Helical sensor for simultaneous measurement of torsion and temperature

Abstract

Based on our current research on long-period fiber gratings (LPFGs), we propose a novel fiber-based sensor for simultaneous measurement of torsion and temperature. The proposed sensor cleverly combines CO2 laser polishing with pre-twist that can introduce elliptical birefringence in the fiber to improve sensing performance. Through comparative measurement experiments, we investigate the torsion characteristic of the sensor and the effect of different degrees of pre-twist on it. Experimental results show that the highest torsion sensitivity of two resonant dips can reach 0.635 nm/(rad/m) and −0.654 nm/(rad/m) in the range of 0 rad/m − 12.6 rad/m, while in the range of −12.6 rad/m − 0 rad/m the sensitivities are 0.14 nm/(rad/m) and −0.083 nm/(rad/m) respectively due to inhomogeneous elliptical birefringence. Meanwhile, the temperature sensitivity of the two resonant dips are calculated to be 62.5 pm/°C and 66.8 pm/°C, respectively. Due to the different sensitivities of temperature and torsion, the matrix method can be used for simultaneous measurement of two parameters to ignore crosstalk. As a result, the proposed sensor shows competitiveness in practical engineering applications.