Spectral Evolution in Fiber Lasers with Soliton Self-Frequency Shift Effect

The generation and evolution process of red shifting in a ultrafast fiber laser with the soliton self-frequency shift are investigated by numerical simulation. And the effect of different parameters including the pump strength, the length of dispersion shift fiber, the modulation depth of saturable absorber and the initial field on the red shifting are analyzed for the first time to our knowledge. By optimizing these parameters, a soliton with the maximum red shifting beyond the laser's gain bandwidth is obtained. In addition, within a narrow parameter range, we have also achieved a novel red-shift period-doubling bifurcated soliton with a periodic switching central wavelength.