Construction of cascaded Fabry–Perot interferometers by four in-fiber mirrors for high-temperature sensing

An optical fiber high-temperature sensor is proposed and demonstrated by use of cascaded Fabry-Perot interferometers based on four in-fiber mirrors fabricated by femtosecond laser inscription. The output fringe pattern of the device exhibits dominant/highly distinguishable dip wavelength, which helps in unambiguous measurement beyond the free spectral range. The device has excellent thermal stability in high temperature up to 1100°C, and the temperature sensitivity obtained is 9.91 pm/°C within the temperature range of 100°C to 400°C, and 15.88 pm/°C within the temperature range of 400°C to 1100°C, respectively. The device features compact size, simple fabrication, and convenient operation, which make it attractive for monitoring of extreme environment.