| 摘要 |
PURPOSE:To prevent cracking of soot when soot layers having large outer diameter is deposited by VAD method. CONSTITUTION:Soot layers are successively formed on the bottom end of a target rod 1 to form a cylinderical soot 2 by using burners 4, 5, 6 while the target rod is rotated and drawn by a rotating drawing device 3. A gas supply device 7 is controlled by a controller 8 to control the flow rate of gas supplied to burners 4-6 in such a manner that the outer diameter of the second soot layer deposited with the burner 5 does not exceed four times of the outer diameter of the first soot layer deposited with the burner 4, and that the outer diameter of the third soot layer deposited with the burner 6 does not exceed four times of the outer diameter of the second soot layer 2 deposited with the burner 5. |
