Fabrication of periodically poled low-loss rubidium exchanged ridge waveguides in z-cut KTP

Potassium titanyl phosphate (KTP) crystals are very attractive candidates for non linear optical frequency mixing. In particular, waveguides in KTP have found many applications, for example, highly-efficient second harmonic generation or as single photon sources for quantum optical applications. We report on the first fabrication and (non linear) characterization of periodically poled ridge waveguides in z-cut potassium titanyl phosphate. In periodically poled and surface near rubidium ion exchanged KTP we fabricated ridge waveguides by precise diamond-blade dicing. Single mode waveguides at telecom wavelengths (1550 nm) can be realized in a 6-8 µm wide ridge. Low attenuation values of 1.3 dB/cm (1.6 dB/cm) were determined at a wavelength of 1550 nm for TE (TM) polarization. Furthermore, by using an optimized Rb-exchange and dicing process, we also fabricated waveguides at 800 nm with a width of 1.9-3.2 µm. In this kind of waveguides we achieved in a type II SHG-process a conversion from 780 nm to 390 nm with an efficiency of 1.6%/W · cm².