ACS Nano. 2015 Mar 24;9(3):2968-80. doi: 10.1021/nn507148z. Epub 2015 Feb 17.
Fano resonance arising from the interaction between a broad "bright" mode and a narrow "dark" mode has been widely investigated in symmetry-breaking structures made of noble metals such as plasmonic asymmetric oligomers or other well-designed nanostructures. However, Fano resonance in nanoscale all-dielectric dimers has not been experimentally demonstrated so far. We report the first experimental observation of directional Fano resonance in silicon nanosphere dimers (both homodimer and heterodimer) and clarify that the coupling between magnetic and electric dipole modes can easily generate Fano resonance in all-dielectric oligomers, distinctly differing from conventional Fano resonances based on electric responses or artificial optical magnetism. A silicon nanosphere dimer, exhibiting a strong magnetic response inside and an electric enhancement in the gap, is an excellent structure to support magnetic-based Fano scattering. Interactions between magnetic and electric dipoles can suppress backward scattering and enhance forward scattering at Fano wavelengths. This directional scattering is much more prominent than that from a single silicon sphere and shows promising applications in areas such as directional nanoantenna or optical switching, opening up avenues for developing all-dielectric low-loss metamaterials or nanophotonic devices at visible wavelengths.
源于宽“亮”模与窄“暗”模相互作用的 Fano 共振，已在由贵金属制成的打破对称性结构中得到广泛研究，例如等离子体非对称低聚物或其他精心设计的纳米结构。然而，纳米级全介质二聚体中的 Fano 共振迄今尚未在实验中得到证实。我们首次报道了在硅纳米球二聚体（同核和异核）中定向 Fano 共振的实验观察，并阐明了磁偶极子和电偶极子模式之间的耦合可轻易在全介质低聚物中产生 Fano 共振，这与基于电响应或人工光学磁学的传统 Fano 共振明显不同。硅纳米球二聚体在内部表现出强磁响应，在间隙中具有电增强，是支持基于磁的 Fano 散射的理想结构。磁偶极子和电偶极子之间的相互作用可以抑制 Fano 波长处的反向散射并增强正向散射。这种定向散射比单个硅球的散射更为显著，在定向纳米天线或光开关等领域具有广阔的应用前景，为开发可见光波段的全介质低损耗超材料或纳米光子器件开辟了道路。
