Integrated turnkey soliton microcombs
Optical frequency combs have a wide range of applications in science and technology. An important development for miniature and integrated comb systems is the formation of dissipative Kerr solitons in coherently pumped high-quality-factor optical microresonators. Such soliton microcombs have been applied to spectroscopy, the search for exoplanets, optical frequency synthesis, time keeping and other areas. In addition, the recent integration of microresonators with lasers has revealed the viability of fully chip-based soliton microcombs. 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.
Additional Information© 2020 Springer Nature Limited. Received 22 November 2019. Accepted 23 March 2020. Published 17 June 2020. We thank G. Keeler, S. Papp, T. Briles, J. Norman and M. Tran for discussions, Y. Tong and S. Liu for assistance in characterizations, and Freedom Photonics for providing the lasers. The Si₃N₄ microresonators were fabricated at the EPFL Center of MicroNanoTechnology (CMi). This work is supported by the Defense Advanced Research Projects Agency (DARPA) under DODOS (HR0011-15-C-055) programmes of the Microsystems Technology Office (MTO). Data availability; The data that support the findings of this study are available from the corresponding authors upon reasonable request. Code availability: The code used in this study is available from the corresponding authors upon reasonable request. These authors contributed equally: Boqiang Shen, Lin Chang, Junqiu Liu, Heming Wang, Qi-Fan Yang. Author Contributions: B.S., L.C., Q.-F.Y., J.L., T.J.K., J.E.B. and K.V. conceived the experiment. D.K., L.C., B.S. and Q.-F.Y. packaged the chip. J.L., R.N.W., J.H. and T.L. designed, fabricated and tested the Si3N4 chip devices. H.W. constructed the theoretical model. Measurements were performed by B.S., L.C. and Q.-F.Y. with assistance from H.W., C.X., W.X., J.G., L.W. and Q.-X.J. All authors analysed the data and contributed to writing the manuscript. J.E.B., K.V. and T.J.K. supervised the project and the collaboration. The authors declare no competing interests.
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