Wave propagation in a continuously twisted biaxial dielectric medium parallel to the helical axis

An analytic solution is presented for the propagation of electromagnetic waves parallel to the helical axis of a continuously twisted biaxial dielectric medium. The two optical axes of this unidirectionally inhomogeneous medium lie in a plane normal to the helical axis and are separated by a constant phase shift. The 4 × 4 matrix method of optics is used. The obtained result generalizes the well known exact solution for the continuously twisted uniaxial dielectric medium and provides a further advance towards the understanding of the optical properties of cholesteric liquid crystals and other similar anisotropic materials