Mach–Zehnder-Sagnac interferometric curvature sensor based on polarization-maintaining multi-mode fiber using a specified core offset

An interferometric bending sensor based on polarization-maintaining fiber (PMF) in combination with multi-mode fiber (MMF) is proposed and demonstrated experimentally. One end of MMF was fusion spliced to PMF, and the other was fusion spliced to the single mode fiber (SMF) pigtail of a 3 dB optical fiber coupler with a core offset. One stress zone in lead-out Panda type PMF was intentionally aligned and fusion spliced to the core of SMF to enhance mode coupling. A pronounced interference pattern with a fringe contrast of 28.1 dB was obtained, and a bending sensitivity of 18.66nm/m-1 was achieved experimentally. Such a bending sensor with easy fabrication could be a potential candidate for curvature measurements.