Toroidal Metaphotonics and Metadevices

Abstract

Toroidal moments in artificial media have received growing attention and considered as a promising framework for initiating novel approaches to manage intrinsic radiative losses in nanophotonic and plasmonic systems. In the past decade, there has been substantial attention on the characteristics and excitation methods of toroidal multipoles-in particular, toroidal dipole-in 3D bulk and planar metaplatforms. The remarkable advantages of toroidal resonances have thrust the toroidal metasurface technology from relative anonymity into the limelight, in which researchers have recently centered on developing applied optical and optoelectronic subwavelength devices based on toroidal metaphotonics and metaplasmonics. In this focused contribution, the key principles of 3D and flatland toroidal metastructures are described, and the revolutionary tools that have been implemented based on this topology are briefly highlighted. Infrared photodetectors, immunobiosensors, ultraviolet beam sources, waveguides, and functional modulators are some of the fundamental and latest examples of toroidal metadevices that have been introduced and studied experimentally so far. The possibility of the realization of strong plexciton dynamics and pronounced vacuum Rabi oscillations in toroidal plasmonic metasurfaces are also presented in this review. Ultimate efficient extreme-subwavelength scale devices, such as low-threshold lasers and ultrafast switches, are thus in prospect.

Plasmonic semiconductor nanogroove array enhanced broad spectral band millimetre and terahertz wave detection

“…For such millimetre and terahertz wave detector, due to the involvement of a couple antenna, we usually do not use quantum efficiency to evaluate its performance. For a photodiode, its quantum efficiency can be expressed as ƞ = ( I p / e )/( P / hv ) = ( I p / P ) × ( hv / e ) = R A × ( hv / e ) 3 , 8 , where I p is the photocurrent, e is the element charge, P is the incident power, hv is the quantum energy of the incident photon, and R A is the responsivity in A/W. The typical value of ƞ for a photodiode is less than 100%.…”

“…Millimetre and terahertz wave detectors have a wide range of applications in areas such as communications, security, biological diagnosis, spectroscopy, and remote sensing 1 – 8 . They are the components that can transform light information loaded by long-wavelength millimetre and terahertz waves into electrical signals.…”

Functionalized terahertz plasmonic metasensors: Femtomolar-level detection of SARS-CoV-2 spike proteins

“… 47 , 48 The scanning electron microscope (SEM) image of the fabricated planar metasurface is shown in the inset of Figure 2 b, which comprises periodic arrays of engineered Au metamolecules (details on numerical and experimental steps are explained in Supplementary Information). Considering the excitation principle of a toroidal dipole in planar metasurfaces, [ 49 , 50 , 51 ] we theoretically verified the formation of this mode through vectorial surface current density map to exhibit the required discrepancy between the direction of induced magnetic moments in proximal resonators. In particular, a destructive interference between these oppositely pointed magnetic moments in adjacent resonators leads to the formation of a head-to-tail configuration consisting of a confined arrangement of both charges and currents, which results in the projection of a dynamic toroidal dipole from the scatterer ( Fig.…”

Theoretical Analysis of Terahertz Dielectric–Loaded Graphene Waveguide

“…It is worth mentioning that we set τ = 0.5 ps in the above investigations. Actually, τ is related to E F and is given by τ = nE F / eV F 2 [ 67 , 68 ], where n = 10,000 cm 2 /(V·s) is the carrier mobility of graphene and V F = 10 6 m·s −1 . As a result, τ is 0.9 (1.2) ps for E F = 0.9 (1.2) eV.…”