G. Guida

AN INTRODUCTION TO PHOTONIC BAND GAP (PBG) MATERIALS

This paper introduces photonic band gap (PBG) materials that are periodic dielectric or metallo-dielectric materials conceived to control the propagation of electromagnetic waves. Firstly, the principle of these materials is explained. Doped PBG materials are then presented with their main properties and applications. New phenomena like super-prism or super-lens are also introduced. A review of different numerical methods used to study photonic band gap materials and to analyze their properties is given next. Manufacturing processes are then briefly described and foreseen applications are presented. Finally, the new field of the controllable photonic band gap materials is introduced.

Negative permittivity and permeability of gold square nanospirals

The optical properties of square nanospirals made of gold have been investigated numerically in the hundred terahertz range as a function of the geometrical parameters of the nanospirals. It is shown that the permittivity values of the nanospirals originate from the longitudinal surface plasmon resonances of the arms composing the nanospirals. A magnetic resonance was also observed whose magnitude and position increased with the number of winding. Above three windings the gold nanospirals exhibited negative values of the real part of the permeability above 400 THz.

Silver square nanospirals mimic optical properties of U-shaped metamaterials

We present a study of the optical properties of three-armed square nanospirals made of silver and realized as nanostructured thin films with Glancing Angle Deposition. Calculation of current flows in the nanospirals show excited resonant modes resembling those observed in U-shaped resonators. Four principal resonances were determined: near 200 THz and 480 THz for one polarization and 250 THz and 650 THz for the polarization orthogonal to the first one. In particular, a mode with anti-parallel current flow in opposite arms, associated with the observed resonance near 650 THz, indicates the existence of a magnetic-like resonance in the square nanospiral arrays. The robustness of the resonances against variations in the structural parameters of the nanospirals was investigated. This study revealed that the main parameter driving the position of the resonances was the overall dimension of the nanospiral, directly related to the length of their arms. Optical properties of a sample were measured by generalized spectroscopic ellipsometry at near-normal incidence, and evidence conversion between polarization states even for light polarized in the plane containing one of the arms in agreement with the numerical study. The measurements compared favorably to the results of the numerical simulations taking into account the disorder in the sample.

Dissociating the effect of different disturbances on the band gap of a two-dimensional photonic crystal

In this article, we dissociate the effect of the three generic disturbances on the band gap of a bidimensional metallic photonic crystal made of parallel rods. The disturbances are investigated separately. They are deviations from the perfectly periodic position, the angle between rods constituting the photonic crystal and different sizes in rod diameters. Numerical simulations and experimental measurements have been performed in the microwave region and the results compared. The effects of these disturbances on a localized state are discussed as well. When the disturbance level is weak (i.e., a few percent), the band structure is conserved: the slopes at the edge and the band-gap width are the same as for the perfect structure. By contrast, the bandpass is reduced by about −1 dB. For an important disturbance the crystal becomes practically unusable due to the deep random modifications of its band structure. In all cases when the band gap exists, the transmission peak associated with the localized state is present.

Simulation of two-dimensional Kerr photonic crystals via fast Fourier factorization

We present an adaptation of the fast Fourier factorization method to the simulation of two-dimensional (2D) photonic crystals with a third-order nonlinearity. The algorithm and its performance are detailed and illustrated via the simulation of a Kerr 2D photonic crystal. A change in the transmission spectrum at high intensity is observed. We explain why the change does not reduce to a translation (redshift) but rather consists in a deformation and why one side of the bandgap is more suited to a switching application than the other one.

Three-dimensional metallic nanostructures synthesized by Glancing Angle Deposition

Glancing Angle Deposition has been used to synthesize silver square nanospirals over large surfaces. It is shown numerically that such nanospirals exhibit the resonant plasmonic modes necessary to produce metamaterials at optical frequencies. The resonances remained as long as the angle of incidence of light did not vary by more than 20°. Samples were realized with different size of nanospirals. For the dimensions allowing for excitation of a magnetic-like mode at optical frequencies, generalized ellipsometric measurements have been performed. A good agreement between measurements and calculations was obtained.