  A scheme to distinguish entangled two-photon-polarization states (ETP) from
two independent entangled one-photon-polarization states (EOP) is proposed.
Using this scheme, the experimental generation of ETP by parametric
down-conversion is confirmed through the anti-correlations between three
orthogonal two-photon-polarization states. The estimated fraction of ETP among
the correlated photon pairs is 37% in the present experimental setup.
