Nonlinear wave mixing in a multilongitudinal-mode erbium-doped fiber laser

The emission spectrum of an erbium-doped fiber ring laser is shown to result from the nonlinear wave mixing taking place between the multiple oscillating longitudinal modes. The dependence of the resultant spectral broadening upon the signal power circulating in the laser cavity is investigated both theoretically and experimentally. In the case considered here, the extent of this spectral broadening is shown to be restrained only by the spectrally discriminating element inserted in the laser cavity. Predictions of the numerical simulations for the signal buildup and propagation in the laser cavity are found to be in good agreement with the experiment.