Fabrication and characterization of planar ion‐exchanged KTiOPO4 waveguides for frequency doubling

Optical waveguides can be formed in potassium titanyl phosphate (KTiOPO4, KTP) crystals by an ion‐exchange process. Waveguides were fabricated in KTP substrates by exchanging rubidium ions for potassium ions. The resulting refractive index profile was measured as a function of diffusion time and temperature. Based on these characterization measurements, the phase‐matching properties of the planar waveguide for guided‐wave second‐harmonic generation were modeled. Second‐harmonic generation of blue/green light was observed at wavelengths shorter than the bulk phase‐matching limit, in good agreement with the results of numerical modeling.