Stavroula Foteinopoulou

Refraction in media with a negative refractive index.

We show that an electromagnetic (EM) wave undergoes negative refraction at the interface between a positive and negative refractive index material, the latter being a properly chosen photonic crystal. Finite-difference time-domain (FDTD) simulations are used to study the time evolution of an EM wave as it hits the interface. The wave is trapped temporarily at the interface, reorganizes, and, after a long time, the wave front moves eventually in the negative direction. This particular example shows how causality and speed of light are not violated in spite of the negative refraction always present in a negative index material.

Negative refraction and left-handed behavior in two-dimensional photonic crystals

We systematically examine the conditions of obtaining left-handed (LH) behavior in photonic crystals. Detailed studies of the phase and group velocities as well as the phase

Electromagnetic wave propagation in two-dimensional photonic crystals: A study of anomalous refractive effects

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In- and out-of-plane propagation of electromagnetic waves in low index contrast two dimensional photonic crystals

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Theoretical investigation of one-dimensional cavities in two-dimensional photonic crystals

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Experimental verification of backward wave propagation at photonic crystal surfaces

refractive indices are given. The existence of negative refraction does not guarantee the existence of negative index of refraction and so LH behavior. A wedge type of experiment is suggested, which can unambiguously distinguinsh between cases of negative refraction that occur when left-handed behavior is present from cases that show negative refraction without LH behavior.

Delay-time investigation of electromagnetic waves through homogeneous medium and photonic crystal left-handed materials

We systematically study a collection of refractive phenomena that can possibly occur at the interface of a two-dimensional photonic crystal with the use of the wave vector diagram formalism. Cases with a single propagating beam in the positive or negative direction as well as cases with birefringence were observed. We examine carefully the conditions to obtain a single propagating beam inside the photonic crystal lattice. Our results indicate that the presence of multiple reflected beams in the medium of incidence is neither a prerequisite nor does it imply multiple refracted beams. We characterize our results with respect to the origin of the propagating beam and the nature of propagation left-handed or not. We identified four distinct cases that lead to a negatively refracted beam. Under these findings, the definition of phase velocity in a periodic medium is reexamined and its physical interpretation discussed. To determine the “rightness” of propagation, we propose a wedge-type experiment. We discuss the intricate details for an appropriate wedge design for different types of cases in triangular and square structures. We extend our theoretical analysis and examine our conclusions as one moves from the limit of photonic crystals with high-index contrast between the constituent dielectrics to photonic crystals with low modulation of the refractive index. Finally, we examine the “rightness” of propagation in the one-dimensional multilayer medium and obtain conditions that are different from those of two-dimensional systems.

Guided Waves in a Bilayer Film Made of Right- and Left-Handed Materials

Propagation of electromagnetic waves through a two-dimensional triangular lattice has been studied for different values of refractive index contrast between the constituent dielectrics, and for angles of incidence both in and out of the plane of periodicity. Transmission results have been obtained both experimentally and with the transfer matrix technique, and good agreement has been found between the two. Comparison with band structure calculations has also been made.

Extra-ordinary modulators with 2D photonic materials (Conference Presentation)

We study numerically the features of the resonant peak of one-dimensional (1-D) dielectric cavities in a two-dimensional (2-D) hexagonal lattice. We use both the transfer matrix method and the finite difference time-domain (FDTD) method to calculate the transmission coefficient. We compare the two methods and discuss their results for the transmission and quality factor Q of the resonant peak. We also examine the dependence of Q on absorption and losses, the thickness of the sample, and the lateral width of the cavity. The Q-factor dependence on the width of the source in the FDTD calculations is also given.

Topological and complex birefringent metamaterial (Conference Presentation)

Backward wave propagation is the true manifestation of left-handed electromagnetism and not negative refraction which occurs also at the interface of right-handed systems. Here we experimentally demonstrate in a direct fashion the backward wave propagation phenomenon, which takes place at the surface of a properly designed photonic crystal. Our microwave experiment could open other venues for the verification of left-handed behavior in optical metamaterials.