Modeling the colors of phase noise in optomechanical oscillators

Optomechanical oscillators (OMOs) combine the co-existing high quality factor mechanical and optical resonances in an integrated device to realize low phase noise RF oscillations. While several attempts have been demonstrated towards modeling the phase noise in such oscillators, the close-to-carrier phase noise models in literature do not account for $1/f^3$ (pink noise) and higher order slopes in the phase noise spectra. Here we present a phase noise model, corroborated with experimental characterization of phase noise of two monolithic integrated silicon OMOs, accounting for contributions to the phase noise due to thermomechanical, and adsorption-desorption (AD) noise. The model shows good agreement with experimental data and provides further insights into the mechanisms underlying the noise processes contributing to different slopes in the phase noise spectra in OMOs.