Polarization squeezing in vertical-cavity surface-emitting lasers

We further elaborate the theory of quantum fluctuations in vertical-cavity surface-emitting lasers (VCSELs), developed in Ref. \cite{Hermier02}. In particular, we introduce the quantum Stokes parameters to describe the quantum self- and cross-correlations between two polarization components of the electromagnetic field generated by this type of lasers. We calculate analytically the fluctuation spectra of these parameters and discuss experiments in which they can be measured. We demonstrate that in certain situations VCSELs can exhibit polarization squeezing over some range of spectral frequencies. This polarization squeezing has its origin in sub-Poissonian pumping statistics of the active laser medium.