Two-wave mixing in photorefractive ion-implanted KNbO_3 planar waveguides at visible and near-infrared wavelengths

We report what is to our knowledge the first observation and characterization of the photorefractive effect in ion-implanted KNbO3 waveguides. The implantation was performed with 2.6-MeV He ions at a dose of 7.5 × 1014 cm−2. We measured two-wave-mixing gains of ~8 and ~2 cm−1 at wavelengths of 514.5 and 810 nm, respectively, and grating buildup times in the visible and the near infrared of typically 40 μs at a power level of 10 mW. Electrons are found to be the dominant charge carriers, implying that the gain direction is reversed in the waveguide as compared with that of the bulk crystal.