Nonlinear thermal effects in optical microspheres at different wavelength sweeping speeds

Results of detailed experimental investigations of the power and sweeping speed dependent resonance bandwidth and resonance wavelength shift in microsphere resonators are presented. The experimental manifestations of the nonlinear effects for the different sweeping modes are considered and a possibility of separation between the Kerr and thermal nonlinearities is discussed. As it follows from the detailed comparison between theory and experiments, a single mode theoretical model, based on the mean field approximation, gives a satisfactory description of the experimental data only at small coupling powers and fast sweeping. For example, the values of Kerr nonlinearity, obtained through the fitting of the experimental data, are far from the expected, commonly used ones.