  The dynamics of optical switching in semiconductor microcavities in the
strong coupling regime is studied using time- and spatially-resolved
spectroscopy. The switching is triggered by polarised short pulses which create
spin bullets of high polariton density. The spin packets travel with speeds of
the order of 106 m/s due to the ballistic propagation and drift of
exciton-polaritons from high to low density areas. The speed is controlled by
the angle of incidence of the excitation beams, which changes the polariton
group velocity.
