Localized structures in nonlinear optical systems and materials

Diffractive effects in passive nonlinear optical resonators can lead to pattern forming bifurcations with subcritical character. When the pattern (in our case, a regular hexagonal lattice of intensity peaks) coexists with the homogeneous solution, localised structures can be excited, consisting in a single intensity peak in the transverse plane. This solution has the characteristics of a two-dimensional spatial soliton, and is highly degenerate with respect to the peak location. We investigate the procedures by which such peaks can be turned on by injecting narrow laser pulses, the conditions to ensure independence among the peaks and the way to erase a localised structure without affecting the others. These features suggest the possibility to encode optical information in the structure of the field profile.