Formation of polarisation-squeezed light in type II optical frequency doubling

A new efficient method for the generation of light with a nonclassical polarisation state is proposed. This method is based on second-harmonic generation by mixing the fundamental-frequency radiation with ordinary and extraordinary polarisations in a quadratically nonlinear crystal. It is shown that fundamental-frequency radiation with strongly suppressed quantum fluctuations of the Stokes parameters can be obtained at the output from this crystal.