Whispering-gallery modes in a triple-layer-coated microsphere resonator for refractive index sensors
Whispering-gallery modes in a triple-layer-coated microsphere resonator for refractive index sensors
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用于折射率传感器的三层涂层微球谐振器中的回音壁模式
DOI：
10.1016/j.optcom.2018.06.017
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发表时间：
2018-11
影响因子：
2.4
通讯作者：
Wang Keyi
中科院分区：
文献类型：
--
作者：
Wang Mengyu;Jin Xueying;Li Fei;Cai Bolin;Wang Keyi
在这项研究中，一个高灵敏度的折射率（RI）传感器的设计通过功能性涂层的高，低，高RI从内到外的光学微球谐振腔的外表面上的三层。通过电磁场分析，从理论和数值上给出了普通微球和三层包覆微球中回音壁模的特性。当优化微球与波导之间的差距时，发现这种三层涂层微球谐振器中的回音壁模式被有效地激发。两个包层模式，称为内模（IM）和外模（OM），表现在两个高RI层。潜在的RI传感应用程序产生的IM和OM的耦合，此后使用微扰理论和时域有限差分法进行了研究。结果发现，OM的传感性能可以超过单层涂层微球的灵敏度。具体地，通过调整中间低RI层的膜厚度，可以实现49.5nm/RIU（折射率单位）的增加的灵敏度。当在中间层中施加厚涂层时，IM和OM的灵敏度存在模式键合。检测限，或品质因数，也通过使用近似理论进行了研究。结果表明，有可能达到检测限，变化为10 - 10 - 6。该研究的理论和数值预测提供了指导方针，改进微球RI传感器的设计和制造。
In this study, a highly sensitive refractive index (RI) sensor is designed by functionally coating three layers of high, low, and high RI from inside to outside on the external surface of an optical microsphere resonator. The properties of whispering-gallery modes, confined in normal microspheres, as well as triple-layer-coated microspheres are presented theoretically and numerically through electromagnetic analyses. The whispering-gallery modes in such a triple-layer-coated microsphere resonator are found to be efficiently excited when optimizing the gap between the microsphere and waveguide. Two cladding modes, referred to as the inner mode (IM) and outer mode (OM), are exhibited in two high-RI layers. Potential RI-sensing applications stemming from the coupling for the IM and OM are investigated thereafter using the perturbation theory and the finite difference time domain method. It is found that the sensing properties of the OM can exceed single-layer-coated microspheres in terms of sensitivity. Specifically, an increased sensitivity of 49.5 nm/RIU (Refractive Index Unit) can be achieved by tailoring the film thickness of the middle low-RI layer. When applying a thick coating in the middle layer, there is a mode bonding in the sensitivity for the IM and OM. The detection limit, or quality factor, is also investigated by using an approximate theory. Results demonstrate that it is possible to reach a detection limit with a variation of∼ 10− 6. The study’s theoretical and numerical predictions provide guidelines for the improved design and fabrication of microsphere RI sensors.
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