| 摘要 |
PURPOSE: To turn the axial refractive index of the porous preformed material after transparently vitrified invariant, by dehydrating a porous preformed material made by accumulating fine glass particles so as to axially alter the bulk density, and then by conducting a transparent vitrification. CONSTITUTION: H2 gas, O2 gas, a glass stock gas, carrier gas and a dopant gas for refractive index control, are fed to a core synthesizing burner 5 and a clad synthesizing burner 6 to effect hydrolysis in the flames to produce fine glass particles which are then accumulated on the surface of a starting material to be pulled up under revolution, thus making a porous preformed material 3. In this case, the flow of the H2 gas to be fed to the burner 4 is controlled by a controller 7 to obtain the porous preformed material 3 with its bulk density altered axially. The preformed material 3 is then put in a hot oven and fed, with the end thereof as the forefront, into the high-temperature zone of the oven where it is dehydrated, and the resultant material is fed into the second high-temperature zone of the oven where it is transparently vitrified. |
