Passively stable 0.7-octave microcombs in thin-film lithium niobate microresonators

The optical frequency comb based on microresonators (microcombs) is an integrated coherent light source and has the potential to promise a high-precision frequency standard; self-reference and a long-term stable microcomb are the keys to this realization. Here, we demonstrated a 0.7-octave spectrum Kerr comb via dispersion engineering in a thin-film lithium niobate microresonator, and the single-soliton state can be accessed passively with long-term stability over 3 h. With such a robust broadband coherent comb source using thin-film lithium niobate, a fully stabilized microcomb can be expected for massive practical applications.