Wide-Frequency vibration positioning of asymmetric interferometers based on dual endpoint detection and iterative VMD

• Dual endpoint detection and generalized cross-correlation improve the positioning accuracy. • Wide-band flexible positioning with a sensing length of 90 kilometers. • Effective extraction and positioning of weak interference signals. Vibration sensors based on asymmetric dual Mach-Zehnder interferometers (ADMZIs) enhance sensing accuracy. However, the inherent asymmetry of ADMZIs significantly affects positioning accuracy. To address this issue, this paper proposes a time-delay estimation and positioning scheme based on dual endpoint detection (DED) and iterative variational mode decomposition (IVMD), which has been validated through practical experimentation. The proposed scheme begins by performing dual endpoint detection on the two vibration signals. Iterative variational mode decomposition is then applied, extracting the envelope signal to mitigate the asymmetry between the signals. Finally, the generalized quadratic cross-correlation (GQCC) method is used to estimate the time delay and determine the vibration position along the sensing fiber. Experimental results demonstrate that this method accurately localizes vibration intrusion signals over sensing lengths of up to 90 km. For high-frequency and strong vibration signals, the positioning standard deviation is approximately 40.2 m, while for low-frequency and weak vibration signals, it is about 209.9 m. The proposed scheme excels in processing low-frequency and weak vibration signals, significantly improving the practicality of vibration sensing systems based on asymmetric interferometers.