Design and simulation of plasmonic metamaterials for sub-wavelength imaging in the visible range
Date of Issue2013
School of Electrical and Electronic Engineering
Photonics Research Centre
The resolution of conventional optical lens system is limited by diffraction to about half-wavelength of the incident light. Plasmonic metamaterials, which rely on surface plasmons (SPs) to confine and transmit the electromagnetic (EM) energy, provide a way to circumvent the diffraction-limit. Over the past decades, many plasmonic metamaterial lenses were proposed. However, there are still many issues such as the large material losses and short image transfer distance need to be addressed to realize these lenses. This PhD project numerically investigates several novel plasmonic metamaterial structures and optimizes their performances for sub-wavelength imaging in the visible range. Four kinds of plasmonic metamaterial lenses were investigated. They are the multilayered planar metal-dielectric (MD) structures, the hyperlenses, the dielectric nanorod chain array embedded in the metal and the planar magnifying lens. The first part of this thesis investigates the imaging performance of the multilayered planar MD structures and the hyperlens. It is found that the imaging performances of them depend on both the super-guiding and transmission properties. A figure of merit (FoM) which accounts both the super-guiding and the transmission was developed to optimize their imaging performance. Numerical simulations showed that the proposed FoM works well for both planar MD structure and hyperlens, and it could be used to optimize the geometric parameters, as well as the working wavelength of such MD structures. The imaging properties of the hyperlens were also examined by a transfer matrix formulation that was developed for evanescent waves in cylindrical coordinate. It is found that the accessible range of the evanescent waves in the hyperlens is larger than that in the planar MD structures, indicating that higher resolution can be achieved by the hyperlens. Furthermore, the imaging properties of a hemispherical hyperlens for two-dimensional imaging were also investigated. Numerical simulations showed that the hemispherical hyperlens responses to linearly polarized lights regardless of their polarization directions, but only recovers portion of the image along the electrical field direction. In this work, a superposition method by combining the images obtained under different polarization directions was proposed and numerically demonstrated to obtain the complete image. The second part of the thesis discusses two novel plasmonic metamaterial lenses including the dielectric nanorod chain array embedded in the metal and the planar magnifying lens. The dielectric nanorod chain array embedded in the metal was covered first. Unlike conventional metamaterial lenses that rely on metallic structures as the main transmission medium, the proposed lens uses dielectric as the main medium for image transfer. Numerical simulations revealed that such lenses suppress the coupling among the transmission channels, and transfer the image to a distance comparable to the wavelength. At 560 nm, the proposed dielectric nanorod chain lens demonstrated a resolution of 50 nm. The last section of the thesis discusses a unique planar magnifying lens made of two symmetrically arranged unidirectional surface plasmon polaritons (SPPs) generators and a multilayered MD structure. Both numerical simulations and theoretical analysis showed that the proposed unidirectional SPPs generator could be used as a scanning probe for high performance imaging. At 533 nm, a resolution of 45 nm and a magnification of 41 were demonstrated. Such a lens has a high potential to be used as a lab-on-chip device for imaging of DNA or virus in a micro-fluid channel.
DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics