Negative Refraction In Photonic Crystals Research Articles

Towards focusing using photonic crystal flat lens

AbstractWe report on the numerical simulation and fabrication of a two-dimensional flat lens based on negative refraction in photonic crystals. The slab acting as a lens is made of an hole array (operating at the wavelength of 1.5 μm) etched in a InP/InGaAsP/InP semiconductor layer. We first study the key issues for the achievement of a negative refractive index taking advantage of folding of dispersion branches with main emphasis in dispersion properties rather than the opening of forbidden gaps. The diffraction and refraction regimes are analysed according to the comparison of the wave-vector with respect to the relevant dimensions of the hole array. In the second stage, we illustrate technological challenges in terms of e-beam lithography on a sub-micron scale and deep reactive ion etching for an indium phosphide based technology.

Tunable negative refraction photonic crystals achieved by liquid crystals

The photonic crystal with a square lattice of Si cylinders surrounded by nematic liquid crystals is investigated. The directors of the liquid crystal are parallel to the two dimensional PC plane. The transversed electric (TE) modes are studied. The plane wave expansion method is used to calculate the equi-frequency surface (EFS). The negative refraction phenomenon is found and the refractive angle can be tuned by changing the directors of the nematic liquid crystals.

Refraction and rightness in photonic crystals

We present a study on relation between the refraction and rightness effects in photonic crystals applied on a 2D square lattice photonic crystal. The plane wave (the band and equifrequency contour analyses) and FDTD calculations for both TM and TE modes revealed all possible refraction and rightness cases in photonic crystal structures in the first three bands. In particular, we show for the first time, a possibility of the left-handed positive refraction. This means that left-handedness does not necessarily imply negative refraction in photonic crystals.

New evidences of negative refraction in photonic crystals

To verify the behavior of negative refraction in photonic crystals, we design a point source imaging system in which a point source is placed at a distance in front of photonic crystals slab. The distance is equal to the thickness of the slab. By numerical simulation based on the finite-difference time-domain (FDTD), the light beam inside the slab just focuses from one side to the other side of the slab and makes a clear image. Our result proves that negative refraction occurs inside PC for a certainty on special condition.

Negative refraction in two-dimensional photonic crystals

We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index neff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths.

Negative-refraction phenomenon at multiple frequency bands from electromagnetic crystals

Negative refraction in photonic crystals at the lower bandgap edges has been identified by many researchers. In this paper, we experimentally demonstrate that such negative refractions can also be found in an electromagnetic crystal consisting of metallic wires at multiple frequencies in the passbands in addition to the lower edges of bandgap. The experimental results are in very good agreement with the simulations. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 465–469, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20854

Analysis of wave propagation in a two-dimensional photonic crystal with negative index of refraction: plane wave decomposition of the Bloch modes

This work presents a comprehensive analysis of electromagnetic wave propagation inside a two-dimensional photonic crystal in a spectral region in which the crystal behaves as an effective medium to which a negative effective index of refraction can be associated. It is obtained that the main plane wave component of the Bloch mode that propagates inside the photonic crystal has its wave vector k' out of the first Brillouin zone and it is parallel to the Poynting vector ( S' ? k'> 0 ), so light propagation in these composites is different from that reported for left-handed materials despite the fact that negative refraction can take place at the interface between air and both kinds of composites. However, wave coupling at the interfaces is well explained using the reduced wave vector ( k' ) in the first Brillouin zone, which is opposed to the energy flow, and agrees well with previous works dealing with negative refraction in photonic crystals.

Wide-angle beam splitting by use of positive–negative refraction in photonic crystals

We present a positive-negative refraction effect in which, under certain conditions, an incident plane wave launched into a photonic crystal excites a positive-refracted Bloch wave and a negative-refracted Bloch wave simultaneously, both of which maintain the polarization. By utilizing this phenomenon, wide-angle beam splitting can be realized at the microscale level. Numerical simulations are employed to demonstrate this anomalous refraction behavior.

Negative refraction in photonic crystals

We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.