In this papers, the influence of the line-width of probe light on the phase noise of phase extracted based phase-sensitive optical time domain reflectometry (Φ-OTDR) is theoretical analyzed and experimentally investigated. Analysis indicates that broad line-width probe light suffers time varying wavelength drift and high level of laser phase noise, and thus guarantees high level phase noise of the Φ-OTDR. In distributed acoustic sensing along 500 m sensing fiber, the phase noise is evaluated for probe lights of different line-widths, and experimental results display that the phase noise increases as the line-width of probe light broadens.
In a phase extraction based phase-sensitive optical time domain reflectometry (Φ-OTDR), external perturbation induced phase variation of Rayleigh backscattered light-wave (RBL) is obtained from time varying interference signal that is comprised of two RBLs with a spatial shift along the sensing fiber. In this paper, the phase of the interference signal in the phase extraction based Φ-OTDR is studied. Derivation is performed on the interference signal considering the interference of multiple RBL within probe pulse covered fiber section. Theoretical analysis and experimental results reveal that the phase of interference signal are wavelength independent while the intensity of interference signal are wavelength dependent.
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