Modulation instability and pattern formation of incoherent light

Summary form only given. Modulation Instability (MI) is a universal process that appears in most nonlinear wave systems in nature. Because of MI, small amplitude and phase perturbations (from noise) grow rapidly under the combined effects of nonlinearity and diffraction (or dispersion, in the temporal domain). As a result, a broad optical beam (or a quasi-CW pulse) disintegrates during propagation, leading to filamentation or to break-up into pulse trains. Modulation instability is largely considered as a precursor of solitons, because the filaments (or pulse trains) that emerge from the MI process are actually trains of almost ideal solitons. We have theoretically demonstrated that MI can also exist in relation with partially-incoherent wave-packets or beams and shows a threshold-like dependence of the involved nonlinearity.