Modulated amplitude waves and the transition from phase to defect chaos

The mechanism for transitions from phase to defect chaos in the one-dimensi onal complex Ginzburg-Landau equation (CGLE) is presented. We describe peri odic coherent structures of the CGLE, called modulated amplitude waves (MAW s). MAWs of various periods P occur in phase chaotic states. A bifurcation study of the MAWs reveals that for sufficiently large period, pairs of MAWs cease to exist via a saddle-node bifurcation. For periods beyond this bifu rcation, incoherent near-MAW structures evolve towards defects. This leads to our main result: the transition from phase to defect chaos takes place w hen the periods of MAWs in phase chaos an driven beyond their saddle-node b ifurcation.