Q factors and resonant states of whispering-gallery-mode dielectric microdisk cavities for lasing applications

Abstract

We study the effect of boundary roughness on the resonant states broadening of the optical whispering-gallery-mode microdisk lasing cavities. We develop a new, computationally effective, and numerically stable approach based on the scattering matrix (S-matrix) technique that is capable to deal with both arbitrary complex geometry and inhomogeneous refraction index inside the two-dimensional cavity. The method presented has been applied to study the effect of surface roughness and inhomogeneity of the refraction index on <i>Q</i>-values of microdisk cavities for lasing applications. We demonstrate that even small surface roughness (&Delta;<i>r</i>&lang; &lambda;/50) can lead to an extreme degradation of high-<i>Q</i> cavity modes by many orders of magnitude. The results of numerical simulation are analyzed and explained in terms of wave reflection at a curved dielectric interface combined with the examination of Poincare surfaces of section as well as Husimi distributions.