  An arbitrary polarization state of a single-mode biphoton is considered. The
operationalistic criterion is formulated for the orthogonality og these states.
It can be used to separate a biphoton with an arbitrary degree of polarization
from a set of biphotons orthogonal to it. This is necessary fro the
implementation of quantum cryptography protocol based on three-level systems.
The experimental test of this criterion amounts to the observation of the
anticorrelation effect for a biphoton with an arbitraty polarization state.
