Dielectric perturbations: anomalous resonance frequency shifts in optical resonators

Small perturbations in the dielectric environment around a high quality whispering gallery mode resonator usually lead to frequency shift of modes directly proportional polarizability perturbation. Here, we report experimental observations strong shifts that can be opposite and even exceed contribution perturbations' polarizability. The frequencies lithium niobate are shifted using substrates refractive indices ranging from 1.50 4.22. Both blue- red-shifts observed, as well an increase linewidth, when moved into evanescent field mode. We compare results theoretical model by Foreman et al. provide additional intuitive explanation based on Goos-H\"anchen for optical domain.