Second-harmonic generation in optical fibers on a continuous-wave background

We predict that a different type of second-harmonic generation (SHG) in nonlinear optical fibers is possible for the waves excited from a continuous-wave background. We show that in a normal dispersion regime and near the zero-dispersion point of a single-mode optical fiber the phase-matching condition of the SHG can be satisfied by suitably choosing the wave vectors and frequencies of fundamental and second-harmonic waves. Using a multiscale method the nonlinearly coupled envelope equations for the SHG are derived and their explicit solutions are provided and checked by numerical simulation.