THz difference-frequency generation in MOVPE-grown quantum cascade lasers

We report mass-producible room-temperature electrically-pumped THz sources based on intra-cavity difference-frequency generation in mid-infrared InGaAs/AlInAs/InP quantum cascade lasers. Devices are grown by a commercial foundry using metal organic vapor phase epitaxy. A dual-stack active region possessing giant optical nonlinearity for 3.5 THz generation and a non-collinear Cherenkov waveguide THz outcoupling scheme is employed. Fabry-Pérot devices provided broad emission in the 3-4 THz range with a peak power of 5 μW. Single color THz sources were processed using surface distributed feedback gratings to produce narrowband < 8 GHz emission at 3.5 THz with nearly 40 μW of peak power and a mid-infrared-to-THz conversion efficiency of 0.36 mW/W². To better understand the dynamics of the DFG process, time gated spectral measurements of the mid-infrared pumps were performed and simultaneous lasing over the duration of the applied bias pulse was observed, thereby resulting in efficient difference frequency generation.