Optical fiber distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (φ-OTDR) is in great demand in many long-distance application fields, such as railway and pipeline safety monitoring. However, the DAS measurement distance is limited by the transmission loss of optical fiber and ultralow backscattering power. In this paper, a DAS system based on multispan relay amplification is proposed, where the bidirectional erbium-doped fiber amplifier (EDFA) is designed as a relay module to amplify both the probe light and the backscattering light. In the theoretical noise model, the parameters of our system are carefully analyzed and optimized for a longer sensing distance, including the extinction ratio (ER), span number, span length, and gain of erbium-doped fiber amplifiers. The numerical simulation shows that a bidirectional EDFA relay DAS system can detect signals over 2500 km, as long as the span number is set to be more than 100. To verify the effectiveness of the scheme, a six-span coherent-detection-based DAS system with an optimal design was established, where the cascaded acoustic-optic modulators (AOMs) were used for a high ER of 104 dB. The results demonstrate that the signal at the far end of 300.2 km can be detected and recovered, achieving a high signal-to-noise ratio of 59.6 dB and a high strain resolution of 51.8pε/√Hz$51.8\mathrm{p}\mathrm{\epsilon }/\sqrt{\mathrm{Hz}}$ at 50 Hz with a 20 m spatial resolution. This is, to the best of our knowledge, a superior DAS sensing distance with such a high strain resolution.

中文翻译：

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基于优化设计的双向EDFA中继的300公里超长光纤DAS系统

基于相敏光时域反射计（φ-OTDR）的光纤分布式声学传感（DAS）在铁路和管道安全监测等许多长距离应用领域有着巨大的需求。然而，DAS 测量距离受到光纤传输损耗和超低反向散射功率的限制。在本文中，提出了一种基于多跨度中继放大的 DAS 系统，其中双向掺铒光纤放大器 (EDFA) 被设计为中继模块，以放大探测光和反向散射光。在理论噪声模型中，我们的系统参数经过仔细分析和优化，以实现更长的传感距离，包括消光比 (ER)、跨度数、跨度长度和掺铒光纤放大器的增益。数值仿真表明，只要设置跨度数大于100，双向EDFA中继DAS系统可以检测到超过2500 km的信号。为验证该方案的有效性，基于六跨度相干检测的DAS建立了具有优化设计的系统，其中级联声光调制器 (AOM) 用于 104 dB 的高 ER。结果表明，可以检测和恢复300.2 km远端的信号，实现了59.6 dB的高信噪比和高应变分辨率。其中级联声光调制器 (AOM) 用于 104 dB 的高 ER。结果表明，可以检测和恢复300.2 km远端的信号，实现了59.6 dB的高信噪比和高应变分辨率。其中级联声光调制器 (AOM) 用于 104 dB 的高 ER。结果表明，可以检测和恢复300.2 km远端的信号，实现了59.6 dB的高信噪比和高应变分辨率。51.8 p ε / √50 Hz 时的Hz$51.8\mathrm{p}\mathrm{\epsilon }/\sqrt{\mathrm{Hz}}$，空间分辨率为 20 m。据我们所知，这是具有如此高应变分辨率的卓越 DAS 传感距离。