| 摘要 |
PURPOSE:To enable the addition of even a dopant having low vapor pressure into a prescribed preform, by successively depositing a quartz glass layer and a dope layer in a glass pipe and successively carrying out the oxidation of the dope layer and the diffusion of the dopant into the glass layer. CONSTITUTION:A clad-forming glass layer 8 having a prescribed thickness is deposited on the inner circumference of a rotating quartz glass pipe 1 in CVD process and another clad-forming glass layer 9 is deposited on the inner circumference of the layer 8. A raw material 5 for dope is heated in the pipe 1 with a burner 7 in a doping process after forming the layers 8, 9 and the evaporated raw material is deposited on the inner circumference of the layer 9 to form a deposited dopant layer 10. No oxidation of the layer 10 occurs in the above process since the layer 10 is formed in an O2-free atmosphere. After forming the layers 8-10, the pipe 1 is heated while supplying O2 into the pipe 1 to oxidize the layer 10. The pipe 1 is collapsed in an electrical furnace and, at the same time, the layer 10 is diffused into the layer 9 by the heat of collapse to obtain a quartz glass preform 11. |
