Abstract: The method for producing and processing a preform comprises a preliminary process phase, in which silica grain is supplied into the interior space of a silica tube having an open upper end and a closed lower end, in order to obtain an unprocessed preform, and includes a final process phase, in which the interior space of the silica tube is closed, a condition of reduced pressure is generated, the unprocessed preform is heated with a final process temperature in order to fuse the silica tube and the silica grain. According to the invention the silica grain entering the interior space is thermally treated during the preliminary process phase with an intermediate process temperature that lies under the melting point of the silica grain.

Abstract: A method for producing an optical fibre which has been treated with titanium dioxide to improve its corrosion resistance includes stretching an assembly consisting of an outer sleeve having engaged therein a bar which is partially or entirely made of synthetic silica. When treating said fibre, the outside of the coupling sleeve is coated, prior to assembling the components, with a deposit of vitrified synthetic silica containing titanium dioxide.