Vibration detection and reconstruction based on Φ-OTDR with dual AOM

In the current practical application, the signal of the balance detector in Φ-OTDR system is transmitted at about 100MHz, with the A/D sampling rate is usually above 2GS/s, which requires higher requirements on acquisition equipment and signal processing equipment. The cost and stability of its equipment could not be completed. In order to solve this kind of problem, a phase-sensitive optical time-domain reflectometric (Φ-OTDR) system based on dual AOM which add frequency shift structure for local oscillator light is proposed. This system could obtain the position information and timefrequency characteristics of vibration signal simultaneously under lower sampling frequency by reducing the frequency shift of the backward-scattering Rayleigh light signal. Under the condition of low sampling rate, the initial impulse energy loss is reduced to improve the quantitative analysis ability of disturbance signals. The experimental results show that the spatial resolution of 5m is achieved on the 1.43km sensing fiber, the details of the original backscatter Rayleigh signal could appear as a sinusoidal signal and impulse energy of them is stronger. After noise reduction, the SNR could be increased from 10.37dB to 20.59dB for signal reconstruction with a disturbance frequency of 500Hz. The improvement of the SNR indicates that the Φ-OTDR detection of the dual AOM is feasible and effective in the detection of weak stress signal monitoring at low sampling rate.