Abstract: An improved method of manufacturing an optical fibre by vapor phase deposition of layers of cladding and core material for an optical fibre on the inside of a tubular substrate, followed by heating of the tube to cause it to collapse into a preform and drawing of the preform to form the fibre, includes performing the collapse with the introduction of chlorine gas acting as a drying agent. An alternative to chlorine gas is a vapor which decomposes in situ to yield chlorine without producing a solid deposit.

Abstract: An optical fibre capable of monomode transmission in, and having a wavelength of zero dispersion in, the 1.55 .mu.m window and having a core comprising silica and germanium dioxide and a cladding comprising silica is drawn from an appropriate preform at a temperature in the range from 1900.degree. C. to 2000.degree. C. Fibres thus produced have low loss compared with fibres drawn at higher temperature.

Abstract: An oxide glass is dried by passing through a melt of the glass fluorine or another perhalogenated compound including fluorine atoms. For example, C.sub.3 F.sub.8 (e.g. after pre-cracking) can be used to reduce the OH content of a borosilicate glass, and the loss of an optical fibre drawn from such a glass, to low levels.

Abstract: A range of alkali metal borosilicate glass compositions modified by the addition of alkaline earth metal oxides has been found to be especially suitable for the production of graded index optical fibre using the double crucible method. A core glass from this range may be paired with a suitable cladding glass, which may be another glass from the same range or an unmodified alkali metal borosilicate, so that in the nozzle of the double crucible thermal diffusion takes place to give a composition gradient of alkaline earth metal oxide and hence a refractive index gradient. The fibres thus obtained have better refractive index profiles if the proportions of the oxides in the core and cladding glasses are chosen so as to exclude a simple ion-exchange mechanism. Fibres having numerical apertures of up to 0.268 and best loss values as low as 5.0 dB/km have been prepared.

Abstract: A glass suitable for use as the core glass in a high numerical aperture optical fibre has a composition selected from the range of glasses which comprise(i) from 15 to 25 mole percent of soda,(ii) from 25 to 65 mole percent of silica and germania, taken together, the content of germania not exceeding 42 mole percent,(iii) up to 22.5 mole percent of boric oxide and barium oxide, taken together, the content of boric oxide not exceeding 20 mole percent, and the content of barium oxide not exceeding 12 mole percent, and(iv) from 0.01 to 1 weight percent of a redox buffering agent. The glass can be prepared by controlling the partial oxygen pressure of the melt so that it is approximately 10.sup.-5 atmospheres. An optical fibre can be produced, by using a soda-boro-silicate clad glass, and a core glass having the composition in the above range.

Abstract: A graded index optical fiber is produced in a double crucible with an elongate heated exit nozzle. The core and cladding glasses of the fiber diffuse into one another in the nozzle.

Abstract: A range of alkali metal borosilicate glass compositions modified by the addition of alkaline earth metal oxides has been found to be especially suitable for the production of graded index optical fibre by thermal diffusion using the double crucible method. A core glass chosen from this range may be paired with a suitable cladding glass so that, in the nozzle of the double crucible, alkaline earth metal exchange occurs to give a composition gradient of alkaline earth metal oxide and hence a gradation of refractive index. Using these glasses, fibres have been produced having refractive index profiles that approximate closely to the ideal parabolic distribution, numerical apertures of up to 0.21, and best loss values as low as 6.4 dB/km at 850 nm.