Optimization of corrugation-free Rb-exchanged waveguide in periodically poled KTiOPO4

Integrated highly efficient frequency converters provide a compact solution to the problem of interfacing components of a quantum network, which operate at different wavelengths. Potassium titanyl phosphate (KTP) has unique properties and offers the possibility of fabricating periodically poled waveguides, which exhibit quasi-phase matching. These characteristics are essential for an efficient conversion. We present our studies on rubidium-exchanged waveguides fabricated in periodically poled KTP. We confirmed that face polarity affects the diffusion mechanism of the rubidium, thus leading to different waveguide depths depending on the exposed face's polarity. Simulations show that this effect could significantly reduce the efficiency of a nonlinear conversion process. Employing energy dispersive X-ray spectroscopy (EDX), we analyzed different sets of fabrication parameters. Based on these results, we are able to produce waveguides with reduced corrugations, promising a huge increase in efficiency and significant reduction in losses for integrated optical devices.