Overcoming Performance Limitations in Optomechanical Oscillators for GHz-Frequency Timing Applications

Optomechanical oscillators offer a transformative approach to ultra-high-frequency timing applications, where traditional MEMS-based solutions face inherent trade-offs between frequency and stability. Despite breakthroughs in GHz sensing, their adoption as timing references has been hindered by poorly understood limitations of short-term stability. Here, we present a comprehensive experimental and theoretical investigation of phase-noise dynamics in silicon microdisk optomechanical oscillators operating in both self-oscillation and electrically driven feedback regimes. We identify particular mechanisms limiting the achievable signal-tonoise ratio in optomechanical transducers, arising from an improper transduction configuration-a limitation likely widespread across current optomechanical architectures. Counterintuitively, we show that reducing transduction sensitivity enhances phase-noise performance by broadening the oscillator's dynamic range. Our analysis points to achievable signal-to-noise ratios exceeding 130 dB at 1 GHz (and an equivalent phase noise of -119 dBc/Hz), paving the way for optomechanical oscillators to surpass state-of-the-art MEMS timing devices. These results establish a general framework for the design of optomechanical oscillators and demonstrate their potential as enabling components for next-generation technologies such as sensing, quantum computing, space systems, and radio astronomy.