We present a continuative definition of topological charge to depict the
polarization defects on any resonant diffraction orders in photonic crystal
slab regardless they are radiative or evanescent. By using such a generalized
definition, we investigate the origins and conservation of integer polarization
defects across the whole Brollouin zone. We found that these polarization
defects eventually originate from the mode degeneracy that is induced by
lattice coupling as a consequence of momentum space folding, or inter-band
coupling that can be either Hermitian or Non-hermitian. By counting all types
of polarization defects, the total topological charge numbers in a given
diffraction order is a conserved quantity across the whole Brillouin zone that
is determined by lattice geometry only