Fourier control of pattern formation in an interferometric feedback configuration

We present a control method for the minimally invasive manipulation of patt ern states occurring in feedback systems with an optical nonlinearity. An i nterferometric feedback configuration is used to control spontaneously form ed patterns by the method of Fourier filtering. This method is minimally in vasive since the pattern forming feedback arm remains unchanged, while the energy removed by the filter or the control signal added to the system by t he second control feedback arm tends to a small level when the desired patt ern is obtained. Here, we present experimental results for a photorefractiv e two-arm feedback system, including switching from hexagons to rolls or sq uares by positive (in-phase) control and manipulation of the hexagon orient ation by negative (out-of-phase) control. A comparison with results of a nu merical simulation based on a thin saturable Kerr-slice model is performed. (C) 1999 Elsevier Science B.V. All rights reserved.