Abstract:A reflective torsion sensor based on the few-mode fiber tilted Bragg grating is designed. The fundamental mode and the secondorder mode in the fiber core can be mutually coupled at the small-angle tilted grating. Through analyzing the couple reflection peak intensity, the torsion angle can be detected. The influence of the tilt angles on the mode coupling efficiency is analyzed with different small-angle tilted gratings written on the few-mode fiber. The tilted gratings are on-line written by using the phase mask method on a fiber drawing tower. The gratings with title angle of 1° is selected to perform single-point and double-point torsion experiments. Experimental results show that the reflection peak of the cross coupling between the fundamental mode (LP01 ) and the second-order mode (LP11 ) is sensitive to the twisting of the optical fiber. Thus, the twisting angle can be measured. The torsional sensitivity is 0. 52 dB/ (rad·m -1 ) during the counterclockwise twist from -50° ~ -150°, while the torsional sensitivity is 0. 34 dB/ (rad·m -1 ) in the 40° ~ 190° clockwise twist angle range. The sensor has the potential to realize multi-point torsion sensing with a single fiber, which has application prospects for multi-point torsion monitoring.