Radiations by ‘‘solitons’’ at the zero group-dispersion wavelength of single-mode optical fibers

Nonlinear pulse propagation at the zero group-dispersion wavelength is studied analytically. It is discovered that, after the characteristic initial frequency splitting, evolution of the pulse envelope that is shifted down to the anomalous regime is described by the nonlinear Schrödinger equation with higher-order dispersion as a perturbation. The effect of the perturbation on the pulse is to excite radiation at a frequency inversely proportional to the small parameter β. The amplitude of the radiation is exponentially small (∝exp(-1/β)] and can be calculated only by the perturbation method that goes beyond all orders.