Distributed-Feedback Quantum Cascade Laser at 3.2 μm

This paper presents distributed feedback quantum cascade lasers (DFB QCLs), processed in buried heterostructure which include a quarter-wave shift defect in the center of the grating. The grating was incorporated with plasma etching using standard optical lithography. Due to the defect the devices are assumed to lase in the middle of the stopband emerging from the DFB grating. The measured emission was between 3.19 and 3.3 μm with output peak power of up to 120 mW at -20 °C. Threshold current densities reached down to 4.8 kA/cm² and a tuning range of 10.5 cm^-1 was measured while varying the temperature between -20 to 30 °C. Single mode emission was observed with side mode suppression ratios of above 20 dB with spectral linewidth of around 11 GHz.