Method for manufacturing an optical fiber preform

A method of manufacturing a glass preform having a circular cross section and a predetermined radial refractive index distribution, from which an optical communication fiber may be drawn, comprising the steps of:

• (a) disposing a start member in spaced axial alignment with a burner tip including a plurality of concentric nozzles,
• (b) rotating said start member,
• (c) blowing a first gaseous raw glass material having a first dopant concentration which increases the index of refraction of the resulting glass through a central nozzle of said burner tip and toward said start member,
• (d) blowing a second gaseous raw glass material having a second dopant concentration which decreases the index of refraction of the resulting glass through a first concentric nozzle of said burner tip surrounding said central nozzle and toward said start member,
• (e) blowing an inflammable gas including hydrogen and oxygen through outer concentric nozzles of said burner tip surrounding said first concentric nozzle, whereby soot-like glass particles are synthesized proximate said burner tip through flame hydrolysis by burning said inflammable gas and deposit on the end of said start member,
• (f) withdrawing said start member from said burner tip to maintain a substantially constant spacing therebetween, whereby a soot-like glass rod having a circular cross-section is grown on said start member having a predetermined radial dopant concentration distribution, and
• (g) heating said soot-like glass rod to render it to be a transparent glass preform having a predetermined radial refractive index distribution.