Fronts and localized structures in a liquid-crystal-light-valve with optical feedback

Abstract

We show that in a liquid-crystal-light-valve with optical feedback the Freedericksz transition displays a subcritical character. Experimentally, we determine the extension of the bistable region and we study the propagation of fronts connecting the different metastable states. Theoretically, we derive an amplitude equation, valid close to the Freedericksz transition point, which accounts for the subcritical character of the bifurcation. When, in the space of parameters, we move far from the Freedericksz transition point, we adopt a mean-field model which is able to capture the qualitative features of all the successive branches of bistability. Close to the points of nascent bistability, by including diffraction effects we show the appearance of localized structures. Highly symmetric configurations of localized structures may be observed in the experiment by imposing a N-order rotation angle in the feedback loop. For increase of the input light intensity complex spatio-temporal dynamics arise, with either periodic or irregular oscillations in the position of the localized states. Rings dynamics is also observed, by the introduction of a small nonlocal shift in the feedback loop.