Optical waveguides – Optical transmission cable – Loose tube type
Patent
1998-03-19
1999-12-14
Bovernick, Rodney
Optical waveguides
Optical transmission cable
Loose tube type
385109, 385113, G02B 644
Patent
active
060028254
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an opt al cable comprising a reinforcing structure for providing sufficient tensile and compression strength for the cable, and one or more longitudinally extending fibre channels in which optical fibres in the form of single fibres, fibre bundles or fibre ribbons are positioned.
BACKGROUND AND PRIOR ART
An optical cable of the type described above is known, for example, from European Patent No. 0 136 913. According to this publication, optical fibres are placed in secondary sheathing tubes reinforced with glass fibres, and these secondary sheathing tubes are positioned around a central strength and support member. The cable thus requires secondary sheathing tubes reinforced with glass fibres and a separate strength and support member, although the cable may be thinner than conventional cables, since the secondary sheathing tubes reinforced with glass fibres contribute to the tensile strength of the cable. Such elements for receiving tensile and compression stresses are necessary simply because the coefficient of heat expansion of the plastic material in the secondary sheathing tube is high as compared with the almost nonexistent heat expansion of optical fibres.
As the aim has been metal-free optical cables, constructions similar to the one disclosed in European Patent No. 0 136 913 cited above have been provided wherein elements with tensile strength are positioned in a cable or its sheathing, e.g. in the form of longitudinally oriented bundles of glass, carbon or plastic fibres. Such fibre-reinforced cables are known, for instance, from Finnish Patent No. 91 680 and European Patent Application No. 0 461 871. The problem with the fibre-reinforced cables of these publications is that they are complicated and expensive to manufacture. The fibre bundles must at first be twisted around the cable core and then be impregnated with plastic, hot-melt adhesive or the like to provide an integral sheathing. This renders the manufacturing process of the cable complicated and expensive.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an optical cable which avoids the problems associated with the above-mentioned known constructions. This is achieved with a cable of the invention, which is characterized in that the fibre channel/fibre channels is/are defined directly by said reinforcing structure, and that the reinforcing structure is made of plastic reinforced with fibre bits.
Although the fibre channel or fibre channels may be conventional straight cylindrical channels, the fibre channel is preferably arranged to extend spirally in the reinforcing structure to provide the fibres in the fibre channel with extra length as compared with the length of the reinforcing structure.
When a spiral fibre channel, for example, is used, the amount of material in the reinforcing structure is naturally so large that, when it is made of plastic reinforced with fibre bits, sufficient tensile and compression strength is provided for the cable without further operations.
The fibre bits are preferably bits of mineral, glass, plastic or similar fibres, or mixtures of such fibre bits.
Selecting a suitable material and properties for the fibres and, optionally, using combinations of different fibres provides a reinforcing structure which, in addition to the necessary tensile properties, also has the compression strength required by thermal stability in the longitudinal direction and a suitable coefficient of heat expansion. Furthermore, the reinforcing structure can be provided with a desired impact resistance, transverse strength and suitable flexibility so that the cable can be handled in the conventional manner.
Preferably, the reinforcing structure reinforced with fibre bits is extruded in one process step from plastic in which fibre bits are embedded.
The advantages of the cable of the invention particularly if the cable comprises a spiral channel within the reinforcing structure--are small size, good flexibility in all directions, metal-free constructio
REFERENCES:
patent: 4420220 (1983-12-01), Dean et al.
patent: 4514035 (1985-04-01), Steinmann et al.
patent: 4770489 (1988-09-01), Saito et al.
patent: 4875757 (1989-10-01), Greveling
patent: 5320788 (1994-06-01), Schneider et al.
patent: 5345525 (1994-09-01), Holman et al.
Suvanto Markku
Tuunanen Vesa
Bovernick Rodney
Hao Victoria D.
NK Cables OY
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