3D Television Technology

Polarizers

Polarization of light can be shown simply with what is known as a polarizing sheet or polaroid. A polaroid is a sheet of film which only allows light of a certain linear polarization through. Holding a polaroid to natural light and rotating it will not result in any notable results, since the light is unpolarized. However, if you look through the polaroid at an LCD laptop screen (which emits linearly polarized light) and rotate the polaroid, the screen will dim and brighten, repeating the pattern twice in a full rotation. This can be seen in the animation below. Videos and applets showing polarization in action can be found here.

A light wave strikes a polaroid at various angles. If the polaroid is aligned parallel to the electric field, the light travels through the polaroid completely. If the polaroid is aligned 45 degrees to the electric field, the light through is reduced. However, if the polaroid is aligned perpendicular to the electric field vector, no light is seen behind the polaroid.

Another device used to manipulate polarized light is the wave retarder, which if properly configured can convert linearly polarized light to circularly polarized light and vice versa. The wave retarder works by slowing down the electric field in one direction, introducing whats known as a phase shift. This causes the shape the ray traces out to change. This can be seen in the image below. Note in the image below that, despite the polarization changing, the direction the light travels does not change, only the direction of the electric field vector.

Circularly polarized light striking a quarter wave plate (type of wave retarder) and becoming linearly polarized. The final linear polarizer shows that the light is indeed linearly polarized. The "left-handed" description of circular polarization describes how the electric field rotates. Arrows show the electric field vector.[1]

The best way to see how polarizers work isn't through animations, but through toying with the polaroid sheets in person. If you can grab a couple of polaroid sheets, or just want to see what the polaroids actually do, check out our videos section for some quick experiments. Be sure to take the quiz after!