Yao Jiazhen, Han Bing, Jiang Xinli, Cao Shanshan, Fu Yun, Rao Yunjiang, Ran Zengling, Wang Wenyu, Guan Hongjian, Long Jingfeng
Opt Express. 2021 Mar 15;29(6):8216-8222. doi: 10.1364/OE.417360.
Fiber-optic distributed acoustic sensing (DAS) technology with high spatial and strain resolutions has been widely used in many practical applications. New methods to enhance the phase sensitivity of sensing fiber are worth exploring to further improve DAS performances, although the standard single-mode fiber (SSMF) has been widely used for DAS technology. In this work, we propose and demonstrate the concept of enhancing the phase sensitivity of DAS by softening the cladding of the sensing fiber, for the first time. The theoretical analysis indicates that softening sensing fiber cladding is an effective way to improve phase sensitivity. Thus, we fabricated cladding softened fibers (CSFs) and tested their phase sensitivities experimentally. According to the results, it is found that the phase sensitivity of the CSF with 0.48 WT% phosphorus-doping concentration and 80 µm cladding diameter is 22% and 54% higher than that of the non-phosphorus-doping fiber with 80 µm cladding diameter and SSMF, respectively. The results show that by reducing fiber cladding Young's modulus with higher phosphorus-doping concentration, the DAS phase sensitivity can be enhanced effectively, verifying the theoretical analysis. Also, we found that the phase sensitivity enhancement of the sensing fiber has a linear relationship with the cladding phosphorus-doping concentration, i.e. Young's modulus. In conclusion, the reported CSF paves a way for improving the DAS phase sensitivity and would be applied to other major optical fiber sensing systems as a better sensing element over SSMF due to the enhancement in the elasto-optical effect of the sensing fiber.
具有高空间和应变分辨率的光纤分布式声学传感（DAS）技术已在许多实际应用中得到广泛使用。尽管标准单模光纤（SSMF）已广泛用于DAS技术，但探索提高传感光纤相位灵敏度的新方法对于进一步提升DAS性能仍具有重要意义。在这项工作中，我们首次提出并论证了通过软化传感光纤包层来提高DAS相位灵敏度的概念。理论分析表明，软化传感光纤包层是提高相位灵敏度的有效途径。因此，我们制备了包层软化光纤（CSF）并对其相位灵敏度进行了实验测试。结果发现，磷掺杂浓度为0.48 WT%、包层直径为80 µm的CSF的相位灵敏度分别比包层直径为80 µm的非磷掺杂光纤和SSMF高22%和54%。结果表明，通过提高磷掺杂浓度降低光纤包层杨氏模量，可以有效提高DAS相位灵敏度，验证了理论分析。此外，我们发现传感光纤的相位灵敏度增强与包层磷掺杂浓度（即杨氏模量）呈线性关系。总之，本文报道的CSF为提高DAS相位灵敏度铺平了道路，并且由于传感光纤弹光效应的增强，作为一种比SSMF更好的传感元件，将应用于其他主要光纤传感系统。
