Ultrahigh-sensitivity directional torsion sensor based on a helical asymmetric twin-core fiber Michelson interferometer

We propose an ultrahigh-sensitivity directional torsion sensor based on a Michelson interferometer configured with a helical asymmetric twin-core fiber (ATCF). The sensor structure integrates a helical ATCF, a thermally diffused 3-dB coupler, and a gold reflective film, with the central core serving as the reference arm and the eccentric core as the sensing arm. Torsion test results show that the sensor achieves a maximum sensitivity of −17.55 nm/(rad/m). It realizes clear discrimination of torsion direction by distinguishing the blue/red shifts corresponding to clockwise/counterclockwise torsion. The temperature cross-sensitivity is as low as −0.016 (rad/m)/°C owing to the dual-core design, experiencing nearly identical thermal expansion. Compared with reported fiber torsion sensors, this sensor features a compact structure, low cost, and high stability, holding great application potential in fields such as structural health monitoring and precision manufacturing.