Exploring octave-spanning solitons in photonic-crystal resonators

We speed up the dispersion engineering of octave-spanning soliton microcombs with an advanced parameter-search algorithm and analytical model. With systematic device geometry parameter scans and volume manufacturing in a integrated-photonics foundry, we realize a single-chip solution for octave-span microcombs. Dispersive-wave mode-switching phenomena, caused by nonlinear self-interactions of few-cycle duration solitons, allows for post-fabrication tuning of the soliton spectrum, yielding sufficient signal-to-noise ratio for carrier-envelope offset frequency detection. We further utilize Photonic-Crystal Resonators (PhCR) to streamline the challenging dynamical evolution of a Kerr resonator from the empty state to a soliton. A nano-pattern sidewall modulation couples counter-propagating light in one mode of an PhCR. With the mode split as an parameter to manipulate the pump field in a PhCR, we can reduce relative difference in the power of nonlinear states, especially during the transition from the chaos state to the soliton state. This enables not only spontaneous soliton generation without complex, fast frequency control of the pump laser, but also favorable nonlinear evolution of the PhCR field state for solitons. Our designs and experiments facilitate microcomb spanning from 780 nm to 2200 nm with pump laser wavelengths at 1064 nm and 1550 nm.