Liao Ruolin, Tang Ming, Zhao Can, Wu Hao, Fu Songnian, Liu Deming, Shum Perry Ping
Opt Express. 2019 Jan 21;27(2):1693-1705. doi: 10.1364/OE.27.001693.
Coding technique has long been investigated as a solution to improve the signal-to-noise ratio (SNR) without sacrificing spatial resolution in optical time domain reflectometry (OTDR) systems. The past researches have been focusing at the construction of new codes, the combination of coding and other techniques, and the application of coding technique to versatile distributed optical fiber sensing systems such as Raman OTDR and Brillouin optical time domain analyzer, where the results are fruitful. Here, we reveal that oversampling after photodetection opens up a new dimension for coded OTDR other than code length and code type. We demonstrate that the coding gain can be further improved by harnessing the oversampling. Furthermore, the photodetector's bandwidth-limited feature can also be used to select the optimal sampling rate in order to obtain additional SNR enhancement. We believe this principle could be applied to any practical correlation-coded OTDR-based distributed fiber sensing systems with sufficient SNR enhancement. Our findings can serve to update existing instruments based on correlation-coded OTDR in a straightforward manner and at a relatively low cost.
长期以来，编码技术一直作为一种解决方案被研究，旨在提高光时域反射仪（OTDR）系统中的信噪比（SNR），同时不牺牲空间分辨率。过去的研究主要集中在新编码的构建、编码与其他技术的结合，以及编码技术在诸如拉曼OTDR和布里渊光时域分析仪等通用分布式光纤传感系统中的应用，这些研究成果丰硕。在此，我们揭示了光检测后的过采样为编码OTDR开辟了除码长和码型之外的新维度。我们证明，通过利用过采样可以进一步提高编码增益。此外，光电探测器的带宽受限特性还可用于选择最佳采样率，以获得额外的SNR增强。我们相信，这一原理可应用于任何具有足够SNR增强的基于相关编码OTDR的实际分布式光纤传感系统。我们的研究结果可用于以直接的方式且以相对较低的成本更新基于相关编码OTDR的现有仪器。
