PREPARATION OF PARENT MATERIAL FOR OPTICAL FIBER

PURPOSE:To prepare the titled parent material having a refractive index distribution constantly controlled to an optimum value with sufficient reproducibility constructing a burner for discharging source gas to be used for deposition of soot to a concentric multilayered structure and feeding an inert gas from the center of the burner. CONSTITUTION:Flame hydrolysis of a gaseous starting material for the glass is carried out by feeding O2 to the outermost layer 1, H2 to the second layer 2, inert gas to the third layer 3, gaseous starting material to the fourth layer 4, each counting from the outside, of a concentric multilayered burner 41, and an inert gas is fed to the central layer 5. Obtd. fine particles of the glass are deposited on the soot 42. By this method, the reaction efficiency at the central part is reduced and the temp. near the center of the bottom surface is lowered. Therefore, sharp distribution of refractive index is eliminated and a parent material for an optical glass fiber having an optimum refractive index distribution is obtd.