Development of ultralow-loss glasses by controlling density fluctuations

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Since light scattering loss in silica fiber is dominantly caused by "frozen-in" density fluctuations at the glass transition temperature, investigations of structural relaxation around the glass transition temperature are necessary for developing ultralow-loss silica glasses. In this project we tried to measure various properties of silica glasses over a wide-temperature range including the glass transition temperature, and have elucidated structural relaxation processes and their impurity effects as follows :(1)OH or Cl enhances the alpha -relaxation governed by viscous flow, and also generates a sub-relaxational process.(2)he sub-relaxational process is local structural change caused by impurity diffusion.From these results, we have established controlling the structural relaxation by impurity doping, which is a basic technology to develop ultralow-loss glasses. For example, the light scattering loss was reduced by 13% by the addition of only 10 wt.ppm Na_2O to silica glass. This method is also useful for developing silica glasses with high performances such as high UV-proof and high heat-proof properties.