A method for the manufacture of a precursor for a primary optical fiber preform by a plasma deposition process and a precursor for a primary preform provided with unglazed and vitrified silica layers deposited on its inner surface.

摘要

A method for the manufacture of a precursor for a primary optical fiber preform by a plasma deposition process and a precursor for a primary preform provided with unglazed and vitrified silica layers deposited on its inner surface. The present invention relates to a method for the manufacture of a precursor. In other words, the present invention relates to a method for a primary preform for optical fibers by means of an internal plasma deposition process, which method comprises the steps of: providing a hollow substrate tube having a side of supply and a discharge side; creating a first plasma reaction zone having first reaction conditions within said hollow substrate tube by electromagnetic radiation to deposit non-vitrified silica layers on at least part of the inner surface of said substrate tube in or near a reversal point on the discharge side to provide a substrate tube having unglazed layers on at least part of its inner surface; and subsequently creating a second plasma reaction zone having second reaction conditions within said hollow substrate tube by electromagnetic radiation to deposit vitrified silica layers into said substrate tube having non-vitrified layers in said substrate. at least a part of an inner surface to obtain a substrate tube having deposited unglazed and vitrified silica layers; and cooling the deposited unglazed silica layer tube obtained in step iii) to obtain said precursor to a primary preform.