Research on temperature sensing characteristics with cascaded fiber Sagnac interferometer and fiber Fabry–Perot interferometer-based fiber laser

We have proposed and experimentally demonstrated a compact temperature sensor based on cascaded fiber Sagnac interferometer (FSI) and fiber Fabry–Perot interferometer (FFPI) with Vernier effect. The FSI is composed of a certain length of panda polarization-maintaining fiber and a 3-dB four-port coupler, whereas FFPI consists of two collimators and a wave plate. Both are used for temperature sensing, but where FSI is more sensitive to temperature than FFPI, the free spectral ranges of the two interferometers differ by 0.12 nm. The experimental results show that the temperature sensitivity is increased from −1.7 nm / ° C (single FSI) and 0.008 nm/°C (single FPI) to 10.28 nm/°C (cascade configuration), which is basically consistent with the theoretical analysis (10.82 nm/°C).