  Optical frequency comb based on microresonator (microcomb) is an integrated
coherent light source and has the potential to promise a high-precision
frequency standard, and self-reference and long-term stable microcomb is the
key 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 hours. With such a robust broadband coherent comb source using thin film
lithium niobate, fully stabilized microcomb can be expected for massive
practical applications.
