Numerical model for nonlinear polarization rotation mode-locked fiber laser

Employing nonlinear Schrodinger equations, a numerical model for nonlinear polarization rotation mode-locked fiber laser was put forward. Jones matrix was used to describe polarization controllers while two-level Giles model was used to calculate the gain. This numerical model has clear physical significance and is conducive to analyze the influence of pump power. With 1.0 m-long erbium doped fiber, 5.8 m-long single mode fiber and 85:15 output coupler, ultrashort pulse with the root-mean-square width of 0.30 ps was derived when pump power was 25 mW. The influence of pump power on the waveform and optical spectrum of mode-locked pulse was investigated, and the relation between pump power and gain distribution in erbium doped fiber was discussed. Mode-locked pulse was derived in experiment, whose optical spectrum was similar with numerical result in shape. The average power of pulse was measured and the variation trend is in line with theoretical result.