Temperature Insensitive Birefringent LPG Twist Sensing Based on the Polarization Properties

A fiber twist sensor based on the polarization-dependent loss (PDL) properties of the core-only photo-induced birefringent long period fiber grating (LPG) is first proposed. The PDL response to the twist effect on the LPG is studied theoretically and experimentally. The results show that the difference between the maximum values of the two lobes in the PDL spectrum shows a high sensitivity and a sectionalized linearity response to the twist angle. Moreover, this sensor can measure the twist angle and determine the twist direction simultaneously and the performance of the sensor is not affected by temperature variations. For twist length of 3.5 cm, the proposed sensor shows sensitivities of 1.911 dB/rad over the twist range from 0° to 80° and 0.92 dB/rad when the twist angle is higher than 80°.