Dynamic Measurement Based on the Linear Characteristic of Phase Change in $\Phi$ -OTDR

Phase optical time domain reflectometer (Φ-OTDR) is capable of quantitatively gauging the perturbations on the fiber based on the linear relationship between the phase change and the strain of the fiber. However, various noises in the coherent Φ-OTDR system may deteriorate the accuracy of quantitative measurement. In this letter, the characteristic of the phase evolution along fiber is analyzed and the phase change is recovered through differential calculations in the direction of both fiber length and time. According to the linear characteristic of phase change, the accurate measurement result is finally obtained by fitting the trace of phase change with the method of total least square. The experimental results agree well with the theoretical analysis and five sets of measurements for the sinusoidal vibration are exceedingly consistent with each other. The variation coefficients of amplitude and frequency are 0.1931% and 0.0127%, respectively. And the minimum value of R-square representing the similarity between the measured waveform and the driving signal is 0.9999.