Research progress in lithium niobate on insulator lasers

Lithium niobate on insulator (LNOI) is considered one of the most competitive integrated photonics platforms due to the excellent optical properties of lithium niobate crystal and their compatibility with semiconductor micro/nano processing. Based on the continuous improvement of micro-nano fabrication technology, various transmission and control devices, such as low-loss waveguides and high-quality factor micro-cavities, showing better performance than traditional bulk materials devices, have been realized on LNOI. However, as an essential part of integrated photonics, the research of LNOI laser has made a breakthrough recently. Lithium niobate is an indirect bandgap material and thus tough for electroluminescence. It is a feasible and straightforward scheme to realize optically pumped laser based on rare-earth ion doping. This paper summarizes our research group's recent research progress on realizing microdisk, microring, and single-mode lasers based on rare-earth-ion-doped LNOI and related works from other groups. We hope this review could benefit the related research on the active devices on LNOI.