Quantum Transmission Line Modelling and Experimental Investigation of the Output Characteristics of a Terahertz Quantum Cascade Laser

We describe a new approach to modelling the optoelectronic properties of a terahertz-frequency quantum cascade laser (THz QCL) based on a quantum transmission line modelling (Q-TLM) method. Parallel quantum cascade transmission line modelling units are employed to describe the dynamic optical processes in a nine-well THz QCL in both the time and frequency domains. The model is used to simulate the current-power characteristics of a QCL device and good agreement is found with experimental measurements, including an accurate prediction of the threshold current and emitted power. It is also confirmed that the Q-TLM model can accurately predict the Stark-induced blue shift of the emission spectrum of the THz QCL with increasing injection current. Furthermore, we establish the new Q-TLM model to describe the properties of a THz QCL device incorporating a photonic lattice patterned on the laser ridge, by linking the transmission line structure to each scattering module. The predicted effects of the lattice structure on the steady-state emission spectra of the THz QCL, including the side-mode suppression, are found to be in good agreement with experimental results. Our Q-TLM modelling approach is a promising tool for the future design of THz QCLs and analysis of their temporal and spectral behaviors.