Directional bending sensing characteristics of in-line Mach-Zehnder interferometer based on asymmetrical twin-core fiber

We propose and experimentally demonstrate a simple directional bending sensor based on an in-line Mach-Zehnder interference structure of the single mode fiber (SMF)-multimode fiber (MMF)-asymmetrical twin-core fiber (ATCF)- MMF-SMF. Due to the asymmetric structure in twin-core fiber, this sensor can discriminate different bending directions. The interference spectrum shifts with the change of curvature. Furthermore, the sensor exhibits a linear response with a maximum bending sensitivity of 33.48 and -38.72 nm/m-1 in the curvature range from 0 to 3.01 m-1 for bending directions at -x (180°) and +x (0°) directions, respectively. The proposed fiber sensor has great potential in the future Internet of Things (IoT) due to its advantages, such as low cost, compactness, and high bending sensitivity.