Spectral sideband distribution asymmetry in fiber laser

A ring fiber laser with SESAM mode-locking mechanism is constructed. The spectral sideband distribution asymmetry of solitons is observed in the fiber laser. There are different order sidebands distributed in two edges of the soliton spectrum. Through experimentally studying the effect of the different gain media lengths on the mode-locked solitons, it is found that the spectral sideband asymmetry occurs at the long wavelength band of erbium-doped fiber (EDF) gain profile. The origin of sideband asymmetry is owing to the secondary amplification gain profile of EDF, which is pumped by the first gain peak at 1530 nm. Furthermore, an extra in-line polarizer is imported in the cavity for studying the effect of the polarization bias on sidebands. It is found that the polarization bias in the cavity is an important control method to adjust the power and generate the spectral sidebands. However, the polarization bias does not decide the generation of spectral sideband distribution asymmetry.