Heteroclinic structure of parametric resonance in the nonlinear   Schr\"odinger equation
  We show that the nonlinear stage of modulational instability induced by parametric driving in the {\em defocusing} nonlinear Schr\"odinger equation can be accurately described by combining mode truncation and averaging methods, valid in the strong driving regime. The resulting integrable oscillator reveals a complex hidden heteroclinic structure of the instability. A remarkable consequence, validated by the numerical integration of the original model, is the existence of breather solutions separating different Fermi-Pasta-Ulam recurrent regimes. Our theory also shows that optimal parametric amplification unexpectedly occurs outside the bandwidth of the resonance (or Arnold tongues) arising from the linearised Floquet analysis. 
M. Conforti, A. Mussot, A. Kudlinski, S. Rota-Nodari, G. Dujardin, S.   De Bievre, A. Armaroli, and S. Trillo
nlin.PS nlin.SI physics.optics