497-km distributed acoustic sensing with 20-m spatial resolution 45-pε/√Hz strain resolution and broad-bandwidth

Distributed acoustic sensing (DAS) along 497 km fiber link with relay amplifiers of bidirectional erbium-doped fiber amplifier (EDFA) is reported. By utilization of optical pulse compression distributed acoustic sensing (OPC-DAS) system and proposed multi-mode multiplexing scheme, the sinusoidal vibration oscillating at 240 Hz at the far end of 497 km fiber link is successfully restored with a spatial resolution of 20 m and a strain resolution of 45 pε/√Hz. To the best of our knowledge, this is the longest distance reported to date for a DAS system using EDFA as the relay module, while maintaining such high spatial resolution, high strain resolution, and wide frequency response range (FFR). Furthermore, a weak vibration with peak-to-peak amplitude of 5 nε is correctly located at the end of fiber under test (FUT), with a signal-to-noise ratio (SNR) of 10 dB.