In this paper, stimulated Brillouin scattering induced noise in Brillouin optical time domain analyzers is experimentally and theoretically investigated. The noise mainly comes from the beating between the probe wave and the spontaneous Brillouin scattering component and from phase-to-intensity conversion. The noise in the time and frequency domain has been measured along the fiber. The results reveal that, compared to gain based sensors, the loss based ones show a lower Brillouin induced noise level. Furthermore, the Brillouin noise is characterized in dependence on the spatial resolution. This investigation provides a deep insight to the frequency dependence of the noise distribution, which might contribute to signal-to-noise ratio enhancement in Brillouin-based distributed sensing.
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