Low-Threshold Continuous-Wave Operation of Distributed-Feedback Quantum Cascade Laser at $\lambda \sim 4.6\ \mu$m

Room-temperature continuous-wave (CW) operation of distributed-feedback quantum cascade laser (DFB-QCL) emitting at 4.6 μm is presented. Strain-compensation combined with two-phonon resonance in active region design promises low-threshold current density. A record low-threshold current density of 1 kA/cm ² for DFB-QCL operated in CW mode at 30°C is realized without a high-reflectivity coating on the rear facet. Reliable dynamic single-mode emission with a sidemode suppression ratio of about 30 dB is achieved from 10 to 50°C.