Polarization Fluctuations Demonstrate Nonlinear Anisotropy of a Vertical-Cavity Semiconductor Laser

We report observation of polarization fluctuations in vertical-cavity semiconductor lasers, which allows us to demonstrate and quantify the importance of nonlinear polarization anisotropy. We focus on three aspects, which all fit within the same theoretical framework: (i) a nonlinear spectral redshift, (ii) an extra four-wave mixing peak in the optical spectrum, and (iii) correlations between the polarization fluctuations.