Patent ID: 9593037
Date: 2017-03-14
CPC Classifications: C03B,C23C

Claim:
1. A method for carrying out a plasma deposition process, comprising the steps of: i) providing a hollow substrate tube; ii) supplying a supply flow of dopant-containing glass-forming gases to the substrate tube of step i), wherein the supply flow comprises a main gas flow and one or more secondary gas flows, the main gas flow primarily comprising the glass-forming gases and the one or more secondary gas flows primarily comprising precursors for dopant(s); iii) inducing a plasma by means of electromagnetic radiation in at least a part of the substrate tube of step ii) to create a reaction zone in which deposition of one or more glass layers onto an interior surface of the substrate tube occurs; iv) moving the reaction zone back and forth in a longitudinal direction over the substrate tube between a reversal point located near the supply side and a reversal point located near the discharge side of the substrate tube, wherein each forward movement and back movement is a stroke; wherein the at least one or more secondary gas flows through a mass flow controller and a valve positioned between the mass flow controller and the hollow substrate tube, the mass flow controller maintaining a constant flow of the at least one secondary gas originating from the mass flow controller regardless of an opened or closed state of the valve; wherein the flow of the one or more secondary gas flows is interrupted by closing the valve one or more times during step iii), each interruption having a start point and an end point as a function of an axial position of the plasma along the length of the substrate tube; wherein the start point and the end point of each interruption both lie within the same stroke; and wherein each interruption has a duration of no more than 10% of a total time of the stroke thereby achieving uniform thickness and uniform refractive index profile of the deposited glass layers in an axial direction.