Optical fiber preform cladding fluorine doping method

Abstract

The present invention discloses an optical fiber preform cladding fluorine doping method, which comprises the following steps: depositing a core layer loose body on a target rod; heating the outer surface of the core layer loose body to form a dense layer, such that density of the dense layer is higher than density in the core layer loose body; depositing an inner cladding loose body outside the dense layer to form a core rod loose body comprising the core layer loose body and the inner cladding loose body; taking the target rod out to form a center hole in the center of the core rod loose body; placing the core rod loose body into a glass transition furnace, carrying out heating dewatering in a dewatering atmosphere, and introducing dewatering gas into the center hole during heating; heating the core rod loose body in a fluoride atmosphere, such that fluorine is selectively doped into the inner cladding loose body to form step refraction index distribution; and carrying out glass transition on the core rod loose body, such that the center hole is shrunk, the core layer loose body forms a core layer, and the inner cladding loose body forms an inner cladding so as to form a core rod. With the method, OH<-> content in the core layer can be effectively reduced, attenuation of optical fiber 1383 nm can be reduced, and fluorine distribution in a radial direction of the cladding is uniform.

Description

technical field [0001] The invention relates to a method for manufacturing an optical fiber preform, in particular to a method for doping the cladding of an optical fiber preform with fluorine. Background technique [0002] Optical fiber preform is the raw material for drawing optical fiber. Its basic structure includes a core layer and a cladding layer with a lower refractive index (the cladding layer can also include an inner cladding layer and an outer cladding layer). SiO 2 It is the main glass former used to make optical fiber preforms, and its refractive index can be changed by doping to form a waveguide structure. Generally doped with GeO in the core layer 2 , so that the refractive index of the core layer is higher than that of the cladding pure silica glass. The relative difference between the refractive index of the core layer and the cladding layer is expressed by the relative refractive index difference Δ, and the refractive indices of the core layer and the c...

AI Technical Summary

Problems solved by technology

This method has the following problems: Since the blowtorch sprays fluorine-containing gas to a certain part of the loose body from one direction, it is difficult to ensure the axial and radial uniformity of fluorine doping

The problem caused by this is: since the core layer and cladding layer of the deposited mandrel are both loose bodies containing a large number of pores, when vitrification is doped with fluorine, fluorine not only diffuses into the cladding layer, but also enters the core layer, resulting in It is difficult for fluorine to be selectively doped into the cladding layer to form a refractive index profile structure

Obviously, this method is as difficult to form a step-type refractive index profile structure as the method of the US patent application with the publication number US2002 / 0073740 A1

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