Monolithic gain–storage separation in low-noise supercavity lasers

Abstract Vertical-cavity surface-emitting lasers offer low power and wafer-scale integration, but their short cavities confine optical gain and photon storage to the same active region, limiting photon lifetime and spectral coherence. Here we propose a monolithic surface-emitting supercavity laser that functionally decouples optical gain from photon storage by coupling an active cavity to multiple passive storage cavities. Controlled intercavity coupling is achieved through precise engineering of the reflection, transmission, and phase matching of the connecting DBR mirrors. By tailoring the supermode profile and coherently redistributing its optical field among the active and passive cavities, we demonstrate a monolithic surface-emitting supercavity laser with an enlarged effective photon-storage volume and reduced noise. The coupled cavities yield a quality factor of 22,499 and a cold-cavity photon lifetime of 20.1 ps, while the supercavity laser retains low-threshold single-mode operation, a Lorentzian linewidth of 0.41 MHz, a frequency-noise floor of 2.0 × 10 5 Hz 2 Hz⁻¹ and a high-frequency relative-intensity-noise floor near − 145 dBc Hz⁻¹ without external feedback. When the laser is locked to a Cs reference, the atomic-clock testbed reaches an Allan deviation of 8.7 × 10⁻ 13 at 8,192 s. This architecture establishes gain–storage separation as a scalable route to coherent surface emitters.