Synchronous Sisyphus effect in diode lasers subject to optical feedback

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