Integrated turnkey soliton microcombs

Optical frequency combs have a wide range of applications in science and technology 1 . 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 microcombs 10 have been applied to spectroscopy 11 – 13 , the search for exoplanets 14 , 15 , optical frequency synthesis 16 , time keeping 17 and other areas 10 . 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 Si 3 N 4 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. A turnkey regime for soliton microcombs is demonstrated, in which solitons are generated by switching on a co-integrated pump laser, eliminating the need for photonic and electronic control circuitry.