Using Thin Films of Phase-Change Material for Active Tuning of Terahertz Waves Scattering on Dielectric Cylinders

The scattering of electromagnetic waves by isotropic dielectric cylinders can be dramatically modified by means of vanadium dioxide (VO2) thin-film coatings. Efficient dynamic control of scattering is achieved due to the variations in material parameters realizable by means of external biasing. In this paper, we study the scattering of terahertz waves in a case where the coating shells are made of VO2, a phase-change material, whose thin films may work rather as electromagnetic phase screens in the insulator material phase, but as lossy quasi-metallic components in the metallic material phase. The shells that uniformly cover the dielectric cylinders are investigated. Attention will be paid to the demonstration of the potential of VO2 in the external control of diverse scattering regimes of the dielectric-VO2 core-shell scatterer, while conductivity of VO2 corresponds to rather insignificant variations in temperature. In line with the purposes of this work, it is shown that the different resonant and nonresonant regimes have different sensitivity to the variations in VO2 conductivity. Both the total scattering cross section and field distributions inside and around the core are studied, as well as the angle-dependent scattering cross section.

Validation of electromagnetic field enhancement in near-infrared through Sierpinski fractal nanoantennas

We introduced fractal geometry to the conventional bowtie antennas. We experimentally and numerically showed that the resonance of the bowtie antennas goes to longer wavelengths, after each fractalization step, which is considered a tool to miniaturize the main bowtie structure. We also showed that the fractal geometry provides multiple hot spots on the surface, and it can be used as an efficient SERS substrate.

Unidirectional transmission in photonic-crystal gratings at beam-type illumination

Unidirectional transmission is studied theoretically and experimentally for the gratings with one-side corrugations (non-symmetric gratings), which are based on two-dimensional photonic crystals composed of alumina rods. The unidirectional transmission appears at a fixed angle of incidence as a combined effect of the peculiar dispersion features of the photonic crystal and the properly designed corrugations. It is shown that the basic unidirectional transmission characteristics, which are observed at a plane-wave illumination, are preserved at Gaussian-beam and horn antenna illuminations. The main attention is paid to the single-beam unidirectional regime, which is associated with the strong directional selectivity arising due to the first negative diffraction order. An additional degree of freedom for controlling the transmission of the electromagnetic waves is obtained by making use of the asymmetric corrugations at the photonic crystal interface.

Transmission enhancement through deep subwavelength apertures using connected split ring resonators

We report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of lambda/31 x lambda/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries.