A rate equation analysis of actively mode-locked semiconductor lasers

A rate equation has been used to analyze the actively mode-locked diode laser which is biased with a subthreshold dc current upon which a sinusoidal signal, whose frequency is equal to the mode spacing (or its multiple) of the external cavity, is superimposed. Steady-state operation of the laser enables us to find out many important parameters of the system. Based upon the experimental observations, we have established the time evolution of the injection carrier density which suggests the existence of a subpulse following the main pulse and provides the possibility of predicting the time gap between them. Meanwhile, the average output power of the laser, the threshold condition of the mode-locked oscillator, the arrival time of the main pulse at the gain medium, the temporal difference between the main pulse, and the peak of the small-signal gain have also been derived.