New Methods for Brillouin Optical Time Domain Analysis

Brillouin optical time domain analysis (BOTDA) is one of the most important distributed optical fiber sensor technologies thanks to its capability of monitoring both temperature and strain distribution over tens of kilometers of sensing fibers with a single interrogator. BOTDA sensors have found important applications in structural health monitoring, safety and environmental engineering. Their employment is still limited by two factors: on one hand, the high complexity (and cost) for a single interrogator unit reduces the applications where BOTDA can compete with classical point-like sensors. On the other, the time required to obtain a single temperature/strain distribution is in the order of several minutes, limiting BOTDA to static or quasi-static measurements. In this thesis solutions are proposed for these limitations. In the first part, two different pump-probe laser sources based on Brillouin ring lasers (BRL) are shown and evaluated as low-cost alternatives to traditional sources employed in BOTDA. The first source, which is based on a long cavity BRL, is shown to be successfully employable in BOTDA measurements up to at least 10 km of range. The second source, which is based on a doubly resonant short cavity BRL, shows further improvements in intensity noise, output light spectral linewidth and tunability of the pump-probe frequency shift, at the cost of a slightly more complex hardware requirement, which still remains less severe than traditional sources. In the second part, a fast BOTDA design based on a closed-loop control was explored and improved, with a particular focus in its signal processing methods. Finally, a new adaptive signal filtering technique to improve noise suppression is proposed and demonstrated.