Ultra-low bending and temperature crosstalk directional torsion sensor by few-mode fiber based Mach-Zehnder interferometer.

• Our sensor has a significant intensity response of torsion in the range from −200° to 200°. • The sensitivity of ∼1.1 dB/(rad/m) is achieved with the maximum of 1.17 dB/(rad/m) and the measured error of less than 0.03 rad/m. • Our sensor has the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃. • Our sensor has the merits of ease of fabrication and cost-efficiency. In this paper, a few-mode-fiber based in-line Mach-Zehnder interferometer is proposed and completed for directional torsion sensing by core-offset splicing technique. The optimal offset and fiber length for fabrication are gained and the comprehensive tests are conducted in terms of torsion, bending and temperature. The experimental results show that our sensor has obvious intensity variation with the applied shear strain. The torsion sensitivity reaches ∼1.1 dB/(rad/m) in the range from −13.08 rad/m to 13.08 rad/m, but with the wavelength shift of 0.102 nm/(rad/m). In addition, thanks for the tiny bending and temperature responses of −0.055 dB/m−1 and 0.014 dB/℃, the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃ are gained simultaneously, which dramatically improves the practicality of fiber-optic torsion sensor. [ABSTRACT FROM AUTHOR]