Quantum cascade lasers with double-quantum-well superlattices

A quantum-cascade laser using a double-quantum-well graded superlattice as the active region is presented. Each SL period consists of two strongly coupled quantum wells resulting in the splitting of the lowest miniband into two minibands. These two minibands can be designed to be flat and to contain delocalized, spatially symmetric wavefunctions under an applied electric field which in turn leads to a high optical dipole for the interminiband transition. In addition, the new design allows independent control of the energy levels of the lowest two minibands, their width and the splitting separating them, enhancing design flexibility. Using a cascade design of 55 pairs of alternated active regions and injectors, pulsed laser action is achieved at λ = 11.6 μm. Peak output powers reach 120 mW at 7 K and approximately 12 mW at the maximum operating temperature of 195 K.