Method for producing a preform for light waveguides

Claim 1

In a method of producing a glasy preform for a light waveguide including depositing a glass forming layer on a tubular substrate disposed in a reaction chamber, and subsequently subjecting said glass forming layer to a heating process to convert said glass forming layer to a glassy layer; the improvement wherein said step of depositing comprises: providing a gaseous mixture of silicon tetrachloride (SiCl 4 ) gas and water vapor; cooling and maintaining said substrate at a temperature between 20° C. and 800° C. while heating said reaction chamber to a temperature of substantially greater than 800° C.; and flowing a stream of said gaseous mixture through the reaction chamber to react said silicon tetrachloride gas with said water vapor to precipitate a glass forming layer of silicon dioxide particles from the reacted gas and water vapor on the cooled substrate.