Effects of laser intensity noise on polarimetric distributed feedback fibre laser ultrasonic sensor

The influence of the relative intensity noise, in particular the relaxation oscillation noise, of a distributed feedback (DFB) fibre laser on the performance of a polarimetric DFB fibre laser ultrasonic sensor is investigated theoretically and experimentally. A novel demodulation algorithm for the DFB fibre laser ultrasonic sensor is used to demodulate the polarization beat frequency and eliminate the effects of the intensity noise completely. The sensing system is demonstrated to demodulate time varying ultrasonic signals at 2.25 MHz and 10 MHz