Polarization effects in the diffraction of light by a planar chiral structure.

We analyze polarization changes of light diffracted on a planar chiral array from the standpoint of the Lorentz reciprocity lemma and find biorthogonality in the polarization eigenstates for waves diffracting though the grating in the opposite direction. Both reciprocal and nonreciprocal components in the polarization azimuth rotation of the diffracted light are identified. The structural chirality of the array arrangement and the chirality of individual elements of the array give rise to polarization effects.