Performance and reliability of quantum cascade lasers

Abstract

We present the burn-in behavior and power stability of multiple quantum cascade lasers (QCLs) that were measured to investigate their long-term performance. For these experiments, the current to the QCL was cycled every ten minutes, and the output power was monitored over time for durations as long as two months. A small increase in power for a given injection current is observed for almost all of the QCLs tested during the burn-in period. Although the amount and duration of the burn-in varied among the devices tested, we observed that QCLs that operated with a lower threshold current exhibited a smaller burn-in change from initial conditions for the first ten hours of operation. This correlation, however, disappeared at longer operation times. The effect of packaging the QCLs is also investigated to determine its impact on performance and reliability. The power stability is measured for the packaged QCLs along with changes in the operational conditions. Although the temperature of the QCL is kept constant with a thermistor and thermoelectric cooler (TEC) inside the package, the case temperature is varied to monitor its correlation with any changes in power or frequency. Power changes and small frequency shifts are observed under these conditions. One possible explanation for these changes is the influence of optical feedback from the anti-reflection (AR) coated window in the package. The data from all of these experiments is presented.