Ultrasensitive temperature sensor based on cascading a polarization mode interferometer with a Fabry-Perot interferometer

An ultrasensitive temperature sensor based on cascading a polarization mode interferometer (PMI) with a Fabry-Perot interferometer (FPI) is proposed and demonstrated. The sensing interferometer PMI is fabricated by splicing high-birefringence ultra-fine polarization-maintaining fiber (UFPMF) with a polarizer for temperature sensing. The FPI, made by splicing a section of hollow core photonic crystal fiber (HCPCF) between two single mode fibers (SMFs), is temperature-insensitive and is used as a reference interferometer. The free spectral ranges (FSRs) of PMI and FPI can be made close to each other by adjusting the length of the UFPMF, thus producing a vernier effect and achieving sensitivity enhancement. Experimental results show that the temperature sensitivity of the cascaded sensor is enhanced from −1.134 nm/°C for sensing PMI to 54.589 nm/°C, and its detection limit (DL) is degraded from 3.98 × 10−3 °C for sensing PMI to 5.13 × 10−3 °C, so that the appropriate sensor should be selected depending on the detection requirements in practical applications. The proposed sensor has high sensitivity, simple structure, easy manufacture, and low cost, and is suitable for application fields requiring high-sensitivity temperature measurement.