Patent ID: 6138478
Filing Date: 2000-10-31
Classification: C03B

Abstract:
A method for manufacturing a preform comprising the steps of:a. arranging a dielectric starting body within a tubular vessel, said vessel defines a channel, wherein said tubular vessel has two concentric walls restricting an annular volume;b. supplying said channel with a reactive gas containing a coating material precursor;c. generating a plasma zone in said channel via a resonator;d. aligning said starting body in said vessel such that said plasma zone concentrically envelopes said starting body;e. controlling axial movement of said resonator relative to, said starting body such that a desired layer of coating material reactively deposits on said starting body to form said preform;f. employing a step for suppressing deposition on inside surfaces of said vessel, which further comprises:f.sub.1. permeating a suppressing gas through an inner wall surface of said tubular vessel; andf.sub.2. configuring said resonator in such a way as to generate only an E.sub.020 field configuration whose E-field is equal to zero on said vessel's inside walls and whose E-field reaches its maximum value on said starting body's periphery.