Coexistence of attractors in a laser diode with optical feedback from a large external cavity.

The coexistence of several attractors in the coherent collapsed state of a laser diode with optical feedback is investigated. These attractors are unstable tori that bifurcate from different external cavity modes. As the feedback rate is increased, these tori undergo different types of quasiperiodic routes, such as frequency locking, period doubling, or the appearance of a third incommensurate frequency. In the fully developed coherent collapsed state, the tori are all unstable, and the phenomenon of intermittence appears. Lyapunov exponent calculations demonstrate that this state presents hyperchaotic and highdimensional dynamics. These results are explained qualitatively in terms of the multiattractor behavior found.