Temperature measurement by thermal luminescence of partially replaced core optical fiber

A partially replaced core optical (PARCO) fiber - a fiber chip doped with high concentration of oxyhydrate (OH) inserted into a pure silica core fiber to measure temperatures with a spatial resolution. A heating experiment was performed at elevated temperatures with a PARCO fiber under gamma ray irradiation. The PARCO fiber had a characteristic thermal luminescent peak at 1390 nm that exhibited temperature dependence. When the temperature was raised up to 1000 °C, the other broad luminescence bands than the peak at 1390 nm was generated and grew. Optical surface observation showed that morphology change of a flat clad surface was taking place, suggesting some thermal damage of the surface. The damaged area had positive correlation with the intensity of the observed broad luminescence band. Transmission electron microscopy (TEM) showed that the damage related with the crystallization of the glassy structure of fused silica in the near-surface region.