Microscopic model for polarization switching in optically anisotropic VCSELs

摘要

Abstract: A microscopic model for polarization switching in optically anisotropic VCSELs is presented. Our approach includes: (1) steady-state microscopic theory for the optical response of semiconductor quantum wells describing the dynamics of charge carriers and of interband polarizations in realistic bandstructures, including Coulomb-interaction correlations; (2) vectorial eigenmode calculation and the resulting expansion of the electromagnetic field in the laser in terms of vectorial eigenmodes of a whole structure, their polarization properties, mode-dependent losses and frequencies; (3) realistic model for optical anisotropies resulting from intentional or unintentional strain in an active quantum-well layer. The resulting steady-state input/output characteristics of linearly polarized microscopic eigenmodes of VCSELs are investigated in details. Linear stability analysis of these modes reveals the polarization switching behavior observed experimentally in practical VCSEL structures. We demonstrate that any nonzero uniaxial strain which may be present in the lattice structure (for instance, left over after the fabrication process) causes the laser to start lasing in a polarization eigenstate which is gain-preferred, but, for larger pumping currents, this polarization becomes unstable and the laser would switch to the orthogonal eigenstate.!39