Temperature-Immune High-Sensitivity Curvature Sensor Based on Symmetric Eight-Core Fiber mach-Zehnder Interferometer

A high-sensitivity curvature Mach-Zehnder Interferometer (MZI) fiber sensor utilizing eight-core fiber (ECF) with temperature immunity was demonstrated and proposed. The sensor is constructed by sandwiching the ECF between two sections of single-mode fiber (SMF), and the ends of the SMFs are fused with spherical structures, forming a symmetric structure of the SMF-Spherical structure-ECF-Spherical structure-SMF. The ECF provides a multi-path transmission for different light modes to obtain the interference phenomenon. The spherical structure can effectively improve the splitting and combining of the light beams between SMF and ECF. In the curvature detection, the maximum curvature sensitivity is 101.18569 dB/m⁻¹ with a range from 0 m⁻¹ to 0.09142 m⁻¹ and a linearity of 0.989, which is the highest curvature sensitivity, to the best of our knowledge, in the intensity-modulated multi-core fiber MZI sensors. Furthermore, when the temperature range changes between 62°C and 94°C, the maximum temperature sensitivity can reach only −0.05202 dB/°C. These results indicate that the proposed sensor can minimize the cross-sensitivity between curvature and temperature measurements, which provides effective experimental support for the research of high-performance optical fiber sensors based on multi-core fiber.