Direction-discriminable torsion sensor based on a helical taper long period fiber grating

A torsion sensor, which is based on a helical taper long-period fiber grating (HTLPFG), has been proposed and experimentally verified. In this sensor, the torsional sensitivity was notably improved by raising the torsional angle of the taper. The torsion degree was achieved by setting the rotation amount of the rotatable clamp. As the torsion degree increases from 0.1 circles to 0.5 circles, the sensor's torsion sensitivity was improved from -38.97 nm/(rad/mm) to -99.18 nm/(rad/mm) near wavelength 1430 nm and from -67.1 nm/(rad/mm) to -119.5 nm/(rad/mm) near wavelength 1550 nm, respectively. However, the temperature sensitivity of the sensor is almost unaffected by the torsion degree. Therefore, the torsion sensor proposed in this paper increases the torsion degree of the taper within a certain range, which can not only improve the torsion sensitivity but also reduce the temperature crosstalk.