Self modulation phenomena in an external-cavity semiconductor laser

We report the observed self-modulation phenomena in an external-cavity semiconductor laser, in which a slant ridge-loading waveguide was formed for the gain medium. A region beside the ridge at a cleaved end of the waveguide served as a saturable absorber for self-modulation. Under different conditions of injection current and cavity alignment, we observed three laser operation regimes, including pure cw oscillation, constant-amplitude pulse-like signal on the top of a cw component, and amplitude-modulated pulse-like signal coexistent with a cw component. The amplitude modulation phenomenon is different from the previously reported concurrence of mode-locking and self-pulsation. A model was proposed to explain the observed results.