Design of Low-Loss Surface-Plasmon Quantum Cascade Lasers

A low-loss waveguide design for the mid-infrared surface-plasmon quantum cascade lasers (QCLs) is proposed. A waveguide loss of 6.5–8 cm-1 with a confinement factor above 50% is obtained by modulating the doping concentration and thickness of the In0.53Ga0.47As (InGaAs) contact layer to around 1.3×1019 cm-3 and 100 nm. The overlapping of lasing mode with the highly lossy surface plasmons is therefore substantially reduced. The delocalizing the lasing mode profile to the substrate improves the far field angle of the lasing beam in the epilayer direction with a reduction about 25°.