Abstract
AbstractGreat 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 almostπphase 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 ofλ = 600 nm.
Highlights
Localized surface plasmon resonances (LSPR) as a result of collective oscillation of free electrons in noble metals has drawn significant interest in the past years, owing to their capability of manipulating light at the nanoscale and owning extremely strong near-field enhancement [1, 2]
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
Phase modulation on the initial phase of waveguide diffraction lights by plasmon resonance overturns the interference process between optical waveguide and direct transmission lights to constructive interference in a metallic photonic crystal slab, which is the physical origin of Fano resonance in waveguide-plasmon photonic crystal structures [30, 31, 34]
Summary
Localized surface plasmon resonances (LSPR) as a result of collective oscillation of free electrons in noble metals has drawn significant interest in the past years, owing to their capability of manipulating light at the nanoscale and owning extremely strong near-field enhancement [1, 2] Those properties enable the applications of plasmonic nanostructures in improved photovoltaic [3], chemical/biological sensors [4, 5], and surface-enhanced molecular spectroscopies including surface-enhanced Raman scattering [6] and enhanced fluorescence [7]. Functional nanodevices with ultrathin and simple designs can provide more possibilities for the mass production with simple preparation processes and at a low cost While, their inadequate phase accumulation by just tuning the size or geometry of the nanodevices [15, 26, 27], makes them usually suffer from fundamental limitations on their efficiency in wave transformation. That may facilitate the applications in, for example, tunable passband optical filters, optical sensors, and color holography
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