High Efficiency Quantum Cascade Lasers Based on Excited-States Injection

In this letter, quantum cascade lasers (QCLs) based on excited-states injection are presented. The operating voltage is significantly reduced compared with the conventional groundstate injection design. Devices emitting at ~5.25 μm were fabricated through standard buried-heterostructure processing. Stable single-mode emission was observed by implementing a buried first-order distributed feedback (DFB) grating. The maximum output power of the DFB QCL with 2-mm cavity length was more than 300 mW at 10 °C with a high wall-plug efficiency of 5.6% in continuous-wave mode.