Modulation optical system including a compensator conditioning oblique and skew rays
View Patent ↗A projection display apparatus ( 10 ) uses a modulation optical system ( 200 ) that includes a liquid crystal device ( 210 ) in combination with a wire grid polarization beamsplitter ( 240 ), a wire grid polarization analyzer ( 270 ) and a projection lens ( 285 ) to form an image. In order to achieve high contrast and maintain high brightness levels, a compensator ( 260 ) is provided for minimizing leakage light for pixels in the black (OFF) state. A number of configurations are possible, such as with the compensator ( 260 ) disposed in the optical path between the liquid crystal device ( 210 ) and the wire grid polarization beamsplitter ( 240 ) and with a secondary compensator ( 265 ) disposed between wire grid polarization analyzer ( 270 ) and the wire grid polarization beamsplitter ( 240 ).
1. A modulation optical system for providing high contrast modulation of an incident light beam, comprising:
(a) a wire grid pre-polarizer for pre-polarizing said beam of light;
(b) a transmissive liquid crystal device for selectively modulating said polarized beam of light having to encode image data thereon in order to form a modulated beam;
(c) a wire grid polarization analyzer which transmits said modulated beam and blocks light of the opposite polarization; and
(d) a compensator located between said wire grid pre-polarizer and said wire grid polarization analyzer which conditions oblique and skew rays.
2. The system of claim 1 wherein said compensator comprises one or more birefringent layers, wherein said birefringent layers comprise at least one of the following; an A-plate film, a C-plate film, or a biaxial film.
3. The A-plate according to claim 2 wherein the optical axis of said A-plate is substantially parallel to sub-wavelength wires of said wire grid polarization analyzer.
4. The A-plate according to claim 2 wherein the optical axis of said A-plate is substantially perpendicular to sub-wavelength wires of said wire grid polarization analyzer.
5. The system of claim 1 wherein a reflective liquid crystal device has a vertically aligned construction.
6. The apparatus of claim 1 wherein the polarization axis orientation of said wire grid pre-polarizer is perpendicular to the polarization axis orientation of said wire grid polarization analyzer.
7. The apparatus of claim 1 wherein the polarization axis orientation of said wire grid pre-polarizer is parallel to the polarization axis orientation of said wire grid polarization analyzer.
8. The system of claim 1 wherein said compensator is located between said transmissive liquid crystal device and said wire grid polarization analyzer.
9. The system of claim 1 wherein said compensator is located between said wire grid pre-polarizer and said transmissive liquid crystal device.