Theoretical-Experimental Study of the Vectorial Modal Properties of Polarization-Stable Multimode Grating VCSELs

Vertical-cavity surface-emitting lasers (VCSELs) with a monolithically integrated grating in the outcoupling aperture have proven to generate a stable and predictable polarization of the emitted light. This paper provides further insight into the polarization anisotropies of grating-controlled highly multimode VCSELs by direct experimental measurements of crucial vectorial characteristics, i.e., modal dichroism and birefringence. This is achieved by a careful analysis of linewidths and peak positions of the dominant and the suppressed polarizations of the emission spectra recorded close to threshold. These experimental results allow us for the first time to compare the observed dichroism and birefringence directly with simulations performed with a fully vectorial, three-dimensional model. Large dichroisms exceeding 30 GHz, even for higher transverse modes, were found to agree very well with the simulations. Such high dichroisms clearly indicate the excellent capability of integrated surface gratings for reliable polarization control, even under extreme operation conditions.