Picosecond spectra of gain-switched AlGaAs/GaAs multiple quantum well lasers

The temporal waveform of the single longitudinal modes emitted by gain-switched AlGaAs/GaAs multiple quantum well lasers is analyzed by means of a synchroscan streak camera system coupled to a spectrograph. It is found that only 50% of the number of the longitudinal modes contributing to the time-averaged spectrum are present during the first relaxation oscillation. The time-dependent shift of the envelope of the mode spectrum is quantitatively explained by a spectral shift of the gain maximum as a function of the time-varying charge carrier density. The results demonstrate that, for the analysis of transient multimode spectra of gain-switched injection lasers, inclusion of the energy dependence of the gain and gain compression is mandatory.