Optica 5, 1438–1441 (2018)

Although periodically poled lithium niobate (PPLN) waveguides are a popular choice for constructing optical wavelength converters due to their large χ2 nonlinear coefficient, long device lengths and high pump powers are often needed. Now, Cheng Wang and colleagues from the USA and Hong Kong have fabricated a nanostructured PPLN waveguide and used it to enable efficient nonlinear wavelength conversion in smaller device geometries. The device is fabricated on an x-cut magnesium-oxide-doped lithium-niobate-on-insulator substrate, with metal poling finger electrodes patterned on top. The poled region has a width and length of 75 μm and 4 mm, respectively. Each poled region has three ridge waveguides and a poling period of 4.1 μm. The device yielded second-harmonic generation at 1,550 nm with an efficiency more than an order of magnitude higher than the previous record in PPLN waveguides.