Noise Correlation, Regenerative Amplification, and the Linewidth Enhancement Factor of a Vertical-Cavity Surface-Emitting Laser

This letter reports on amplitude and frequency noise correlation measurements as well as on optical injection experiments related to the linewidth enhancement factor a of a vertical- cavity surface-emitting laser (VCSEL). It is shown that the correlation in VCSELs is not dominated by alpha; consequently, such experiments yield very little information on its value. Measuring the regenerative amplification of a weak injected optical probe turned out to be a robust approach that can not only give accurately the relaxation oscillation frequency and the damping rate but a good estimate of alpha as well. Finally, these experiments are combined with previously published data to increase the number of techniques applied to the measurement of alpha of a single semiconductor laser up to 11.