Sideband injection locking of a laser cavity-soliton

Microcombs, optical frequency combs generated with integrated high Q-factor optical resonators, have emerged as a transformative tool in optics, offering compact chip-scale frequency comb sources that enable advances in metrology, spectroscopy and communications. Limiting factors include efficiency, robustness against environmental noise and long-term stability. A key requirement for many applications is the locking of two major degrees of freedom of the comb, the carrier offset and repetition rate frequencies, on which the positions of the comb teeth depend.
All-optical approaches to locking microcombs are attractive, such as by injection locking [1] using an additional continuous-wave pump injected within the resonator close to a comb line. The beating between the dissipative Kerr soliton and the additional pump forms an optical lattice trap [2] in the background field that locks the pulse’s momentum. Laser cavity-soliton (LCS) microcombs offer improved stability, efficiency and robustness compared to other soliton microcomb schemes [3,4]. Injection of an external pump for stable interactions and spectral shaping has been demonstrated in LCS microcombs [5], self-oscillating microcombs that operate without an external pump to drive the comb generation, however, so far, these combs have not been locked optically.
We report on the first carrier offset locking of a LCS to an external reference, with a study of the locking mechanism in this type of cavity, where a microresonator is nested within a fibre loop.
This technique is an important step toward fully stabilising a laser cavity-soliton microcomb, a critical feature to many applications that require stable, compact and efficient frequency comb sources in PNT, spectroscopy,astrophysics and communications.

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