Abstract

We present measurements of the intensity autocorrelation function of the output of a free-running GaAlAs diode laser. To our knowledge these are the first such measurements performed on the output of semiconductor lasers. Our data displays large structure at the relaxation oscillation frequency and shows that the presence of many small secondary modes that accompany the predominant mode in so-called single-mode diode lasers have a significant effect on the fluctuations of the total output of the laser. The autocorrelation function reveals features that depend on the number of secondary modes lasing and, in fact, could be used to measure how many contribute to the fluctuating intensity. The correlations of these features damp away faster than the relaxation-oscillation features. The damping can be modelled by a simple multimode phase diffusion model. Our measurements also show that measurements of the intensity autocorrelation function of the output of a diode laser are a sensitive indicator of the presence and magnitude of external optical feedback.

© 1992 Optical Society of America