Polarization fluctuations in vertical-cavity surface-emitting lasers: a key to the mechanism behind polarization stability

We investigate the effects of the electron-hole spin dynamics on the polarization fluctuations in the light emitted from a vertical-cavity surface-emitting laser (VCSEL). The Langevin equations are derived based on a rate equation model including birefringence, dichroism and two carrier density pools separately coupled to right and left circular polarization. The results show that the carrier dynamics phase lock the polarization fluctuations to the laser mode. This is clearly seen in the difference between the fluctuations in ellipticity and the fluctuations in polarization direction. Separate measurements of the polarization fluctuations in ellipticity and in the polarization direction can therefore provide quantitative information on the nonlinear contribution of the carrier dynamics to polarization stability in VCSELs.