High‐Quality‐Factor Mid‐Infrared Toroidal Excitation in Folded 3D Metamaterials

Abstract

With unusual electromagnetic radiation properties and great application potentials, optical toroidal moments have received increasing interest in recent years. 3D metamaterials composed of split ring resonators with specific orientations in micro-/nanoscale are a perfect choice for toroidal moment realization in optical frequency considering the excellent magnetic confinement and quality factor, which, unfortunately, are currently beyond the reach of existing micro-/nanofabrication techniques. Here, a 3D toroidal metamaterial operating in mid-infrared region constructed by metal patterns and dielectric frameworks is designed, by which high-quality-factor toroidal resonance is observed experimentally. The toroidal dipole excitation is confirmed numerically and further demonstrated by phase analysis. Furthermore, the far-field radiation intensity of the excited toroidal dipoles can be adjusted to be predominant among other multipoles by just tuning the incident angle. The related processing method expands the capability of focused ion beam folding technologies greatly, especially in 3D metamaterial fabrication, showing great flexibility and nanoscale controllability on structure size, position, and orientation.

Nonradiating photonics with resonant dielectric nanostructures

“…To bring the unique properties of anapoles to the macroscopic scale, the resonators supporting anapole states could be arranged into periodic arrays. The toroidal dipole moment in metasurfaces was analyzed theoretically and experimentally at different frequency ranges, from microwaves to the visible spectrum (see for example [131][132][133][134][135]). The majority of considered designs contains metallic parts, which do not give essential contribution to losses in microwave and THz regions because of extremely small skin depth at such frequencies.…”

Anapole Mode Sustaining Silicon Metamaterials in Visible Spectral Range

“…Primarily, because of the ability to concentrate strong electromagnetic fields inside a point nonradiating source or scatterer and ensuring the suppression of radiation in an external field. Therefore, metamaterials with anapole mode demonstrated extremely high Q‐factor so that manifested themselves as perfect resonator …”

Microwave toroidal dipolar response in an asymmetric planar metamaterial

“…In 2010, Zheludev et al firstly declared their numerical and experimental observations of a toroidal dipolar response by the means of metamaterials in the microwave region [5]. This novel discovery causes great concern on the often ignored toroidal multipoles and inspires many related researches on toroidal responses in microwave [6][7][8][9], terahertz [10,11], mid-infrared [12] and optical regions [13,14]. At the same time, it also provides a basis for related researches in resonant transparency [15], permittivity sensor [16], polarization twister [17], toroidal lasing spacer [18], electromagnetically induced transparency [19], and so on.…”