Optical nonlinearity of thin film lithium niobate: devices and recent progress

Thin-film lithium niobate (TFLN), also known as lithium niobate on insulator, is an important integrated optical platform due to its broad transparency window (from ultraviolet to mid-infrared) and exceptional nonlinear optical (NLO) properties. TFLN is a revolutionary technology that revitalizes micro/nano photonics based on LN, which holds prime importance in on-chip frequency conversion owing to its remarkable NLO properties. This review focuses on the optical nonlinearity of thin film lithium niobate and its applications in integrated optics. We commence with a brief overview of the TFLN platform. Followed by an introduction to the common device structures. We then present the recent advancements of TFLN in NLO frequency conversion, including chi(2) based optical frequency generation processes (second harmonic generation, sum frequency generation, and difference frequency generation, etc), frequency comb generation, and supercontinuum generation, etc. Finally, we propose future prospects for nonlinear photonic integrated circuits based on the TFLN platform.