A side-leakage photonic crystal fiber torsion sensor for measuring torsion angle and determining torsion direction simultaneously

Abstract

A highly sensitive torsion sensor, which can measure the torsion angle and determine the torsion direction simultaneously, is proposed and experimentally demonstrated by using side-leakage photonic crystal fiber (SLPCF) based Sagnac loop. When the SLPCF is turned in the clockwise direction, the transmission spectra of the torsion sensor shift towards the shorter wavelength side; whereas the transmission spectra of the torsion sensor shift towards the longer wavelength side when the SLPCF is turned in anticlockwise direction. Experimental results demonstrate that the length of the SLPCF inserted into Sagnac loop plays an important role for determining the torsion sensitivity and the torsion angle range. For the SLPCF with shorter length, the torsion sensor has the larger torsion sensitivity, but the torsion angle measuring range would be decreased. The opposite situation takes place for the SLPCF with longer length used in the torsion sensor. When the length of SLPCF is 14.85 cm, the torsion sensitivity of the sensor is up to 0.9354 nm/(°) and the torsion angle range from -90° to +90°; When we increase the length of SLPCF to 32 cm, the torsion sensitivity of the sensor gets down to 0.2132 nm/(°), but the torsion angle range can be expanded as from -180° to +180°. To eliminate the perturbation of environmental temperature, we adopt a two-dimensional measuring matrix to achieve simultaneous measurements of the torsion angle and temperature. In other words, using two-dimensional measuring matrix can also eliminate the perturbation of the environmental temperature to the measured result of torsion angle.