Multimode directionality in all-dielectric metasurfaces

Abstract

We demonstrate that spectrally diverse multiple magnetic dipole resonances can be excited in all-dielectric structures lacking rotational symmetry, in contrast to conventionally used spheres, disks or spheroids. Such multiple magnetic resonances arise from hybrid Mie-Fabry-Pérot modes, and can constructively interfere with induced electric dipole moments, thereby leading to novel multi-frequency unidirectional scattering. Here we focus on elongated dielectric nanobars, whose magnetic resonances can be spectrally tuned by their aspect ratios. Based on our theoretical results, we suggest all-dielectric multimode metasurfaces and verify them in proof-ofprinciple microwave experiments. We also believe that the demonstrated property of multimode directionality is largely responsible for the best efficiency of all-dielectric metasurfaces that were recently shown to operate across multiple telecom bands.

Near‐Infrared Super‐Absorbing All‐Dielectric Metasurface Based on Single‐Layer Germanium Nanostructures

“…Multipole decompositions of the scattering behavior of a single Ge disk are conducted in vacuum (See Supporting Information for details of conducting multipole decompositions). Its total scattering cross section can be decomposed into the contributions from the electric dipole ( ED ), the magnetic dipole ( MD ), the electric quadrupole ( EQ ), and the magnetic quadrupole ( MQ ), as shown in Figure a.…”

Nonradiating anapole states in nanophotonics: from fundamentals to applications

“…In addition, the presence of higher-order anapole states can be also seen in a broader frequency range (or equivalently with larger particle sizes). Such a higher-order anapole state A 2 can be treated as a hybridization of the first-order anapole state A 1 and a Fabry-Perot resonance, which enables a stronger localization of near-field energy [59]. Recently, the exotic feature of higher-order anapole states was thoroughly investigated by Zenin et al [18] using near-field optical microscopy (SNOM) and has been utilized in multispectral field enhancements [60] and nonlinear optics [61].…”

High Q-Factor Resonance in a Symmetric Array of All-Dielectric Bars

“…And it can be easily fabricated by plasma-enhanced chemical vapor deposition (PECVD), electron-beam lithography, residual resist etching and lift-off process [6,35]. Unlike most previously reported rod-type all-dielectric metasurfaces, where normal incident light polarized along the rods is used to excite a broad ER [5,6,36,37,39], in this paper, the electric field of the incident wave is polarized perpendicular to the rods (i.e., in x-axis). Numerical simulations are conducted using the commercial CST software (CST Studio Suite 2014, CST company, Darmstadt, Germany) at frequency-domain, and periodic boundary conditions are utilized both in x and y directions and open boundary condition are used in the wave propagating direction of z.…”

“…According to the Maxwell electromagnetic theory, a strong magnetic field (Figure 2d) at the cross-section (y-z plane) is induced along the azimuth by the large displacement current, which corresponds to ER and a typical high order 12 TE  mode of the rod resonator [40], though it is usually hybridized due to the coupling between neighboring rods [41]. As Yang et al [39] indicated that both ER and MR contributed to the resonance in a long rod silicon metasurface when a normal incident light is polarized along the rods, to further confirm the distinct ER and MR behavior, we also adopted a standard S-parameter retrieval method [42] to compute the effective permittivity and permeability shown in Figure 3. At the resonance wavelength of ~1187 nm, it shows negative permeability and positive permittivity which explain that this resonance is mainly attributed to the MR, but affected by the coupling between the MR and the ER.…”