Laser cavity-soliton microcombs

Microcavity-based frequency combs, or ‘microcombs’ 1 , 2 , have enabled many fundamental breakthroughs 3 – 21 through the discovery of temporal cavity-solitons. These self-localized waves, described by the Lugiato–Lefever equation 22 , are sustained by a background of radiation usually containing 95% of the total power 23 . Simple methods for their efficient generation and control are currently being investigated to finally establish microcombs as out-of-the-lab tools 24 . Here, we demonstrate microcomb laser cavity-solitons. Laser cavity-solitons are intrinsically background-free and have underpinned key breakthroughs in semiconductor lasers 22 , 25 – 28 . By merging their properties with the physics of multimode systems 29 , we provide a new paradigm for soliton generation and control in microcavities. We demonstrate 50-nm-wide bright soliton combs induced at average powers more than one order of magnitude lower than the Lugiato–Lefever soliton power threshold 22 , measuring a mode efficiency of 75% versus the theoretical limit of 5% for bright Lugiato–Lefever solitons 23 . Finally, we can tune the repetition rate by well over a megahertz without any active feedback. By nesting a Kerr microresonator in a fibre loop with gain, 50-nm-wide bright microcavity-based soliton combs with a mode efficiency of 75% can be induced at average powers more than one order of magnitude lower than the Lugiato–Lefever soliton power threshold, facilitating real-world applications.