Guided acoustic wave Brillouin scattering has gained considerable interest in recent years because of its capacity to detect mechanical features of materials surrounding the optical fiber. Nevertheless, distributed measurements using this mechanism are rarely taken because of the impracticality of the method’s forward scattering mechanism. Recently, remarkable work using ingenious schemes has managed to address the difficulty, which opens a brand new way to achieve position-resolved substance identification. However, due to the long acoustic wave lifetime and insufficient signal-to-noise ratio (SNR), current spatial resolution is restricted to 15–50 m, which is far from practical requirements. Here we propose a novel opto-mechanical time-domain analysis based on coherent forward stimulated Brillouin scattering probing to greatly improve the achievable spatial resolution. The coherent transverse acoustic wave is first created by a long activation pulse and then probed by a short two-tone probe pulse. The two-tone probing process involves a coherent stimulated interaction between the probe pulse and the excited transverse acoustic wave. The interaction, which we first propose here, shows a distinct phase-sensitive characteristic. This new coherent stimulated probing process, if it is well controlled, will enhance the forward stimulated Brillouin scattering intensity and thus improve the SNR of the sensing. Moreover, higher SNR backward stimulated Brillouin scattering is used to detect the intensity evolution of the probe pulse. Owing to this new sensing scheme combined with a more robust demodulation algorithm, we demonstrated a 2 m spatial resolution opto-mechanical measurement over a 225 m long fiber in which we were able to distinguish air from alcohol. These advances greatly facilitate the practicability of forward stimulated Brillouin scattering.

中文翻译：

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基于相干正激受激布里渊散射探测的光机械时域分析

近年来，由于声波布里渊散射能够检测光纤周围材料的机械特征，因此引起了人们的极大兴趣。然而，由于该方法的前向散射机制不切实际，因此很少使用这种机制进行分布式测量。最近，使用巧妙方案的出色工作设法解决了这一难题，这为实现位置解析的物质识别开辟了一条崭新的途径。但是，由于声波寿命长且信噪比（SNR）不足，当前的空间分辨率被限制在15-50 m，这与实际要求相去甚远。在这里，我们提出了一种基于相干正向激励布里渊散射探测的新型光机械时域分析方法，以大大提高可实现的空间分辨率。相干横向声波首先由长激活脉冲产生，然后由短二音调探查脉冲探查。两音探测过程涉及探测脉冲和激发的横向声波之间的相干激发相互作用。我们在这里首先提出的相互作用显示出明显的相敏特性。如果可以很好地控制这种新的相干受激探测过程，它将增强前向受激布里渊散射强度，从而改善传感的SNR。此外，较高的SNR后向激发布里渊散射用于检测探测脉冲的强度演变。由于这种新的传感方案与更强大的解调算法相结合，我们证明了在225 m长的光纤上进行了2 m的空间分辨率光机械测量，从而能够区分空气与酒精。这些进展极大地促进了前向刺激的布里渊散射的实用性。