Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Patent
1993-03-04
1994-08-02
Jones, W. Gary
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
65 45, 65 325, 65DIG16, 651342, 501 40, C03B 5225
Patent
active
053342321
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for the preparation of halide, preferably fluoride, glass articles, e.g., preforms suitable for drawing into fibre.
2. Related Art
Halide, and especially fluoride, glass fibre is used where transmission in the wavelength band 2000 nm to 4500 nm is required. Halide fibres also display good transmission outside this band, e.g., over the range 500 nm to 2000 nm but competitors, e.g., SiO.sub.2 based fibres, have good transmission in this region. However, the competitors have such high attenuations in the band 2000 nm to 4500 nm that they are excluded for consideration when it is required to use the fibre at this wavelength.
In most cases, the preparation of halide fibres involves first the preparation of the core and clad glasses, the casting of these two glasses to make a preform and the drawing of the preform into fibre. It is important to avoid contamination during the preparation of the glasses and their casting. For this reason it is usual to carry out these stages in isolation chambers which are provided with a dry inert atmosphere at slightly above the pressure outside the isolation chamber. The inert atmosphere is usually nitrogen for reason of cheapness but other inert gases, e.g., argon or helium, could also be used. It is also advantageous to submit the melt to an oxidation process and mixtures of inert gas and oxygen are used for this purpose. The transmission properties of a halide fibre are determined to a large extent by chemical considerations, e.g, the chemical composition of the core glass and the clad glass. It is also important that the two glass compositions cooperate to provide guidance and are compatible with one another during the preparative stages, especially the drawing.
The selection of the chemical compositions of the core and clad glasses together with the careful preparative techniques indicated above are important to achieve low attenuation but it appears that mechanical imperfections, e.g., crystals and bubbles, in the fibre can also cause attenuation, probably because mechanical imperfections can scatter the light.
SUMMARY OF THE INVENTION
This invention is based upon the discovery that mechanical imperfections can be caused during the preparation of the glasses and in the casting of the preform and it has most surprisingly been discovered that subjecting the melts to treatment under the atmospheric conditions specified below, substantially reduces the incidence of mechanical faults whereby fibre with lower attenuation is achieved. It will be appreciated that subjecting solid glass to the specified treatment will have little or no effect upon its properties and it is the molten glasses which benefit from said treatment applied during the latter stages of their preparation and/or during casting. The melting of the halide glasses is carried out in contact with atmospheres, especially controlled atmospheres, which are conveniently provided in a chamber attached to an apparatus such as a glove box. The term "controlled atmosphere" includes inert atmosphere consisting of inert gases such as nitrogen, helium and argon. At certain stages of the process the controlled atmosphere may be pure oxygen or oxygen mixed with an inert gas. The atmospheric conditions mentioned above comprise a flow of gas at low pressure through the atmosphere which is in contact with the melt. Said flow of gas is preferably at a flow rate of 0.1 to 100 liters/minute, e.g., 2 liters/minute as measured at NTP (normal temperature and pressure). These correspond to ranges of 7.times.10.sup.-6 to 7.times.10.sup.-3 moles/second and 1.5.times.10.sup.-4 moles/second respectively. Said low pressure is preferably below 500 mbars (millibars), especially below 150 mbar, e.g., within the range 5 to 150 mbars.
The invention is further defined in the claims.
During the casting of preforms, it is desirable that the pouring of the core is carried out at a lower temperature and pressure than the pouring of the cladding, e.g., 20.degre
REFERENCES:
patent: 4217166 (1980-08-01), Nink
patent: 4659352 (1987-04-01), Robinson
patent: 4659355 (1987-04-01), Maze et al.
patent: 4729777 (1988-03-01), Mimura
patent: 4741752 (1988-05-01), France
patent: 4826954 (1989-05-01), Suzuki et al.
patent: 4835235 (1989-05-01), DeMartino et al.
patent: 4885019 (1989-12-01), Hutta
patent: 4897100 (1990-01-01), Nice
patent: 4913836 (1990-04-01), East
patent: 4954288 (1990-09-01), East
patent: 4970120 (1990-11-01), Laschewsky et al.
patent: 5034277 (1991-07-01), Laschewsky et al.
Patent Abstracts of Japan, vol. 12, No. 410, Oct. 28, 1988, & JP A 63147838 (Nippon Telegr. & Teleph. Corp.) Jun. 20, 1988.
Patent Abstracts of Japan, vol. 14, No. 184, Apr. 13, 1990, & JP A 2030635 (Sumitomo Electric Ind. Ltd.) Feb. 1, 1990.
Chemical Abstracts, vol. 102, No. 24, 1985 (Columbus, Ohio), pp. 280-281, abstract 2008282a (Nippon Telegraph & Telephone Public Corp.) Jan. 21, 1985.
Carter Steven F.
France Paul W.
Williams John R.
British Telecommunications public limited company
Hoffman John
Jones W. Gary
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