A Stable and Highly Sensitive Directional Torsion Sensor Based on a Helical Double Cladding Microstructured Multicore Fiber

A helical double cladding seven-core microstructured fiber (HSCMOF) sensor is demonstrated for inline torsion and direction measurement. To fabricate the device, a segment of SCMOF with a double cladding structure constructed by air holes is pretwisted and spliced between two single-mode fibers to form a Mach–Zehnder interferometer (MZI). Due to the special structure, the proposed sensor not only reaches the torsion sensitivities as high as 515.7 and −294.7 pm/(rad/m) in clockwise (CW) and counterclockwise (CCW) directions, respectively, but also eliminates the cross sensitivity to external temperature and refractive index (RI) interferences, which continues to be an issue that persist in normal helical fibers. We envision that the sensor can be applied in harsh environments, such as health monitoring and underwater exploration.