Enhanced performance of quantum cascade Raman laser

We present a self-consistent numerical approach for quantum cascade Raman laser (QC-RL) with a modified design to improve the device performance. Our modeling approach is based on monolithic integration of stimulated Raman scattering (SRS) and electrically pumped QC laser. The laser band structure utilizing techniques with both material-dependent effective mass and band nonparabolicity is calculated by solving the Schrodinger–Poisson equations self-consistently. A detailed analysis of output characteristics of the obtained structure is carried out within a simplified 4-level rate equations model taking into account the SRS process. The model accurately explains the operating characteristics found in QCLs, such as damping transient response and non-resonant behavior of modulation frequency response. Furthermore, modification of the structure is focused on improving the SRS in the QC-RL. This leads to an enhancement of the device performance such as threshold current, external quantum efficiency, conversion efficiency, turn-on delay and modulation response. The excellent agreement of the experimental data with the simulated light output-current characteristics confirms the validity of the model.

The design and modeling of a quantum cascade Raman laser based on monolithic integration of stimulated Raman scattering and pump source. This potential-energy profile of the conduction band illustrates the monolithic integration concept of the quantum cascade Raman laser. Energy levels involved in stimulated emission (levels 6, 5 and 4), which serves as a pump laser, are shown, as well as the energy levels required for stimulated Raman scattering (levels 1, 2 and 3), which absorbs pump photons and emits photons as longer wavelength. The yellow arrows indicate the direction of electron flow. For clarity, only the moduli squared of the most important wave functions are shown.Figure optionsDownload as PowerPoint slide