| 摘要 |
PROBLEM TO BE SOLVED: To reduce a used amount of a dopant for changing a refractive index, when producing a glass preform by VAD method.SOLUTION: An addition amount of a dopant when depositing a non-effective part Gb of a glass fine particle deposited body G, at the deposition start time and at the deposition finish time, is reduced furthermore than an addition amount when depositing an effective part Ga of the glass fine particle deposited body G, during at least a half or longer of a deposition time for depositing the non-effective part Gb.SELECTED DRAWING: Figure 1 |
