  Lithium niobate on insulator (LNOI), regarded as an important candidate
platform for optical integration due to its excellent nonlinear, electro-optic
and other physical properties, has become a research hotspot. Light source, as
an essential component for integrated optical system, is urgently needed. In
this paper, we reported the realization of 1550-nm band on-chip LNOI
microlasers based on erbium-doped LNOI ring cavities with loaded quality
factors higher than one million, which were fabricated by using electron beam
lithography and inductively coupled plasma reactive ion etching processes.
These microlasers demonstrated a low pump threshold of ~20 {\mu}W and stable
performance under the pump of a 980-nm band continuous laser. Comb-like laser
spectra spanning from 1510 nm to 1580 nm were observed in high pump power
regime, which lays the foundation of the realization of pulsed laser and
frequency combs on rare-earth ion doped LNOI platform. This work has
effectively promoted the development of on-chip integrated active LNOI devices.
