Quantum Cascade Lasers with Heterogeneous, Stacked Cascades: Sum-Frequency and Second Harmonic Generation

Quantum cascade (QC) lasers have recently been demonstrated with stacked, interdigitated or collaborative cascades. Different active regions, in all cases of the "three-well vertical transition" type and designed at different emission wavelengths, were stacked -- with matching injector regions -- and inserted into one waveguide core. This approach is attractive for multi-wavelength generation, as it is insensitive to cross-absorption with the intrinsically narrow optical intersubband transitions being transparent on both its energy sides. Furthermore, the cascading scheme, characteristic for QC-lasers, implies that the electric current passes consecutively through all active regions, avoiding competition between the various wavelength lasers. Here, we present a novel application of stacked heterogeneous cascades, in which we integrate two sub-stacks of different wavelength QC-lasers with a superlattice (SL) section designed to generate a sum-frequency signal.