A new curvature sensor based on SMS fiber structure using ring-core fiber and its demodulation by microwave photonic filter

Curvature measurement is important in the fields of structure health monitoring, robot-pose measurement, etc. The curvature-sensor with high resolution is highly needed. In this paper, an optical curvature sensor with high resolution based on single-mode-multimode-single-mode (SMS) structure using ring core fiber (RCF) is proposed and its demodulation is realized by the microwave photonic filter (MPF). The SMS fiber structure is a typical in-fiber Mach-Zehnder interferometer (MZI). The operating principle of the proposed sensor is that different curvatures will cause the variations of the interference spectrum of the SMS-sensor, and then the variations are converted into the frequency-shift of the MPF. Theoretical analysis and experiment are verified. The measured sensitivity is -147.634 MHz/m^-1, and the resolution is 6.774 × 10^-6m^-1 which is the highest value up to now.