Synchronous Sisyphus effect in diode lasers subject to optical feedback

Diode lasers exposed to moderate optical feedback, when biased near threshold, exhibit low-frequency intensity fluctuations in the RF spectrum that materialize as dropout events in the intensity time series. We recorded high-quality intensity time traces and frequency spectra of these events that show a new phenomenon in which the dropout events synchronize and appear at regular time intervals. The fine structure of the individual dropouts is recorded with an ultrafast digitizer that reveals the presence of fast oscillations occurring in the picosecond range. Numerical work based on the single-mode single-delay Lang and Kobayashi rate equations shows a locked state consisting of sharp intensity pulses that are slowly modulated and locked to an extraordinarily regular pattern. [S1050-2947(99)01608-X].