Analysis of the beat noise induced by the lock-in detection in Brillouin optical correlation domain analysis

We present theoretical and experimental analysis of the beat noise occurring in distributed fiber sensors based on Brillouin optical correlation domain analysis (BOCDA). The origin of the beat noise turns out to lie in the variation of the Brillouin gain induced by the chopping of the intensity-modulated pump wave in the lock-in detection applied for the signal processing of a BOCDA system. Additionally, a variable-frequency lock-in detection technique is suggested as an effective way of the noise suppression.