Optimally clocked trim retarders

1. A liquid crystal display based projection system comprising:

a light source;

a first polarizer for receiving light from the light source and transmitting a first linearly polarized light having a first linear polarization axis; a liquid crystal display panel for optically modulating the first linearly polarized light, the liquid crystal display panel having a slow-axis and a fast-axis;

a second polarizer for receiving the optically modulated light and for transmitting a second linearly polarized light having a second linear polarization axis;

a projection lens for projecting the second linearly polarized light onto a screen; and

a trim retarder disposed between the liquid crystal display panel and at least one of the first and second polarizers, the trim retarder having an in-plane retardance greater than a residual in-plane retardance of the liquid crystal display panel and having a slow axis, an azimuthal angle of the slow axis selected to be in an azimuthal angle range predetermined to provide a system contrast level that is substantially unaffected by at least one of an orientation of the slow axis of the liquid crystal display panel and orientations of the first and second polarizers.

2. The liquid crystal display based projection system according to claim 1 , wherein the liquid crystal display panel is a transmissive liquid crystal display panel.

3. The liquid crystal display based projection system according to claim 1 , wherein the liquid crystal display panel is a reflective liquid crystal display panel, the first and second linear polarization axes are orthogonal, and the first and second polarizers comprise a same polarization beamsplitter.

4. The liquid crystal display based projection system according to claim 3 , wherein the polarization beamsplitter is a MacNeille-type polarization beamsplitter cube.

5. The liquid crystal display based projection system according to claim 3 , wherein the polarization beamsplitter is a wire grid polarizer orientated at off-normal incidence.

6. The liquid crystal display based projection system according to claim 3 , wherein the liquid-crystal display panel comprises a vertically-aligned nematic liquid crystal on silicon (VAN-LCoS) panel.

7. The liquid crystal display based projection system according to claim 5 , wherein the liquid-crystal display panel comprises a vertically-aligned nematic liquid crystal on silicon (VAN-LCoS) panel.

8. The liquid crystal display based projection system according to claim 7 , comprising a pre-polarizer disposed for transmitting the first linearly polarized light to a first side of the wire grid polarizer and a clean-up polarizer for receiving the second linearly polarized light reflected from a second opposite side of the wire grid polarizer.

9. The liquid crystal display based projection system according to claim 7 , wherein the azimuthal angle range is predetermined to provide a substantially same system contrast level when the slow axis of the trim retarder is orientated to a first position for a first orientation of the liquid crystal display panel, to a second position for a second orientation of the liquid crystal display panel, to a third position for a third orientation of the liquid crystal display panel, and to a fourth position for a fourth orientation of the liquid crystal display panel, each of the first, second, third, and fourth orientations of the liquid crystal display panel having the slow axis of the liquid crystal display panel in a different quadrant.

10. The liquid crystal display based projection system according to claim 7 , wherein the azimuthal angle range is predetermined to provide a substantially same system contrast level when the slow axis of the trim retarder is orientated in a same position for mirrored orientations of the wire grid polarizer.

11. The liquid crystal display based projection system according to claim 9 , wherein the azimuthal angle is less than about 45 degrees from the first linear polarization axis.

12. The liquid crystal display based projection system according to claim 1 , wherein the azimuthal angle is less than about 45 degrees from the first linear polarization axis.

13. The liquid crystal display based projection system according to claim 1 , wherein the slow axis of the trim retarder is substantially parallel to the first linear polarization axis.

14. The liquid crystal display based projection system according to claim 1 , wherein the azimuthal angle range is determined in dependence upon the orientation of the slow axis of the liquid crystal display panel.

15. The liquid crystal display based projection system according to claim 9 , wherein the azimuthal angle range is determined in dependence upon the orientation of the slow axis of the liquid crystal display panel.

16. The liquid crystal display based projection system according to claim 15 , wherein the azimuthal angle range is predetermined to provide a system contrast level that is substantially unaffected by the off-normal orientation of the wire grid polarizer.

17. The liquid crystal display based projection system according to claim 15 , wherein the azimuthal angle range is in a quadrant that mirrors a quadrant containing the slow axis of the liquid crystal display panel about an axis perpendicular to the first linear polarization axis.

18. The liquid crystal display based projection system according to claim 17 , wherein the trim retarder is an asymmetric trim retarder.

19. The liquid crystal display based projection system according to claim 15 , wherein the trim retarder is a symmetric trim retarder, and wherein the azimuthal angle range is in one of a first quadrant that mirrors a quadrant containing the slow axis of the liquid crystal display panel about an axis perpendicular to the first linear polarization axis and a second quadrant rotated about 180.degree. from the first quadrant.

20. The liquid crystal display based projection system according to claim 5 , wherein the liquid crystal display panel is one of a plurality of liquid crystal display panels, the wire grid polarizer is one of a plurality of wire grid polarizers, and the trim retarder is one of a plurality of trim retarders, and wherein the azimuthal angle of the slow axis of each trim retarder in the plurality is substantially parallel to the first linear polarization axis.

