Semiclassical model for the relative intensity noise of intersubband quantum cascade lasers

We present a semiclassical noise model for the relative intensity noise of quantum cascade (QC) lasers based on a 3-level rate equation approach for a cascaded active region. We analyze the intensity noise properties with respect to the individual noise sources contributing to the RIN as well as the influence of the number of gain stages incorporated into the active region. We find that by increasing the number of gain stages in the active region, the overall contribution of non-radiative losses of carriers out of the upper laser level become the dominant noise source. Furthermore, we investigate the influence of the electron lifetime on the intensity noise properties. We find that the different noise properties of QC lasers compared to interband semiconductor lasers result from the joint effect of the short electron lifetime and the cascaded active region.