The distributed Brillouin sensing technique has been developed rapidly since its first demonstration three decades ago. Numerous investigations on the performance enhancement of Brillouin sensors in respect to spatial resolution, sensing range, and measurement time have paved the way to its industrial and commercial applications. This chapter provides an overview of different Brillouin sensing techniques and mainly focuses on the most widely used one, the Brillouin optical time domain analysis (BOTDA). The history and the development of Brillouin sensing regarding the performance enhancement in various methods and their records will be reviewed, commented, and compared with each other. As well, related sensing errors and limitations will be discussed, together with the corresponding strategies to avoid them.

In this article, we demonstrate the noise reduction and signal to noise ratio (SNR) enhancement in Brillouin optical time-domain analyzers (BOTDA). The results show that, although the main noise contribution comes from the Brillouin interaction itself, a simple low pass filtering on the detected radio frequency (RF) signal reduces remarkably the noise level of the BOTDA traces. The corresponding SNR enhancement depends on the employed cut-off frequency of the low pass filter. Due to the enhancement of the SNR, a mitigation of the standard deviation error of the Brillouin frequency shift (BFS) has been demonstrated. However, RF filters with low cut-off frequency could lead to distortions on the trace signals and therefore detection errors on a non-uniform BFS. The trade-off between the noise reduction and the signal distortion as well as an optimal cut-off frequency are discussed in detail.

The excess noise due to stimulated Brillouin scattering (SBS) in gain and loss-based Brillouin optical time-domain analyzers (BOTDA) has been investigated theoretically and experimentally for the first time to the best of our knowledge. This investigation provides a full insight to the SBS-induced noise distribution, which mainly comes from phase-to-intensity conversion noise and the beating noise between the probe wave and spontaneous Brillouin scattering. A complete theoretical model, which is in good agreement with the experimental results, is presented to describe the noise. The results show that a loss-based BOTDA setup gives a better noise performance than a gain-based one in both time and frequency domain. The SBS-induced noise has been characterized in dependence on the pump and probe power and the spatial resolution.

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We report a spectrum sensing technique for RF signals. A multi-channel signal discrimination is illustrated based on the group delay by Brillouin scattering-induced transparency. The technique is reconfigurable and feasible for broad spectrum bands.