We report on the observation of spatiotemporal dynamics on picosecond time scales for an antireflection-coated ridge waveguide laser diode that is only 5 µm wide. Depending on the applied current, three dynamic regimes can be distinguished, showing the transition from regular to irregular spatiotemporal emission. We discuss the underlying mechanisms and develop a comprehensive understanding of this dynamic behavior. First, for moderate pumping, we find a typical relaxation oscillation behavior of the fundamental lateral mode. Second, at intermediate current levels, we observe lateral high-frequency switching of the output intensity between the left-hand and the right-hand parts of the active region. The switching frequency increases linearly with the excitation current and is of the order of 10 GHz. We give evidence that this switching behavior results from the coexistence and interaction of fundamental and first-order lateral modes that belong to different longitudinal mode families. The observed dependence of the switching frequency on the bias current can be attributed to a change in the width of the emission profile. Third, at high pumping levels, irregular spatiotemporal dynamics with the coexistence of low- and high-frequency spatial switching and temporal pulsations can be found. Finally, the influence of waveguide design and consequences for applications are considered and discussed.
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