Fabrication of ridge waveguides in potassium titanyl phosphate (KTP) for nonlinear frequency conversion

We discuss results on a novel fabrication scheme for optical ridge waveguides in KTP by combination of ridge definition using a diamond blade dicing saw and Rb/Ba ion exchange. In contrast to conventional waveguides in KTP, our samples were prepared in substrates that have their z-axis lying in the surface plane, perpendicular to the waveguide. The ridge waveguides were ion-exchanged through their cut flanks followed by further annealing treatment in air. This results in a homogeneous refractive index increase across the rectangular waveguide cross section. Since Rb ions are only mobile along the z-axis, they cannot diffuse into the depth. Therefore, the fabricated waveguides can withstand elevated temperatures. We determined propagation losses to be only 0.3dB/cm (0.4dB/cm) for TE (TM) polarization at ∼1060nm. These novel waveguides can allow for improved mode overlap in frequency conversion processes and better coupling of light from a fiber to the waveguide.