Nonlinear optical waveguides fabricated in Mg-doped LiNbO₃ by swift heavy ion irradiation: anomalous photorefractive damage behavior

Abstract

Using swift heavy fluorine ion irradiation, we have successfully fabricated optical waveguides in Mg-doped LiNbO₃ substrates. A systematic characterization of these structures has been carried out including refractive index profiles, propagation losses, nonlinear coefficients, and, specially, photorefractive optical damage. Step-like refractive index profiles with Δn _e ≈ 0.1 and Δn _o ≈ 0.2, propagation losses lower than 0.5 dB/cm and high nonlinear optical coefficients similar to those of the substrate have been obtained. Unexpectedly, the photorefractive damage is only moderately reduced with regard to the one presented in congruent LiNbO₃ waveguides. Specifically, light intensity damage thresholds I _th are only a factor 2 higher at RT and a factor 4 at 90 °C with regard to undoped waveguides. At this latter temperature, a remarkably high I _th = 30.000 W/cm² is reached. A final discussion on the observed anomalous optical damage behavior induced by swift heavy ion irradiation is also included.