21. The liquid crystal display based projection system according to claim 5 , wherein the liquid crystal display panel and the wire grid polarizer are part of a first color channel in the projection system, and wherein a second liquid crystal display panel and a second wire grid polarizer are part of a second color channel in the projection system, the wire grid polarizer being a minor image of the second wire grid polarizer, the liquid crystal display panel having a slow axis orientation substantially the same as a slow axis orientation of the second liquid crystal display panel.

22. The liquid crystal display based projection system according to claim 5 , wherein the azimuthal angle range is determined using one of four calculated over-clocking angles, and wherein the azimuthal range is selected to avoid calculated over-clocking angles corresponding to system contrast levels most dependent on the off-normal orientation of the wire grid polarizer.

23. The liquid crystal display based projection system according to claim 1 , wherein the azimuthal angle range is predetermined to provide a system contrast level that is substantially unaffected by the orientations of the first and second polarizers.

24. The liquid crystal display based projection system according to claim 1 , wherein the azimuthal angle range is predetermined to provide a system contrast level that is substantially unaffected by the orientation of the slow axis of the liquid crystal display panel.

25. A method of clocking a trim retarder comprising:

providing a first trim retarder to compensate for residual in-plane retardance of a first liquid crystal display panel in a liquid crystal display based projection system, the liquid crystal display based projection system including:

a light source;

at least one polarizer for receiving light from the light source, for transmitting a first linearly polarized light having a first linear polarization axis to the first liquid crystal display panel, and for receiving a second linearly polarized light having a second linear polarization axis from the first liquid crystal display panel; and,

a projection lens for projecting the second linearly polarized light onto a screen, the first trim retarder having an in-plane retardance greater than a residual in-plane retardance of the first liquid crystal display panel and having a slow axis, determining a first azimuthal angle range for an azimuthal angle of the slow axis of the first trim retarder, the first azimuthal angle range selected to provide a system contrast level that is substantially unaffected by at least one of an orientation of the slow axis of the first liquid crystal display panel and an orientation of the at least one polarizer; and orientating the first trim retarder such that the azimuthal angle of its slow axis is within the first azimuthal angle range.

26. A method according to claim 25 , comprising: providing a second trim retarder to compensate for residual in-plane retardance of a second liquid crystal display panel in the liquid crystal display based projection system, the second trim retarder having an in-plane retardance greater than the residual in-plane retardance of the second liquid crystal display panel and having a slow axis; determining a second azimuthal angle range for an azimuthal angle of the slow axis of the second trim retarder, the second azimuthal angle range selected to provide said system contrast level; and orientating the second trim retarder such that the azimuthal angle of its slow axis is within the second azimuthal angle range.

27. A method according to claim 25 , comprising: providing a second trim retarder to compensate for residual in-plane retardance of a second liquid crystal display panel in another liquid crystal display based projection system, the second trim retarder having an in-plane retardance greater than the residual in-plane retardance of the second liquid crystal display panel and having a slow axis; determining a second azimuthal angle range for an azimuthal angle of the slow axis of the second trim retarder, the second azimuthal angle range selected to provide said system contrast level; and orientating the second trim retarder such that the azimuthal angle of its slow axis is within the second azimuthal angle range.

28. A method according to claim 25 , wherein the at least one polarizer comprises a wire grid polarizer, the wire grid polarizer having a first side for receiving the light from the light source, and a second opposite side for transmitting the first linearly polarized light, for receiving the optically modulated light, and for reflecting the second linearly polarized light.

29. A method according to claim 28 , wherein the first liquid-crystal display panel comprises a vertically-aligned nematic liquid crystal on silicon (VAN-LCoS) panel.

30. A method according to claim 28 , wherein determining the first azimuthal angle range includes calculating four possible over-clocking angles and selecting the first azimuthal angle range to exclude over-clocking angles that provide system contrast levels most dependent on the orientation of the wire grid polarizer.

31. A method according to claim 28 , wherein determining the first azimuthal angle range includes calculating four possible over-clocking angles and selecting the first azimuthal angle range to exclude over-clocking angles that provide system contrast levels most dependent the orientation of the first liquid crystal display panel.

32. A method according to claim 28 , wherein determining the first azimuth angle range includes selecting the first azimuthal angle range to be between 0 and 44.degree. from the first linear polarization axis.

33. A method according to claim 27 , wherein the first and second trim retarders are fabricated with substantially the same parameters.

34. A method according to claim 25 , wherein determining the first azimuthal angle range includes selecting the first azimuthal angle range to provide substantially the same system contrast level for configurations having mirrored orientations of the at least one polarizer and a same liquid crystal display panel slow axis orientation.

35. A method according to claim 25 , wherein determining the first azimuthal angle range includes selecting the first azimuthal angle range to provide a system contrast level that is substantially obtainable for four different slow axis quadrant orientations of the liquid crystal display panel.