Development of ultralow-loss glasses by controlling density fluctuations

由于石英光纤中的光散射损耗主要是由玻璃化转变温度下的“冻结”密度起伏引起的，因此研究玻璃化转变温度附近的结构弛豫对于开发超低损耗石英玻璃是必要的。在本项目中，我们试图在包括玻璃转变温度在内的宽温度范围内测量石英玻璃的各种性质，并阐明了结构驰豫过程及其杂质效应如下：(1)OH或Cl增强了粘性流动所支配的α-驰豫过程，并产生了亚弛豫过程。(2)亚驰豫过程是由杂质扩散引起的局部结构变化。根据这些结果，我们建立了通过掺杂来控制结构驰豫的方法，这是开发超低损耗玻璃的基本技术。例如，仅在石英玻璃中添加10wt.ppm的Na2O，光散射损耗就降低了13%。该方法也可用于开发高抗紫外线、高耐热等高性能的石英玻璃。

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.