Chip-scale modulation-free laser stabilization using vacuum-gap micro-Fabry-Pérot cavity.

Narrow-linewidth lasers are essential for a wide range of applications in atomic clocks and precision sensing, where achieving high-frequency stability is as critical as ensuring scalability, portability, and cost-effectiveness in developing stable laser systems. Conventional electro-optic stabilization techniques, such as Pound-Drever-Hall locking to ultrahigh-finesse resonators held in a vacuum chamber, provide excellent performance but remain challenging to scale. Here, we demonstrate a cavity-coupled interferometric laser stabilization technique implemented on a silicon photonic chip and integrated with a wafer-scale vacuum-gap micro-Fabry-Pérot cavity. The optical cavity operates in air, achieving a Q factor of 2.0 × 109 and a fractional frequency instability of 1.45 × 10-12 at 1-second averaging time. Integration of the proposed technique with the compact cavity yields more than 38-fold reduction in the integrated linewidth and 30-decibel suppression of frequency noise at 10-hertz offset. The hybrid-integrated platform provides a route to scalable ultrastable lasers for field-deployable precision systems beyond laboratory environments.