Color selective light modulators employing birefringent stacks

DETAILED DESCRIPTION The present invention provides a color selective polarization modulator and a high brightness color filter or display system.
Color separation is accomplished with nearly lossless retarder films, providing high color contrast between transmission and extinction, with steep transition slopes.
Each filter stage is a color selective light valve which varies the transmission (or reflection) of one color without modulating the complementary color.
A stage can switch between transmitting white (or black) and transmitting a filtered spectrum.
Two or more stages can be used in series, each stage independently controlling the transmission of a primary color.
In a preferred embodiment each stage can control the analog intensity control of the primary color at each pixel, thus eliminating the need for an external gray-scale pixelated display.
One preferred embodiment eliminates internal polarizers between stages, thereby providing a full-color display with only an input polarizing means and an output polarizing means.
The color selective polarization modulator can be for example an electro-optic or magneto-optic modulator having a modulation state of polarization and an isotropic state of polarization, and a retarder stack comprising one or more retarders.
The modulation state of polarization is an input polarization for which the transmitted state of polarization depends on the voltage applied to the modulator.
The isotropic state of polarization is an input polarization for which the transmitted state of polarization is substantially independent of the voltage applied to the modulator.
The retarder stack chromatically preconditions the light such that a first spectrum is placed in the modulation state of the modulator and a second, complementary, spectrum is placed in the isotropic state.
The modulator thereby modulates the state of polarization of the first spectrum, but leaves the polarization of the complementary spectrum substantially unmodulated.
In a preferred embodiment the spectra are additive and subtractive primary spectra