PURPOSE: To produce the title base material having a desired refractive index distribution by controlling the temp. distribution on the growing surface of a porous base material and the concn. of GeO2 in the material after which the material is heat defoamed and converted into a transparent glass base material.
CONSTITUTION: By regulating the kind and the flow rate of an inert gas and the flow rate of an oxyhydrogen flame the temp. for synthesizing glass fine particles is set in a temp. range where SiCl4→SiO2 reaction efficiency is high and GeCl4→ GeO2 reaction efficiency is low, whereby Si and Ge are spouted as SiO2 and GeCl4, respectively in a stream of glass fine particles, and GeCl4→GeO2 reaction is induced on the surface of porous base material 77 with reaction efficiency corresponding to the temp. of the spot. Thus, a GeO2 concn. distribution is formed in material 77, and the temp. distribution on the growing surface of material 77 is measured with two-dimensional measuring unit 74. This distribution is compared to the set temp. distribution of comparator 712, and the result is fed back to auxiliary heat source 73 to correct the surface temp., thereby controlling the GeO2 concn. distribution.
KAWACHI MASAO
TOMARU AKIRA
EDAHIRO TAKAO
