Bifurcation cascade in a semiconductor laser subject to optical feedback

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