High Sensitive Torsion Sensor Based on Cascaded Pre-Twisted Taper and Multi-Mode Fiber Sheets

A higher sensitivity Mach-Zehnder interferometric (MZI) torsional sensor for detecting torsion rate and discerning torsion direction is proposed in this letter. The torsion sensor is fabricated using multi-mode fiber sheets (MMFs) which are respectively cascaded at two ends of the pre-twisted taper. The MMFs are composed of multi-mode fiber which is 3 mm in length. The role of the pre-twisted taper is predominantly to provide permanent spiral deformation in single-mode fiber (SMF). Experimental results show that the wavelength drifts of Dip 1453 nm and Dip 1586 nm are linear with the twist at an angle of π/3 ~ π/3. Within the torsion rate range of 0 ~ -9.97 rad/m (counterclockwise), the torsion sensitivities of Dip 1453 nm and Dip 1586 nm are -0.740 nm/(rad/m) and -0.576 nm/(rad/m), respectively. Conversely, when the torsion rate is in the range of 0 ~ 9.97 rad/m (clockwise), the torsion sensitivities of Dip 1453 nm and Dip 1586 nm are 0.481 nm/(rad/m) and 0.185 nm/(rad/m), respectively. In addition, the wavelength drifts of Dip 1453 nm and Dip 1586 nm are linear with temperature in the range of 50 ~ 150 °C, and the temperature sensitivities are 49 pm/°C and 75 pm/°C, respectively. The feasibility of the proposed torsion sensor to measure torsion rate and identify the direction of torsion is verified by the above experimental results.