Abstract
Over the past three decades, extensive research activity on Brillouin scattering-based distributed optical fiber sensors has led to the availability of commercial instruments capable of measuring the static temperature/strain distribution over kilometer distances and with high spatial resolution, with applications typically covering structural and environmental monitoring. At the same time, the interest in dynamic measurements has rapidly grown due to the relevant number of applications which could benefit from this technology, including structural analysis for defect identification, vibration detection, railway traffic monitoring, shock events detection, and so on. In this paper, we present an overview of the recent advances in Brillouin-based distributed optical fiber sensors for dynamic sensing. The aspects of the Brillouin scattering process relevant in distributed dynamic measurements are analyzed, and the different techniques are compared in terms of performance and hardware complexity.
Highlights
Research and investment toward the development of distributed optical fiber sensors able to detect dynamic phenomena such as vibrations and sound waves have increased
The growing interest mainly comes from areas such as the oil and gas extraction companies [1], geophysics [2,3], and structural health monitoring [4]. In some applications, such as perimeter control and anti-intrusion, the simple detection of vibrations and their localization is sufficient, and this led to the development of the so-called distributed acoustic sensors (DAS) based on Rayleigh scattering [5,6]
The first report of a relatively high acquisition rate was demonstrated with a configuration [39], which, which, according according to to what what discussed discussed earlier, earlier, is the less favorable for BOCDA configuration distributed dynamic dynamic sensing sensing
Summary
Research and investment toward the development of distributed optical fiber sensors able to detect dynamic phenomena such as vibrations and sound waves have increased. The growing interest mainly comes from areas such as the oil and gas extraction companies [1], geophysics [2,3], and structural health monitoring [4] In some applications, such as perimeter control and anti-intrusion, the simple detection of vibrations and their localization is sufficient, and this led to the development of the so-called distributed acoustic sensors (DAS) based on Rayleigh scattering [5,6]. On the other hand, when accurate and reliable measurements of the vibrations is required, sensors based on the Brillouin scattering can represent the right solution. The simple (but costly) adoption of a polarization-maintaining (PM) fiber as the sensing fiber, leads to obvious advantages in terms of acquisition speed, as it eliminates the averaging requirements usually associated with the polarization scrambling of the pump, and required to compensate the Brillouin gain fluctuations due to the fiber birefringence. The paper is organized as follows: after a brief recall of the Brillouin analysis and the discussion on the main factors limiting its application to dynamic sensing, the main technical solutions that have been devised to overcome the problem will be described along, in some cases, with illustrative experimental achievements
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