube during winding up on to the drum and are prevented from leading to differences in length which can lead to breakage of the optical fibres when the photoconductor arrangement is extended. The advantages of the loose arrangement of the optical fibres are retained, however, since the support elements provided do not restrict the mobility of the fibres in the tube. The low bearing force of the support elements on the fibres permits relative movement in the longitudinal direction with regard to the arrangement. When a radial pressure arises on the tube, the fibres have sufficient room to deflect. The arrangement in accordance with the invention permits processing of optical fibres without a casing. An example of embodiment of the invention is shown in the drawings. It shows a view and four sections at different points through the photoconductor arrangement. The optical fibre or fibre group is designated 2. A woollen thread 3 winds helically round the optical fibre the thread supporting the fibre at a spacing from the inner wall of the tube 1 and giving it a path which is wound slightly eccentrically and spirally round the tube axis 4. The four cross-section A to D show the eccentric position of the optical fibres in four different positions. It can be seen that the optical fibre rotates round the tube axis in a longitudinal direction with a small radius. WHAT WE CLAIM IS;

1. An optical fibre cable comprising a tube and an optical fibre element in the tube, the optical fibre element following a helical path about the centre of the tube and being supported so as not to touch the tube wall.

7. A cable according to Claim 6, wherein the strand is a woollen thread.