High sensitivity and directional recognition torsion sensor based on rotating distributed slot long-period fiber grating

Abstract

In this paper, a rotationally distributed slot type long period fiber grating torsion sensor is proposed. The sensor employs CO2 laser to etch grooves on the fiber surface in a structure helically distributed slot around the fiber axis, which breaks the circular symmetry of the fiber and introduces a residual twisting force, thus introducing a large amount of elliptical birefringence. By investigating the effect of different periods on the torsional sensitivity, the torsional sensitivity is effectively improved. The experimental results indicate that the torsion sensitivity of the sensor is up to 0.42 nm/(rad/m) in the measurement range of −13.08 rad/m to 13.08 rad/m, which is 10 times more sensitive than that of the traditional torsion sensor, and the direction of torsion can be detected. The temperature characteristics of the sensor are also investigated, and the temperature sensitivity in the detection range of 30 °C to 120 °C is 76 pm/°C, with a temperature crosstalk of 0.18(rad/m)/°C. This sensor provides a new solution for LPFG torsion sensing enhancement, which can be used in the field of engineering structure monitoring with high torsion sensitivity requirements.