Highly efficient frequency converter in spatially single mode PPKTP waveguides at NIR wavelengths

Waveguide circuits play a key role in modern integrated optics and provide an appealing approach to scalability in quantum optics. We report on periodically poled waveguides in z-cut potassium titanyl phosphate (KTP), a material that has recently received growing interest due to its unique dispersion properties. We fabricated channel and ridge waveguides, which are spatially single mode at 800nm. In combination with a periodic poling the devices facilitate type-II second harmonic generation. We achieved a conversion from 792nm to 396nm with a high efficiency of 6.6%/(W · cm²) in ridge waveguides. In channel waveguides, a conversion from 801nm to 400.5nm with a high efficiency of 2.3%/(W · cm²) was measured. The temperature dependence of the second harmonic process was found to be 53pm/K in ridges and 35 pm/K in channel waveguides, respectively. Due to the low-temperature dependence and high nonlinear conversion efficiency, our waveguides lend themselves to operations in classical nonlinear integrated optics and future integrated quantum networking applications.