Coupled-cavity AlInAs/InGaAs/InP quantum cascade lasers fabricated by focused ion beam processing

Focused ion beam processing has been applied to fabricate coupled-cavity AlInAs/InGaAs/InP quantum cascade lasers. The evolution of the mode spectrum of the two coupled Fabry-Perot cavities, controlled by the driving currents of both sections leading to single mode operation, has been observed. Theoretical analysis of the observed behavior, supported by extensive numerical modeling is given. The analysis showed that the most efficient single mode operation takes place in the case of relatively close current densities in both sections of coupled-cavity quantum cascade lasers, which assures the overlap of the gain spectra. In such a configuration, fine tuning of the currents allows the favoring of the mode that coincides with gain peaks and suppresses all others.