Fourier control of pattern formation in an interferometric feedback configuration

We present a control method for the minimally invasive manipulation of pattern states occurring in feedback systems with an optical nonlinearity. An interferometric feedback configuration is used to control spontaneously formed patterns by the method of Fourier filtering. This method is minimally invasive since the pattern forming feedback arm remains unchanged, while the energy removed by the filter or the control signal added to the system by the second control feedback arm tends to a small level when the desired pattern is obtained.

Here, we present experimental results for a photorefractive two-arm feedback system, including switching from hexagons to rolls or squares by positive (in-phase) control and manipulation of the hexagon orientation by negative (out-of-phase) control. A comparison with results of a numerical simulation based on a thin saturable Kerr-slice model is performed.