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