设计了一种基于金属-介质-金属波导的半圆形谐振腔与矩形谐振腔的耦合结构, 采用有限元方法研究了该结构的传播特性.结果表明：透射光谱中产生一个类似Fano共振线型的共振谷, 该Fano共振由半圆形谐振腔的宽谱共振和矩形谐振腔的窄谱共振相互耦合所导致.变化谐振腔的结构参量, 发现该Fano共振谷位置依赖于矩形谐振腔的几何参量, 而对两谐振腔相对位置的微小移动不敏感；同时, 改变两谐振腔的并联方式, 研究了两种衍生结构的传播特性, 发现这些结构均可产生明显的Fano共振.此外, 通过在谐振腔中填充不同折射率的介质材料, 研究了三种结构基于Fano共振效应的折射率传感特性, 其折射率敏感度最高达到750 nm/RIU.研究结果可为未来芯片上基于表面等离极化激元波导的高灵敏折射率传感器的设计提供理论依据.

A plasmonic structure consisting of a metal-insulator-metal waveguide, a rectangular cavity and a semi-circular cavity was proposed to investigate the transmission properties by the finite-element method. Simulation results show that there is a sharp and asymmetric Fano profile in transmission spectrum, which is due to the interaction of the local discrete state and the continuous spectrum caused by the rectangular cavity and the semi-circular cavity, respectively. After changing the parameters of cavities, it was found that this Fano resonance position exhibits dependence on the parameters of the rectangular cavity, while is not sensitive to the tiny movement between the two resonators. Meanwhile, the propagation properties of two derivative structures were also studied by changing the mix of two resonators, and the transmission spectrums of these structures can exhibit a sharp and asymmetric Fano profile. In addition, the application of these structures in sensors was also studied by filled the cavities with different refractive index materials, the maximum sensitivity value of which is up to 750 nm/RIU. These studies will provide some theoretical basis for the future high sensitive microchip sensor based on surface plasmon polaritons waveguide.