Compensated color management systems and methods
View Patent ↗Beamsplitters are frequently used in projectors based on reflective liquid crystal display for separating input and output light, and more recently for color management systems. Rather stack filters are used in such systems to orthogonally polarize primary colors, converting polarizing beamsplitters to color splitters and combiners. Geometric polarization rotations induced by beamsplitters at moderate f-numbers have the effect of significantly degrading performance. Because retarder stacks in general rely on a specific input polarization to perform properly, such skew rays are responsible for color cross-talk. Retarder stacks designed according to the present invention are sensitive to the symmetries that exist between input and output polarizer configurations. These stacks provide the polarization transformations that will compensate for skew rays, such that normal incidence performance is maintained for all incident light.
1. An optical filter comprising:
at least three retarders,
wherein the at least three retarders act as a half wave plate to light of a first spectrum; and
wherein the at least three retarders act as a half wave plate with a π/4 displaced optical axis to light of a second spectrum.
2. The optical filter of claim 1 , wherein the at least three retarders act as a half wave plate with an orientation of 0° in the first spectrum and 45° in the second spectrum.
3. The filter of claim 1 , wherein the at least three retarders have wavelength stable half wave retardation and wavelength stable eigenpolarization in at least one of the first spectrum and the second spectrum.
4. The filter of claim 1 , wherein the at least three retarders are achromatic in the first spectrum and the second spectrum.
5. The filter of claim 1 , further comprising a first beam splitter in optical series with the at least three retarders.
6. The filter of claim 5 , wherein the first beam splitter is a polarizing beam splitter.
7. The filter of claim 5 , wherein the first beam splitter is a dichroic beam splitter.
8. The filter of claim 5 , wherein the first beam splitter is a partially metallized mirror beam splitter.
9. The filter of claim 5 , further comprising a second beam splitter in optical series with the at least three retarders and the first beam splitter.
10. The filter of claim 9 , wherein the first beam splitter and the second beam splitter have mutually orthogonal normal vectors.
11. The filter of claim 1 , further comprising:
a first beam splitter and a second beam splitter,
wherein the at least three retarders are between the first beam splitter and the second beam splitter; and
wherein skew light ray polarization effects of the first beam splitter are offset by skew light ray polarization effects of the at least three retarders and second beam splitter.
12. The filter of claim 1 , further comprising a color projection system.
13. The filter of claim 1 , wherein the at least three retarders are an out-of-plane uniaxial compensator.
14. The filter of claim 13 , wherein the at least three retarders have an optical axis θ between about 26.0° to 26.5°.
15. The filter of claim 1 , wherein the at least three retarders have a substantially wavelength stable eigenpolarization along a direction of a design axis of the at least three retarders.
16. An optical filter method, the steps of the method comprising:
retarding light of a first spectrum; and
retarding light of a second spectrum;
wherein a half wave of retardation is provided by the retarding light of the first spectrum; and
wherein a retardation equivalent to a half wave plate with a π/4 displaced optical axis is provided by the retarding light of the second spectrum.
17. The method of claim 16 , wherein the retarding light of the first spectrum and the retarding light of the second spectrum are achromatic.
18. The method of claim 16 , further comprising separating light into two different paths.
19. The method of claim 18 , wherein the separating is according to polarization.
20. The method of claim 18 , wherein the separating is according to light wavelength.
21. The method of claim 16 , further comprising:
a first separating of light into a first path and a second path;
a second separating of light into a third path and a fourth path;
wherein the optical retardation occurs after the first separating but before the second separating such that skew light ray polarization effects of the first separating are compensated by the optical retardation so as to match skew light ray polarization effects of the second separating.
22. The filter of claim 21 , wherein
the first path and the third path are parallel; and
the second path and fourth path are antiparallel.
23. The method of claim 16 , wherein the retarding light of the first spectrum and the retarding light of the second spectrum have substantially wavelength stable eigenpolarizations.