Dispersion effects on the performance of whispering gallery mode based optoelectronic oscillators

Optoelectronic oscillators (OEOs) based on optical whispering gallery mode resonators (WGMRs) are amongst state-of-the-art technologies to generate ultra-low phase noise microwave signals. In this paper, a WGMR-based OEO is designed and effects of dispersion on its performance, such as phase noise, amplitude, and frequency of oscillation are theoretically investigated which are verified by simulations. Dispersion causes each mode existing inside a WGMR to experience a distinctive optical delay depending on its frequency. Considering the material and geometric dispersion of the WGMR used as the storage element of the OEO, we show that dispersion does not mainly affect the amplitude of oscillation while it affects the frequency of oscillation and phase noise of the output microwave signal. Indeed, through calculating the group delay and the group delay dispersion, we show that laser frequency noise (LFN) is converted into the phase noise of the generated microwave signal via the dispersion of the optical WGMR. Theoretical calculations are verified by the results obtained from two other previously published methods, i.e. the Langevin approach and the conversion matrix approach.