Tailoring Ion-Exchange for Controlled Coercive Field Engineering and Improved Optical Integration of KTiOPO4

KTiOPO4 (KTP) is a ferroelectric nonlinear optical material which is transparent within the visible and infrared wavelengths. Its high anisotropy along the polar axis makes this material advantageous over other materials such as lithium niobate, lithium tantalate or gallium arsenide, for high aspect ratio and short period quasi-phase matching (QPM) domain gratings. Developments in doping via ion exchange have enabled the modulation of the materials coercive field (Ec). This has brought the engineering of domain gratings in KTP into the sub-µm regime, enabling a host of processes which before were only theoretical. In this work we bring new developments in the field of coercive field engineering and ion-exchange in KTP. We demonstrate a new Ec engineering method, based on Ba-doping, which has a negligible effect on the refractive index and induced stress in the KTP crystal contrary to the previously established Rb-doping based Ec engineering method. We investigate the two differing mechanisms of Ec modulation of these two methods, showing the effect of charge screening through the vacancy injection of Ba-ions, and the the conduction path blocking properties of Rb-ions. We compare the degree of Ec modulation for different dopant concentrations of Rb and Ba, through switching time measurements, and determine the transition point between the two Ec modulation mechanisms. Further, we explore the diffusion dynamics of mixed Rb/K/Ba dopant systems during both diffusion and subsequent annealing, to characterize the non-classical diffusion gradients observed in diffused channel waveguides in KTP. Finally, we apply coercive field engineering in designing and fabricating a switchable QPM device for electrical-optical integration. This work brings new understanding and new applications to KTP and shows the path forward towards high-aspect ratio integrable, multifunctional, tailored QPM devices.