Effect of coupling of spontaneous emission to the lasing mode in a two level model of quantum cascade lasers

In this paper, an improved two level model of quantum cascade lasers is extended to include the coupling of the spontaneous emission to the lasing mode. The variation of the electron numbers at the two levels, their difference and the variation of the light output with injected current are examined. The normalized modulation response for different ratios of the injected current to the threshold current is given