Polarization Independent Nanobeam Cavity Tuning using Annular Photonic Crystals

摘要

Nanobeam cavity waveguides have drawn great attention of the researchers due to being a useful optical platform for several applications, e. g. optical switching and filtering. Almost all of the past studies investigated high quality (Q) factors without considering polarization independency. In the literature Zhang et al. proposed a device that enables high Q for both transverse electric (TE) and transverse magnetic (TM) modes for a specific frequency. In our study we demonstrate a three-dimensional study of polarization independent nanobeam cavity waveguide that consists of annular photonic crystals (PCs) showing similar optical properties for both TE and TM modes. Besides, a detailed analysis of the shift of the overlapped frequency is investigated with respect to height and width variation of the nanobeam structure. The designed waveguide is composed of 12 air holes and 4 annular PCs located in the Silicon (n_(Si)=3.46). The radii of all air holes in the structure are 0.36a. The annular PCs at the interior section have inner dielectric radii of 0.18a and the outer ones have inner dielectric radii of 0.20a. Silica (n_Silica)=1.52) material is used as a substrate. The width and height of the waveguide may be tuned in order to obtain high Q factors at the desired frequency for both polarizations. In our analysis, we investigated the relation between widths, height and cavity frequency for both TE and TM cases. Obtained frequencies are fitted to cubic polynomials of the structural parameters width and height. Overlapped frequency curve is revealed by an equalization of the polynomials of TE and TM resonant frequencies. The findings elucidate the effect of the parameters on the overlap mechanism of resonant mode matching for both polarizations.