Ultrahigh-efficiency wavelength conversion in nanophotonic periodically poled lithium niobate waveguides

Periodically poled lithium niobate (PPLN) waveguides are a powerful platform for efficient wavelength conversion. Conventional PPLN converters, however, typically require long device lengths and high pump powers due to the limited nonlinear interaction strength. Here we use a nanostructured PPLN waveguide to demonstrate an ultrahigh normalized efficiency of 2600%/W-cm(2) for second-harmonic generation of 1.5 mu m radiation, more than 20 times higher than that in state-of-the-art diffused waveguides. This is achieved by a combination of sub-wavelength optical confinement and high-fidelity periodic poling at a first-order poling period of 4 mu m. Our highly integrated PPLN waveguides are promising for future chip-scale integration of classical and quantum photonic systems. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement