Apparatus and method for performing a PCVD process

A method for depositing one or more doped or undoped glass layers onto the interior of a glass substrate tube having a supply side and a discharge side via an apparatus;

• the apparatus comprising an applicator having an inner wall and an outer wall and a microwave guide for guiding microwaves, wherein the microwave guide opens into the applicator, with the applicator extending around a cylindrical axis and being provided with a passage adjacent to the applicator's inner wall, through which microwaves supplied via the microwave guide can exit, the glass substrate tube being positionable over the cylindrical axis, the applicator being surrounded by a furnace that extends over the cylindrical axis, wherein the applicator is movable via an applicator stroke along the cylindrical axis between a point of reversal located at the glass substrate tube's supply side and a point of reversal located at the glass substrate tube's discharge side, wherein the furnace is reciprocally movable via a furnace stroke with respect to the glass substrate tube along the longitudinal axis thereof;
• wherein the substrate tube is placed over the cylindrical axis, within the inner wall of the applicator, to which interior of the substrate tube glass-forming precursors are supplied, while the applicator is surrounded by a furnace that extends over the cylindrical axis, wherein the substrate tube and the applicator are essentially co-axial, wherein the applicator is moved reciprocally along a length of the substrate tube during the deposition process to create plasma conditions for forming glass layers on the interior surface of the glass substrate tube, wherein the furnace is moved with respect to the substrate tube along the longitudinal axis thereof during the deposition process, and wherein the furnace stroke is different from the applicator stroke.