Estimation of the effect of thermal waveguiding on the splitting between the two fundamental polarization modes in VCSELs

The polarization state of a beam emitted from VCSELs has been observed to be almost always oriented along the <110> or <11~0> crystallographic axes and can switch (even in the fundamental mode) when the current, temperature, optical feedback, etc. are changed, even by small amounts. Several mechanisms have been proposed which could be grouped as 1) the gain (material or modal) difference models, 2) the gain saturation (hole burning) models and 3) the spin flip models, each highlighting a different aspect of the physics inside the resonator cavity. In the contribution, we do not aim at introducing yet another model for the polarization-switching behavior, but would rather like to evaluate the effect of the thermal waveguide on the relative position (i.e. the splitting between) the fundamental modes. The rationalization behind this approach is the critical dependence of for example the material gain difference or cross-saturation coefficients on this splitting and the experimentally observed jump.