Optical fiber temperature sensor with Vernier effect formed by Mach–Zehnder interferometer cascaded Sagnac interferometer based on Hollow-core photonic crystal fiber

This research proposes a Mach–Zehnder interferometer (MZI) based on hollow-core photonic crystal fiber (PCF) and a Sagnac interferometer (SI) based on polarization maintaining fiber (PMF). A stable reference interferometer is formed by using PCF which is insensitivity to temperature and the temperature monitoring is realized by using PMF which is sensitivity to temperature. The two interferometers are cascaded through a 3 dB optical fiber coupler to generate the Vernier effect by controlling the lengths of the two fibers, thereby improving the temperature sensitivity of the sensing structure. The length of PCF is 1.22 mm and PMF is 1.65 m, the experimental results show that the highest temperature sensitivity of 12.02 nm/°C is obtained. The proposed sensor not only has ultra-high temperature sensitivity, but also has scarcely response to physical quantities, such as refractive index, strain and so on. This sensor has reduced the generation of cross-talk in the measurement process, and has great application prospects in several fields. •A high-sensitivity temperature sensor based on the Vernier effect was proposed.•The effect of crosstalk during measurement was reduced.•The cascade configuration is easy to control and fabricate.•The combination of PCF and PMF provides a novel idea for the design of sensors.•The all-fiber structure is applicable to a wide range and has strong practicability.