Distributed optical fiber sensing exploring forward stimulated Brillouin scattering (FSBS) has received wide attention, as it indicates a new sensing method to measure the liquid property surrounding an optical fiber. In the existing techniques, backward stimulated Brillouin scattering is adopted for detection of the sensing signal, which requires time-consuming signal acquisition and post-processing. In this work, an approach that distributedly measures FSBS spectra is proposed and demonstrated based on coherent detection. While an excitation pulse with single-frequency amplitude modulation is used to induce a guided acoustic mode in the fiber, a following pulse is adopted to probe the induced phase modulation. Using a chirped fiber Bragg grating array, an enhanced-backward-propagating sensing signal is generated from the probe pulse. Heterodyne coherent-detection-based phase demodulation is then realized by mixing the sensing signal with a local oscillator. The FSBS spectra can then be reconstructed from the beat signals with only one round of frequency sweeping. With significantly accelerated signal acquisition and simplified post-processing, the proposed distributed acoustic sensing system has achieved spatial resolution of 5 m over a 500-m sensing range.

中文翻译：

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啁啾光纤布拉格光栅阵列实现的基于相干检测的分布式声阻抗传感

探索前向受激布里渊散射（FSBS）的分布式光纤传感受到了广泛的关注，因为它为测量光纤周围的液体特性提供了一种新的传感方法。在现有技术中，采用反向受激布里渊散射来检测传感信号，需要耗时的信号采集和后处理。在这项工作中，提出并演示了一种基于相干检测的分布式测量 FSBS 光谱的方法。采用单频幅度调制的激励脉冲在光纤中诱导引导声模时，采用跟随脉冲来探测诱导的相位调制。使用啁啾光纤布拉格光栅阵列，从探测脉冲产生增强的反向传播传感信号。然后通过将传感信号与本地振荡器混合来实现基于外差相干检测的相位解调。然后可以只用一轮频率扫描从差拍信号中重建 FSBS 频谱。通过显着加速信号采集和简化后处理，所提出的分布式声学传感系统在 500 米的传感范围内实现了 5 米的空间分辨率。