The digital coherent detection method is employed into the ?-OTDR. The heterodyne detection offers very high optical gain while the digital signal processing serves as an effective tool to rebuild the instantaneous electric field of Rayleigh scattering light by analyzing the beating signal. Both amplitude and phase signal are obtained in our experiment. PZT vibration measurement verifies that the phase difference signal well represents the external perturbation signal and also with higher SNR. The proposed new?-OTDR system shows a good application foreground in the area of distributed vibration measurement.
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