| 摘要 |
PROBLEM TO BE SOLVED: To provide a new method for sintering a porous preform by which the uniformization of the refractive index distribution and formation thereof into a rectangular shape in the longitudinal direction can be carried out and an increase in transmission loss can be prevented. SOLUTION: A heating element 4 for OH removal treatment having a length surrounding the whole of an SiO2 layer 2 and a heating element 5 for transparentizing and vitrifying are arranged in the upper part and the lower part around a furnace core tube 3 for passing a porous preform p obtained by a vapor axial deposition(VAD) method therethrough and the OH removal treatment is carried out with the heating element 4 for the OH removal treatment. The resultant porous preform p is then intactly moved in the interior of the furnace core tube 3, subsequently sintered on the side of the heating element 5 for transparentizing and vitrifying and transparentized and vitrified. Thereby, since the temperature distribution is uniformized, the shortening of the variation breadth of the specific refractive index and uniformization of the refractive index distribution, formation, etc., thereof into a rectangular shape in the longitudinal direction can be achieved. |
