Material and waveguide dispersion in a symmetric planar chirowaveguide

Abstract

An isotropic chiral medium is a circularly birefringent medium where both optical rotation and circular dichroism can be observed. In the last years considerable theoretical and experimental work has been published on the electromagnetic properties and applications of isotropic chiral materials. Guided electromagnetic waves in open and closed chirowaveguides have been systematically analyzed [1]. In open chirowaveguides both surface and semi-leaky modes can propagate [2]-[4]. Optical rotation and circular dichroism depend on the wavelength. However, as far as the authors are aware, the influence of material dispersion on the overall dispersion relations of chirowaveguides has been disregarded so far – in spite of the fact that this may be the most important contribution to the total dispersion. Artificial chiral media can be obtained by a mixture of chiral inclusions randomly embedded in some isotropic dielectric host medium. In fact, any material is nonhomogeneous at a certain microscopic length scale and hence homogenization theories play a key role in obtaining the phenomenological frequency-dependent constitutive relations, either in the Boys-Post form or in the Tellegen form, to describe the medium at the macroscopic or continuum length scales. By using the Lorenz-Lorenz theory of elastically bond electrons and generalizing it to pure chiral dense materials in a way that leads to the chiral Clausius-Mossotti equation, instead of using the Maxwell-Garnett homogenization procedure, the frequency-dependent constitutive relations are readily obtained. Dispersion is the key issue when we analyze pulse propagation in waveguides. Material as well as waveguide dispersion should be considered if the overall group-velocity dispersion (and higher-order dispersion, if necessary) has to be determined. In this communication a symmetric chiral slab waveguide is considered. This type of symmetric planar waveguide using isotropic chiral media is particularly useful for single-mode operation [5]. We use the frequency-dependent constitutive relations of an isotropic chiral medium to study the influence of material dispersion on the overall dispersion relations for the surface modes propagating in this slab waveguide.