We demonstrate narrow- linewidth ultrafast tunable integrated lasers based on heterogeneously integrated thin-film lithium niobate on ultra-low loss silicon nitride integrated photonic circuits. Using self-injection locking of a hybrid microresonator, we achieve a tuning speed of > 10 peta-Hertz-per-second. We also perform FMCW LiDAR ranging experiments. (C) 2022 The Author(s)