Localized structures in the liquid crystal light valve experiment

We will review the conditions for the appearance of coherent or localized states in a nonlinear optical feedback system, with particular reference to the Liquid Crystal Light Valve (LCLV) experiment. The localized structures here described are of dissipative type, that is, they represent the localized solutions of a pattern-forming system. We will show that different types of localized states are observed in the system and can be selected depending on the control parameters: round localized structures that interact forming bound-states, triangular localized structures, characterized by the presence of phase singularities, localized peaks, appearing above a structured background. Then, we will discuss the nonvariational behaviors of such coherent states, like the bouncing of round localized structures and the chaotic front propagation for the triangular ones. We will present the full model equations for the LCLV system as well as a one-dimensional spatially forced Ginzburg-Landau equation, which is the simplest model accounting for the phenomenology observed in the experiment.We will show how, by using a properly intensity/phase modulated input beam, we can either induce a large pinning effect or control the dynamics of large arrays of localized structures, addressing each site independently from the others. Finally, the propagation properties of localized structures will be presented.