What is polarization?
Polarization is a phenomenon in which the oscillations of an electromagnetic wave are aligned in a single plane. After polarization, the electromagnetic wave becomes a plane wave (*).
Fig. 1. Polarization of a wave using a wire-grid polarizer.
The illustration above shows the phenomenon of electromagnetic wave polarization using a wire-grid polarizer, which is most commonly a polarizing film.
Light consists of electromagnetic wave oscillations occurring in various planes, represented in the image by red lines of varying intensity. The polarizer is oriented in such a way that it only allows waves oscillating in the vertical plane to pass through — shown as the most intense red line in the image. From that point on, the light becomes polarized.
To the human eye, polarized light is indistinguishable from unpolarized light.
In nature, polarized light is created through a process called reflection polarization, where light becomes naturally polarized when it strikes a reflective surface at a shallow angle. Such light no longer carries information about the shape and color of the object being viewed, but instead causes glare. This phenomenon is known as light glare. In everyday language, glare refers to any blinding reflected light.
Light glare is an undesirable phenomenon, and there are many ways to eliminate it. If the glare is caused by polarized light, it can be effectively reduced by placing a polarizing film in the path of the light beam, oriented in such a way as to “cross” the planes of polarization.
Wave Cancellation Using a Polarizer
Fig. 2. Cancellation of a polarized wave using a polarizer (polarizing film).
The glare will be eliminated, while the remaining light will pass through the film. This is the principle behind polarized sunglasses and polarizing filters for cameras.
(*) Only in the case of linear polarization – another type of polarization is circular polarization, where the plane wave additionally rotates during one wave period. Circular polarization is discussed in the article Circular Polarizing Film.