Hybrid Sapphire Dual-Fabry—Perot-Cavities Sensor for High Temperature and Refractive Index Measurement

We presented a hybrid sapphire dual-Fabry-Perot- cavities sensor for high temperature and refractive index measurement. A double-sided polished sapphire solid wafer is connected in series with a double-sided parallel sapphire C-ring and a single-sided polished sapphire mirror to form the hybrid Fabry-Perot interferometer. The double-sided polished sapphire solid wafer acts as the first Fabry-Perot cavity for temperature sensing, and the sapphire hollow C-ring cavity constitutes the second Fabry-Perot cavity for measuring the refractive index of external environment medium. The single-sided polished sapphire mirror serves as the most distal reflector. Heterogeneous fiber splicing between sapphire fiber and multimode silica fiber is realized to achieve long-distance transmission of interference signals. A series of high temperature measurement experiments range of room temperature to 1080 °C in an air environment and refractive index measurement experiments in a liquid environment were carried out. Based on the changing rates of corresponding Fabry-Perot cavity optical path difference against refractive index and temperature, we calculated the sensitivities of the sensor. The refractive index and temperature sensitivities were 2.0659 × 10
⁵
nm/RIU in the RI range of 1.3330~1.3741 and 7.837 nm/ °C at 1080 °C.