Light bending and quasi-transparency in metallic graded photonic crystals Emmanuel Centeno a, * , Eric Akmansoy b , Kevin Vynck a,c , David Cassagne a , Jean-Michel Lourtioz b a Groupe d’Etude des Semiconducteurs, Universite ´ Montpellier II, UMR 5650 du CNRS Place Euge `ne Bataillon, 34095 Montpellier, France b Institut d’Electronique Fondamentale, Universite ´ Paris-Sud, UMR 8662 du CNRS, 91405 Orsay, France c European Laboratory for Non-linear Spectroscopy (LENS), University of Florence, Via Nello Carrara 1, 50019 Sesto-Fiorentino (FI), Italy Received 29 May 2009; received in revised form 28 September 2009; accepted 23 October 2009 Available online 29 October 2009 Abstract Graded photonic crystals (GPhCs) have the remarkable ability to bend the path of light on the wavelength scale. A mirage effect has recently been reproduced experimentally in a two-dimensional structure made of metallic rods operating in the microwave regime (Akmansoy et al., 2008 [7]). This paper is intended to provide some theoretical insight onto the optical properties of metallic GPhCs and to report on the existence of a distinct regime of operation, in which light passes through the structure in a weakly curved trajectory. Experimental results are in good agreement with theoretical predictions, thereby further proving the ability of GPhCs to mold the flow of light in different ways at different frequencies. # 2009 Elsevier B.V. All rights reserved. PACS : 42.70.Qs; 42.25.Bs; 42.79.Fm Keywords: Graded photonic crystals; Metallic photonic crystals; Wave propagation 1. Introduction Atmospheric mirages are one of the most popular optical illusions, deviating light rays to reproduce a shifted image of faraway objects. The light bending effect, appearing on account of the air refractive index variation with the altitude, is typically performed on the kilometer scale, depending on the strength of the optical index gradient. Recent researches have now shown that the path of light can be curved at the wavelength scale using so-called graded photonic crystals (GPhCs), which similarly exhibit space-dependent dispersion properties, resulting in a progressive reorientation of the direction of light propagation in space [1–7]. Smooth gradients of the GPhC structural parameters have actually been shown to induce giant effective phase index gradients, thereby making light twistable in very sharp turns within optical thicknesses of only a few wavelengths [2]. In a more technological context, GPhCs provide a way to bend light without requiring the incorporation of defects, in contrast to conventional (periodic) photonic crystals, which rely on the existence photonic band gaps [8]. Such dispersion-based systems find use in a wide panel of different applications, including compact optical routing systems, wavelength filters and super-lenses [9–13]. Recently, the concept of GPhCs has been validated by the experimental demonstration of a mirage effect in www.elsevier.com/locate/photonics Available online at www.sciencedirect.com Photonics and Nanostructures – Fundamentals and Applications 8 (2010) 120–124 * Corresponding author. E-mail address: centeno@ges.univ-montp2.fr (E. Centeno). 1569-4410/$ – see front matter # 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.photonics.2009.10.003