Output pulse width of mode-locked ring laser based on Er3+-doped fibre amplifier and semiconductor optical amplifier

The time width and the spectral width of the output pulse of ring laser based on Er³⁺-doped fibre amplifier and semiconductor optical amplifier have been investigated theoretically. Influences of Er³⁺-doped concentration, active region width, input current, the length of the cavity imposed on the spectral bandwidth of the output pulse have been analysed and discussed. By using the analyses and conclusions in this study, the authors can control the pulse width by adjusting the related parameters and optimise the structure of the mode-locked laser system.