Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Patent
1992-05-20
1993-08-31
Gonzalez, Frank
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
385 71, 385 86, 385 87, 385 99, G02B 644
Patent
active
052416119
DESCRIPTION:
BRIEF SUMMARY
This invention relates to joints for cables. The invention is particularly applicable to a sealed joint for a submarine cable, especially an optical fibrebased cable.
Submarine cables are made up of a series of lengths which are joined before being deployed from a ship. Normally, the lengths are joined in the factory. However, in circumstances of repair, lengths have to be joined onboard ship. In the case of optical fibre telecommunication cables, the quality and repeatability of splicing techniques has improved considerably over recent years such that it is now possible to produce multiple fibre, low loss splices between lengths of cable with a good probability of success at the first attempt.
Previously, however, optical fibre splices were significantly less reliable. Only single splices could be performed at a time. Because the splicing process could not be guaranteed to produce an acceptable splice first time with a sufficiently good probability, it was necessary to allow for a spare meter, or so, of optical fibre in order to account for the likelihood of having to reconnect badly spliced fibres. Thus, each time a splice had to be repeated a few centimeters of fibre had to be cut off the spare length. Not all splices are unsuccessful within the first few attempts. Because of this a joint between two fibres had to allow for the maximum amount of spare fibre not used up in repeating the splicing procedure.
One of the main factors affecting the useful life of an optical fibre is the amount of stress to which it is subjected. Bending a fibre induces stress in it. It is, therefore, necessary to consider this fact in the manner in which the spare fibre at a joint is stowed.
Statistically, a fibre that has passed its quality control standard load test should only be subjected to bends of a minimum diameter of about 60 mm if it is to stand an acceptable chance of functioning properly for a projected minimum 25 year working life. Because of this constraint joints between cables have to accommodate 60 mm diameter loops of spare fibre. The result of this is that a 25 mm diameter cable carrying a group of optical fibres has to balloon out to a 100 to 120 mm diameter joint. The joints constitute a flexural discontinuity in the cable as well as a dimensional one. This can be problematic when the joined cables are deployed using winching gear and are paid out over the side of a ship.
Furthermore, the known joints are complex assemblages requiring portions for transmitting tension between the joined cables, a bobbin on which to wind the spare optical fibre and terminating arrangements for the end of each cable for separating the optical fibres.
It is also the case that the original manufacturer of the cable will need to apply other processes to the joined lengths. Typically, extra external armour wire layers are added. To do this the cable has to pass through an armouring machine which will not accept bulky conventional joints. Thus, armouring has to be split into discrete steps between the joints and additional steps to cover the joints themselves.
In U.S. Pat. No. 4,227,770 there is described a submarine optical fibre cable in which a central strength member is provided with helically cut grooves to receive optical fibres. Steel wires are wound helically around the strength member and fibres with the direction of lay of the wires opposite to that of the grooves. Additionally, there is disclosed a technique for jointing two such cables. A tubular metallic ferrule with an external flange at one end is swaged over the steel wires of a prepared cable end, with the ferrule's flange towards the cable end. Both cable ends are ferruled in this way, the fibres of the cable ends are optically coupled, and the cable ends secured one to the other using a split cylindrical coupling, formed of two similar semi-cylindrical parts, the bore of which is provided with recesses to receive the flanges of the ferrules. The two halves of the cylindrical coupling are held together using either a circumferential band clip or screws which pa
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patent: 4799760 (1989-01-01), Beatty et al.
patent: 5048921 (1991-09-01), Jones et al.
British Telecommunications public limited company
Gonzalez Frank
LandOfFree
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