Thermodynamic approach of supercontinuum generation

The interpretation of the mechanisms underlying supercontinuum (SC) generation, although generally well understood, constitutes a difficult problem due to the multitude of nonlinear effects involved. This paper investigates theoretically, numerically and experimentally the highly nonlinear regime of SC generation in a two zero dispersion wavelengths (ZDW) photonic crystal fiber (PCF). The numerical simulations of the NonLinear Schrodinger Equation (NLSE) reveal that a high power optical field exhibits an incoherent regime that prevents the generation of coherent soliton structures. The simulations also show that, in this regime, the Raman effect essentially leads to the generation of a spectral incoherent soliton in the normal dispersion regime. Besides spectral incoherent solitons, a peculiar feature revealed by the simulations is that the spectral broadening inherent to SC generation saturates during the propagation of the field. This is a consequence of the natural thermalization of the optical field to equilibrium: once the field has reached thermal equilibrium its spectrum no longer evolve during the propagation.