Patent ID: 6574993
Filing Date: 2003-06-10
Classification: C03B

Abstract:
A method of applying glass layers, which may or may not be doped, to the interior of a substrate tube by means of a chemical vapour deposition (CVD) technique, using a reactive gas mixture, in order to obtain a preform that exhibits a precisely defined refractive index profile, the method comprising the following steps:a) determining the desired refractive index profile of the preform to be manufactured, b) precisely adjusting both the composition and the supply rate of the reactive gas mixture for manufacturing the intended preform, in conformity with the refractive index profile determined in step a), c) introducing the reactive gas mixture, under the conditions adjusted in step b), into the substrate tube and effecting a reaction therein so as to achieve deposition of the glass-forming oxides onto the interior of the substrate tube and maintaining the overall volumetric deposition rate of the glass-forming oxides onto the interior of the substrate tube at a substantially constant level, d) collapsing the substrate tube obtained from the deposition process of step c) into a preform and subsequently subjecting said preform to a refractive index profile measurement, e) comparing the refractive index profile determined in step a) with the refractive index profile measured in step d), and f) correcting the differences in refractive index profiles measured in step e) by adapting the composition of the reactive gas mixture as a function of time during a subsequent deposition process.