Steven K. Morrison

Tunable split-ring resonators for nonlinear negative-index metamaterials

We study experimentally the dynamic tunability and self-induced nonlinearity of split-ring resonators incorporating variable capacitance diodes. We demonstrate that the eigenfrequencies of the resonators can be tuned over a wide frequency range, and significantly, we show that the self-induced nonlinear effects observed in the varactor-loaded split-ring resonator structures can appear at relatively low power levels.

Engineering of directional emission from photonic-crystal waveguides

We analyze, by the finite-difference time-domain numerical method, different ways to enhance the directional emission from photonic-crystal waveguides through the recently predicted beaming effect. We demonstrate that the substantial enhancement of the light emission can be achieved by adjusting the input wavelength, using a positive surface corrugation, increasing the refractive index of the surface layer, and inducing a near-surface mode.

Scattering of electromagnetic waves in metamaterial superlattices

The authors acknowledge support from the Australian Research Council and thank Ekmel Ozbay for providing additional details of the experimental results published earlier by his group.

Beaming effect from increased-index photonic crystal waveguides

We study the beaming effect of light for the case of increased-index photonic crystal (PhC) waveguides, formed through the omission of low-dielectric media in the waveguide region. We employ the finite-difference time-domain numerical method for characterizing the beaming effect and determining the mechanisms of loss and the overall efficiency of the directional emission. We find that, while this type of PhC waveguide is capable of producing a highly collimated emission as was demonstrated experimentally, the inherent characteristics of the structure result in a restrictively low efficiency in the coupling of light into the collimated beam of light.

Tamm states and nonlinear surface modes in photonic crystals

We predict the existence of surface gap modes, known as Tamm states for electronic systems, in truncated photonic crystals formed by two types of dielectric rods. We investigate the energy threshold, dispersion, and modal symmetries of the surface modes, and also demonstrate the existence and tunability of nonlinear Tamm states in binary photonic crystals with nonlinear response.

Beaming Effect and Directional Emission from Photonic-Crystal Waveguides

It is known that free-space focusing of light from sub-wavelength apertures, the so-called beaming effect of light, can be achieved through the excitation of radiative surface modes and their subsequent constructive interference in space surrounding the apertures. This effect, studied extensively in metallic thin films, has recently been shown to exist in photonic-crystal structures. In this paper, we present a comprehensive study of the beaming effect and light directional emission achieved through simple geometric and material engineering of the surface and near-surface structures in two types of photonic-crystal waveguides, classified as increased- and decreased-index structures. We analyze different methods to enhance the directional emission and calculate the resulting efficiencies, highlighting the influence of reflections and matching conditions at the waveguide terminations.

Observation of enhanced beaming from photonic crystal waveguides

We report on the experimental observation of the beaming effect in photonic crystals using experimentally mapped spatial field distributions of energy emitted from a subwavelength photonic crystal waveguide into free-space, rendering with crisp clarity the diffractionless beaming of energy. Our experimental data agree well with our numerical studies of the beaming enhancement in photonic crystals with modulated surfaces. Without loss of generality, we study the beaming effect in a photonic crystal scaled to microwave frequencies and demonstrate the technological capacity to deliver long-range wavelength-scaled beaming of energy.

Surface Modes and Tamm States in Photonic Crystals

Optical surface modes are specific states of electromagnetic waves localized at the interface separating two dissimilar media where the wave vector becomes complex causing the wave to exponentially decay away from the surface. These general conditions permit surface modes to form in a wide range of systems including layered optical media, optical waveguides, metallic thin films, carbon nano-tubes, and photonic crystals. Equally remarkable are the effects based on surface modes, such as extraordinary optical transmission through subwavelength apertures and beaming of light. In this paper, we analyse the surface modes, also known as Tamm states for electronic systems, along two surface orientations of a semi-infinite binary photonic crystal formed by a square lattice of high dielectric rods in vacuum. We reveal the conditions required to form localised surface modes in this system without perturbation of the surface layer, such as a reduction in the surface rod radius or refractive index. In this way, we demonstrate the existence of intrinsic surface modes at a photonic crystal surface. In addition to the study of linear surface states, we introduce a third-order optical nonlinearity to the surface layer and analyse the properties of the nonlinear surface Tamm states. We investigate the energy threshold, dispersion, and modal symmetries of the surface states, and illustrate their nonlinearity-induced tunability.

Experimental studies of binary metamaterials

The authors introduce and study metamaterial superlattices in the form of binary structures of wires and split-ring resonators. The structures are created by sequences of printed circuit boards with split-ring resonators and wires, with the boards are arranged in the form of a superlattice. First, the free space scattering properties of composite structures were experimentally studied by measuring transmission and reflection of electromagnetic waves from a regular structure with different spacing between the boards. Then, the boards were arranged in the form of a superlattice, and the resonance splitting in the metamaterial was observed. In contrast to earlier studies, where multiband left-handed properties were obtained by using several resonant constituents in the metamaterial, the multiband effect in this setup is obtained by using identical resonators with varied spacing to form a superlattice.

Self-collimation and beam splitting in chalcogenide glass and photopolymer photonic crystals

Utilizing the parameters of two-dimensional photonic crystals fabricated in chalcogenide-glass slab waveguides and photopolymers we study numerically the self-collimation effect in low-index photonic crystals and suggest a novel type of beam splitter based on the beam self-collimation.