Abstract

The need for small laser devices that produce low divergence circular beams (e.g., coupling into fibers) has initiated intense research in the field of vertical cavity surface emitting lasers (VCSELs). Actual devices turn out to operate in a single transverse TEM₀₀-mode only close to threshold; in general they lase in several transverse modes.^1-3 Ideally one expects spherically symmetrical Laguerre-Gaussian higher-order modes with degenerate frequencies. In practice one often observes non-degenerate Hermite-Gaussian modes, indicative of spatial anisotropy. We have studied the effect of this anisotropy on the polarization characteristics of a 1 × 16 array of VCSELs; more specifically we investigated the coupling between the polarization and the transverse intensity distribution. We show how the results can be understood in terms of stress-induced and modal birefringence.

© 1994 IEEE