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 -pi/3 similar to pi/3. Within the torsion rate range of 0 similar to -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 similar to 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 similar to 150 degrees C, and the temperature sensitivities are 49 pm/degrees C and 75 pm/degrees 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.