We study the multimode operation regimes of midinfrared quantum cascade lasers (QCLs), taking into account nonlinear phase-sensitive interactions between transverse modes. We show the possibility of the coherent coupling of several transverse modes, which results in a number of interesting effects including frequency and phase locking between transverse modes, bistability, and beam steering. We present an analytical model for the modal dynamics and its numerical analysis. Effects of amplitude and phase fluctuations on the modal stability are explored. The theoretical results are in agreement with our experimental measurements of buried heterostructure QCLs.
We propose and theoretically investigate mid/far-infrared photodetectors based on frequency up-conversion in a
near-resonant cascade of interband and intersubband transitions in high optical nonlinearity asymmetric quantum
well structures. Such structures can yield high detectivity and responsivity in the bandwidth of the order of
30% of a central frequency in the mid-infrared range. Resonant up-conversion detectors can be designed for
both collinear and perpendicular pump and signal beams. They can be integrated with semiconductor pump
lasers to yield compact devices. We present specific device designs based on GaAs/AlGaAs and InGaAs/AlInAs
heterostructures and calculate their expected figures of merit.