Eliminating polarization noises in a pulsecoded Brillouin fiber sensor via periodic polarization scrambling

Gain-related polarization noise, induced by the use of random polarization scrambling (PS) for the purpose of eliminating polarization fading, is a main performancelimiting issue for a current pulse-coded Brillouin optical time-domain analysis (BOTDA) fiber sensor. Here, a periodic PS approach based on differ-frequency acousto-optic modulation is proposed to reduce polarization noises. It not only permits enough polarization states for polarization fading suppression, but also considerably reduces the polarization randomness between the pump and probe at any fiber position for polarization noise reduction compared to the commonly used random PS approach. This enhances the signal-to-noise ratio of Brillouin gain by ~ 4 dB, resulting in the enhancement of the measurement accuracy by a factor of 2.5 at the far fiber end. Our work reveals that periodic PS offers new possibilities for mitigating polarization-related impairments in Brillouin fiber sensors since it enables moderate polarization randomness.