| 摘要 |
PURPOSE:To obtain a preform of a low temperature loss with hardly any residual amount of OH groups, by feeding chlorine-containing He gas from the terminal of a calcining furnace on the side for feeding a preform into the furnace and using a furnace core tube having a specific inside diameter in transparently vitrifying a porous preform for an optical fiber by a vapor axial deposition method. CONSTITUTION:A furnace core tube 21 having an inside diameter (a) thereof in relation to the diameter (b) of a porous preform to be calcined for an optical fiber satisfying condition of 0.8a<b<0.95a is placed in the interior of a calcining furnace. The porous preform 22 for the optical fiber is then fed into the furnace core tube 21 by a vapor axial deposition method and chlorine-containing He gas is simultaneously fed from the terminal in the furnace on the side for feeding the preform 22 to calcine and transparently vitrify the preform 22. As a result, mixing of the outside air into the furnace can be suppressed to thereby produce the aimed transparent preform which is subjected to sufficient dehydroxylation treatment for the optical fiber of a low loss. |
