Localized versus delocalized patterns in a nonlinear optical interferometer

We compare the morphology of the spatial structures displayed by an optical system consisting of a liquid crystal light valve (LCLV) in a feedback configuration, as the feedback is gradually tuned from purely diffractive to mixed interferential and diffractive. Different kinds of spatially coherent structures (e.g. hexagons, rolls), as well as localized structures and space–time turbulent patterns are observed. The features of the localized structures change with the parameter setting, and certain regions of the parameter space provide stable clusters of isolated spots (‘molecules’). Numerical simulations based on a Kerr-like model of the LCLV are in agreement with the experimental observations. We analyse the links between the observed behaviours and the results of a linear-stability analysis of the underlying homogeneous stationary states.