Leakage characteristics of open chirowaveguides – Dielectric slabs and optical fibers

Abstract

Chiral or optically active media are known since the beginning of the nineteenth century [1]. However, it was only recently that the scientific community has shown a systematic interest in the electromagnetic properties and applications of these special isotropic materials [2]. Guided electromagnetic waves have been analyzed in chirowaveguides [3]. In particular, surface modes have been studied in planar and circular open chirowaveguides [3]. In unbounded chiral media two circularly polarized characteristic waves can propagate. In open chirowaveguides a surface mode exists when, in the cladding region, both characteristic waves are evanescent. However, if one of the two characteristic waves is totally transmitted while the other is evanescent, then a semi-leaky mode occurs. A semi-leaky mode is basically a semi-guided mode that is continuously radiating energy into the cladding through leakage. This effect, well-known both theoretically and experimentally in anisotropic waveguides [4], has also been shown to exist in dielectric planar chirowaveguides [5]. In [5], a chiral thin-film with a chiral substrate and an achiral cover was shown to support semi-leaky waves as long as the chirality was properly chosen. More recently, we have shown that in chiral optical fibers semi-leaky waves can also propagate provided that both core and cladding are chiral media [6]. In this communication, we show that semi-leaky waves also exist even in the case where only the cladding is chiral while the core is a common isotropic (or achiral) medium. In fact, as long as the cladding is chiral, two characteristic waves exist outside the core, thus creating the necessary conditions for the occurrence of semi-leaky waves. Furthermore, we show that this special case can also be found in planar dielectric chirowaveguides – a new result that was not previously considered in [5].