Spatial versus Temporal Deterministic Wave Breakup of Nonlinearly Coupled Light Waves

We investigate experimentally the competition between spatial and temporal breakup due to modulational instability in ${\chi }^{(2)}$ nonlinear mixing. The modulation of the wave packets caused by the energy exchange between fundamental and second-harmonic components is found to be the prevailing trigger mechanism which, according to the relative weight of diffraction and dispersion, leads to the appearance of a multisoliton pattern in the low-dimensional spatial or temporal domain.