Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Patent
1993-01-26
1994-08-16
Lindsay, Robert L.
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
65412, 65416, C03B 37023
Patent
active
053375858
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for producing an optical fiber by stretching a heated assembly consisting of an outer sleeve which is partially or entirely made of synthetic silica with a bar engaged therein.
It also concerns an optical fiber made in accordance with this method.
It is known that doping the superficial layer of silica based optical fibers with titanium dioxide considerably increases the fiber's corrosion resistance when restrained. The parameter n, representing fiber susceptibility to corrosion derived from measurements of dynamic fatigue, can exceed 50, whereas it is approximately 20 for pure silica fibers.
One known doping procedure consists of covering non-vitrified preform by external deposition with supplemental deposition of silica, also non-vitrified, containing up to 20% molar proportion titanium dioxide. This preform then must be dried and vitrified before finally being stretched into an optical fiber over ten kilometers long and mechanically reinforced by doping it with superficial titanium dioxide.
Certain optical fibers, especially monomodal fibers, may be produced using methods which consist of depositing suitably doped silica inside a tube which is then held inside a bar, then engaging said bar inside an outer sleeve. This assembly constitutes a composite preform from which the optical fiber is produced by stretching it while hot.
This composite preform does not lend itself to doping with titanium dioxide as is done on mono-block preforms; as a result, up until now, it has not been possible to treat fibers produced by this process with titanium dioxide for improved corrosion resistance.
The aim of the present invention is to overcome this disadvantage.
This aim is achieved by the method of the invention, characterized in that before assembling the components, the outer sleeve is coated with a deposit of vitrified silica containing titanium dioxide.
According to a preferred embodiment said titanium dioxide is deposited in vapor phase using a plasma torch.
The titanium dioxide is preferably obtained by oxydizing a volatile or transportable component of titanium in the gas state in said plasma torch. This component may be a halogen such as titanium tetrachloride.
The titanium oxide is preferably deposited and vitrified at the same time as the silicon or silica oxide.
According to a preferred embodiment, the molar proportion of titanium dioxide is from 2 to 40% of the proportion of silica and preferably approximately equal to 10% of that proportion.
The present invention will be better understood with reference to the description of one preferred embodiment and to the attached drawing, in which:
FIG. 1 is a schematic illustration of the first, already known phase of the process consisting of making a standard preform according to the MCVD interior deposition method (Modified Chemical Vapor Deposition).
FIG. 2 shows a new phase which consists of doping an outer tubular sleeve with titanium dioxide with direct vitrification of the resulting deposit.
FIG. 3 shows the phase of assembling the standard preform restrained in a bar inside the sleeve, and
FIG. 4 is a schematic illustration of the operation of stretching the composite assembly to form an optical fiber.
With reference to the drawings, first a component in the form of a bar (inner member) 10 is made from silica tube 11 which has been coated inside with synthetic silica before being compressed. A heat source 12 activates this interior deposition operation, which source may consist of an oxyhydrogen torch producing an interior tube temperature of approximately 1700.degree. C., while a first oxygen current 13 which has been immersed in a silicon tetrachloride bath 14 and a second oxygen current 15 which has been immersed in a germanium tetrachloride bath 16 simultaneously pass through the tube. This process is known by the name MCVD (Modified Chemical Vapor Deposition). Said bar 10 may also be produced by vitrifying a cylinder consisting entirely of synthetic silica; in both cases, the synthetic silica is doped so it for
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Berthou Herve
Sandoz Frederic
CABLOPTIC S.A.
Lindsay Robert L.
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