Broad transparency window and high piezoelectric, acousto-optic, second-order nonlinear, and electro-optic (EO) coefficients characterize crystalline lithium niobate (LN) as the “silicon in photonics.”1–7 Recent breakthroughs in the nanofabrication technology on thin-film LN platforms4 gave birth to a variety of integrated photonic devices such as high-performance EO modulators,8,9 broadband optical frequency combs,10–12 and high efficiency frequency converters.13–15 To build a monolithic integrated photonic system on an LN chip, the capacity of microlaser fabrication on this platform is essential. The high EO coefficient of LN ensures that such lasers outperform all other on-chip counterparts in broad range and real-time wavelength tunability. However, similar to silicon, LN itself does not provide optical gain for lasing. Therefore, to functionalize LN, doping of the gain medium is necessary. In particular, to make lasers operating at widely needed telecom wavelengths, the erbium ion () is a favorable choice of dopant.16–22 More importantly, to enable many applications and outperform silicon counterparts, such lasers should operate at a single frequency with an ultranarrow linewidth and fast wavelength tunability.23–27 According to the Schawlow–Townes theory, the laser fundamental linewidth is quadratic inversely proportional to the undoped cavity factor.28–30 Therefore, increasing the factor will quadratically reduce the linewidth of a microlaser. The highest factors demonstrated to date are those of whispering gallery mode (WGM) microcavities where light confinement is achieved by continuous total internal reflection at the smooth resonator periphery.31 However, the dense WGMs within the optical gain bandwidth would easily lead to multifrequency lasing in a microcavity. To reduce the number of modes, attempts have been made to reduce the microcavity size,23 which inevitably increases the radiation loss and decreases the mode volume, leading to a reduction of both the factor and optical gain in the microcavity. Consequently, the pump threshold increases while the laser power remains low.