Numerical simulation of a mode-locked quantum dot external cavity laser

The mode-locked characteristics of a quantum dot hybrid soliton pulse source (QD-HSPS) utilising a linearly chirped fibre Bragg grating (FBG) are investigated using the time-domain solution of coupled wave equations and rate equations. The effect of carrier dynamics on the output pulse of the QD-HSPS is also described. The numerical results indicate that the spontaneous coupling factor, carrier recombination time in QD and the length of the laser strongly affect the system operation, whereas there is no significant effect of carrier recombination in the wetting layer or of the carrier emission from the QD to the wetting layer or of the relaxation time from the wetting layer to the QD. Furthermore, it is also shown that by using the optimum parameters a QD-HSPS utilising a linearly chirped Gaussian-apodised FBG produces considerably shorter pulses when compared with a multi-quantum-well HSPS (MQW-HSPS) utilising linearly and non-linearly chirped gratings, along with an increase in the mode-locking frequency range.