Nonlocal Effect Compensation in Frequency-Fixed Probe Based BOTDA Sensor

Abstract

The robustness of a recently proposed Brillouin optical time-domain analysis sensor based on dual-tone probe wave with fixed frequency separation is deeply studied. It is discovered that when the distribution of Brillouin frequency shift (BFS) along the sensing fiber is not entirely uniform, non-local effect might be imposed at the middle of sensing fiber, which gives rise to systematic frequency error on the local estimated BFS. Aiming at solving this problem, we propose an approach that acquires both the upper and lower probe sidebands simultaneously using two photodiodes, and the average between the Brillouin gain and loss spectral is calculated to eliminate the detrimental impact of the non-local effect. Moreover, the impact of probe power on the distortions of both pump pulse and Brillouin gain/loss spectrum is experimentally investigated, thus the maximum allowable power of the injection probe wave is determined.