Patent ID: 8011209

Claim:
A method of making a glass, the method comprising the steps of: (1) determining a final set-value concentration of a refractive index control substance depending on a target refractive index of the glass; (2) putting a soot glass deposit body having an effective portion in a container; (3) doping the refractive index control substance into the soot glass deposit body by supplying a doping gas into the container and discharging the gas from the container, wherein the doping gas contains the refractive index control substance; and (4) consolidating the soot glass deposit body by heating, wherein in the process of doping the refractive index control substance, the container is first supplied with the doping gas including the refractive index control substance having a concentration set to be higher than the final set-value concentration, then supplied with the doping gas including the refractive index control substance having a set-value concentration lower than the final set-value concentration or the gas including none of the refractive index control substance and finally, supplied with the doping gas including the refractive index control substance having the final set-value concentration into the container such that the refractive index control substance is doped into the soot glass deposit body, and wherein the refractive index control substance gas is flowed at a flow rate f satisfying an equation: f/V <0.012(minute −1 ), in which f (slm) represents a flow rate of the refractive index control substance gas and V (liter) represents a volume obtained by subtracting the volume of the effective portion of the soot glass deposit body from a capacity of the container corresponding to a part surrounding the effective portion of the soot glass deposit body.