In fiber Bragg grating twist sensor based on analysis of polarization dependent loss

In this paper, a new technique exploiting the polarization properties of normal fiber Bragg grating (FBG) for twist sensing is firstly proposed and experimentally demonstrated. The evolution of the polarization dependent loss (PDL) response of the FBG with respect to the twist is studied. The physical model is presented and a numerical simulation based on the transfer matrix method is used to calculate the PDL spectrum of the twisted FBG. The theoretical and experimental results suggest that the PDL response of the FBG have higher twist sensitivities than that of the reflected or transmitted amplitude spectra. Based on comprehensive analysis of the resonant wavelength and the amplitude of the two main lobes of the PDL spectrum, this sensor can measure twist angle and determine twist direction simultaneously. Moreover, the performance of the sensor is not affected by strain and temperature variations.