Highly sensitive fiber optic sensing system based on two fiber Bragg gratings and microwave photonic filter for temperature measurement

We propose and experimentally demonstrate a highly sensitive fiber optic sensing system based on two fiber Bragg gratings (FBGs) and microwave photonic filter (MPF) for temperature measurement. The reflection intensity of the two FBGs is determined by their wavelength location at the optical spectrum of the fiber optic interferometer sensor. The reflected light of the two FBGs are used as the two taps of the MPF, and the change of the FBGs’ intensity caused by the temperature variations on the fiber optic interferometer sensor can be mapped to the change of the MPF’s intensity. In our experiment, we have used the Sagnac interferometer (SI) as the temperature sensing element for a demonstration. The temperature applied to the SI can be demodulated by detecting the intensity of the MPF. The experimental results show that by detecting the intensity one of the peaks of the MPF, the sensitivity of 23.22 dB/°C, 13.71 dB/°C, 8.95 dB/°C can be achieved when the two FBG’s wavelength interval is 0.5 nm, 1nm, and 1.5nm, respectively.