High-Sensitive Curvature Sensor Based on Negative Curvature Hollow Core Fiber

A high-sensitive curvature sensor based on the negative curvature hollow core fiber (NCHCF) is proposed and demonstrated. The graded index fiber (GIF) is introduced between single-mode fiber (SMF) and NCHCF for the cascaded structure of SMF-GIF-NCHCF-GIF-SMF. Compared to the structure without GIF, the coupling efficiency is improved by 16.5%. For the cascaded structure, multi-mode interference (MMI) and anti-resonance (AR) mechanisms coexist in the transmission spectra. The experimental results show that MMI-based dips have a blue shift as curvature increases while AR is not sensitive to its variation. As such, the self-referencing approach is employed for improving the performance of the curvature sensor with a sensitivity of up to -5.27 nm/m(-1). Furthermore, the temperature sensitivity of the sensor is -0.003 nm/degrees C, indicating negligible temperature crosstalk. With the advantages of compactness, efficient coupling, high sensitivity, and negligible temperature crosstalk, the curvature sensor shows prospects in structural security monitoring, the aviation industry, energy exploration, and other fields.