  We study the entanglement evolution of a quantum optical vortex state
propagating through coupled lossless waveguides. We consider states generated
by coupling two squeezed modes using a sequence of beam splitters and also by
subtracting photons from the signal in spontaneous parametric down conversion.
We reconstruct the Wigner function at a later time to study the correlation and
quantify the entanglement after propagation using \emph{logarithmic
negativity}.
