A. Zimmermann’s research while affiliated with Technical University of Darmstadt and other places

A novel scheme for all-optical image processing is suggested, which is based on spontaneous pattern-formation processes. The spatiotemporal instabilities, connected with these self-organization effects, appear in many nonlinear optical systems and mostly obstruct the intended application. We propose to utilize the particular features of pattern formation for parallel image processing, namely the sensitivity to external influences, the selection of well-defined final states, and the rotational and translational invariance. We report here on a single-feedback experiment with a liquid crystal light valve as the optical nonlinearity. In this experiment, the recognition of hexagonal structures is realized. We characterize the response dynamics and study associative properties of this scheme. The extension to square patterns is discussed, and first steps towards a practical implementation are undertaken in providing a simple post-processing scheme and testing the concept on realistic input images.

A nonlinear optical system, which spontaneously forms hexagonal patterns, is exposed to a weak, spatially modulated forcing. As forcing, stationary hexagonal patterns are used under variation of their transverse wave number. In the experiment, we observe a locking when the forcing wave number is close to one of the critical wave numbers of the unforced system. Outside the locking regimes, forcing provokes spatiotemporal disorder. The system response is characterized quantitatively with respect to its dynamics and to its spatial order.