 Unpolarized light ray enters through the left face of the crystal, as shown in the diagram, and is split into two orthogonally polarized, differently directed rays by the birefringence property of the calcite.The "ordinary" ray, or "o"-ray, experiences a refractive index of "n"o = 1.658 in the calcite and undergoes total internal reflection at the calcite–glue interface because its angle of incidence at the glue layer (refractive index "n" = 1.55) exceeds the critical angle for the interface.It passes out the top side of the upper half of the prism with some refraction, as shown.