Thermal nonlinearity can produce oscillatory instability in optical microspheres. We experimentally demonstrate this instability and analyze the conditions needed to observe this regime. The observed behavior is in good agreement with the results of numerical simulation. In pure fused silica with low optical absorption the thermal oscillations are suppressed owing to an interaction of thermal and Kerr nonlinearities. We also describe experimentally observed slow and irreversible thermo-optical processes in microspheres.
Properties of whispering gallery modes in microresonators of di erent t ypes proposed lately may be analyzed with the help of introducing equivalent spheroid. We describe and compare two methods of approximate calculation of scalar eld equation in such spheroid.
Quasiclassical approach and geometric optics allow to describe rather accurately whispering gallery modes in convex axisymmetric bodies. Using this approach we obtain practical formulas for the calculation of eigenfrequencies and radiative Q-factors in dielectrical spheroid and compare them with the known solutions for the particular cases and with numerical calculations. We show how geometrical interpretation allows expansion of the method on arbitrary shaped axisymmetric bodies.
Using quasiclassical approach rather precise analytical approximations for the eigenfrequencies of whispering gallery modes in convex axisymmetric bodies may be found. We use the eikonal method to analyze the limits of precision of this approach using as a practical example spheroidal dielectric cavity. The series obtained for the calculation of eigenfrequency is compared with the known series for dielectric sphere and numerical calculations.
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