Abstract: The field is that of methods for providing fiber-optic final preforms obtained by external plasma overcladding build-up around a primary preform. The method involves providing a final preform starting from a primary preform by external plasma deposition of silica grain over a primary preform, the outer peripheral layer of the primary preform consisting of a fluorine-doped silica tube. The build-up process involves forming a first overcladding using fluorine-doped synthetic silica grain followed by a second overcladding step using natural silica grain. The optical fibers obtained and their associated optical fiber preforms are also disclosed.

Abstract: The invention relates to a method of doping silica with fluorine. The method described comprises mixing a powder of silica granules with a solid fluorine compound, thermally decomposing the solid fluorine compound under an inert atmosphere, and densifying the granules to obtain dense grains of doped silica. It is preferable to use ammonium bifluoride. The invention is applicable to preparing high index silica glass, in particular for fabricating optical fiber preforms.

Abstract: The invention relates to a method of doping silica with fluorine. The method described comprises mixing a powder of silica granules with a solid fluorine compound, thermally decomposing the solid fluorine compound under an inert atmosphere, and densifying the granules to obtain dense grains of doped silica. It is preferable to use ammonium bifluoride. The invention is applicable to preparing high index silica glass, in particular for fabricating optical fiber preforms.