Polarization (also polarisation) is a property of waves that describes the orientation of their oscillations. Electromagnetic waves such as light, along with other types of wave, exhibit polarization.
By convention, the polarization of light is described by specifying the direction of the wave's electric field. When light travels in free space, in most cases the polarization propagates as a transverse wave—the polarization is perpendicular to the wave's direction of travel. In this case, the electric field may be oriented in a single direction (linear polarization), or it may rotate as the wave travels (circular or elliptical polarization). In the latter cases, the oscillations can rotate rightward or leftward in the direction of travel, and which of those two rotations is present in a wave is called the wave's chirality or handedness.
Light itself are a form of electromagnetic waves that are emitted by a light source. A single light source usually emits electromagnetic waves of different shapes and orientations – for example, the light emitted by a projector moves into a specific direction while the electromagnetic waves move up and down or left and right along that direction.
Polarization filters also called polarizers are optical instruments that work like an "optical fence" – they only permit light of a defined orientation to pass. If non-polarized light hits a polarizer, only those light waves that are in alignment with the optical fence are allowed to pass through. All other light is filtered out. The light that has passed the filter is called polarized and all light waves oscillate in along a single plain.
Thus, if a linear polarization filter is turned by 90 degrees, light that was able to pass through it before is blocked and other light waves can now pass the filter.
In the case of passive 3D stereo projections, polarizers are mounted on the projectors such that the orientation of the polarization of the filters is orthogonal to each other (i.e. at an angle of 90 degrees). The same applies to the 3D stereo glasses worn by the spectator. The polarization of the glasses is identical to the polarization angle of the filters mounted on the projectors. This is how passive 3D stereo projections ensure that the left eye only sees the picture projected by the left projector and vice versa.
Whenever polarizers are used, some of the light of the projector is blocked from reaching the screen. Thus these filters always reduce the brightness of the projection. In general the following holds: The higher the degree of the transmission of the polarizer, the brighter the projection of the picture. Leveraging coated filters is advantageous – they improve transmission.
|left linear filter||right linear filter||Note|
|\||/||Standard "V-shaped" oriantation for 3D Glasses: left eye at -45°, right eye at -45°|
|--|||||Used by Russian "ETUD"-Projector, part of the FED Camera System|
A linear polarizing filter followed by a quarter-wave plate, whose slow and fast axes are at 45° to the axis of the polarizer, becomes a circular polarizing filter and incident unpolarized light emerges as circularly polarized light. This will not work if the order of the polarizer and wave plate is reversed. A quarter-wave plate converts circularly polarized light into linearly polarized light.
Depending on the orientation of the linear polarized part of the circular polarizer, there are slight differences between the filter types. Various companies use different systems:
|left linear component||right linear component||Note|
|--||--||RealD, where left and right filter is oriented horizontal = 0°|
|/||/||Zalman 22" monitor, where linear orientation is +45°|
|\||\||Acer Notebook, where filter orientation is -45°|
|||||||not used yet
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