The dynamics of a unidirectional erbium-doped fiber laser is investigated on a time scale short enough to observe, with good resolution, its behavior for individual round-trips in the laser cavity. With an intracavity polarization controller, a rich variety of nonlinear phenomena, ranging from self-pulsing to square-wave antiphase patterns in two orthogonal states of polarization, are observed. These patterns evolve continuously in time. A stochastic delay-differential equation model is proposed to describe this system. Numerical simulations show that this model satisfactorily accounts for all types of qualitative behavior and reveal that the inclusion of spontaneous-emission noise is necessary to reproduce the observed continuous pattern evolution. Two different, typical types of nonlinear dynamical states are found both numerically and experimentally: a deterministic, low-dimensional regime and a noise-driven high-dimensional motion.

DOI:https://doi.org/10.1103/PhysRevA.55.2376