Optical cable

[0002] The invention concerns an optical cable or cable element.

[0003] Known in the art is an optical cable consisting of a plurality of individual optical waveguides. The optical waveguides are collected into individual optical waveguide bundles, each optical waveguide bundle being surrounded by a plastic covering. Within the plastic covering, in addition to the optical waveguides, is a compound of incompressible material, e.g. petroleum jelly. Several such optical waveguide bundles are stranded together and the stranded assemblage is surrounded by a plastic jacket. Embedded opposite one another within the wall of the plastic jacket are two tensile-stress-and compression-resistant elements (International Wire & Cable Symposium Proceedings 1999, Page 106).

[0004] This known cable is distinguished by a high fibre density. Thus, the cable has up to 144 fibers, with a cable outer diameter of 13.5 mm. The two tensile-stress/compression elements present in the cable jacket give the cable a high load capability in respect of tensile stress and compression. A further advantage is that the fibers are easily accessible.

[0005] The object of the present invention is to provide for a cable which has the same advantages as the known cable but which has a smaller outer diameter with the same number of fibers or an equal outer diameter with a higher number of fibers.

[0006] This object is achieved by the optical cable or cable element with a plurality of optical waveguide elements which are stranded together and each consist of several optical waveguides, collected into a bundle, and of a plastic covering surrounding the bundle with a maximum free space of 0.1 mm, and of a non-compressible filling compound filling the intermediate spaces between the optical waveguides, and with a layer of longitudinally aligned glass or plastic fibers surrounding the optical waveguide elements and with an extruded outer jacket of a polymer, the outer jacket compressing the layer radially.

[0007] The essential advantage of the cable according to the invention compared with the known cable lies in the fact that the tensile-stress/compression elements in the wall of the jacket can be omitted. The bending behaviour of the cable is improved substantially as a result. The tensile-stress/compression stability is provided by the layer compressed by the outer jacket. In addition, the compressed layer protects the optical waveguides from transverse forces, which has a positive effect on the transmission characteristics. By comparison with the known cable, a cable diameter reduction of up to 25% is achieved.

[0008] The invention is described more fully with reference to the embodiment examples depicted schematically in FIGS. 1 to 3, wherein:

[0009] FIG. 1 shows a cable with 144 fibers

[0010] FIG. 2 shows a cable with 1008 fibers

[0011] FIG. 3 also shows a cable with 1008 fibers

[0012] The optical cable or cable element 1 depicted in FIG. 1 consists of twelve optical waveguide elements 2, which are stranded together, the direction of lay being always the same or changing after some turns (SZ stranding).

[0013] Each optical waveguide element contains twelve optical waveguides 3 which are disposed within a thin covering 4 of soft plastic. The thin, soft covering 4 renders possible removal of the covering 4 by the hands or fingers only, so that the optical waveguides 3 become accessible without additional tools.

[0014] An incompressible compound, which serves as a support for the thin covering 4 and also affords longitudinal water-tightness, can also be contained within the covering 4, between the optical waveguides 3.

[0015] The stranded assemblage formed from the optical waveguide elements 2 is surrounded by a layer 5 which acts as a tensile-stress/compression protection. The layer 5 preferably consists of glass yarns. Over the glass yarn layer 5 is a further jacket 6, e.g. of polyethylene, which is applied in such a way that the layer 5 below it is compressed.

[0016] The free spaces between the optical waveguide elements 2 and the layer 5 are either filled with a filling compound or are occupied by several threads or yarns 7 of a material which swells upon the ingress of water.

[0017] FIG. 2 shows an optical cable which consists of seven cable elements 1 stranded together, as depicted in FIG. 1. The cable elements 1 are stranded together in either the same or a reversing direction of lay. The stranded assemblage constructed from the cable elements 1 is surrounded by an outer jacket 8, e.g. of polyethylene. Disposed in the free spaces between the cable elements 1 and the outer jacket 8 are threads or yarns 9 of a material which swells upon the ingress of water. Alternatively, the free spaces can also be filled with a filling compound, e.g. petroleum jelly. In the case of this cable construction, a layer of glass fibers, not depicted, can be disposed between the stranded assemblage and the outer jacket 8, being compressed by the outer jacket 8 in the same manner as the layer 5 in FIG. 1.

[0018] FIG. 3 depicts an optical cable which has a central tensile-stress/compression element 11, e.g. of glass-fibre reinforced plastic, around which seven cable elements 1—as depicted in FIG. 1—are stranded in the same or a reversing direction of lay. The stranded assemblage of the cable elements 1 is surrounded by an outer jacket 10, e.g. of polyethylene.

[0019] In this case, likewise, a plurality of threads or yarns 9 of a material which swells upon the ingress of moisture is disposed in the free spaces between the cable elements 1 and the outer jacket 10. Alternatively, the free spaces can be filled by a filling compound, e.g. a petroleum jelly based compound.