Weakly vectorial lasers with intracavity wave retardation plates can exhibit a rich variety of unusual dynamic polarization characteristics. For example, the output of an external-cavity semiconductor laser with an intracavity quarter-wave plate shows polarization self-modulations alternating between TE and TM modes at a fundamental frequency corresponding to twice the cavity round-trip time and at odd harmonics of this fundamental frequency. Higher-order harmonics greater than the 30th harmonic at frequencies above 5 GHz have been observed, which is much higher than the relaxation-oscillation frequency of the laser. As the pumping level is increased, the period-doubling route to chaos and hysteresis behaviour associated with higher harmonic bifurcations and multiple stable states has also been observed. These experimental results as well as preliminary numerical simulation results are summarized on the basis of a fairly simple model. Apart from possible applications, these results raise interesting questions about the fundamental polarization and nonlinear dynamic characteristics of such lasers. Some of these general issues are discussed.
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