Control of spatio-temporal complexity in nonlinear optics

Spatio-temporal complexity is a common phenomenon in nonlinear optics. The coupling of diffraction with optical nonlinearities often leads to regular or irregular spatial structures either stationary, oscillatory or temporall y erratic: In order to utilise the large flexibility of spatially extended optical systems, control is necessary. Here we provide evidence of successf ul control techniques developed for models of nonlinear optical devices. Ap plication of standard methods for the control of chaos lead to stabilisatio n of multi-transverse mode lasers at low pump values. Phase masks are used to control the position of Optical Bullet Holes (localised structures in th e plane perpendicular to the direction of light propagation). Stabilisation , selection and tracking of unstable patterns is achieved by control techni ques using instantaneous feedback appropriately filtered in Fourier space. Finally, elimination of spatio-temporal disorder is demonstrated in a wide variety of nonlinear optical systems by generalising the Fourier method dev ised for the control of unstable spatio-temporal structures. (C) 1999 Elsev ier Science Ltd. All rights reserved.