  We study the behaviour of the Negativity of Wigner Function (NWF) as a
measure of entanglement in non-Gaussian states under quantum polarisation
converter devices. We analyze comparatively this quantity with other measures
of entanglement in a system prepared in a superposition of two-mode coherent
states. We show that the (WF) can be identified as a quantifier of non-Gaussian
entanglement.
