This invention provides chromaticity compensation for color filters having nematic liquid crystal tuning elements, as well as fast-transition tuning units for use in combination with chromaticity compensation. The filters of this invention have two stages formed by three linear polarizers in series, as least two of which are color polarizers. Within each stage is a tuning unit comprising a nematic liquid crystal cell switchable between a first state wherein the polarization of light is orthogonally transformed and a second state wherein the polarization is unchanged. In the first state the liquid crystal cell chromaticity introduces significant distortion to the filter stage, but in the second state it does not. Chromaticity compensation is achieved in this invention by optimizing the use of the undistorted normal states and by judicious choice of the design wavelengths of the liquid crystal cells. This invention further provides compound tuning units, for use in the chromaticity compensating filter, that allow the use of fast unenergized-to-energized transitions in switching between three primary colors. A first embodiment of the compound tuning unit uses a half-wave bias retarder oriented at .+-.45.degree. in combination with the nematic liquid crystal cell. A second embodiment of the compound tuning unit uses two nematic liquid crystal cells. A third embodiment of the compound tuning unit uses a half-wave bias retarder oriented at about .+-.67.degree. or .+-.23.degree. in combination with the nematic liquid crystal cell.
A color shutter, comprising first, second and third polarizers, first and second retarders, first and second polarizing rotators, and at least one absorption type partial polarizer. The color shutter is constructed such that the first retarder is arranged between the first polarizer and the second polarizer, that the second retarder is arranged between the second polarizer and the third polarizer, that the first polarizing rotator is arranged between the first polarizer and the second polarizer, that the second polarizing rotator is arranged between the second polarizer and the third polarizer, at least one of the first polarizing rotator and the second polarizing rotator is arranged in a manner to be sandwiched between the second polarizer and the first or second retarder, that the absorption type partial polarizer is arranged between the first polarizing rotator and the first retarder and/or between the second polarizing rotator and the second retarder, and that the transmitted light can be changed into the three primary colors of RGB by selecting the voltage applied to the first and second polarizing rotators.
This invention provides achromatic liquid crystal compound retarders, achromatic polarization switches, and achromatic shutters using the liquid crystal compound retarders. It further provides achromatic variable retardance smectic liquid crystal retarders. The compound retarder of this invention comprises a central liquid crystal retarder unit and two external passive retarders positioned in series with and on either side of the liquid crystal retarder unit. The liquid crystal retarder unit comprises either (1) a rotatable smectic liquid crystal half-wave retarder or (2) first and second liquid crystal variable retarders having retardance switchable between zero and half-wave. The external passive retarders are equal in retardance and orientation to each other. Design equations determine the retardance of the external elements and their orientation relative to the central retarder to obtain a particular achromatic retardance for the compound structure.
This invention provides achromatic compound retarders, achromatic polarization switches, and achromatic shutters using the liquid crystal compound retarders. It further provides achromatic variable retardance smectic and nematic liquid crystal retarders. The achromatic compound retarders according to the invention are used to create achromatic inverters for display applications. The display comprises one or more retarders having in-plane retardance and in-plane orientation, at least one of the retarders being an actively controlled liquid crystal retarder, and a ferroelectric liquid crystal display, wherein the one or more retarders work in combination with the ferroelectric liquid crystal display to provide four states of brightness.
Projection display systems for light valves such as liquid crystal display panels, and in particular to the use of color component rotators, such as retardation filters, to provide for improved projection display architectures.
