A Sagnac Interferometer-Based Twist Angle Sensor Drawing on an Eccentric Dual-Core Fiber

A fiber twist angle sensor has been theoretically proposed and experimentally verified by employing a fiber Sagnac loop interferometer based on a self-made eccentric dual-core fiber. The asymmetry of the dual-core fiber structure made the deformation of the fiber more obvious under the action of twist and enabled the designed sensor to identify the direction of twist angle. A clockwise (CW) and counterclockwise (CCW) rotation of a 5-cm-long eccentric dual-core fiber in the Sagnac loop generated a phase difference, which induced a red or blue shift of the interference spectrum, and the purpose of twist angle sensing was achieved by monitoring the spectral shift. The size of the twisted object should be larger than 5 cm, so that the sensor can be placed on the surface of the object to measure the twist deformation. In the measuring range from -90 degrees to 90 degrees, the twist angle-based sensitivity and twist rate-based sensitivity of the designed sensor were, respectively, investigated in CW and CCW directions: the former was 45.2 pm/degrees in CCW direction (-90 degrees to 0 degrees) and 12 pm/degrees in CW direction (0 degrees-90 degrees), and the latter was 129.49 pm/(rad/m) in CCW direction (-31.4 to 0 rad/m) and 34.38 pm/(rad/m) in CW direction (0-31.4 rad/m). The satisfactory sensitivity, stability, and repeatability make it a competitive alternative in twist angle sensing region, which can be widely used in engineering, biomedical, and other twist angle sensitive fields.

Automated summary

A fiber twist angle sensor based on a self-made eccentric dual-core fiber and a Sagnac loop interferometer has been proposed and verified experimentally. The sensor can accurately measure the twist angle and identify its direction, showing good sensitivity, stability, and repeatability.