Mallik Arun Kumar, Farrell Gerald, Ramakrishnan Manjusha, Kavungal Vishnu, Liu Dejun, Wu Qiang, Semenova Yuliya
Opt Express. 2018 Nov 26;26(24):31829-31838. doi: 10.1364/OE.26.031829.
A novel fiber optic sensing configuration for simultaneously measuring ammonia vapor (NH) concentration and relative humidity (RH) in air is proposed and experimentally demonstrated. The system comprised two silica whispering gallery mode (WGM) microsphere resonators coated with different polymer layers. One of the microspheres was dip-coated with sol gel silica polymer and another with a 0.5 % wt./vol. agarose hydrogel. WGMs in both microspheres were excited simultaneously by evanescent coupling using a single adiabatic fiber taper. The optical properties of both coating layers change due to their exposure to ammonia and water molecules in the surrounding atmosphere, resulting in the spectral shifts of the WGM resonances relevant to each of the microspheres. By measuring the relevant WGMs' spectral shifts, the NH concentration in air and the RH can be determined simultaneously. The experimentally demonstrated sensitivity of the proposed sensor array to ammonia was estimated as 19.07 pm/ppm (NH molecules in air) and its sensitivity to relative humidity as 1.07 pm/% RH. Detailed studies of the coatings' cross-sensitivity and temperature dependence are also presented. The proposed sensor array is compact, highly sensitive and potentially low cost.
提出并通过实验证明了一种用于同时测量空气中氨气（NH）浓度和相对湿度（RH）的新型光纤传感配置。该系统由两个涂覆有不同聚合物层的二氧化硅回音壁模式（WGM）微球谐振器组成。其中一个微球浸涂有溶胶 - 凝胶二氧化硅聚合物，另一个浸涂有0.5%重量/体积的琼脂糖水凝胶。使用单个绝热光纤锥通过倏逝耦合同时激发两个微球中的WGM。由于它们暴露于周围大气中的氨和水分子，两个涂层的光学性质都会发生变化，从而导致与每个微球相关的WGM共振的光谱偏移。通过测量相关WGM的光谱偏移，可以同时确定空气中的NH浓度和RH。所提出的传感器阵列对氨气的实验证明灵敏度估计为19.07 pm/ppm（空气中的NH分子），对相对湿度的灵敏度为1.07 pm/%RH。还给出了涂层交叉敏感性和温度依赖性的详细研究。所提出的传感器阵列紧凑、高度灵敏且潜在成本低。
