Different types of sideband generation in a passively mode-locked soliton fiber laser

We report on the experimental observation of sideband generation in a passively mode-locked erbium-doped fiber laser. The fiber laser has a conventional ring-cavity configuration for passive mode locking based on nonlinear polarization rotation. Self-starting and stable mode-locking operation is easily achieved in the laser. The output soliton pulses have a duration of about 248 fs and a repetition rate of 13.7 MHz at 1565-nm wavelength. Detailed pulse dynamics of the laser is measured under different operation conditions. Dip-type sidebands are observed on the soliton spectra of the laser, which have clearly different characteristics to those of the conventional Kelly sidebands. The soliton operation of the fiber laser is numerically simulated based on the coupled Ginzburg-Landau equations. The simulation results are consistent with the experimental observations, which confirm that dip-type spectral sidebands can appear on the soliton spectra of a uniform soliton-emission fiber laser.