Directional color routing assisted by switchable Fano resonance in bimetallic metagrating

Abstract

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.

High-efficiency broadband blazed metagrating working in visible light

“…The above excellent works still have some disadvantages, such as complex structure or not with high peak efficiency. Some metagratings with high diffraction efficiency based on simple structures have been proposed [23,34]. They are mainly based on the coupling between modes to extract the energy to a specific radiation channel, which mostly depends on the resonance effect.…”