Broadband transistor-injected dual doping quantum cascade laser

A novel design-friendly device called the transistor-injected dual doping quantum cascade laser (TI-D²QCL) with two different dopings in each stack of a homogeneous superlattice is proposed. By adjusting the base–emitter bias V_be of the bipolar transistor to supply electrons in the dual doping regions, charge quasi-neutrality can be achieved to generate different optical transitions in each cascading superlattice stack. These transitions are then stacked and amplified to contribute to a broad flat gain spectrum. Model calculations of a designed TI-D²QCL show that a broad flat gain spectrum ranging from 9.41 µm to 12.01 µm with a relative bandwidth of 0.24 can be obtained, indicating that the TI-D²QCL with dual doping pattern may open a new pathway to the appealing applications in both mid-infrared and terahertz frequency ranges, from wideband optical generations to advanced frequency comb technologies.