GB2060929A

GB2060929A - An optical fibre unit for an optical cable

Info

Publication number: GB2060929A
Application number: GB8027448A
Authority: GB
Original assignee: Kokusai Denshin Denwa KK
Current assignee: KDDI Corp
Priority date: 1979-08-24
Filing date: 1980-08-22
Publication date: 1981-05-07
Also published as: GB2060929B

Abstract

An optical fibre unit for an optical cable. The unit comprises a synthetic resin layer (13) in which one or more optical fibres are seated and a water impervious layer (14,) which is located outside of the synthetic resin layer. Examples of such a water impervious layer includes an oil impregnated fibrous layer (14) of plaited or parallelly arranged vegetal fibres, a metal film deposited by non-electrolytic plating e.g. copper or silver or a metal tape (14b). The synthetic resin may be of silicone rubber and an outer layer of nylon provided. <IMAGE>

Description

SPECIFICATION An optical fibre unit for an optical cable The present invention relates to a fibre unit for disposition in, for example, an optical submarine cable.

With recent developments in optical fibre with an extremely low transmission loss of 0.5 dBikm and semi-conductor lasers which oscillate at a room temperature and have a long life exceeding ten thousand hours, optical fibre communications have now reached the stage of practical use. To use optical fibres for communications the fibres must be formed into cables. In order to bring optical fibre communications into practice, the manner in which the optical fibre, which is thin and liable to increase its transmission loss when bent even slightly, is formed into a cable is important.

In view of the above, an object of the present invention is to provide a fibre unit for an optical submarine or land cable which is capable of reducing permeation of sea water to the optical fibre and minimizing the influence of the sea water permeation when the cable is broken.

In accordance with the present invention, there is provided an optical fibre unit for an optical cable in which a plurality of optical fibres are covered by a layer of synthetic resin, the optical fibre unit comprising a layer impervious to water and located outside the synthetic resin layer seating therein at least one of the plurality of optical fibres.

In accordance with a further aspect of the present invention there is provided an optical fibre unit for an optical submarine cable in which an outer coating is disposed outside of a synthetic resin layer covering a plurality of optical fibres, the optical fibre unit comprising a fibrous layer impregnated with oil and interposed between the outer coating and the synthetic resin layer seating therein at least one of the plurality of optical fibres.

In accordance with a still further aspect of the present invention, there is provided an optical fibre unit for optical cable in which a plurality of optical fibres are covered with a layer of synthetic resin, the optical fibre unit comprising a water-tight metal film layerformed on the synthetic resin layer seating therein at least one of the plurality of optical fibres.

In a preferred embodiment of the present invention, the layer of synthetic resin is composed of silicone rubber.

Embodiment of the present invention will be described below by way of example with reference to the accompanying drawing and by comparison with conventional examples.

In the accompanying drawings: Figures 1A and 1B are cross-sectional views of an optical submarine cable and an optical fibre unit heretofore employed; Figures 2 and 3 are respective cross-sectional views of an optical fibre unit and an optical fibre, illustrating embodiments of the present invention; Figure 4 is a cross-sectional view showing an example of an optical submarine cable structure using the optical fibre unit of the present invention; Figures 5A, 5B and 5C are perspective views showing examples of the construction of an oilimpregnated fibre layer; and Figures 6, 7 and Bare cross-sectional views of fibre units, illustrating further embodiments of the present invention.

To make clear differences between the prior art and the present invention, an example of the prior art will first be described.

Figures 1A and 1 B illustrate the cross-sectional structure of a conventional submarine cable using optical fibres. First, twelve optical fibres 1, each given a primary coating of polyurethane, are twisted around a steel wire 2 and covered by a nylon jacket 4, with a layer 3 of polyester or elastomer of small elasticity (for example, HYTRELL (Trade Mark) produced by Du Pont) filled therebetween, providing an optical fibre unit 5 such as shown in Figure 1 B. Next, strand wires 6 are disposed around the unit for providing a required tensile force and a water pressure resisting function and further covered with an aluminium layer serving as a power-supplying feeder, an insulating low-density polyethylene layer 8 and an outer coating 9, thus providing a multi-core optical submarine cable.However, such a synthetic resin of vinyl system is essentially permeable to water; hence, it is impossible to prevent gradual entrance of sea water into submarine cable which has lain in the sea for a long time. Especially, with a defect such as a breakage in the cable, since its broken cross-section is exposed to sea water, sea water entering the cable through air gaps or joints between coatings flows in the axial direction of the cable and, with the lapse of time, soaks the optical fibre 1,causing it to be easily broken.

The present invention will hereinafter be described in more detail.

Figure 2 is a cross-sectional view of an optical fibre unit, showing an embodiment of the present invention, in which a layer 14 of plaited vegetal threads impregnated with oil such as, for example, silicone oil, is interposed between a silicone rubber layer 13 and a nylon coating 9 of the fibre unit 5, as shown in figure. With such an arrangement, the layer 14 of plaited threads blocks not only water entering from the circumferential direction of the unit 5 but also water entering in the axial direction of the unit 5 from a joint between the nylon layer 9 and the silicone rubber layer 13 when the cable is broken.

