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1. (WO2017148528) A METHOD FOR MANUFACTURING A PREFORM FOR OPTICAL FIBERS.

Pub. No.:    WO/2017/148528    International Application No.:    PCT/EP2016/054598
Publication Date: Sat Sep 09 01:59:59 CEST 2017 International Filing Date: Fri Mar 04 00:59:59 CET 2016
IPC: C03B 37/018
C03B 37/014
C03B 37/012
Applicants: PRYSMIAN S.P.A.
Inventors: GONNET, Cedric
ADIGRAT, Antonio
COCCHINI, Franco
SCHIAFFO, Antonio
MILICEVIC, Igor
VAN STRALEN, Mattheus Jacobus Nicolaas
KRABSHUIS, Gertjan
Title: A METHOD FOR MANUFACTURING A PREFORM FOR OPTICAL FIBERS.
Abstract:
The present invention relates to a method for manufacturing a preform for optical fibers, which method comprises the sequential steps of: i) deposition of non-vitrified silica layers on the inner surface of a hollow substrate tube; ii) deposition of vitrified silica layers inside the hollow substrate tube on the inner surface of the non-vitrified silica layers deposited in step i); iii) removal of the hollow substrate tube from the vitrified silica layers deposited in step ii) and the non-vitrified silica layers deposited in step i) to obtain a deposited tube;iv) optional collapsing said deposited tube obtained in step iii) to obtain a deposited rod comprising from the periphery to the center at least one inner optical cladding and an optical core; v) preparation of an intermediate layer by the steps of: * deposition of non-vitrified silica layers on the outside surface of the deposited tube obtained in step iii) or deposited rod obtained in step iv) with a flame hydrolysis process in an outer reaction zone using glass-forming precursors, and subsequently; * drying and consolidating said non-vitrified silica layers into a vitrified fluorine-doped silica intermediate cladding layer; and * in case preceding step iv) was omitted collapsing; to provide a solid rod comprising from the periphery to the center the intermediate layer, at least one inner optical cladding and an optical core; wherein a fluorine-comprising gas is used during the deposition and/or drying and/or consolidating and wherein the intermediate layer has a ratio between the outer diameter of the intermediate cladding layer (C) to the outer diameter of the optical core (A) that is at least 3.5; vi) deposition of natural silica on the outside surface of the intermediate cladding layer of the solid rod obtained in step v) by melting natural silica particles in an outer deposition zone to produce an outer cladding whereby a preform is obtained.