Phase noise performance of optoelectronic oscillators based on whispering-gallery mode resonators

Optoelectronic oscillators based on whispering-gallery mode resonators (WGMRs) are efficient oscillators for ultra-stable microwave generation, in which the energy can be stored in an ultra-high Q-factor resonator instead of the usual long delay line. In this paper, we derive a stochastic model for the calculation of the phase noise performance in these systems considering three different configurations, namely, the case where the energy is stored in high-Q disk-shaped WGMR, the case where energy is stored in an optical delay-line only, and the case for which the energy is stored simultaneously by the resonator and the delay line. Our investigations explain how the WGMR can be optimally used for spurious peak rejection in optoelectronic oscillators. Our experimental measurements are found to be in excellent agreement with analytical and simulation results.