Hybrid-Locked Kerr Microcombs for Flexible On-Chip Optical Clock Division

TL;DR

This paper introduces a novel hybrid locking scheme for chip-scale microcombs, enabling flexible and independent stabilization of comb teeth, which enhances the potential for portable, integrated optical clocks with high precision.

Contribution

It presents a universal on-chip optical clock architecture with hybrid passive-active locking, allowing independent control of microcomb teeth and reducing technical noise.

Findings

Achieved residual relative frequency instability of 1e-16.

Enabled independent locking of any two microcomb teeth.

Demonstrated flexible partial and full optical division.

Abstract

Optical atomic clocks deliver unrivaled precision, yet their size and complexity still confine them to specialized laboratories. Frequency combs provide the crucial optical-to-microwave division needed for clock readout, but conventional fiber- or bulk-laser combs are far too large for portable use. The advent of chip-integrated microcombs, frequency combs generated in micron-scale resonators, has revolutionized this landscape, enabling fully miniaturized, low-power clocks that bridge optical and radio-frequency domains on a single chip. Nevertheless, stabilizing a microcomb solely through pump laser control entangles otherwise independent feedback parameters, injects extra technical noise, and prevents flexible partial division of the optical frequency. Here, we propose and demonstrate a universal on-chip optical-clock architecture that supports both partial and full optical division. A hybrid passive-active scheme enables locking any two microcomb teeth independently, eliminating cross-coupling of control loops. Using the pump laser as a nonlinear actuator to stabilize an arbitrary tooth, we achieve a residual relative frequency instability of 1e-16. This advance brings integrated optical clocks closer to real-world deployment and opens new avenues for precision timing and navigation.