Patent ID: 9643879
Date: 2017-05-09
CPC Classifications: C03B

Claim:
1. A method for manufacturing a primary preform for optical fibres by an internal plasma deposition process, comprising the steps of: (i) providing a hollow substrate tube; (ii) depositing a plurality of non-vitrified silica layers on an inner surface of the hollow substrate tube by inducing a plasma with electromagnetic radiation with first reaction conditions and depositing a plurality of vitrified silica layers on the substrate tube having non-vitrified silica layers on at least a part of its inner surface by inducing a plasma with electromagnetic radiation with second reaction conditions; (iii) cooling the substrate tube of step (ii) having the plurality of non-vitrified and vitrified silica layers deposited on the inner surface of the hollow substrate tube thereby producing a precursor for a primary preform; and (iv) collapsing the precursor for the primary preform produced in step (iii) thereby forming the primary preform, wherein: any non-vitrified layers remaining in the precursor for the primary preform are vitrified during the collapsing of step (iv) while forming the primary preform.