Patent ID: 7391946

Claim:
A method for producing an optical fiber preform using MCVD (Modified Chemical Vapor Deposition), comprising: (a) forming at least one base clad layer by depositing soot including SiO 2 and GeO 2 on an inner wall of a quartz tube and heating the quartz tube with the soot deposited at a high temperature; (b) forming at least one dehydrated clad layer with a refractive index substantially identical to that of the base clad layer by repeating the following steps at least once: an accumulation step for introducing a soot forming gas into the quartz tube together with a carrier gas and heating an inside of the quartz tube to a temperature of 1000° C. to 1400° C. to generate soot including SiO 2 and GeO 2 , and then accumulating the soot on the base clad layer; a dehydration step for introducing a dehydration gas into the quartz tube and heating the inside of the quartz tube to a temperature of 600° C. to 1200° C. to remove hydroxyl groups (OH) and moisture in the soot and the quartz tube; and a sintering step for heating the inside of the quartz tube with the soot deposited at a temperature higher than 1700° C. so that the soot is sintered and vitrified, (c) forming at least one core layer with a relatively higher refractive index on the clad layer by repeating the following steps at least once: an accumulation step for introducing a soot forming gas into the quartz tube together with a carrier gas and heating the inside of the quartz tube to a temperature of 1000° C. to 1400° C. to generate soot, and then accumulating the soot on the dehydrated clad layer; a dehydration step for introducing a dehydration gas into the quartz tube and heating the inside of the quartz tube to a temperature of 600° C. to 1200° C. to remove hydroxyl groups (OH) and moisture in the soot and the quartz tube; and a sintering step for heating the inside of the quartz tube with the soot deposited at a temperature higher than 1700° C. so that the soot is sintered and vitrified.