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A novel and small curvature sensor based on butterfly-shape Mach-Zehnder interferometer

A novel hollow-core fiber (HCF) curvature sensor based on a tapered HCF sandwiched between two single mode fibers (Butterfly-Shape Structure) is proposed and experimentally demonstrated. The collapsed region around the first fusion interface excites the high-order modes, and the butterfly shape couples the high-order modes back into the core and interferes with the fundamental mode in the second fusion interface. Simulation of the butterfly-shape structure is carried out using the beam propagation method to determine an optimized size of sensing element. The experimental results show that the variation of the interference spectrum light intensity is almost linearly proportional to the change of curvature, and the curvature sensitivity and resolution of the proposed sensor can be up to −10.9041dB/m−1 and 0.000917m1 respectively in the range from 0.387 to 1.285m−1. The proposed curvature sensor is compact size, high sensitive, and inexpensive.