All‐Dielectric Kissing‐Dimer Metagratings for Asymmetric High Diffraction

Abstract

and vortex beam generators. [10][11][12] In particular, phase-gradient metasurfaces can cumulatively produce blazed phase profiles for essential far-field interference to redirect the incident wave to the anticipated direction under normal incidences. [13][14][15] However, these approaches suffer from the intrinsic restriction owing to the limited number of elements in a supercell which can fit into each periodically repeated units to discretely map the desired phase profiles. Apparently, phase-gradient metasurfaces inevitably deteriorate beam steering performance at large bending angles with significantly degraded efficiencies. [13][14][15] To tackle this challenge, high diffraction metagratings capable of ultrahigh angle beam bending were proposed. [16][17][18][19][20][21][22][23][24][25][26][27][28] Breaking the symmetry of the illumination condition of the metagrating can allow high diffractions, funneling light into the desired diffraction order with high efficiencies at oblique incidences. [16][17][18][19][20][21][22][23] Based on this scheme, high diffractions in either reflection mode using metallic metagratings [16][17][18][19] or in the transmission mode using all-dielectric metagtratings [20][21][22][23] have been achieved. Alternatively, at symmetric illumination condition, asymmetric building blocks with multiple separate inclusions of different dimensions or geometries were usually considered as a necessity to generate far-field interference for directional scattering patterns without adversely affecting each other's mode. Engineering the directional scattering patterns of periodically repeated building blocks of the metagrating demonstrates the potential to channel the incident light into desired diffraction orders at will. [24][25][26][27][28] In particular, high-index all-dielectric nanoantennas featured with geometry-tunable multiple Mie resonances for associated novel effects [26] open a new route to selectively enhance/suppress a single diffraction order in both reflection and transmission modes. However, the innate frequency divergence of multiple separate inclusions hinders the high diffraction efficiency from wide frequency and angle range, which are highly desirable for various beam steering applications. Moreover, the diffraction efficiency is strongly dependent on the separation between such asymmetric nanoantennas, which exacerbates challenges for stringent fabrication precision.Here, we propose a kind of kissing-dimer metagratings (Figure 1a), which can steer the illumination light Transcending the common perceptions of phase-gradient metasurfaces, metagratings emerge as a new paradigm for wavefront manipulation directly on the desired diffraction order with ultrahigh deflection angles. However, previous metagratings rely on directional scattering caused by multiresonant interference between multiple separate inclusions, of which the high diffraction efficiencies are only optimized with limited bandwidth and incident angle tolerance. Here, a kind of asymmetric kissing-dimer metagrating...

Displacement-mediated bound states in the continuum in all-dielectric superlattice metasurfaces

“…Metasurfaces, which consist of periodic arrays of carefully designed nanostructures, provide a versatile platform to accurately control the properties of light, including phase, amplitude, polarization and frequency spectrum of light [1]. In recent years, metasurfaces based on dielectric materials with high refractive index have been used to develop numerous compact optical devices due to their low loss properties, including at lenses [2][3][4], beam de ectors [5,6], holograms [7,8], etc. Searching for the ultrahigh Q-factor resonant structures with strong mode coupling has attracted much attention recently [9][10][11].…”

Single‐Layered Reflective Metasurface Achieving Simultaneous Spin‐Selective Perfect Absorption and Efficient Wavefront Manipulation

“…[ 1–4 ] By introducing strong interactions between electromagnetic (EM) waves and meta atoms, metasurfaces have shown great potentials in full vectorial EM manipulation in terms of amplitude, phase, as well as polarizations. So far, many exotic applications such as perfect absorption, [ 5,6 ] anomalous beam deflection, [ 7,8 ] vortex beam generation, [ 9 ] flat lensing, [ 10,11 ] and meta‐hologram [ 12 ] have been realized with simultaneous high performance and compactness compared with their traditional counterparts. Besides, metasurface‐based devices can even achieve counterintuitive functionalities that can hardly be realized by natural materials, such as carpet cloaking [ 13 ] and daytime radiative cooling.…”

Subwavelength Silicon Nanoblocks for Directional Emission Manipulation

“…Studies have shown the unique capability to create unidirectional light radiation in multiple architectures, including single-element nanospheres [ 8 , 9 ], nanodisks [ 11 , 12 , 13 , 14 , 15 ], nanowires (cylinders) [ 16 , 17 , 18 , 19 ], rectangular patches [ 20 ], V-shaped [ 21 ] and stair-shaped nanoantennas [ 22 ], as well as multi-element array nanoantennas [ 23 , 24 , 25 , 26 ]. There are also many efforts in the field to achieve bi- or multi-directional scattering/emission [ 9 , 13 , 15 , 21 , 23 , 27 , 28 ].…”