Phase-modulation-based periodic polarization scrambling for polarization noise mitigation in a pulse-coded Brillouin fiber sensor

Periodic polarization scrambling (PS) has been found an effective way of eliminating polarization noises in a pulse-coded Brillouin optical time-domain analysis fiber sensor. It is realized by periodically changing the phase difference between the two orthogonal components of a light. Here, we use phase modulation to generate periodic PS, which utilizes the different modulation efficiencies of the fast and slow axes of a phase modulator. This method not only reduces system complexity but also alleviates non-local effect compared to our previous approach based on differ-frequency acousto-optic modulation (AOM). Experimental results show that it enhances the signal-to-noise ratio of Brillouin gain by ~ 4 dB compared to the commonly used random PS. Further, owing to the reduction of non-local effect, ~ 4-MHz Brillouin frequency shift measurement error is avoided compared to the AOM-based approach.