Abstract

A novel and small curvature sensor based on the butterfly-shaped Mach–Zehnder interferometer is proposed and experimentally demonstrated. The sensing element is a tapered hollow-core fiber sandwiched between two single-mode fibers. The fusion-collapsed region around the first fusion interface excites the high-order modes, and the butterfly-shaped structure couples the high-order modes back into the core and interferes with the fundamental mode in the second fusion-collapsed interface. Simulation of the butterfly-shaped structure is carried out by the beam propagation method to determine an optimized size of sensing element. The experimental results show that the light intensity variation of the interference spectrum is almost linearly proportional to the change of curvature, and the curvature sensitivity and resolution of the proposed sensor can be up to −10.9041 dB/m−1 and 0.000917 m−1, respectively, in the range from 0.387 to 1.285 m−1. The proposed curvature sensor is compact in size, high sensitive, and inexpensive. The excellent electromagnetic interference resistance and fabrication simplicity make the device an attractive candidate for curvature measurement in harsh environments.

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