Temperature sensor based on fiber Bragg grating combined with a microwave photonic-assisted fiber loop ring down

A temperature sensor based on fiber Bragg grating (FBG) combined with a microwave photonic-assisted fiber loop ring down (FLRD) is proposed and experimentally investigated. An optical edge filter (OEF) is inserted in the FLRD to provide a wavelength dependent loss; thanks to the linear response of the OEF, the wavelength shift of the FBG caused by the applied temperature is linearly converted to the additional loss of the FLRD. The frequency response of the FLRD is measured by a vector network analyzer (VNA), the time domain ring-down curves are calculated by applying invert faster Fourier transform (IFFT) to the frequency response. Subsequently, the relationship between the ring-down time and the temperature applied to the FBG is obtained. Results show a good linearity between the ring-down time and the temperature. Limited by the VNA used in our experiment, the sensitivity of the proposed sensor is 6.30 ns/°C in the temperature range of 40-45 °C with a resolution of ±0.14 °C.