Optimization of semi-insulating surface-plasmon waveguides within terahertz QCL's using computational models

Abstract

The possibility of a compact source of coherent terahertz radiation is being realized through the development of quantum cascade lasers (QCL's). These lasers consist of a semiconducting heterostructure active region and an internal waveguide that make intraband lasing transitions possible. The use of terahertz QCL's in promising applications such as medical imaging, defense, and security is currently limited by low output laser power. Systematic optimization of the QCL's waveguide reduces mode losses, improves confinement, and increases output power. Waveguide optimization is especially important for lasers operating at low terahertz frequencies where semi-insulating surface-plasmon waveguide performance degrades significantly. Prediction codes have been developed that systematically optimize semi-insulating surface-plasmon waveguides. The methods and results of these optimizations will be presented for a full suite of terahertz QCL waveguides at different frequencies. The use of the optimization code to investigate graded-doping waveguide structures will also be presented.