Bifurcation cascade in a semiconductor laser subject to optical feedback

We investigated a single mode semiconductor laser system pumped near thresh old and subject to optical feedback from a short distance. We found both ex perimentally and numerically that as the feedback strength is increased the laser undergoes a cascade of bifurcations as one external cavity mode beco mes unstable and the next one with higher intensity becomes stable only to be destabilized and replaced by the next stable external cavity mode. In th e stable regions the laser operates in the so-called maximum gain mode and the unstable regions exhibit chaos which evolves into low-frequency fluctua tions characterized by intensity dropouts. [S0031-9007(98)08369-0].