Photonic Metamaterials

Photonic metamaterial study investigates fabrication, characterization and applications of metamaterials operating at the infrared and visibile regimes of the electromagnetic spectrum. Applications include optical superlens, optical isolators, electro-optical modulators and optical switching.

Miniaturized Microwave Absorbers

Extremely thin, narrow band microwave absorbers can be realized by using a two-dimensional array of subwavelength resonators as a perfect magnetic conductor plane. In this absorber design, a 377 Ohm resistive sheet is backed with the artificial perfect magnetic conductor. Due to the absence of the metallic plate that is used in typical absorbers, this metamaterial loaded absorber is extremely thin and a good candidate for stealth technologies.

Enhanced Transmission Through Subwavelength Apertures

Transmission and diffraction problem of light passing through an aperture of size much smaller than the incident wavelength has been studied since 1940s. The transmission efficiency is demonstrated to be dependent on the physical size of the aperture and wavelength of the incoming light. Enhanced transmission efficiency was demonstrated by the excition of surface plasmon resonances around the aperture. In this study, we propose an alternative solution for enhancement. We place periodic subwavelength resonator to the holes in a way to excite both electric and magnetic resonances. At around the resonance frequency complete transmission can be achieved.

Millimeter-Wave Scale Metamaterials

In this study we designed double negative metamaterials operating at around 100 GHz. Both planar (cutwire pair based) and split ring resonator based metamaterials with simultaneously negative permittivity and permeability were demonstrated. For the characterization we used qualitative effective medium theory and retrieval analyses. Direct observation of negative refraction was performed by synthesizing a flat metamaterial lens and a meta-prism. Unusual properties such as negative refraction, negative phase velocity, focusing and directive far field response were verified.

Deep Subwavelength Resonators

A medium composed of periodically arranged electrically small resonator can possess a negative effective permeability. In order the effective medium concepts to be valid, the electrical size of the medium particles have to be much smaller than the operation wavelength. We have parametrically studied multi-split ring resonators (MSRRs) and spiral resonators (SRs) that can be fabricated via the standard planar substrate based fabrication techniques and can be packed into one-, two- and three- dimensional arrays for the metamaterial applications. Effects of particle length, number of rings, substrate permittivity, filling ratio of the rings, width and seperation between the rings are studied in terms of resonance frequency and resonance strength. We introduced an optimum particle: multi-spiral resonator (MSR), which states a compromise between the electrical size and resonant response strength.

Electrically Small Antennas

Electrically small antennas (ESAs) occupy a volume of the sphere whose radius is a small fraction of the operation wavelength. The challenge of the field is that there are fundamental limitations on antenna quality factor and its electrical size. By exciting metamaterial resonances novel miniaturized antennas can be realized. We showed a split ring resonator loaded monopole antenna with λ/10 electrical size and 40% efficiency. Another design was a loaded patch antenna that utilized resonance at the interface of negative and positive permeability media in circular geometry. We infer from the measurement results metamaterials can play an important role in the development of electrically small antennas.

Negative Refraction in Photonic Crystals

Under certain conditions photonic crystals can exhibit negative refraction and focusing properties. At the fifth transverse electric band of a two-dimensional hexagonal lattice photonic crystal, the negative refraction and focusing properties were demonstrated. The scalibility of these photonic crytals may yield solutions to far field near conversion of nanophotonic devices operating at the optical regime.