Kerr-Induced Synchronization of a Cavity Soliton to an Optical Reference

TL;DR

This paper demonstrates a passive method to synchronize a Kerr frequency comb to a reference laser using Kerr nonlinearity, simplifying optical clock systems and enabling direct control of the comb's repetition rate.

Contribution

It introduces Kerr-induced synchronization (KIS) for microresonator-based frequency combs, eliminating the need for active feedback and complex electronics in integrated photonic clocks.

Findings

KIS enables phase locking of DKS to an external laser.

Theoretical model matches experimental results.

Synchronization allows direct control of comb repetition rate.

Abstract

The phase-coherent frequency division of a stabilized optical reference laser to the microwave domain is made possible by optical frequency combs (OFCs). Fundamentally, OFC-based clockworks rely on the ability to lock one comb tooth to this reference laser, which probes a stable atomic transition. The active feedback process associated with locking the comb tooth to the reference laser introduces complexity, bandwidth, and power requirements that, in the context of chip-scale technologies, complicate the push to fully integrate OFC photonics and electronics for fieldable clock applications. Here, we demonstrate passive, electronics-free synchronization of a microresonator-based dissipative Kerr soliton (DKS) OFC to a reference laser. We show that the Kerr nonlinearity within the same resonator in which the DKS is generated enables phase locking of the DKS to the externally injected reference. We present a theoretical model to explain this Kerr-induced synchronization (KIS), and find that its predictions for the conditions under which synchronization occur closely match experiments based on a chip-integrated, silicon nitride microring resonator. Once synchronized, the reference laser is effectively an OFC tooth, which we show, theoretically and experimentally, enables through its frequency tuning the direct external control of the OFC repetition rate. Finally, we examine the short- and long-term stability of the DKS repetition rate and show that the repetition rate stability is consistent with the frequency division of the expected optical clockwork system.