Photorefraction-assisted self-emergence of dissipative Kerr solitons

Generated in high-Q optical microresonators, dissipative Kerr soliton microcombs constitute broadband optical frequency combs with chip sizes and repetition rates in the microwave to millimeter-wave range. For frequency metrology applications such as spectroscopy, optical atomic clocks and frequency synthesizers, octave-spanning soliton microcombs generated in dispersion optimized microresonator are required, which allow self-referencing for full frequency stabilization. In addition, field-deployable applications require the generation of such soliton microcombs simple, deterministic, and reproducible. Here, we demonstrate a novel scheme to generate self-emerging solitons in integrated lithium niobate microresonators. The single soliton features a broadband spectral bandwidth with dual dispersive waves, allowing 2f-3f self-referencing. Via harnessing the photorefractive effect of lithium niobate to significantly extend the soliton existence range, we observe a spontaneous yet deterministic single-soliton formation. The soliton is immune to external perturbation and can operate continuously over 13 hours without active feedback control. Finally, via integration with a pre-programed DFB laser, we demonstrate turnkey soliton generation. With further improvement of microresonator Q and hybrid integration with chip-scale laser chips, compact soliton microcomb devices with electronic actuation can be created, which can become central elements for future LiDAR, microwave photonics and optical telecommunications.