Single Stack Active Region Nonlinear Quantum Cascade Lasers for Improved THz Emission

We present a single stack active region design for terahertz emission by difference frequency generation in quantum cascade lasers. The active region contains a single design, which is based on multiple optical transitions within one period. This results in both a giant nonlinearity and an ultra-broad optical gain. The provided optical gain spectrum is broad enough to support two distinct mid-infrared modes with a significant spectral separation. For dual-emission, the waveguide contains a buried, index-coupled distributed feedback grating. This grating is based on a sampled approach to provide selective feedback for two midinfrared modes at λ
₁
= 8.39 μm and λ
₂
= 9.38 μm. Simultaneously, the manifold of possible transitions within the active region is designed to provide a peak nonlinear susceptibility of |χ
⁽²⁾
| = 29 nmV
^-1
at the conversion to 3.8 THz. The device emits up to 210-μW THz power at room temperature with a nonlinear conversion efficiency of η = 2.05 mWW
^-2
.