Mode-locked optomechanical frequency combs in a graphene-silica microresonator.

Mode locking is an essential process through which resonant modes achieve stable synchronization via nonlinear interactions. This self-organization allows photonic and electronic sources to produce pulsed waveforms and is vital for applications in ultrafast and high-field optics as well as frequency comb generation. Here, we report a mechanism to include photon-electron-phonon interactions, demonstrating the excitation of mode-locked optomechanical microcombs in a graphene-deposited silica microresonator, determined by the synergy of optomechanical back action and graphene saturable absorption. The circulating optical field induces mechanical oscillations that modulate the light wave, while Pauli blocking in graphene locks a single optomechanical mode, forming a localized coherent optical wave packet within a single microcavity. In addition, using frequency division techniques, the mode-locked optomechanical microcomb achieves repetition stability with phase noise reduced to -110.5 decibels relative to the carrier per hertz at a 1-hertz offset and an Allan deviation as low as 3 × 10-12 @ 20 seconds, comparable to a standard rubidium clock.