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Coherent noise reduction in high visibility phase-sensitive optical time domain reflectometer for distributed sensing of ultrasonic waves
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Phase-sensitive optical time domain reflectometry (\phi \hbox{OTDR} is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, \phi {\rm OTDRs} have been used mostly for the measurement of sub-kHz vibrations, normally in the context of intrusion sensing. In this paper, the authors present an experimental and theoretical description of a high-visibility \phi {\rm OTDR} and its performance when used for ultrasonic vibration measurements. The use of a semiconductor optical amplifier in the setup allows to suppress coherent noise and also to improve the spectral response of the pump pulses. These two advantages greatly decrease the detected intra-band noise thus allowing frequency measurements in the limits set by the time of flight of the light pulses while maintaining the simplicity of the scheme, as no post-processing, extremely high coherence lasers or coherent detection methods are required. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a fully distributed measurement of ultrasonic waves was achieved. The statistical behavior of the system was also described theoretically and characterized experimentally.
Publication year: 2013
Reference: Martins, H.F.; Martin-Lopez, S.; Corredera, P.; Filograno, M.L.; Frazao, O.; Gonzalez-Herraez, M.; “Coherent noise reduction in high visibility phase-sensitive optical time domain reflectometer for distributed sensing of ultrasonic waves”, J. Lightwave Technol. vol: 31, Páginas: 3631 – 3637 (2013); doi: 10.1109/JLT.2013.2286223
Magazine: J. Lightwave Technol.
Running: No.
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