| 摘要 |
PURPOSE:To restrain generation of bubbles caused by viscosity difference by providing an F-doped quartz layer which is doped with F whose dosage is less than the F dosage of an F-doped quartz glass clad between the F-doped quartz glass clad and a pure quartz glass outer layer. CONSTITUTION:An F-doped quartz glass layer whose F dosage is less than that of an F-doped quartz glass clad and viscosity is higher than that thereof is provided between the F-doped quartz glass clad and a pure quartz glass outer layer. Specific refractive index difference DELTA between the F-doped quartz glass clad and the pure quartz glass is -0.4 to 0.7% and specific refractive index difference DELTA between the F-doped quartz glass layer and the pure quartz glass is about -0.2 to 0.6$. The viscosity of the F-doped quartz glass layer provided between the F-doped quartz glass clad and the pure quartz glass outer layer is higher than the viscosity of clad and comes near pure SiO2. Thereby, generation of bubbles caused by the viscosity difference can be restrained. |
