What is Polarization?

Polarization is a property of light, or other electromagnetic radiation, that is primarily understood through studying the waves of the radiation. It was discovered by Etienne Louis Malus, a French physicist in the early 1800s. Visible light is the range of electromagnetic radiation that humans can see, and its wavelengths have a range from about 380 to 740 nanometers. Electromagnetic radiation is radiation that is produced by electric and magnetic fields that travel together at the speed of light through space.

Light has been described as being comprised of two sets of transverse waves that are at right angles to each other. These two sets of waves represent the electric and magnetic segments of radiation. Although polarization can be quite complex, it can better understood using simple examples.

It is sometimes easiest to consider this property if only one of the two sets of waves is considered — the electric set. In unpolarized light, waves are in a jumble of directions. The waves have many different orientations around the direction that the light is going. Each wave is represented by an arrow that is at a right angle to the direction that the wave is moving; however, one arrow may point sideways, one may point upwards, and another may point downwards.

Although unpolarized light may be chaotic, polarization has the opposite effect. Polarized light has the orientation of all the arrows pointing in the same direction. Regardless of which direction the arrows may face, all the arrows follow suit, exactly.

Some scientists may mention circularly polarized light. In that case, the arrow representing the waves of light still exists, but it rotates as the wave moves along. Some have compared the arrow depicting the waves of circularly polarized light to a hand of a clock — rotating around and around as the wave advances.

Polarization is also produced naturally in some instances, such as when light passes through particular crystals or through artificial material designed to create this effect. Polarized sunglasses, for example, work by only letting vertical polarized light in. They are popular among outdoors enthusiasts and people who wish to reduce the glare from the sun.

Radio transmission and receiver antennas also are polarized, and one of the most common uses of this property is in radar. AM and FM radios use vertical polarization while televisions use horizontal polarization. Interestingly, these two directions alternate with the use of satellite communications — even for television use. A satellite can carry two distinct transmissions of a frequency and double the amount of customers that can be served.