NOT KNOWN FACTS ABOUT BIREFRINGENT CRYSTAL

各向异性透明晶体如方解石、石英等的折射率，是其固有的特性，称为永久双折射。If the electric field has the path in the optical axis, one obtains the amazing index ne. This is possible only if the propagation direction (additional precisely, the route from the k vector) is perpendicular to your optical axis. For one