Measurement of the non-uniformity of the wave-vector mismatch in waveguides for second-harmonic generation

For maximum second-harmonic generation (SHG) in a non-linear crystal the wave-vector mismatch along the interaction length should be uniform. However, in some applications a non-uniform wave vector mismatch along the propagation distance improves the performance. For example, in quasi-phasematched (QPM) waveguides with variably-spaced phase-reversed QPM gratings the acceptance bandwidth for SHG was increased. Recently, intensity-dependent phase shifts of the fundamental due to the cascaded second-order nonlinearity in SHG were observed. Due to a non-uniform wave-vector mismatch large fundamental phase shifts were measured in regions of negligible fundamental depletion with low wavelength and temperature depencence. Here, we report on measurements of the non-uniformity of the wave-vector in waveguides for SHG.