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

Abstract

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 mid-infrared modes at λ1=8.39 μ m and $\lambda _{{\text{2 }}}= {\text{9.38}}\, \mu {\text{m}}$ . Simultaneously, the manifold of possible transitions within the active region is designed to provide a peak nonlinear susceptibility of $\vert \chi ^{(2)}{\rm{\vert \, \,= \,\,}} {\text{29 nm}} {\text{V}}^{- 1}$ at the conversion to 3.8 THz. The device emits up to 210- μ W THz power at room temperature with a nonlinear conversion efficiency of $\eta ={\text{ 2.05 mW}} {\text{W}}^{- 2}$ .