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.

A metasurface is one of the most effectual platforms for the manipulation of complex optical fields.

No abstract

Recent progress in the metamaterial-based polarization manipulation of light highlights the promise of novel polarization-dependent optical components and systems. To overcome the limited frequency bandwidth of metamaterials resulting from their resonant nature, it is desirable to incorporate tunability into metamaterial-based polarization manipulations. Here, we propose a dielectric metamaterial for controlling linear polarization conversion using the phase-change characteristic of Ge2Sb2Te5 (GST), whose refractive index changes significantly when transforming from the amorphous phase to the crystalline phase under external stimuli. The polarization conversion phenomena are systematically studied using different arrangements of GST in this metamaterial. The performance of linear polarization conversion and the tunability are also analyzed and compared in three different designs. It is found that phase-change materials such as GST can be employed in dielectric materials for tunable and switchable linear polarization conversion in the telecom band. The conversion efficiency can be significantly modulated during the phase transition. Our results provide useful insights for incorporating phase-change materials with metamaterials for tunable polarization manipulation.