Oriented hyperlens based on passivated porous graphene phases for sub-diffraction visible imaging

Abstract

The performance of conventional imaging lenses, relying on the phase transformation of propagating waves, is impairing due to the aberration and diffraction limits. For imaging beyond the diffraction limit, different superlens designs have been proposed. Although sub-diffraction resolution imaging in the near field has been realized by the superlenses with negative refractive index, magnification of the subwavelength objects into the far field has not been fulfilled. Imaging using “hyperlens” is promising to overcome the energy spreading associated with diffraction, by utilizing negative permittivity parallel to the optical axis, and positive permittivity perpendicular to it. Among various hyperlens implementations, three-dimensional (3D) non-magnetic left-handed- (NMLH), photonic crystal (PhC)- and metamaterial-based hyperlenses have several disadvantages, including short and geometry-dependent bandwidth, signal attenuation, and distortion. Here, we use two porous graphene phases, namely carbon passivated porous graphene (CPG), and silicon passivated porous graphene (SiPG) having worthy anisotropic optical properties in the visible spectrum range, for hyperlens implementation. The geometrical characteristics of the proposed two-dimensional (2D) configurations are investigated with the framework of density functional theory (DFT), and the anisotropic permittivity of monolayer and periodic stack configurations are obtained. Applying porosity in a 3 × 3 graphene unit cell, demonstrated operational frequency shifts from ultraviolet (UV) toward the visible range of the porous graphene-based hyperlens. The subwavelength resolution of the designed flat and oriented CPG and SiPG hyperlenses are illustrated at the wavelengths of 560 nm and 520 nm, and their superiority is shown in comparison with a well-known silver/GaAs metamaterial-based hyperlens. The proposed hyperlens implementation methodology based on stacking of 2D oriented porous sheets is very promising for the far-field super-resolution imaging, having applications in diverse fields of biology, molecular dynamic imaging, and nanolithography.