The unique combination of exceptional material properties of lithium niobate (LN) including nonlinear optical, electro-optic, acoustic-optic, and piezoelectric with the flexibility of dispersion engineering and strong optical mode confinement of the integrated photonics has made lithium-niobate-on-insulator a prominent platform enabling a wide variety of applications spanning nonlinear optics, telecommunications, quantum optics, and microwave photonics. The integrated fabrication on lithium-niobate-on-insulator platform with high quality is the key to fulfilling the full potential of lithium niobate.

We develop and optimize the fabrication process with electron beam lithography and ion beam mill for lithium niobate, and accurately characterize the quality, the etch depth, and the base angle of the structure to help build simulation models with high fidelity. We also experimentally demonstrate an inversely designed grating coupler featuring -3.8 dB coupling loss with 1-dB and 3-dB bandwidth of 71.7 nm and over 120 nm, respectively, and propose a design with double layer inverse taper to achieve -1 dB coupler loss over 100 nm bandwidth for applications that demand ultra-low loss.

Benefitting from the optimized fabrication process, we also demonstrate a dispersion-engineered micro-ring resonator with pulley-type coupler enhancing coupling strength between bus waveguide and the resonator featuring the loaded quality factor up to 2.2 million, which corresponds to the cavity finesse of over 3000. Furthermore, we demonstrate highly efficient second harmonic generation with normalized conversion efficiency of 5200%/W/cm² in a quasi-phase-matched waveguide by electric field periodic poling. Finally, we demonstrate cross-polarized Stimulated Brillouin Scattering gain on a 14 cm-long waveguide on 450 nm-thick lithium-niobate-on-insulator platform with the normalized Stimulated Brillouin Scattering gain of 17 /W/m.