Transport induced pattern selection in a nonlinear optical system

The pattern selection process in a two-dimensional optical system, with a K err nonlinearity inserted in an optical feedback loop, is strongly affected by nonlocal interactions. Experimentally, nonlocality is introduced by mea ns of a lateral transport of the feedback signal. As the transport length i s increased, the system displays a sequence of transition over different cl asses of patterns. In the case of purely diffractive feedback, patterns cor responding to both focusing and defocusing nonlinearities are reported. Whe n interference instead of diffraction operates in the feedback loop, new se lection rules govern both the scale and the spatial symmetry of the observe d structures. In all the cases considered, the stability analysis of the mo del equations yields theoretical predictions in good agreement with the exp erimental results.