Ultracompact optical fiber high‐temperature sensor based on the angled fiber end face

Abstract An ultracompact optical fiber Fabry–Perot interferometric sensor is proposed and demonstrated for high‐temperature measurement. The device is simply a section of single‐mode fiber with angled end face of 45°, the reflected light from the angled fiber end face is directed sequentially to the fiber core–cladding and cladding–air interfaces, respectively, and reflected back, and finally returned to the fiber core after being reflected by the angled fiber end face again. As a result, a Fabry–Perot interferometer is constructed. Because of the thermal‐expansion and thermal‐optical effect of the fiber material, the optical path difference between the core–cladding and cladding–air surfaces is changed with temperature, hence the device is well suitable for temperature measurement. In particular, the fiber device has good high‐temperature sustainability up to 1100°C, which makes it attractive for high‐temperature measurement in a narrow or hard‐to‐reach spatial environment.