Method of purifying natural or synthetic silica, and application thereof to depositing purified natural or synthetic silica on an optical fiber preform

摘要

Natural or synthetic silica is deposited on a preform set into rotation in front of a plasma torch which moves back and forth substantially parallel to a longitudinal direction of the preform, a first feed duct feeds the plasma with grains of natural or synthetic silica while a second feed duct feeds the plasma with a fluorine or chlorine compound, preferably a fluorine compound, mixed with a carrier gas. Any sodium or lithium contained in the grains of natural or synthetic silica react with the fluorine or chlorine of the fluorine or chlorine compound, thereby making it possible to improve the optical quality of fibers drawn from a preform built up with natural or synthetic silica, and to do so at reduced cost.