In-Fiber Fabry–Perot Cavity Sensor for High-Temperature Applications

The fabrication, characterization and encapsulation of a fiber optic temperature sensor based upon a micro Fabry-Perot (F-P) cavity is presented. The F-P cavity is formed between a reflective in-fiber metallic splice and the air-fiber boundary at the end of the sensor. A change in temperature modifies the optical cavity length, and this is observed as a change in the reflected interference spectrum. The sensor has been demonstrated for high-temperature measurement up to 1100 °C. The stability of the sensor system is ~10 °C over a period exceeding 300 h at 1100 °C. Furthermore, a sealed capillary is used as a protective enclosure.