A phase demodulation method for quasi-distributed acoustic sensing (DAS) systems based on a dual-identical-chirped-pulse and weak fiber Bragg gratings (WFBGs) is proposed. Compared to the use of Rayleigh backscattering light in optical fibers, the implementation of WFBGs can contribute to obtaining an optical signal with a higher signal-to-noise ratio (SNR). The dual-identical-chirped-pulse is generated by a time-delay fiber, and the sinusoidal carrier is generated by the interference between the two chirped pulses reflected by adjacent WFBGs. The phase of the sinusoidal carrier represents the dynamic strain change posed on the sensing fiber. Discrete Fourier transform is used to directly retrieve the phase information. The performance of the phase demodulation from interference signals under different sinusoidal carrier frequencies and SNRs is numerically investigated. The piezoelectric transducer is employed to emulate the sound in the experiment to verify the effectiveness of our method. It is shown that the dynamic strain can be well reconstructed at the end of a 101.64 km fiber when the signal SNR is down to 3.234 dB. Our proposed method enables the application of the long-distance sensing in quasi-DAS systems.

中文翻译：

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基于双相同啁啾脉冲和弱光纤布拉格光栅的分布式声传感相位解调方法

提出了一种基于双相同啁啾脉冲和弱光纤布拉格光栅（WFBG）的准分布式声学传感（DAS）系统的相位解调方法。与在光纤中使用瑞利背向散射光相比，WFBG 的实施有助于获得具有更高信噪比 (SNR) 的光信号。双相啁啾脉冲由延时光纤产生，正弦载波由相邻WFBG反射的两个啁啾脉冲之间的干涉产生。正弦载波的相位代表传感光纤上的动态应变变化。离散傅立叶变换用于直接检索相位信息。数值研究了不同正弦载波频率和信噪​​比下干扰信号的相位解调性能。实验中采用压电换能器模拟声音以验证我们方法的有效性。结果表明，当信号信噪比降至 3.234 dB 时，可以很好地重建 101.64 km 光纤末端的动态应变。我们提出的方法使长距离传感在准 DAS 系统中的应用成为可能。