Light has an electromagnetic nature. Electromagnetic waves are transverse: the vectors E and B are perpendicular to each other, and the oscillations occur in the plane that is perpendicular to the direction of propagation.
The light waves emitted by the usual sources of light (lamps, for example) are unpolarized. This means that the oscillations of the vectors E and B occur in all possible transverse directions. Such light is called natural.
Some sources (such as lasers) emit polarized light. The oscillations of the electric and magnetic fields in polarized light do not occur in all directions, but only in the two perpendicular directions. Such light is called linearly polarized.
A general case in polarization of light is the elliptical polarization of light. The elliptically polarized light is a type of superposition of two waves of the same frequency that are linearly polarized in mutually perpendicular planes. The type of elliptical polarization that takes place depends on the relationship between the amplitudes Ex and Ey of the linearly polarized waves, and a phase shift δφ that exists between them. Thus, if E1/E2=1,
for δφ=0 or π the polarization is linear;
and for δφ=π/2 or 3π /2 the polarization is circular (left-sided or right-sided).
In any plane that is perpendicular to the direction of light propagation, the end of vector E in an elliptically polarized wave that moves periodically in an elliptic trajectory.