Two-dimensional front dynamics and spatial solitons in a nonlinear optical system

Two-dimensional fronts and coarsening dynamics with a t{1/2} power law are analyzed experimentally and theoretically in a nonlinear optical system of a sodium vapor cell with single-mirror feedback. Modifications of the t{1/2} power law are observed in the vicinity of a modulational instability leading to the formation of spatial solitons of different sizes. The experimental and numerical observations give direct evidence for the locking of fronts as the mechanism of soliton formation. A phenomenological equation for the dynamics of the domain radius explains the observed behavior.     

Suppression of spatial chaos via noise-induced growth of arrays of spatial solitons

Domain walls with oscillatory tails are commonplace in models of spatially extended nonlinear optical devices. Their interaction and locking at discrete distances lead to asymptotically stable spatial disorder. We show that noise in the presence of domain walls with oscillatory tails can suppress spatial disorder by privileging highly correlated dynamical states consisting of arrays of spatial solitons.     

Manipulation and removal of defects in spontaneous optical patterns

Defects play an important role in a number of fields dealing with ordered structures. We demonstrate theoretically and experimentally the possibility of an active manipulation of defects in terms of an externally induced motion. We focus on the spontaneous formation of two-dimensional spatial structures in a nonlinear-optical system, a liquid crystal light valve under single optical feedback. For a particular parameter setting, a spontaneously formed hexagonal intensity pattern contains several dislocation-type defects. A scheme based on Fourier filtering allows us to restore spatial order in a selectable part of the pattern. Starting without control, the controlled area is progressively expanded, such that defects are swept out of the pattern.     

State dependent pseudoresonances and excess noise

We show that strong response to nonresonant modulations and excess noise are state dependent in generic nonlinear systems; i.e., they affect some output states but are absent from others. This is demonstrated in complex Swift-Hohenberg models relevant to optics, where it is caused by the non-normality of the linearized stability operators around selected output states, even though the cavity modes are orthogonal. In particular, we find the effective parameters that control excess noise and the response to modulations and show cases where these phenomena are enhanced by an order of magnitude.