  The optical spin-Hall effect results in the formation of an antisymmetric
real space polarization pattern forming spin currents. In this paper, we show
that the exciton-polariton parametric scattering allows us to reverse the sign
of these currents. We describe the pulsed resonant excitation of a strongly
coupled microcavity with a linearly polarized pump at normal incidence. The
energy of the pulse is set to be close to the inflexion point of the polariton
dispersion and the focusing in real space populates the reciprocal space on a
ring. For pumping powers below the parametric scattering threshold, the
propagation of the injected polaritons in the effective magnetic field induced
by the TE and TM splitting produce the normal optical spin-Hall effect. Keeping
the same input polarization but increasing the pump intensity, the parametric
scattering towards an idler and a signal state is triggered on the whole
elastic circle. The injected particles are scattered toward these states while
propagating radially all over the plane, gaining a cross linear polarisation
with respect to the pump during the nonlinear process. Eventually, the
propagation of the polaritons in the effective field results in the optical
spin Hall-effect, but this time with inverted polarization domains.
