Abstract
In this paper, we propose and experimentally demonstrate an ultra-long distributed fiber vibration sensing system using unidirectional forward transmission of a continuous-wave signal and coherent detection with digital signal processing. Two optical fibers, which are close to each other, are deployed for sensing. A loop-back configuration is formed by splicing these two optical fibers at the far end of these two fibers. The location of the vibration event is identified by analyzing the null points in the frequency spectrum of the extracted phase signal. Thanks to the nature of unidirectional forward transmission, the Rayleigh backscattering noise can be avoided. Meanwhile, forward transmission enables optical amplifiers to compensate for the signal loss and hence fundamentally overcome the sensing range limit. We successfully demonstrate the localization of single point and multi-point vibrations with measurement errors of less than ±100 m and ±200 m, respectively, over a 500-km sensing range. The proposed scheme opens new possibilities in ultra-long haul distributed optical sensing applications.
Highlights
D ISTRIBUTED vibration sensing (DVS) using optical fibers has been widely applied in many engineering areas including structural health monitoring, oil or gas pipeline leakage monitoring, perimeter protection and seismic sensing applications [1]–[5]
The polarization fading problem can be solved by using the phase and polarization diversity coherent receiver, which has been widely used in long-haul optical communication systems [16] and OTDR based sensing systems [17] to retrieve both the amplitude and phase of the received signal
We have proposed and experimentally demonstrated a unidirectional ultra-long range distributed optical vibration sensing technique using coherent detection, where a pair of optical fibers are deployed at the same location with a loop-back configuration
Summary
D ISTRIBUTED vibration sensing (DVS) using optical fibers has been widely applied in many engineering areas including structural health monitoring, oil or gas pipeline leakage monitoring, perimeter protection and seismic sensing applications [1]–[5]. The directly detected signal exhibits a nonlinear phase to amplitude conversion, which results in a serious distortion of the sensing signal This is especially serious when the vibration amplitude is large or the interferometer sensor is not fixed at the quadrature working point [13]. To solve this problem, various phase detection techniques including phase carrier generation [14] and the use of 3×3 coupler [15], are utilized in interferometer based DVS. Various phase detection techniques including phase carrier generation [14] and the use of 3×3 coupler [15], are utilized in interferometer based DVS These techniques, may result in a complicated signal processing infrastructure which increases the system complexity and measurement time. The proposed scheme provides a new approach for ultralong range and large amplitude DVS sensing
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