  We examine entanglement between number and polarization, or between number
and relative phase, for pairs of coherent states and two-mode squeezed vacuum
via linear entropy and covariance criteria. We consider the embedding of the
two-mode Hilbert space in a larger space to get a well-defined factorization of
the number-phase variables. This can be regarded as a kind of
proto-entanglement that can be extracted and converted into real particle
entanglement via feasible experimental procedures. In particular this reveals
interesting entanglement properties of pairs of coherent states.
