Design and Optimisation of WDM Circular Photonic Crystals Characterised by Induced Anisotropy

In this work we analyze the birefringence effect in circular photonic crystals such as dielectric rings (DR) and photonic crystals with air holes arranged in circular patterns. The dielectric concentric circular patterns admit two preferred electric fields orthogonal components defined by an extraordinary and an ordinary refractive index. These electric fields, localized in the central region of the circular photonic crystal (CPC) will be radiated at different wavelengths. This behaviour allows to characterize the analysed structures as wavelength division multiplexers. We first analyze the induced anisotropy of the multiplexers, and, then, we study the wavelength selectivity. Similar emitted wavelengths related to a air-hole CPC and to a corresponding DR structure are observed. The multiplexing behaviour is numerically modelled by the finite element method approach which provides the emitted resonant wavelengths and the quality Q-factors for a membrane-type optical wavelength division multiplexer obtained by the CPC design.