Changchun Yan

Metal-dielectric composites for beam splitting and far-field deep sub-wavelength resolution for visible wavelengths

We report beam splitting in a metamaterial composed of a silver-alumina composite covered by a layer of chromium containing one slit. By simulating distributions of energy flow in the metamaterial for H-polarized waves, we find that the beam splitting occurs when the width of the slit is shorter than the wavelength, which is conducive to making a beam splitter in sub-wavelength photonic devices. We also find that the metamaterial possesses deep sub-wavelength resolution capabilities in the far field when there are two slits and the central silver layer is at least 36 nm in thickness, which has potential applications in superresolution imaging.

Two-dimensional subwavelength imaging from a hemispherical hyperlens.

We report a hemispherical-shaped hyperlens with subwavelength resolution less than 100 nm. Simulations with the finite-element method show that with a 365 nm illumination, the hemispherical hyperlens isotropically magnifies the image along the radial direction. Under linearly polarized light, portions of an object can be resolved. A complete image of the object can be generated by superposing sufficient number of images obtained with incident light in different polarization directions. Such a hyperlens has great potential for realization of nanoscale imaging.

Metal nanorod-based metamaterials for beam splitting and a subdiffraction-limited dark hollow light cone

We report beam splitting in a metamaterial composed of a metal nanorod array embedded in a dielectric covered by a layer of chromium containing a hole. By simulating distributions of energy flow in the metamaterial, we find that the beam splitting occurs for H-polarized incidence, which is conducive to producing a beam splitter. We also find that a dark hollow light cone can be formed for circularly polarized incidence, which has a potential application in manipulating atoms and molecules.

Dual refractions in metal nanorod-based metamaterials

We report the dual refractions in the metamaterials composed of metal nanorod arrays and alumina at visible wavelengths. By simulating the energy stream distributions of the nanorod arrays for H-polarized waves, we find that the dual refractions exist in the transition region starting from a critical ratio of the wavelength in free space to the neighbor nanorod distance. The critical ratio is a function of the radius of nanorods and the material used but does not vary with incident wavelengths. The dual refractions can serve as a criterion for applicability of the effective medium theory in the metamaterials based on nanorod arrays.

A multi-layered split ring metamaterial for a multiwavelength and tunable lasing spaser

We report a multiwavelength and tunable lasing spaser realized by a gain-assisted metamaterial. The metamaterial consists of three regularly spaced parallel arrays of weakly asymmetric metallic split rings, with the first-layered array located on the gain medium surface and the other two-layered arrays embedded in it. Our simulations demonstrate that the three-layered metamaterial can radiate three-wavelength electromagnetic waves with high Q factors and transmission enhancement, which can be tuned by varying the gain coefficient.

Concentric cylindrical metamaterials for subwavelength dark hollow light cones

We report a concentric cylindrical metamaterial (CCM) which can be used for acquiring a dark hollow light cone (DHLC). The proposed structure is composed of a concentric cylindrical silver‐dielectric multilayer composite, which is covered by a thin layer of chromium (Cr) containing an annulus or a hole opening for incidence. The simulation results show that nanometer-level dark hollow light cones with good quality can be formed in the output for circularly polarized incidence and its position can be monitored by choosing different dielectric materials and dimensions of annular apertures. Such a dark hollow light cone is believed to have potential applications in manipulating atoms and molecules.

Figure of Merit for Optimization of Metal–Dielectric Multilayer Lenses

We propose a figure of merit (FoM) to optimize the multilayered metal-dielectric (MD) structure for subwavelength imaging. The proposed FoM accounts both the waveguiding and transmission properties of the multilayered MD structure. We numerically demonstrate that the FoM can be used to find the optimized geometry parameters, as well as the optimized working wavelength. Such a FoM can act as an efficient tool for design and fabrication of the multilayered MD lenses.

Geometric Parameter Optimization of Far-Field Hyperlens for Super Resolution

We optimize the performance of the hyperlens based on geometric parameters. The theoretical analysis and numerical simulation show that the dispersion relation of the hyperlens can be tuned by adjusting geometric parameters such as the metal filling ratio and number of alternating metal/dielectric layers. The metal filling ratio can be optimized to achieve 0o ray divergence. For the hyperlens with same thickness, increasing the number of metal/dielectric periods can also improve the performance, but the improvement saturates as the number of periods reaches a critical level.

Beam splitting and a hollow light cone from a metamaterial based on a metallic nanorod array

We report beam splitting in a metamaterial composed of a metallic nanorod array embedded in dielectric. By simulating distributions of energy flow in the metamaterial, we find that the beam splitting occurs for H-polarized incidence, which is conducive to producing a beam splitter. We also find that a hollow light cone can be formed for circularly polarized incidence, which has a potential application in manipulating atoms and molecules.

Nanostructured materials for sensing and imaging

From semiconductor quantum well structures to the currently hottest metamaterials, the conquest of nano-world has been occurring in almost every field of research. In the field of quantum well structures for infrared photodetection, the inclusion of dilute nitride layers in the mature GaAs based quantum well structures results in a TE dominate photocurrent and the incorporation of nitrogen in the narrow bandgap InSb materials makes it possible for wide band infrared absorption covering mid and long wavelength infrared range. With the nanostructured materials made of metal and dielectric composites, visible light can be manipulated, which has potential application for super resolution imaging beyond diffraction limit.