Study on Vernier effect of orthogonal Mach-Zehnder interferometers based on Polarization-maintaining fiber

A polarization-maintaining fiber interferometer (PMI) is proposed and experimentally verified for temperature measurement using the Vernier effect. The PMI is fabricated by inserting a section of polarization-maintaining fiber (PMF) between two pieces of multimode fiber (MMF). Owing to the birefringence of PMF, the PMI contains a pair of orthogonal Mach-Zehnder interferometers (MZIs). The interference occurs between the cladding mode and two orthogonal polarization modes that the polarization directions parallel to the slow and fast axis of the PMF, which results in the formation of MZI-X and MZI-Y. The sensing mechanism of the PMI is theoretically studied and experimentally verified. The temperature sensitivity of the PMI reaches −757.27 pm/℃ through demodulating Vernier envelopes generated by two orthogonal MZIs. The length of the proposed PMI is only 15.4 mm, which is much smaller than most sensors based on the Vernier effect. Consequently, the PMI has great potential in the temperature monitoring of small spaces.