Low-frequency fluctuations and polarization dynamics in vertical-cavity surface-emitting lasers with isotropic feedback

We investigate experimentally the polarization dynamics in vertical-cavity surface-emitting lasers exposed to isotropic time-delayed optical feedback. The existence of low-frequency fluctuations with and without the simultaneous excitation of polarization degrees of freedom is demonstrated. The appearance of polarization dynamics is shown to depend on the magnitude of the intrinsic dichroism of the device under study. If there is no polarization dynamics, low-frequency fluctuations of a single mode are observed.