Great progress in nanophotonics has been demonstrated in tailoring the impinging beams. The physics behind those intriguing effects is to a large extent governed by the parameter of the optical phase. While, simple nanostructures usually suffer from fundamental limitations on their efficiency in wave transformation, especially in the transmission system, associated with their inadequate phase accumulation, challenge their implementation in practical application. Here, we describe a transparent nanostructure built from a pair of partially overlapped gold and aluminum semi-nanoshells that show almost π phase accumulation through material-dependent plasmon resonances. Combined with an optical slab waveguide, the bimetallic metagratings exhibit prominent directional color routing properties in transmission light, which result from switchable Fano resonances between plasmon resonances of bimetallic nanostructures and ±1 order waveguide diffraction modes at two opposite oblique incidences due to sufficient phase shift provided by the asymmetric and bimetallic plasmon resonators. Both theoretical and experimental results show that the Fano-resonance-assisted color routing exhibits a relatively broadband tuning range (∼150 nm with an efficiency of up to 50%) and a color routing efficiency of up to 70% at the central wavelength of λ = 600 nm.

中文翻译：

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双金属元光栅中由可切换 Fano 共振辅助的定向颜色路由

纳米光子学在调整入射光束方面取得了巨大进展。这些有趣效应背后的物理学在很大程度上受光学相位参数的支配。然而，简单的纳米结构通常在波变换效率方面受到根本限制，尤其是在传输系统中，由于相位积累不足，对其在实际应用中的实现提出了挑战。在这里，我们描述了由一对部分重叠的金和铝半纳米壳构建的透明纳米结构，通过依赖于材料的等离子体共振显示出几乎 π 相积累。结合光学平板波导，双金属超光栅在传输光中表现出突出的定向颜色路由特性，由于不对称和双金属等离子谐振器提供了足够的相移，因此在双金属纳米结构的等离子谐振和 ±1 级波导衍射模式之间的可切换 Fano 谐振在两个相反的倾斜入射时产生。理论和实验结果都表明，Fano 共振辅助的颜色路由表现出相对宽带的调谐范围（~150 nm，效率高达 50%），并且在 λ 的中心波长处颜色路由效率高达 70% = 600 纳米。