Possible change of the polarization state in the process of propagation is considered theoretically. We were able to suggest a mechanism that allows for a very unusual behavior of the Stokes parameters of the beam. Specially arranged phase conjugation procedure yields the decrease of only one (e.g. |ζ3| ∝ |(|Ex|2 - |Ey|2)|) Stokes component, while the degrees of 45°- and circular polarization, ζ1 and ζ2, are not changing at all
