Design of nonlinearity-enhanced quantum-cascade lasers

We present simulations of mid-infrared quantum-cascade lasers (QCL) with optimized second-harmonic generation (SHG). The optimized design was obtained utilizing techniques from supersymmetric quantum mechanics with both material-dependent effective mass and band nonparabolicity. Two-photon processes are analyzed for resonant cascading triple levels designed for enhancing SHG. Nonunity pumping efficiency from one period of the QCL to the next is taken into account by including all relevant carrier scattering mechanisms between the injector/collector and active regions. Carrier transport and power output of the structure are analyzed by self-consistently solving rate equations for the carriers and photons. Current-dependent linear optical output power is derived based on the steady-state photon population in the active region. The SH power is derived from the Maxwell equations with the phase mismatch and modes overlapping included. Due to stronger coupling between lasing levels, the optimized structure has both higher linear and SH output powers. The optimized structure can be fabricated through digitally grading the submonolayer alloys by molecular beam epitaxy (MBE) technique.