Integrated turnkey soliton microcombs

Optical frequency combs have a wide range of applications in science and technology¹. An important development for miniature and integrated comb systems is the formation of dissipative Kerr solitons in coherently pumped high-quality-factor optical microresonators^2-9. Such soliton microcombs¹⁰ have been applied to spectroscopy^11-13, the search for exoplanets^14,15, optical frequency synthesis¹⁶, time keeping¹⁷ and other areas¹⁰. In addition, the recent integration of microresonators with lasers has revealed the viability of fully chip-based soliton microcombs^18,19. However, the operation of microcombs requires complex startup and feedback protocols that necessitate difficult-to-integrate optical and electrical components, and microcombs operating at rates that are compatible with electronic circuits-as is required in nearly all comb systems-have not yet been integrated with pump lasers because of their high power requirements. Here we experimentally demonstrate and theoretically describe a turnkey operation regime for soliton microcombs co-integrated with a pump laser. We show the appearance of an operating point at which solitons are immediately generated by turning the pump laser on, thereby eliminating the need for photonic and electronic control circuitry. These features are combined with high-quality-factor Si₃N₄ resonators to provide microcombs with repetition frequencies as low as 15 gigahertz that are fully integrated into an industry standard (butterfly) package, thereby offering compelling advantages for high-volume production.