Optically anisotropic media : New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities
(Figure presented.). Six out of seven crystal systems are optically anisotropic and birefringent. We review recent insight that biaxial crystals generally exhibit four singular axes (or exceptional points) which can pairwise degenerate for special cases. Planar anisotropic microcavities are discussed as effectively biaxial systems and we predict exceptional points and demonstrate experimentally pa