  We analyzed polarization changes of light diffracted on planar chiral array
from the standpoint of the Lorentz reciprocity lemma and found the
bi-orthogonality in the polarization eigenstates for the waves diffracting
though the grating in the opposite direction. Both reciprocal and
non-reciprocal component in the polarization azimuth rotation of the diffracted
light were identified. The structural chirality of the array arrangement and
the chirality of individual elements of the array give rise to polarization
effects.
