Polarization state selection, polarization state dynamics, and polarization
switching of a quantum-well Vertical Cavity Surface Emitting Laser for the
lowest order transverse spatial mode of the laser is explored using a recently
developed model that incorporates material birefringence, the saturable
dispersion characteristic of semiconductor physics,and the sensitivity of the
transitions in the material to the vector character of the electric field
amplitude. Three features contribute to the observed linearly polarized states
of emission: linear birefringence, linear gain or loss anisotropies, and an
intermediate relaxation rate for imbalances in the populations of the magnetic
sublevels. In the absence of either birefringence or saturable dispersion, the
gain or loss anisotropies dictate stability for the stronger linearly polarized
mode and switching is only possible if the relative strength of the gain for the
two modes is reversed. When birefringence and saturable dispersion are both
present there are possibilities of bistability, monostrability, and dynamical
instability, including switching by destabilization of the mode with the higher
gain to loss ratio in favor of the weaker mode. We compare our analytical and
numerical results with recent experimental results on bistability and switchings
caused by changes in the injection current and changes in the intensity of an
injected optical signal.
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