基于表面等离激元提出一种由半圆环谐振空腔、挡板及直波导构成的金属-介质-金属波导结构。当入射光波进入该波导结构时,半圆环谐振腔形成两个较窄的离散态与金属挡板形成较宽的连续态发生干涉效应,并形成两个尖锐非对称的共振谱,即两种模式的Fano共振。运用耦合模式理论和有限元分析方法对结构的传输谱特性进行数值仿真分析,研究结构参数和介质折射率参数对传输品质因数和敏感度特性的影响。通过对结构参数进行优化分析,发现可通过改变结构参数对系统的性能进行灵活的调节和优化,并得到两个模式下的品质因数分别为3.05×10 5和4.59×10 5,对应的灵敏度分别为800 nm/RIU和1160 nm/RIU(RIU为折射率单元)。这种灵活的双重Fano共振结构在纳米生物传感器、非线性光学和慢光研究中具有一定的应用价值。

A metal-dielectric-metal waveguide structure comprising a semi-circular resonant cavity, baffle, and straight waveguide based on surface plasmon polaritons is proposed. When the incident light wave entered the waveguide structure, the semi-circular resonant cavity and metal baffle formed two narrow discrete states and a wide continuous state, respectively. Consequently, the interference effect was observed, which can form two sharp asymmetric resonance spectra, that is, two modes of Fano resonance. To conduct numerical simulation analysis on the transmission spectrum characteristics of the structure, the coupled-mode theory and finite element analysis method were used. Moreover, the effects of structural and medium refractive index parameters on the transmission quality factor and sensitivity characteristics were elucidated. By analyzing the optimization of the structural parameters, the system performance can be flexibly adjusted and optimized by modifying the structural parameters. Furthermore, the transmission quality factors in the two modes are 3.05×10 ⁵ and 4.59×10 ⁵, and their corresponding sensitivities are 800 nm/RIU and 1160 nm/RIU, espectively. The proposed flexible dual Fano resonance structure has certain application values in the study of nanobiosensors, nonlinear optics, and slow light.