Since its first synthesis in 1960,lithium niobate (LiNO3,LN) has been widely used in modern optoelectronics industry and nonlinear optics.Its high second-order susceptibility and wide transmission window render LN an excellent platform for applications ranging from frequency conversion to phase modulation.Over the past few years,LN microcavities have attracted intense interest for applications in nonlinear photonics.This scheme combines the crystalline merits of LN and the enhanced lightmatter interaction of whispering gallery mode (WGM) microcavities [1-4].Owing to the commercial implementation of lithium niobate on insulator (LNOI) wafers,on-chip microstructured LN devices,such as optical waveguides and gratings,have been successfully developed.On this basis,novel photonics applications,including efficient electro-optical modulation,optical parametric conversion and optical combs,have been realized at the chip scale [5-7].