Second Harmonic Generation in Lithium Niobate on Insulator

This paper reviews recent advancements in second harmonic generation (SHG) within nanostructures of lithium niobate on insulator (LNOI). SHG devices are classified into in-plane and out-of-plane configurations, highlighting their suitability for different pumping conditions. The in-plane devices, with their small mode volume and ultra-narrow linewidth, demonstrate high-efficiency SHG under continuous wave pumping, making them ideal for miniaturized on-chip integrated devices. In contrast, the vertical cavities are best suited for broadband pulsed lasers, facilitating the creation of compact ultra-thin devices. This review summarizes the recent strides made in enhancing SHG efficiency for different designs in LNOI platform and underscores the potential of LN micro- and nanostructures to fulfill the requirements of modern ultracompact nonlinear devices.