Highly Directive Radiation and Negative Refraction
Using Photonic Crystals

E. Ozbay1, 2, *, I. Bulu1, K. Aydin1, H. Caglayan1, K. B. Alici1, and K. Guven1

1 Department of Physics, Bilkent University, Bilkent, 06800 Ankara, Turkey

2 Nanotechnology Research Center, Bilkent University, Bilkent, 06800 Ankara, Turkey

*e-mail: ozbay@fen.bilkent.edu.tr

Received September 2, 2004

Abstract—In this article, we present an experimental and numerical study of certain optical properties of two-
dimensional dielectric photonic crystals (PCs). By modifying the band structure of a two-dimensional photonic
crystal through its crystal parameters, we show how it is possible to confine the angular distribution of radiation
from an embedded omnidirectional source. We then demonstrate that the anomalous band dispersions of PCs
give rise to completely novel optical phenomena, in particular, the negative refraction of electromagnetic waves
at the interface of a PC. We investigate the spectral negative refraction, which utilizes a transverse magnetic
(TM)-polarized upper band of a PC, in detail and show that a high degree of isotropy can be achieved for the
corresponding effective index of refraction. The presence of nearly a isotropic negative refractive index leads
to focusing of omnidirectional sources by a PC slab lens, which can surpass certain limitations of conventional
(positive refractive) lenses. These examples indicate the potential of PCs for photonics applications utilizing
the band structure.

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