Circular Polarizers

The 3D glasses used in the movies, such as "Star Wars," utilize circular polarization. Circular polarization is more robust than linear polarization. Polarization refers to the direction of the electric field in a light wave. Does it stay aligned in a certain direction? Then it is linear polarization. Does it spiral to the left or to the right? Then it is circular polarization.

Circular polarizers are made of a linear polarizer and a quarter wave plate. The linear polarizers are behind the quarter wave plate on these glasses. The linear polarizers let horizontal polarization through.

In the figures above the inside linear polarizers face one another. When the polarizers are parallel, as in the figure above left, light passes through. When they are orthogonal, as in the figure above right, the light is blocked.

When the glasses are moved so that the quarter wave plates face one another, there is no blockage of light when the orientation changes. Note that the right lens on each is used.

Above both glasses face the same direction. When both are upright or when one is inverted, the sequence of optical elements is quarter wave plate, horizontal linear polarizer, quarter wave plate, and horizontal linear polarizer. This tends to always have a component of radiation which will make it through the system.

When the quarter wave plates face one another, light is blocked by a left circular polarizer (left lens) facing a right circular polarizer (right lens). When the glasses are inverted, a right circular polarizer faces a right circuar polarizer and light transmits.

The reason for the two circular polarizations is that each eye can be given the proper perspective with respect to the other for the 3D effect.