Inducing Photonic Transitions between Discrete Modes in a Silicon Optical Microcavity

We show the existence of direct photonic transitions between modes of a silicon optical microcavity spaced apart in wavelength by over 8 nm. This is achieved by using ultrafast tuning of the refractive index of the cavity over a time interval that is comparable to the inverse of the frequency separation of modes. The demonstrated frequency mixing effect, i.e., the transitions between the modes, would enable on-chip silicon comb sources which can find wide applications in optical sensing, precise spectroscopy, and wavelength-division multiplexing for optical communications and interconnects.