Ring resonator-based surface emitting quantum cascade lasers

We describe the design, simulation, fabrication and operation of ring cavity surface emitting lasers (RCSEL) based on quantum cascade structures for the midinfrared (MIR) and terahertz (THz) spectral range. MIR RCSELs facilitate an enhancement of optical power and a reduction in threshold current density, as compared to Fabry-Perot (FP) lasers. In continuous wave operation the maximum temperature of ring based devices is 50 K higher than in FP emitters. Also in THz QCLs a twofold increase in radiation efficiency is observed when compared to FP lasers. The emitters exhibit a robust single-mode operation around 8 mu m and 3.2 THz, with a side mode suppression ratio of 30 dB. The ring-shaped resonator forms symmetric far-field profiles, represented by a lobe separation of similar to 1.5 degrees and similar to 15 degrees for MIR and THz lasers, respectively.