Demodulation of Polarimetric Fiber Laser Ultrasonic Sensor With Intensity Noise Cancellation

In this paper, the influences of the relative intensity noise, in particular the relaxation oscillation noise, of an erbium distributed feedback (DFB) fiber laser has been investigated theoretically and experimentally for use as a polarimetric ultrasonic sensor. We show that the relaxation oscillation noise and the ultrasonic signal both induce modulation sidebands on the polarization beat frequency of the DFB laser ultrasonic sensor. We present a novel demodulation algorithm for the polarimetric DFB fiber laser ultrasonic sensor, which can effectively eliminate the influences of the intensity noise and slowly varying drift of the polarization beat frequency.