Investigation on the thermo-optic coefficient of silica fiber within a wide temperature range

In this paper, the thermo-optic coefficient of silica fiber is analyzed and measured within a wide temperature range of 0-1200 °C for the first time. To obtain the thermo-optic coefficient, experiments were carried out by using fiber optic extrinsic Fabry-Perot interferometers (EFPIs) embedded in silica fiber. The optical cavity lengths of the EFPIs were measured with white-light interferometry. The experimental results show that the first and second orders of the thermo-optic coefficient are 1.090 × 10^-5/°C and 1.611 × 10^-9/°C², respectively. The quadratic model for the temperature dependence of the basic optical parameter, the refractive index, is rigorous within a wide temperature range. Furthermore, this paper also provides a temperature calibration method for extrinsic Fabry-Perot interferometric temperature sensors. The temperatures measured by the sensors are in excellent agreement with those measured by the reference thermocouple. Hence, this calibration method is promising for temperature sensors with a wide working temperature range.