Micro-cavity based frequency combs, or 'micro-combs' [1,2], have enabled many fundamental breakthroughs [3-21] through the discovery of temporal cavity-solitons. These self-localised waves, described by the Lugiato-Lefever equation [22], are sustained by a background of radiation usually containing 95% of the power [23]. Simple methods for their efficient generation and control are currently being investigated to finally establish micro-combs as out-of-the-lab tools [24]. Here, we demonstrate micro-comb 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 multi-mode systems [29], we provide a new paradigm for soliton generation and control in micro-cavities. 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. Optical frequency combs based on micro-cavity resonators, also called 'micro-combs', offer the promise of achieving the full capability of their bulk counterparts, yet in an integrated footprint [1, 2]. They have enabled major breakthroughs in spectroscopy [3,4], communications [5,6] microwave photonics [7], frequency synthesis [8], optical ranging [9,10], quantum sources [11, 12], metrology [13,14] and astrocombs [15,16]. Of particular importance has been the discovery of temporal cavity-solitons in micro-cavities [17-21]. Temporal cavity-solitons [2,17-23] are an important example of dissipative solitons-self-confined waves balancing dispersion with the nonlinear phase-shift in lossy systems [30]. Practical applications of these pulses for micro-combs, however, still face significant challenges. In particular, they achieve a limited mode efficiency, defined as the fraction of optical power residing in the comb modes other than the most powerful one. Solitons in micro-cavities exist as localised states upon a background, usually a continuous-wave (CW) [2,17-23], which results in a dominant mode in the comb spectrum. In this configuration, described by the

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In many disciplines, states that emerge in open systems far from equilibrium are determined by a few global parameters1,2. These states can often mimic thermodynamic equilibrium, a classic example being the oscillation threshold of a laser3 that resembles a phase transition in condensed matter. However, many classes of states cannot form spontaneously in dissipative systems, and this is the case for cavity solitons2 that generally need to be induced by external perturbations, as in the case of optical memories4,5. In the past decade, these highly localized states have enabled important advancements in microresonator-based optical frequency combs6,7. However, the very advantages that make cavity solitons attractive for memories—their inability to form spontaneously from noise—have created fundamental challenges. As sources, microcombs require spontaneous and reliable initiation into a desired state that is intrinsically robust8–20. Here we show that the slow non-linearities of a free-running microresonator-filtered fibre laser21 can transform temporal cavity solitons into the system’s dominant attractor. This phenomenon leads to reliable self-starting oscillation of microcavity solitons that are naturally robust to perturbations, recovering spontaneously even after complete disruption. These emerge repeatably and controllably into a large region of the global system parameter space in which specific states, highly stable over long timeframes, can be achieved.

Modern optical systems increasingly rely on complex physical processes that require accessible control to meet target performance characteristics. In particular, advanced light sources, sought for, for example, imaging and metrology, are based on nonlinear optical dynamics whose output properties must often finely match application requirements. However, in these systems, the availability of control parameters (e.g., the optical field shape, as well as propagation medium properties) and the means to adjust them in a versatile manner are usually limited. Moreover, numerically finding the optimal parameter set for such complex dynamics is typically computationally intractable. Here, we use an actively controlled photonic chip to prepare and manipulate patterns of femtosecond optical pulses that give access to an enhanced parameter space in the framework of supercontinuum generation. Taking advantage of machine learning concepts, we exploit this tunable access and experimentally demonstrate the customization of nonlinear interactions for tailoring supercontinuum properties.

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