Silicon-photonics-compatible optomechanical oscillator operating in the low-megahertz regime

Integrated optical sources operating at low repetition rates are a practical requirement in distributed fibre-optic sensing (DFOS) architectures, where the pulse period is set by the round-trip delay of long fibre links rather than by arbitrary design choices. Optomechanical oscillators offer a purely optical route to low-frequency signal generation, but experimental demonstrations on silicon photonic platforms have largely concentrated on higher-frequency operation or have relied on external electronic feedback to sustain oscillation. In this work, we demonstrate a silicon-photonic optomechanical oscillator operating in the low-megahertz regime as a self-sustained optical signal source without radio-frequency driving or electronic control. The device is implemented on a silicon-on-insulator platform using a racetrack resonator with a partially suspended waveguide. Stable self-oscillation is observed at a frequency of approximately 5.86 MHz. Time-domain measurements reveal a near-sinusoidal waveform, while frequency-domain spectra show a distinct mechanical resonance with a quality factor of about 1100. By adjusting the laser cavity detuning, the oscillator transitions from a single-tone oscillation state into nonlinear dynamical regimes characterized by pronounced harmonic generation. The evolution of the output spectrum follows the behavior expected from standard optomechanical models based on phase modulation of the intracavity field. Taken together, these results indicate that low-MHz optomechanical oscillators implemented within silicon photonics are experimentally accessible and can serve as compact optical signal primitives for DFOS-oriented integrated photonic systems.