A Stationary Wavelet Transform-Based Positioning Scheme for Long-Range Distributed Fiber-Optic Disturbance Sensor

This article introduces a stationary wavelet transform (SWT)-based positioning scheme that is grounded in an inline asymmetric Mach-Zehnder interferometer-based long-range distributed fiber-optic disturbance sensing system. First, utilizing the light phase modulation theory, the high-frequency components of the received sensing signals are intercepted by the Hilbert transformer finite-impulse response (IIR) filter. Second, to mitigate the asymmetry of the sensing signals stemming from the central wavelengths of the lasers within the system, a SWT-based signal processing algorithm is employed to discern the specific time-frequency variation envelopes from the intercepted signals. Third, a generalized cross-correlational (CC) algorithm is utilized to calculate a fixed time delay between the extracted time-frequency variation envelopes. Finally, accurate disturbance positioning information along the fiber link is demodulated utilizing the derived time delay value. The feasibility and effectiveness of the proposed positioning scheme have been evaluated in the constructed fiber-optic disturbance sensing system. The results show that an average positioning error of 18.5 m was recorded at a point 81 km along the fiber under test. Moreover, the average processing time for this positioning methodology was only 0.12 s. Therefore, it is believed that the proposed positioning strategy based on the constructed distributed fiber-optic disturbance sensing system holds significant potential for applications requiring real time and precise detection of long-distance disturbance events.