We study polarization switching and transverse mode competition in
Vertical Cavity Surface Emitting Lasers in the absence of temperature
effects. We use a model that incorporates the vector nature of the
laser field, saturable dispersion, different carrier populations
associated with different magnetic sublevels of the conduction and
heavy hole valence bands in quantum well media, spin-flip relaxation
processes and cavity birefringence and dichroism. We consider both
index-guided and gain-guided VCSELs, and we find that spin-flip
dynamics and linewidth enhancement factor are crucial for the
selection of the polarization state corresponding to a given injection
current. For index-guided VCSELs the effect of spatial hole burning
on the polarization behavior within the fundamental mode regime is
discussed. For gain-guided VCSELs, transverse mode and polarization
selection is studied within a Maxwell-Bloch approximation which
includes field diffraction and carrier diffusion. Polarization
switching is found in the fundamental mode regime. The first order
transverse mode starts lasing orthogonally polarized to the
fundamental mode. At larger currents polarization coexistence with
several active transverse modes occurs.
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