Symmetry Breaking in Vertical-Cavity Semiconductor Lasers

It seems fair to say that the polarization behavior of semiconductor Vertical-Cavity Surface-Emitting Lasers (VCSELs) is not understood on a fundamental level. In spite of the nominal anisotropy of a VCSEL the polarization is usually reported as being linear, but not very stable. Most authors associate this behavior with native anisotropies due to imperfect device fabrication although also intrinsic nonlinearities of the gain medium have been put forward for explaining the linear polarization. We are involved in a detailed study [1-4] of the various anisotropies of a VCSEL, their interplay, their manipulation and the consequences thereof for the VCSEL polarization. We have found experimentally that the polarization of a practical VCSEL can be largely explained as a consequence of linear anisotropies; nonlinearities play at most a minor role.