On the basis of unitarity of the transformation matrix for inhomogeneously birefringent optical media that may also possess optical activity, it is shown that there are always two perpendicular directions of the polarizer by which the light emerging from the medium is also linearly polarized. These polarization directions of the incident and emergent light are called the characteristic directions. The characteristic directions and phase retardation give an invariant characterization of complicated optical media. Their experimental determination provides information about the parameters of the media. A complete theory of characteristic directions is presented, and several important cases are considered.
© 1986 Optical Society of America
H. K. Aben, "Characteristic directions in optics of twisted birefringent media," J. Opt. Soc. Am. A 3, 1414-1421 (1986)