Temperature-Sensitive Gain Recovery Dynamics of Quantum Cascade Lasers

Abstract

The gain recovery of quantum cascade lasers (QCLs) is assumed to be very fast, on the order of a picosecond, since the carrier transport is dominated by ultrafast electron-LO phonon interactions. The fast gain recovery of almost all QCLs makes it difficult to achieve modelocking using conventional techniques, but the fast gain recovery also leads to an output that closely tracks the injection current, which has advantages for high-speed optical communication. Determining the gain recovery dynamics is thus of great importance in predicting the performance of QCLs. However, due to the complex nature of the carrier transport in QCLs, the gain recovery dynamics is difficult to predict. The transport rates also vary when quantum mechanical designs and operating conditions vary, which makes the prediction of gain recovery even more difficult. In this work, we calculate the gain recovery dynamics of QCLs when the temperature changes. We find that the steady-state gain and the depletion of the gain when pump pulse interacts decrease as the temperature increases. However, gain recovers at an increased rate with reduced coherent oscillations when temperature increases. The results are consistent with the experimental observations