GB2185591A - Optical fibre cable releasing oxygen to combine with free hydrogen - Google Patents

Description

I GB 2 185 591 A 1

SPECIFICATION

Optical fibre cables This invention relates to optical fibre cables, that is to say cables incorporating one or more optical fibres extending longitudinally within a surrounding cover.

Itis now known that transmission losses of optical fibres, at leastforcertain wavelengths, tend to 10 increasewiththe age of thefibres, dueto the gradual absorption of hydrogen bythefibres, evenwhere they are individually provided with protective coatings of synthetic plastics material. It has accordingly been proposed to incorporate within an 15 optical fibre cable a quantity of material which is capable of collecting free hydrogen either by absorption or by chemical action, for example as described in co-pending Patent Application No.

8428102, in orderto reduce the amount of hydrogen 20 available within the cable which could have a detrimental effect on thefibre orfibres contained therein.

According to the present invention an optical fibre cable incorporates, within the said cover, an additive 25 oradditive mixture capable of absorbing water and of gradually releasing oxygen, and a catalytic substance effectiveto cause the oxygen to combine with free hydrogen.

The gradual liberation of oxygen with time 30 ensuresthe continual cleaning up of hydrogen, not 95 onlythat present initiallywithin the cable, butalso thatwhich is gradually evolved or penetrates intothe cable during the life of the cable.

The additive may, for example, consist of 35 oxygen-enriched molecular sieve material in which 100 the action of absorbing water gives rise to the gradual liberation of oxygen.

The catalytic substance preferably consists of palladium,which may be in theform of a coating on 40 afinelydivided carrier material. Forexample, palladised carbon,that isto saycharcoal particles coated with palladium, is especially suitable.

Thefibre orfibres may be loosely accommodated within one or more channelswithin the cable cover 45 preferably following a path which, between theends of the cable, has a length which is greaterthan thatof the cable in orderto preventany undue strain being placed on thefibre orfibres. The additive oradditives togetherwith the catalytic substance mayalso be 50 contained within the said channel orchannels,for example as coatings on the channel orfibrewalls and/or, in the casewhere a channel contains a pluralityof fibres, in the interstices betweenthe fibres themselves, oralternatively distributed within 55 a paste orjelly-like material permeable to hydrogen, such as petroleum jelly or similar material, which permits a degree of movement of the fibre orfibres within the respective channel or channels as the cable is bent orflexed.

In an alternative embodiment where the channel walls are permeable to hydrogen the catalytic substance and possibly also the additive or additives maybe contained within a longitudinally extending channel which does not itself contain any optical fibres. For example where the optical fibres are contained within one or more tubes disposed within the surrounding cover, the catalytic substance and the additive or additives maybe contained either within a separate tube or in the space or spaces 70 within the cover around the fibre-containing tube or tubes and/or, in the case where the cover contains a plurality of tubes, in the interstices between the tubes.

However the catalytic substance and the additive 75 or additives maybe incorporated within the cable in another convenient manner. Instead of a molecular sieve material other materials capable of absorbing or reacting with waterto liberate oxygen could alternatively be used, one such material being barium peroxide.

Threeoptical cables in accordancewith the invention will now be described bywayof example with referenceto Figures 1 to 3 of theaccompanying drawingswhich represent transverse sections through thethreecables.

Theoptical fibre cable illustrated in Figure 1 comprises a cover 1 of extruded thermoplastics material, for example polyethylene, having a plurality of longitudinal ly-extending channels 2 in 90 each of which are located a plurality of optical fibres as at 3, the fibres being loose within, but being of greater length than, the channels in which they are accomodated.

Each channel is filled with petroleum jelly 4 or otherjelly-like substance substantially filling the spaces between the fibres and between the fibres and the wall of the channel, the petroleum jelly orthe like having dispersed within it particles 5 of palladised carbon, togetherwith oxygen enriched molecular sieve material 6, the latter being formed by baking and cooling molecular sieve material in oxygen or an oxygen rich atmosphere.

In use the palladium acts as a catalyst causing any free hydrogen and oxygen presentto combineto 105 form waterwhich is absorbed bythe molecular sieve material,this resulting in the liberation of further oxygen. Bythis means it is ensured thatfree hydrogen which may be evolved during the life of the cable, orwhich penetrates into the channels 2from 110 outside, is cleaned up and its detrimental effect substantially nullified by its combination with the liberated oxygen.

