Mitigating the Impact of Frequency Drift on Φ-OTDR Demodulation With WOA-VMD

To address the issue of frequency drift of the laser in the phase-sensitive optical time-domain reflectometry (<inline-formula> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula>-OTDR) system, this letter utilizes a combination of whale optimization algorithm and variational mode decomposition (WOA-VMD) to mitigate low-frequency noise induced by frequency drift during <inline-formula> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula>-OTDR demodulation. The results show that the proposed method can effectively mitigate the impact of frequency drift on demodulation: when 1 Hz sinusoidal vibration is applied, the waveform bias is reduced from 2.037 rad to 0.087 rad, which is 78% and 96% lower than the twice differential (TD) method and difference-fitting (DF) method respectively; when 0.2 Hz sinusoidal vibration is applied, the waveform bias is reduced from 7.289 rad to 0.193 rad, which is 95% and 96% lower than the TD and DF methods respectively. This method effectively mitigates the influence of frequency drift on <inline-formula> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula>-OTDR demodulation.