Depolarization of light in a graded-index isotropic medium

The effect of depolarization of an incident pure state of polarization propagating through a graded-index multimode two-dimensional optical waveguide is described using the quantum-mechanical method of coherent states. It is shown that the degree of polarization for both the linearly and the circularly polarized radiation decreases with increasing distance owing to the interaction between the polarization (spin) and the beam trajectory (orbital moment). The wave nature of the depolarization is emphasized. The depolarization vanished when the wavelength tends to zero. Oscillations of the polarization degree of pure diffractional origin on propagation of light in a single-mode optical fibre are found.