Polarisation switching in proton-implanted VCSELs

Presents a comprehensive experimental study of the polarisation behaviour of proton-implanted GaAs/AlGaAs VCSELs operating around 850 nm. Whereas until now only switching from the shorter to the longer wavelength (higher to lower photon energy) has been reported experimentally (henceforth referred to as type I switching), we have also observed PS in the opposite direction, occurring at higher injection levels and corresponding to a switching from lower to higher photon energy (type II switching). Secondly, in order to explain some of these experimental results, we propose to take into account not only the temperature and wavelength dependence of the gain, but also the same dependence of the free carrier absorption in the highly p-doped DBR mirror, which is known to be particularly important in VCSELs.