All‐Dielectric Toroidal Metasurfaces for Angular‐Dependent Resonant Polarization Beam Splitting

Abstract

An all‐dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular‐dependent resonant polarization beam‐splitter in the microwave K‐band. The metasurface is fabricated by embedding a square periodic array of high‐permittivity ceramic cuboid resonators in a 3D‐printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p‐(s‐) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full‐wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all‐dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter‐wave components for polarization control, for instance, in the context of 5G wireless communication networks.

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole

“…The Fano resonance caused by the interference and coupling between the narrow discrete mode and broad spectrum has been used in many studies [ 23 , 24 , 25 , 26 ]. In recent years, the toroidal-dipole-supported Fano resonance has been implemented to concentrate the electromagnetic field in a small region of the substrate [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Gupta et al, proposed a two-dimensional metamaterial to acquire a Fano resonance derived from the toroidal dipole.…”

A Bifunctional Silicon Dielectric Metasurface Based on Quasi-Bound States in the Continuum

“…Gorkunov et al [ 31 ] paid attention to the maximum chirality of circular polarized light, and proposed a method to achieve circular dichroism based on their quasi-BICs structure, which has potential in polarization modulation devices, optical sensing, chiral light sources, and so on. Zografopoulos et al [ 32 ] designed all-dielectric metamaterials with strong ring resonance for polarization beam splitting. These devices can perform their own polarization functions independently, but the single function may be a major limitation for the development of devices in the future.…”

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

“…Towards the opposite side of the spectrum, hydrogenated amor-phous Si has been demonstrated as a suitable material in a mid-IR qBIC metasurface 51 , whereas high-resistivity Si (HR-Si) 19,52,53 is the most suitable choice at terahertz (THz) frequencies thanks to its very low carrier concentration and, hence, low absorption losses, and also owing to the overall lack of transparent materials at THz. High-permittivity ceramic or polymer-ceramic composites provide a readily available solution for the demonstration of qBIC metasurface concepts at microwave frequencies 13,26,32,54,55 , although absorption losses stemming from the substrate can contribute considerably to resonance quenching 14,56 .…”

“…High-permittivity ceramic or polymer-ceramic composites provide a readily available solution for the demonstration of qBIC metasurface concepts at microwave frequencies, 13,26,32,54,55 although absorption losses stemming from the substrate can contribute considerably to resonance quenching. 14,56 The effective loss coefficient of a dielectric material can be increased by adding scattering losses stemming from surface roughness, which inevitably results from the etching process to define the metasurface elements. The effect of absorption/ scattering losses can be taken into account in simulations, estimating the saturation of the Q-factor in the low-asymmetry limit, where Q r 4 Q nr .…”

“…High-permittivity ceramic or polymer-ceramic composites provide a readily available solution for the demonstration of qBIC metasurface concepts at microwave frequencies, 13,26,32,54,55 although absorption losses stemming from the substrate can contribute considerably to resonance quenching. 14,56…”