Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne, Switzerland.
ACS Nano. 2013 May 28;7(5):4527-36. doi: 10.1021/nn401175j. Epub 2013 Apr 24.
Fano resonances in hybridized systems formed from the interaction of bright modes only are reported. Despite precedent works, we demonstrate theoretically and experimentally that Fano resonances can be obtained by destructive interference between two bright dipolar modes out of phase. A simple oscillator model is provided to predict and fit the far-field scattering. The predictions are verified with numerical calculations using a surface integral equation method for a wide range of geometrical parameters. The validity of the model is then further demonstrated with experimental dark-field scattering measurements on actual nanostructures in the visible range. A remarkable set of properties like crossings, avoided crossings, inversion of subradiant and superradiant modes and a plasmonic equivalent of a bound state in the continuum are presented. The nanostructure, that takes advantage of the combination of Fano resonance and nanogap effects, also shows high tunability and strong near-field enhancement. Our study provides a general understanding of Fano resonances as well as a simple tool for engineering their spectral features.
报道了仅由明模式相互作用形成的杂交系统中的 Fano 共振。与先前的工作不同，我们从理论和实验上证明，通过两个反相的亮偶极模式之间的相消干涉，可以获得 Fano 共振。提供了一个简单的振荡器模型来预测和拟合远场散射。通过使用表面积分方程方法对大范围的几何参数进行数值计算，验证了这些预测。然后，通过在可见范围内对实际纳米结构进行暗场散射实验测量，进一步证明了该模型的有效性。呈现了一系列显著的特性，如交叉、避免交叉、亚辐射和超辐射模式的反转以及连续体中的束缚态的等离子体等效。利用 Fano 共振和纳米间隙效应相结合的纳米结构还具有高的可调谐性和强的近场增强。我们的研究提供了对 Fano 共振的普遍理解，以及对其光谱特性进行工程设计的简单工具。
