Degradation and intensity fluctuations in CW AlGaAs double-heterostructure junction lasers

The intensity fluctuations in the output of CW AlGaAs semiconductor lasers were measured as functions of pumping current and operating time. The magnitude of fluctuation decreases with increasing aging time. The shift after degradation in the resonant-peak frequency for the normalized pumping rate is small. An increase of the half-width of the resonance peak is also observed, together with an increase of the threshold current and a decrease of the external differential quantum efficiency. The fluctuation spectra due to the quantum shot noise were calculated using rate equations with parametric variation of the pumping rate and the internal quantum efficiency. From the qualitative agreement between calculated and experimental results, changes in the intensity fluctuations after degradation are considered to be partly due to a decrease of the internal quantum efficiency or gain.