Figure 3 is a sectional view of an optical fibre composed of a core la and a cladding layer 1b, showing another embodiment of the present invention. By interposing the oil-impregnated, plaitedthread layer 14 between the nylon coating 9 and the silicone rubber layer 13 of the fibre 1 and assembling a plurality of such fibre structures into a unit, as shown, those effects obtainable with the optical fibre unit of Figure 2 can also be obtained; these effects can be heightened by the combined use of such structures.

Figure 4 is a sectional view illustrating, by way of example, an optical submarine cable structure using the optical fibre unit 5 of the present invention.

Reference numeral 15 indicates a power-feeding and pressure-resisting layer, and 16 designates a coating.

In the above described embodiments, the oilimpregnated fibre layer 14 is described as being plaited as shown in Figure 5A but this layer need not always be plaited, but simply disposed in parallel as shown in Figures 5B and 5C.

As has been described in the foregoing, the above examples of the present invention prevent permeation of sea water and entering of sea water in case of a cable breakage with a very simple construction requiring only the incorporation of an oilimpregnated thread layer in the optical cable and enhances the reliability of the optical submarine cable. Accordingly, the present invention is of great industrial value.

Figure 6 is a cross-sectional view of a fibre unit, illustrating another embodiment of the present invention. In this embodiment, on the surface of a silicone rubber layer 13 coating a primary coating (polyurethane) 12 of an optical fibre 1 a nonelectrolytic plating of, for example, copper, silver or like metal 14a is deposited and, if necessary, the metal layer is further subjected to electrolytic plating to provide a predetermined thickness. A plurality of fibres, each obtained by giving an outer coating 17, for example, of nylon to the plated metal layer, are by means of an outer coating 9 bundled into an optical fibre unit. The silicone rubber layer 13 may sometimes be omitted.In the optical fibre unit of such contruction, since the optical fibres are each covered with the metal layer 1 4a, water entering through the cable armour is completely blocked and water entering into the cable in the case of a cable breakage can also be prevented.

Figure 7 is a cross-sectional view of the fibre unit, illustrating another embodiment of the present invention. A plurality of optical fibres 1 are assembled together by burying them in, for example, a nylon, silicone rubber or like vinyl synthetic resin layer 13 about a tensile force wire 2, and the surface of the synthetic resin layer is coated by nonelectrolytic plating with a metal film layer 14a, which, if necessary, is covered with an outer coating 9 of, for example, nylon. This structure also produces the same effects as those obtainable with the embodiment of Figure 6.

Figure 8 illustrates another embodiment of the present invention which follows a similar idea. In this case, the metal film layer is formed by wrapping around the fibre unit a tape 14b of an aluminium film which has silicone rubber deposited on both its sides.

By forming an optical fibre cable utilizing an optical fibre unit having a construction such as that shown in Figures 6,7 and 8, it is possible not only to realize an optical submarine cable of truly high reliability but also to lay it as an optical communication cable for land use; hence, the present invention is of great practical use.

Claims

1. An optical fibre unit for an optical cable in which a plurality of optical fibres are covered by a layer of synthetic resin, the optical fibre unit comprising a layer impervious to water and located outside the synthetic resin layer seating therein at least one of the plurality of optical fibres.

2. An optical fibre unit for an optical submarine cable in which an outer coating is disposed outside of a synthetic resin layer covering a plurality of optical fibres, the optical fibre unit comprising a fibrous layer impregnated with oil and interposed between the outer coating and the synthetic resin layer seating therein at least one of the plurality of optical fibres.

3. A unit according to claim 2, wherein the fibrous layer in interposed between the outercoat- ing and the synthetic resin layer seating therein a single optical fibre.

4. A unit according to claim 2, wherein the fibrous layer is interposed between the outer coating and the synthetic resin layer seating therein a plurality of optical fibres.

5. A unit according to any of claims 2 to 4, wherein the fibrous layer is a layer of plaited vegetal fibres.

6. A unit according to any of claims 2 to 4, wherein the fibrous layer is a layerofvegetal fibres arranged in parallel.

7. A unit according to any of claims 2 to 6, wherein said outer coating is nylon.

8. An optical fibre unit for an optical cable in which a plurality of optical fibres are covered with a layer of synthetic resin, the optical fibre unit comprising a water-tight metal film layer formed on the synthetic resin layer seating therein at least one of the plurality of optical fibres.

9. A unit according to claim 8, wherein the water-tight metal film layer is formed on the synthetic resin layer seating therein a single optical figure.

10. A unit according to claim 8 wherein the water-tight metal film layer is formed on the synthetic resin layer seating therein a plurality of optical fibres.

11. A unit according to any of claims 8 to 10 wherein the water-tight metal film layer is deposited by non-electrolytic plating.

12. A unit according to any of claims 8 to 10 wherein the water-tight metal film layer is formed by disposing on the synthetic resin layer a metal tape having a synthetic resin deposited on both its sides.

13. A unit acording to any preceding claim wherein the synthetic resin layer is composed of silicone rubber.

14. An optical fibre unit for an optical cable substantially as herein described with reference to and as illustrated in the accompanying drawings.

15. An optical cable comprising an optical fibre unit according to any one of the preceding claims.