Progress in metamaterials: Magnetic hybridization of electric dipole resonance and inhomogeneous structures for thin-film lenses

From earlier theoretical work and practical implementation, understanding of negative index metamaterials (NIMs) has advanced rapidly. Much effort has been put into extending NIMs in the near-infrared (NIR) and in visible regions, where simple scaling of the magnetic response of the structures used for RF breaks down at the NIR. As a solution, a new structure in the form of a fishnet has emerged, and has been shown to successfully act as a new metamaterial in the infrared and visible regions. Attention in the research community is now turning to the direct applications. Here we report progress in the field of metamaterials for the magnetic hybridization of the electric dipole resonance and inhomogeneous metamaterial structures.;From the fundamental and, possibly, application points of view, it is of interest to consider the coupling between the metamaterial magnetic resonance and electric dipole resonances of the absorbing species located in the metamaterial unit cell.;Simple resonance coupling model and numerical rigorous coupled wave analysis (RCWA) were used to investigate the effect of adding a dielectric with a dipole absorption peak to a fishnet metamaterial. Anti-crossing behavior and an exchange of oscillator strength as the metamaterial structural resonance is tuned through the absorption resonance were obtained. Response of the NIM structure with a dielectric material without an absorber shows only a single resonant peak, resulting from the coupling of the broadband negative epsilon with the structurally resonant negative micro associated with the LC circuit between the two metal plates. With the addition of a dipole absorber in the dielectric, the NIM exhibits doubly resonant behavior. Presence of an electric dipole resonance in the dielectric of the fishnet structure manifests itself in a modification of the magnetic permeability, which in turn modifies the negative index behavior. A set of experimental samples were fabricated using standard lithographic processing. An Al-BCB-Al fishnet structure was used. Transmission data was obtained by FTIR. Plotting positions of the resonance peaks in the transmission response against o0 clearly shows coupling between the resonances with hybridization behavior;First step in development of possible application for the metamaterials was done by Driscoll in 2006. He demonstrated a free space focusing by means of Split Ring Resonator structure. We take the next step and demonstrate that fishnet inhomogeneous metamaterial structures can be used for the thin-film lenses in the NIR regime. Here we report the first numerical demonstration of a flat, thin-film (<250 nm) GRIN positive lens operating in the NIR (∼1.55 microm) and based on the fishnet structure. This represents a significant advance toward applications as well as steps forward in design complexity and construction technique.;Complex RCWA based, parametric studies and the optimization for the largest achievable phase shift with smallest variation in transmission have been performed. Proposed (64x64)lambda2 area experimental samples will have small edge effects and act as f/26 lens. The F number can be significantly improved by stacking several layers of NIMs. Preliminary experimental results show a successful pattern transferring in the photoresist layer by the use of Imaging Interferometric Lithography (IIL) tool.