Light-induced damage mechanisms in α-phase proton-exchanged LiNbO3 waveguides

Abstract.

The overall power and far-field pattern of the beam out-coupled from a single-mode planar proton-exchanged LiNbO₃ waveguide in the α-phase have been studied for in-coupled intensities within the range 20–700 W/cm². The steady-state output versus input power response shows three definite stages designated as I, II, and III in order of increasing input intensity. In stage I the output varies linearly with input and the far-field pattern does not show appreciable changes. In stage II, the pattern is considerably broadened and displays a number of steady peaks and dips indicative of a filamentary structure of the beam. As in bulk LiNbO₃, these damage features are explained in terms of parametric processes involving the amplification of scattered (noise) light. An additional broadening is observed in stage III together with the occurrence of a fluctuating profile (chaotic response) attributed to random fluctuations in the coupling parameters. The threshold input intensity separating stages I and II is related to the intensity-dependence of the photovoltaic field.