In Figure 2 there is shown an alternativeform of cable comprising an extruded tubular cover7 115 containing a plurality of separate tubes 8, which are conveniently also formed by extusion and each of which accommodates optical fibres 3 and is filled with petroleum jelly 4 orthe like having dispersed within it particles 5 of palladised carbon and oxygen 120 enriched molecular sieve material 6 as in the cable of Figure 1, the palladised carbon and the molecular sieve material acting in the same way as in the previously described cable to trap hydrogen which may be presentwithin the tubes during the life of the 125 cable.

In a modification of either of the cables illustrated in Figures 1 and 2 the petroleum jelly 4 may be omitted, the palladised carbon and the oxygen enriched molecular sieve material being 130 incorporated within the channels 2 ortubes 8, asthe 2 GB 2 185 591 A casemay be, in some otherway, for example as coatings either on the fibres themselves or on the inner surfaces of the Channels ortubes.

In a further modification illustrated in Figure3,the optical fibres 3 are contained within separate extruded plastictubes 8, within a cover 1 as in the cableof Figure2; butthetubes8do not,inthiscase, contain petroleum jelly orthe palladised carbon or oxygen enriched molecularsieve material. The latter two materials are, however, applied as a coating to the innerwall of the surrounding cover 1 as at 11, or within an additional tube 12 disposed within the cover as at 13. The palladised carbon and molecular sieve material may be held in contact with the cover 15 ortube wall by a suitable bonding medium if desired.

As the plastictubes are permeable to hydrogen the latterwill tend to pass into the space containing the palladised carbon and the molecular sieve material where itwill be combined with oxygen with the 20 formation of waterwhich will be absorbed bythe molecular sieve material with the liberation of further oxygen as previously described.

In another modification of the cable illustrated in Figure 2 petroleum jelly containing palladised 25 carbon and oxygen enriched molecularsieve 90 material, instead of being contained within thetubes 8, may alternatively be disposed in the longitudinal channels provided bythe space orspaces Wormed within the cover7 around, and/or between thetubes.

In any ofthe embodiments above described the cover may be surrounded by on or more outer sheaths in accordance with known techniques. For submarine use such a cable may include a sheath of lead, although otherwater impervious materials 35 may be used.

Moreoverthe palladised carbon and oxygen enriched molecularsieve material may be incorporated within the Gable in any other convenientway.

Claims (11)

1. An optical cable having an outer cover accommodating one or more optical fibres, 45 characterised in that it also incorporates, within the said cover, an additive or additive mixture capable of absorbing water and of gradually releasing oxygen, and a catalytic substance effective to cause the oxygen to combine with free hydrogen.

2. An optical cable according to Claim 1 characterised in thatthe additive consists of oxygen-enriched molecular sieve material in which the action of absorbing water gives riseto the gradual liberation of oxygen.

3. An optical cable according to Claim 1 or2 characterised in thatthe catalytic substance consists of palladium.

4. An optical cable according to Claim 3 characterised in that the palladium is in the form of a 60 coating on a finely divided carrier material.

5. An optical cable according to Claim 4 characterised in that the finely divided carrier material consists of charcoal particles.

6. An optical cable according to any preceding 65 Claim characterised in that the additive or additive mixture and the catalytic substance are contained within each channel that contains one or more opticalfibres.

7. An optical cable according to Claim 6 70 characterised in that the additive or additive mixture and the catalytic substance are coated on the channel orfibre walls.

8. An optical cable according to Claim 6 characterised in that the additive or additive mixture 75 is contained within a paste- orjelly-like material permeable to hydrogen within the said channel.

9. An optical cable according to anyone of Claims 1 to 5 characterised in thatthe channel walls are permeable to hydrogen and the catalytic 80 substance, and possiblythe additive or additive mixture, is contained within a longitudinally extending channel which does not contain any optical fibres.

10. An optical cable according to Claim 9 in that 85 the optical fibres are contained in one or more separate tubes within the outer cover, and the catalytic substance, and possiblythe additive or additive mixture, is contained within the space between thetube ortubes and the cover, orwithin a separate tube within the cover.

11. An optical cable substantially as shown in and as hereinbefore described with reference to Figure 1, 2 or3 of the accompanying drawing.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd, 6187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies maybe obtained.

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