Abstract
Enhanced high-order diffractions which are spatially dispersive are desirable in such as spectroscopy studies, thin-film solar cells, etc. Conventionally, the dielectric gratings can be used to realize the enhanced diffraction, but the facets are usually rugged and optically thick (~μm). Plasmonic materials may exhibit unprecedented ability for manipulating light. Nonetheless, much interest has been focused on the subwavelength metasurfaces working in the zero-order regime. Here, we show that ultra-broadband and strongly enhanced diffraction can be achieved with the super-wavelength metasurfaces. For the purpose, we employ symmetric or asymmetric metal patches on a ground metal plane, which support the localized oscillation of free electrons and enhanced scattering of light. The zero-order reflection is suppressed, giving rise to an enhancement of first-order diffraction (50 ~ 95%) in an ultra-wide bandwidth (600 ~ 1500 nm). The proposed plasmonic structure is planar and ultra-thin (with an etching depth of only 80 nm), showing new potential for constructing compact and efficient dispersive elements.
Highlights
Guo et al investigated a dual-period plasmonic grating, where a larger-period modulation was imposed on the small-period slit or hole arrays in a metal film[26,27]
In the metal-dielectric-metal sandwiches, the top periodic metal patches and the bottom planar metal screen are separated by a thin glass spacer
The thickness of the glass spacer is t = 90 nm
Summary
Guo et al investigated a dual-period plasmonic grating, where a larger-period modulation was imposed on the small-period slit or hole arrays in a metal film[26,27]. With the unit cells of symmetric or asymmetric metal-dielectric-metal sandwiches, wideband and enhanced scattering of light can be induced.
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