3D Television Technology

Polarization of Light

The photographs below were taken with the same camera of the same image, yet look very different. The picture on the right is darker, and many of the objects (notably the clouds) are much sharper. What illusion could cause such a change? The answer is that a polarized filter was used for the photograph on the right. Aside from simply increasing contrast in pictures of clouds, polarization has many unique applications; from communication antennas to trapping atoms to, of course, 3D movies and television.

The photograph on the right differs from the left only by using a polarized filter, greatly altering the brightness and contrast of the picture.[1]

Light is an electromagnetic wave composed of a electric and magnetic fields perpendicular to the direction the light itself travels. Since the light travels in a straight line, the electric field can point anywhere in the 360 degree range that is perpendicular to the light's propagation. The direction the electric field points defines the polarization of the light.

There are three types of polarization: linear, circular and elliptical, relating to how the electric field vector of the electromagnetic wave changes with time. Linearly polarized light has an electric field which is confined to one direction, oscillating back and forth with no rotation. The direction of polarization is defined by which direction the electric field vector points. If two beams of linearly polarized light have electric field vectors which are perpendicular to one another, they are said to be orthogonal, a fancy word meaning they have no overlapping components.

Linearly polarized light, which has an electric field vector (represented by arrows) which stays in one plane.[2]

For circularly polarized light, the electric field has constant amplitude and rotates in time. Circular polarization may be either left-handed or right-handed, depending on which way the electric field rotates. A left-handed and right-handed beam are also said to be orthogonal. Elliptical polarization is in between; while the electric field does rotate, the amplitude is not constant along the rotation. Both linear and circular polarization schemes are special cases of elliptical polarization, however they are by far the two most important forms of polarized light.

 
Left-handed (left) and right-handed (right) circularly polarized light, with the arrows representing the electric field vector.[2]

Light from the sun is unpolarized; each beam has a polarization, but there is no consistency in which direction the light is polarized. This is why polarized sunglasses block out a portion of the light instead of blocking out different amounts of light depending on how your head is tilted. However, to test polarization easily, one can take advantage of the fact that light from an LCD source, such as a laptop screen, is linearly polarized.

It is possible to check for and manipulate polarization with devices known as polarizers, devices described on their own page. Through use of these polarizers, a wide range of applications for polarization become apparent, including creating a 3D effect.