Analysis of surface emitting distributed-feedback quantum cascade laser based on a surface-plasmon waveguide

An analysis of a surface emitting distributed-feedback quantum cascade laser (DFB QCL) based on a surface-plasmon waveguide is presented. The second-order grating realized by the sole patterning of the top metal provides strong feedback. The analysis is based on a coupled-mode theory derived from exact Floquet-Bloch solutions of the infinite periodic structure. The surface outcoupling efficiency and threshold gain for the optimized device design are 43% and 12 cm −1 , respectively, which represent great improve ments on the conventional dielectric waveguide based DFB QCL with typical values of 17.5% and 20 cm −1 .