标题：Highly efficient broadband second harmonic generation mediated by mode hybridization and nonlinearity patterning in compact fiber-integrated lithium niobate nano-waveguides
摘要：The inherent trade-off between efficiency and bandwidth of three-wave mixing processes in χ 2 nonlinear waveguides is the major impediment for scaling down many well-established frequency conversion schemes onto the level of integrated photonic circuit. Here, we show that hybridization between modes of a silica microfiber and a LiNbO3 nanowaveguide, amalgamated with laminar χ 2 patterning, offers an elegant approach for engineering broadband phase matching and high efficiency of three-wave mixing processes in an ultra-compact and natively fiber-integrated setup. We demonstrate exceptionally high normalized second harmonic generation (SHG) efficiency of up to η nor ≈ 460% W−1 cm−2, combined with a large phase matching bandwidth of Δ λ ≈ 100 nm (bandwidth-length product of Δ λ · L ≈ 5 μ m2) near the telecom bands, and extraordinary adjustment flexibility.
