A method for manufacturing a preform for optical fibers.

Abstract

The present invention relates to a method for manufacturing a preform for optical fibers. The 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 bythe 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 anouter 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; andin 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;with a fluorine-comprising gas being used during the deposition and / or drying and / or consolidating, and the intermediate layer having 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; and vi) deposition of natural silica on the outside surface of the intermediate cladding layer of the solid rod obtained instep v) by melting natural silica particles in an outer deposition zone to produce an outer cladding whereby a preform is obtained.

Description

technical field [0001] The present invention relates to a method for manufacturing a preform for optical fibers. Furthermore, the invention relates to the preforms thus obtained and to the optical fibers obtained from the preforms. The present teaching relates to the field of manufacturing optical fibers by means of chemical vapor deposition (CVD) in which a layer of silicon oxide is deposited on a substrate; examples of said chemical vapor deposition are modified chemical vapor deposition (MDD), plasma-enhanced Chemical Vapor Deposition (PECVD or PCVD), and Outside Vapor Deposition (OVD). Background technique [0002] From WO 2015 / 002530 of the applicant is known a method for the manufacture of a primary preform precursor, wherein the method comprises the steps of: i) providing a hollow substrate tube; ii) by means of electromagnetic radiation inside said hollow substrate tube generating a first plasma reaction zone with first reaction conditions to effect deposition of n...

AI Technical Summary

Problems solved by technology

[0003] Commercially available substrate tubes are made difficult to obtain in sufficient quality due to a double constraint; firstly, the substrate tube must have a certain purity of the glass used, and secondly, the substrate tube must be provided with a certain size of outer and inner diameter, and these dimensions are relative to The length of the base pipe must be within very narrow margins

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