GB2051398A - An optical fiber submarine cable - Google Patents

Abstract

A pressure-proof optical fiber submarine cable comprises an outer corrosion-proof sheath 10 containing a plurality of twisted optical fiber assemblies 4 and interstitial filament assemblies 8 with a space 5 provided surrounding the optical fiber assemblies 4 and the interstatial filament assemblies 8. The space 5 is filled with clean water, so that when the cable is laid on the bottom of the sea or other body of water, the water pressure inside the corrosion-proof sheath 10 is maintained equal to the pressure outside the sheath 10. <IMAGE>

Description

SPECIFICATION An optical fiber submarine cable This invention relates to a pressure-proof optical fiber submarine cable adapted to be laid on the bottom of the sea or other body of water.

In view of their low light loss and wide band width characteristics, optical fibers permit communications with a very long distance repeater span. Hence, it is contemplated that they can be used not only in land cables but also in submarine cables which cross lakes or bays as well as in undersea communication cables.

Fig. 1 shows in cross section a conventional coated optical fiber 4 which includes a glass fiber core 1 protected by a first plastics layer 2 and a second plastics layer 3 as disclosed in, for example, U.S. Patent 3,980,390.

When an optical fiber cable comprising an assembly of these optical fibers is laid in the sludge on the bottom of the sea or other body of water (the term "the bottom of the sea or other body of water" as used herein includes the bottoms of shallow and deep sea as well as the bottoms of lakes, marshes and rivers), hydrogen sulfide and other gases in the sludge will penetrate not only the plastics sheath of the cable but also the glass fibers therein and, as a result, the protective plastic layers separate from the fiber cores, causing appreciable deterioration of the mechanical as well as transmission characteristics of the optical fibers.

In order to avoid this problem, the coated optical fiber 4 can be enclosed in a corrosionresistant sheath which comprises lead or aluminum. The metallic corrosion-resistant sheath also serves as a cable tension member and improves the mechanical characteristics of the cable. When such cables are laid on the bottom of the sea or other body of water, they are free from attack by hydrogen sulfide and other harmful gases, but at greater depths of water, they are likely to be crushed by the water pressure.

It is therefor an object of the present invention to provide an optical fiber submarine cable which is resistant to the high water pressures occurring at great depths of water, as well as being resistant to corrosion caused by hydrogen sulfide and other gases generated in the sludge at the bottom of the sea or other body of water.

Accordingly, the present invention resides in a pressure-optical fiber submarine cable comprising a corrosion-proof sheath containing a water-filled space surrounding at least one assembly of twisted optical fiber and interstitial filament.

In the accompanying drawing, Figure 1 is a cross sectional view of a conventional optical fiber structure, Figures 2 and 3 are cross sectional views of optical fiber cables according to respective examples of the present invention, Figure 4 is a schematic representation of a tension member of a cable according to a further example, and Figure 5 is a cross sectional view of a submarine electric power/optical composite cable employing an optical fiber cable as shown in Fig. 2 or 3.

Referring to Figs. 2 and 3, each of the cables shown therein comprises a corrosionproof sheath 10 which is conveniently formed of aluminum or lead and which contains a plurality of twisted optical fiber assemblies 4 and interstitial filament assemblies 8, with a space 5 being provided between each optical fiber assembly and the interstitial filament assembly. The cable 11 further includes a tension member 6, a spacer 7, and an outer wrapping layer 9.

The space 5 in each cable is filled with clean water. The water does not adversely affect the adjacent cable components, and maintains a water pressure inside the corrosion-proof sheath equal to the pressure outside the sheath when the cable is laid on the bottom of the sea or other body of water.

The term "water" used herein means water which does not adversely affect the assembly of twisted optical fibers and interstitial filaments and can be tap water, industrial water or seawater.

Since the optical fiber cable is filled with clean water, the fibers immersed in it wil not undergo any deterioration of its transmission or mechanical characteristics, thus providing a cable with highly stable characteristics. Generally, the cable is filled with clean water immediately before, during, or immediately after the cable laying operation.

In filling the cable with water, it is desirable to inject water from one end of the cable remaining on the land by a pressure pump and at the same time evacuate the other end of the cable which is carried by a cable laying boat with a suction pump. The cable filled with water can then be laid on the bottom of the sea or other body of water by the usual cable laying operation. However, this filling method is quite time consuming because the cable has various reinforcing materials or buffering materials closely packed to protect individual coated fiber structures.

In the further example shown in Fig. 4, the above-described filling problem is overcome by replacing the conventional tension member 6 with a fiber-reinforced plastic or steel wire 11 which is grooved as shown and wrapped coasely with a tape 1 2 so that buffer or other materials may not fall into each groove. With this arrangement, the groove serves as a passageway through which water can be introduced into the cable in a reduced time.

Referring to Fig. 5, in the submarine pow er/optical composite cable shown therein an optical fiber cable 1 3 such as that shown in Fig. 2 or 3 is incorporated together with electric power lines 1 4. The composite cable is armoured with steel wire 16, and if seawater should penetrate an interstitial jute layer 15, the optical cable 1 3 will not be crushed by the seawater, nor will the optical fibers inside the cable be attacked by sludge on the sea bottom for the same reasons described above with respect-to Fig. 2 or 3.

Claims (8)

1. A pressure-proof optical fiber submarine cable comprising a corrosion-proof sheath containing a water-filled space surrounding at least one assembly of twisted optical fiber and interstitial filament.

2. A pressure-proof optical fiber submarine cable comprising a corrosion-proof sheath containing a plurality of twisted optical fiber and interstitial filament assemblies with a space provided surrounding said optical fiber assemblies and said interstitial filament assemblies, wherein said space is filled with clean water, so that when said cable is laid on the bottom of the sea or other body of water, the water pressure inside the corrosion-proof sheath is maintained equal to the pressure outside said sheath.

3. A cable as claimed in Claim 1 or Claim 2, wherein said corrosion-proof sheath further contains a tension member.

4. A cable as claimed in Claim 3, wherein said tension member is grooved.

5. A cable as claimed in any of Claims 1 to 4, wherein said corrosion-proof sheath is formed of lead or aluminum.

6. A pressure-proof optical fiber submarine cable comprising the combination and arrangement of parts substantially as hereinbefore described with reference to, and as shown in, any one of Figures 2 to 4 of the drawings.

7. A composite submarine power/optical cable comprising a pressure-proof optical fiber submarine cable as claimed in Claim 1 or 2.

8. A composite submarine power/optical cable comprising the combination and arrangement of parts substantially as hereinbefore described with reference to, and as shown in, Figure 5 of the accompanying drawings.