Surface acoustic wave modulation of quantum cascade lasers

In this work, a description is given of a simulation technique employed to model the interaction between surface acoustic waves and ridge-waveguide quantum cascade lasers (QCLs). Firstly, a finite-difference time-domain (FDTD) scheme for modelling acoustic wave propagation in arbitrary semiconductor structures is outlined, and verified by comparison with experimental measurements of the frequency response of surface acoustic wave transmission between interdigitated transmitters and receivers on a bulk crystal. The model is developed further to represent the ridge-waveguide as a prominence above the surface and the active region of the laser is accounted for by a free-charge region buried within the structure. The modulation of this free charge, or carrier concentration by the propagating surface acoustic wave, is then used as an input to a rate equation model of a QCL to show how the gain will be affected. It is this control of the gain through the amplitude of the surface acoustic wave which will allow for modulation of the mid-infrared or terahertz output of the laser and hence its incorporation in many new applications.