Study On The Optical Properties Of Metal-dielectric Nanostructures

Plasmonics, which is based on the metal-dielectric nanostructures, is a hot topic in the interdisciplinary field of physics, chemistry, biology, and information technology. Metal-dielectric nanostructures have wide and practical applications in the area of subwavelength optics, surface enhanced Raman scattering, biosensors,enhanced optical transmission, superscattering and so on, due to its novel optical properties, i.e. breaking through diffraction limit, local field enhancement, and sensitivity to the surrounding dielectric medium.In this thesis, we will theoretically study on the dispersion and coupling properties of plasmonic modes. This study would help us to design and control the optical properties of metal-dielectric nanostructures. Our work mainly refers to the dispersion properties of plasmonic lenses, the three-dimensional subwavelength imaging and focusing, the interference of plasmonic modes in single nanoparticle, and a novel imprint lithography for coplanar plasmonic nanostructures fabrication. The thesis consists of four sections that are arranged as following:(1) We study the dispersion properties of plasmonic lenses and its engineering mechanism. The strong dispersion of metallic materials would introduce strong dispersion properties of plasmonic lenses, which would result in different focus positions of the light with different wavelengths. We propose novel compound plasmonic lenses, which consist of metal-insulator-metal waveguides (MIMWGs) and phase zone plates (PZPs), with controllable dispersive properties. Numerical simulation results show that this new type of compound plasmonic lens is capable of not only minimizing the chromatic aberration but also rearranging the order of focal positions for incident light at visible frequencies, which is different from the conventional normal and abnormal dispersion. This study would also be applied to control the dispersion properties of other plasmonic devices.(2) The influence of the dispersion properties of a hyperlens on its imaging or focusing position is investigated. Because the intensity of surface plasmons exponentially decays in the direction perpendicular to the surface between metal and dielectric, the imaging or focusing usually appears at the surface of a hyperlens. By designing curved lineshape of the hyperbolic dispersion combined with the time-reversal technique, the imaging or focusing position could be away from the surface of a hyperlens. The controllable position of an imaging or focusing with super resolution in z-direction would be conducive to the ultimate realization of three-dimensional subwavelength imaging and lithography.(3) A subwavelength nanodisk is designed as a simple candidate to achieve Fano resonances and superscattering. By changing either the height or diameter of a nanodisk, the mode interaction shows high tunability and evolves from the unique Fano-like resonance to superscattering. A model of two-driven coupled oscillators is proposed to quantitatively analyze the evolution. This study shows that the resonance wavelengths and loss of two coupled plasmonic modes can affect their interference phase. Moreover, we show that the superscattering enhances both the far-field scattering and near-field electric field intensity, leading to improved figure of merit for plasmonic refractometric sensing.(4) We develop a new process of planar self-alignment imprint lithography(P-SAIL) to fabricate the metallic and dielectric structures on the same plane. By encoding all of the patterning information onto a multilevel mold,P-SAIL transfers the multilevel imprint processes to a single-imprint process which avoids the alignment and offers higher efficiency and less cost than existing manufacturing methods. It is also highly compatible with roll-to-roll processes. P-SAIL provides a simple and economical approach to fabricate coplanar plasmonic nanostructures.