  In analogy with the spin-squeezing inequality of Wang and Sanders [Physical
Review A 68, 012101 (2003)], we find inequalities describing macroscopic
polarization correlations that are obeyed by all classical fields, and whose
violation implies entanglement of the photons that make up the optical beam. We
consider a realistic and exactly-solvable experimental scenario employing
polarization- squeezed light from an optical parametric oscillator (OPO) and
find that any two photons separated by less than the OPO coherence time are
polarization entangled. The polarization entanglement is robust against losses
and extremely bright: efficiency can exceed that of existing "ultra-bright"
pair sources by at least an order of magnitude. This translation of
spin-squeezing inequalities to the optical domain will enable direct tests of
the squeezing-entanglement relationship.
