Quasi-periodic route to chaos in a near-integrable PDE: Homoclinic crossings

Abstract A new numerical experiment is discussed which shows a quasi-periodic route to intermittent chaos - typical for near-conservative, dispersive waves of small amplitude (nonlinear Schrodinger regime) in one spatial dimension. This route has: temporally one frequency, then two, then chaos; associated spatial symmetry changes; a low dimensional intermittent strange attractor. A nonlinear spectral transform has been used to show: a small number of nonlinear modes in the chaotic state; interaction of coherent modes with radiation modes: and, most importantly, that (unperturbed) homoclinic states are crossed repeatedly in these regimes. These homoclinic states: (a) separate spatially localized modes from radiation modes, and (b) act as sources of extreme sensitivity which can produce temporal chaos: for the first time homoclinic states have been simultaneously associated with both spatial patterns and temporal chaos.