Silicon‐Based Terahertz Meta‐Devices for Electrical Modulation of Fano Resonance and Transmission Amplitude

Abstract

EM waves and have demonstrated novel phenomena like negative refraction, super lenses, invisibility cloaks, slow light effects, and subwavelength resolution imaging. [4-14] To date, silicon has emerged as a popular material choice to design THz metamaterials devices in terms of modulators, absorbers, and polarization converters, [15-18] due to not only its high refractive index and very low absorption losses in the THz frequencies, but also its mature processing technology. The shape and linewidth of an EM resonance depend on the nature and strength of the scattering phenomenon, which are owed to the absence or presence of interference effects occurring in the system. Depending upon the excitation requirements, there are two main kinds of resonances in the planar metamaterials: Lorentz resonance and Fano resonance. The Lorentz resonances exhibit broad and symmetry shape, [19-21] while the Fano resonances show a sharp and asymmetry line shape due to the coherent coupling between the discrete and continuous states. [22-26] Since it was first observed in metamaterials system by breaking the symmetry of the metallic structures, the Fano resonance in metamaterials and plasmonic nanostructures has attracted great Seeking active and effective control over electromagnetic waves has always been an important focus in optics. Fano resonances occur in planar terahertz (THz) metamaterials by introducing a weak asymmetry in a two-gap split ring resonator. Without extra layers of photoactive materials and microelectromechanical structures, a novel and economical scheme based on siliconintegrated THz asymmetric metallic split ring metamaterial is proposed to control Fano resonance and transmission amplitude via electrical excitation. The results show that Fano resonance and transmission amplitude abate drastically with the increase of current bias, due to the loading of electrically formed silicon carrier layer. As the current bias is increased, both the thickness and conductivity of silicon carrier layer are modulated simultaneously. The depth range of modulated silicon carrier layer could reach 250 µm. Besides, a THz transmission amplitude modulator with a modulation depth of 93% is also demonstrated. This work significantly expands the function of silicon-based metamaterials and opens up opportunities for the realization of switchable sensors, filters, and nonlinear devices.

Subwavelength optical localization with toroidal excitations in plasmonic and Mie metamaterials

“…Metamaterials 24‐43 and its two‐dimensional (2D) counterpart metasurfaces 44‐68 made from plasmonic resonant 69‐73 or Mie resonant building blocks 74‐84 are especially promising for the enhancement of light–matter interactions 19,85,86 at a subwavelength scale. Various plasmonic and Mie metamaterials have been proposed for achieving high Q factor response, 87‐96 for example, the trapped mode, which is kind of magnetic mode weakly coupled to free space, was suggested to be excited by introducing symmetry breaking in the shape of structural elements for realizing sharp spectral response 87 .…”

Electrically Tunable Singular Phase and Goos–Hänchen Shifts in Phase‐Change‐Material‐Based Thin‐Film Coatings as Optical Absorbers

“…[ 43 ] In addition, a layer of silicon‐free carriers does not have a significant response to the incident optical waves at low values of the bias current (0 to 100 mA). [ 44 ] In Figure 4b, we show the wavelength‐dependent temperature‐induced refractive index changes of MMA for different currents. Since the refractive index change depends on temperature, we measured the refractive index of MMA for each current (0 to 100 mA) by annealing the Si/MMA cavity for a time interval of 5 min.…”

A Review of Tunable Electromagnetic Metamaterials With Anisotropic Liquid Crystals

“…As for traditional metamaterials, once the structural units are determined, they can only work well at a certain frequency range, which greatly limits their applications in practical engineering. The ever-increasing demand on designing versatile photonic devices inspires the rapid development of tunable metamaterials [31][32][33][34][35]. Several methods have been proposed to broaden their operation bandwidth with the incorporation of active inclusions, such as varactor diodes [36][37][38], semiconductors [39][40][41], ferroelectric [42], phase change materials [43], graphene [44][45][46], and anisotropic materials [47][48][49][50].…”