Polarization fluctuations in vertical-cavity semiconductor lasers

We report, theoretically and experimentally, how polarization fluctuations in vertical-cavity semiconductor lasers are affected by optical anisotropies. We develop a spin-eliminated (class A) description of laser polarization and show how the various model parameters can be extracted from the experimental data. In practice, the linear anisotropies are often much stronger than the nonlinear anisotropies, so that the polarization modes defined by the linear anisotropies form a useful basis. For this case we derive a one-dimensional model for polarization noise, with simple expressions for the relative strength of the polarization fluctuations and the rate of polarization switches. For the other, more extreme, case where the nonlinear anisotropies are as strong (or even stronger) than the linear anisotropies, the spin-eliminated description remains valid. However, in this case the concept of polarization modes is shown to lose its meaning, as a strong four-wave-mixing peak appears in the optical spectrum and polarization fluctuations become highly nonuniform.