Sideband injection locking in microresonator frequency combs

For many applications of microresonator frequency combs, the ability to control the comb's defining parameters is essential. Sideband-injection locking, a technique by which a secondary continuous-wave laser is injected into the microresonator, provides an elegant solution, enabling straightforward control of both the carrier-envelope offset frequency and repetition rate.

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Spectrogram of the microcomb repetition rate under

sideband injection locking conditions.

Continious-wave-driven microresonators are compact femtosecond sources with optical frequency comb spectra. While the pump laser's frequency defines the comb's central line, the repetition rate depends on the resonator's free spectral range and is susceptible to environmental perturbation. An elegant solution is the suitable injection of a secondary laser into the microresonator cavity and onto which one of the comb lines locks, providing direct control to both degrees of freedom. Here, we study such sideband injection-locking in microresonator soliton combs across a wide optical bandwidth and derive the assigned scaling laws. Our findings provide valuable guidelines for the design of sideband injection-locked Kerr-frequency combs, with the potential for low-noise microwave generation, compact optical clocks with simplified locking schemes, and, more generally, all-optically stabilized frequency combs from Kerr-nonlinear resonators.

Reference:

Sideband injection locking in microresonator frequency combs; Thibault Wildi, Alexander Ulanov, Nicolas Englebert, Thibault Voumard, Tobias Her;  APL Photonics 8, 120801 (2023)