High-Sensitivity LPFG Torsion Sensor Based on Indirect Torsion Slot

Long-period fiber gratings (LPFGs) torsion sensors are used for engineering measurements and real-time monitoring of torsion in smart structures. In this article, an indirect torsion slot-based sensor is proposed. The sensor uses a CO2 laser to etch notches on the surface of the fiber, which indirectly introduces a residual twisting force to increase the refractive index difference between the two notch modulations, creating a structure in which the notches are distributed in two rows on the fiber surface. The structure breaks the circular symmetry of the fiber and introduces residual twisting force, which introduces elliptical birefringence in a large amount, and the effect of applying different twisting angles during fabrication on the sensitivity is investigated, which effectively improves the torsional sensitivity. The experimental results show that the sensor torsional sensitivity is up to 1.288 nm/(rad/m) in the measurement range from -6.54 to 6.54 rad/m. The temperature characteristics of the sensor were also investigated, with a temperature sensitivity of 92 pm/degrees C over the detection range from 30(degrees)C to 120(degrees)C. In addition, the sensor has the advantage of low preparation cost and simple process, which has applications scenario in engineering, where high torsional sensitivity is required.