Perfect soliton crystals on demand

Abstract: Recent advance of soliton microcombs has shown great promise to revolutionize many important areas such as optical communication, spectroscopic sensing, optical clock, and frequency synthesis. A largely tunable comb line spacing is crucial for the practical application of soliton microcombs, which unfortunately is challenging to realize for an on-chip monolithic microresonator. The recently discovered perfect soliton crystal (PSC) offers a convenient route to tune the comb line spacing. However, excitation of a PSC is generally stochastic by its nature and accessing a certain PSC state requires delicate tuning procedure. Here we demonstrate the on-demand generation of PSCs in a lithium niobate microresonator. The unique device characteristics allow us to produce a variety of PCSs and to switch between different PSC states, deterministically and repetitively. We utilize the device to show arbitrary dialing of the comb line spacing from 1 to 11 times of the free-spectral range of the resonator. The demonstration of PCSs on demand may now open up a great avenue for flexibly controlling the repetition rate of soliton pulses, which would significantly enhance and extend the application potential of soliton microcombs for communication, signal processing, and sensing.