Highly sensitive temperature and strain sensor based on polarization mode interferometer with Vernier effect

A new cascaded optical fiber temperature and strain sensor based on polarization mode interferometer (PMI) and Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally. The PMI made by fusion splicing a segment of polarization maintaining fiber (PMF) after a polarizer is used as a sensing interferometer. Inte-grating a FPI as a reference interferometer cascaded after the PMI to generate the Vernier effect and improve sensitivity. The FPI is made from a small segment of hollow core photonic crystal fiber (HCPCF), which is fusion spliced to PMF and multi-mode fiber (MMF) at each end to form two reflective surfaces of FPI. Based on nu-merical simulations, a suitable free spectral range (FSR) of the sensor is produced. Experimental results show that the temperature sensitivity can be improved from-1.095 nm/& DEG;C to-22.753 nm/& DEG;C and the strain sensitivity can be improved from 2.17 pm/& mu;& epsilon; to 38.89 pm/& mu;& epsilon; by using the Vernier effect. The measured amplification factors are about 21 and 18,respectively. The high sensitivity of PMI and FPI cascaded sensors with the Vernier effect offers a new option for simultaneous measurements in the field of temperature and strain.