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We study theoretically and demonstrate experimentally generation of coherent optical frequency combs in a sapphire whispering gallery mode resonator. We verify phase locking of the comb harmonics by demodulating the comb on a fast photodiode and by observing the production of a spectrally pure radio frequency signal. Because of excellent optical and superior mechanical properties of the material, the sapphire resonator is an excellent candidate for the on-chip device integration of the comb oscillator. [ABSTRACT FROM AUTHOR]

We report on the study of widely tunable, resonant single-sideband electro-optical modulators based on whispering gallery mode (WGM) resonators, made out of electro-optically active materials. The modulation process involves interaction of different WGM families with an externally applied microwave field. The tunability results from the unequal response of the mode families to either a temperature change or to an applied voltage. We show that the modulator can be used as an efficient microwave photonic receiver that operates either in direct or coherent regime. Due to its resonant nature, the high-Q electro-optical modulator also can be used as a resolution booster for a low-resolution RF spectrum analyzer. [ABSTRACT FROM PUBLISHER]

In this paper, we study an experimental method of evaluation of efficiency of an evanescent field coupling of light to a dielectric whispering gallery mode resonator. We show that change of the relative contrast of the observable optical resonance provides an accurate and complete information about the loaded as well as unloaded bandwidth of the resonator mode. We introduce a model of the coupling that allows for an interpolation of the resonator quality factor using experimental data taken without usage of a frequency tunable narrow line laser, a fast photodiode, as well as a frequency reference. The method is also immune to imperfect geometrical mode matching frequently occurring in a realistic system. We validate this model experimentally at both 1.5 and 4.5μm. [ABSTRACT FROM AUTHOR]