Optical system with reduced color shift

• US 6,535,333 B1
• Filed: 11/21/2000
• Issued: 03/18/2003
• Est. Priority Date: 11/21/2000
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Piepel, Andrew J., Boyd, Gary T., Moshrefzadeh, Robert S.
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): Cruz, Magda
• Application Number:
  US09/717,598
• Time in Patent Office: 847 Days
• Field of Search: 359/456, 359/453, 359/454, 359/455, 359/452, 359/460, 359/493, 359/502, 353/20, 353/84, 349/9
• US Class Current: 359/453
• CPC Class Codes: G03B 21/56 Projection screens

Abstract

An optical system with improved color shift characteristics is described. Preferably, the system comprises a rear projection display that includes a light source providing light in first and second distinct polarization states, and a beaded screen.

Claims

1. An optical system comprising:

an illumination source for providing light having a first polarization state associated with a first color and a second polarization state associated with a second color;

the first polarization state being distinct from the second polarization state,

a screen comprising;

a plurality of refractive elements arranged to provide the optical system with predetermined optical properties,

a light transmitting substrate,

a light absorbing layer associated with the light transmitting substrate for controlling ambient light rejection;

the illumination source and screen defining an optical path for the optical system; and

a polarized light management element, disposed in the optical path, for reducing the color shift of the optical system wherein the screen has a rear side and a viewing side and the polarized light management element comprises a color compensation coating on the rear side of the screen.

2. An optical system according to claim 1 wherein the first color is linearly polarized light and the second color is linearly polarized light.

3. An optical system according to claim 1 wherein the first color is green and the second color is a combination of red and blue (e.g. purple).

4. An optical system according to claim 1 wherein at least one of the first and second colors is a primary color.

5. An optical system according to claim 1 wherein the color compensation coating is a ¼

wave coating.

6. An optical system according to claim 1 wherein the color compensation coating has a non-uniform thickness.

7. An optical system according to claim 1 wherein the color compensation coating has a portion whose thickness is less than a ¼

wave thickness.

8. An optical system according to claim 1 wherein the illumination source provides light in:

a first linear polarization state associated with a first color;

a second linear polarization state associated with a second color; and

a third linear polarization state associated with a third color, wherein the first, second and third colors are different than each other and offset from each other.

9. A rear projection screen for use in an optical system having off-axis viewing angles and utilizing an illumination source that provides light having a first polarization state associated with a first color and a second polarization state associated with a second color;

the first polarization state being distinct from the second polarization state, the first and second colors having transmission intensities at off-axis viewing angles, the rear projection screen comprising;

a plurality of refractive elements; and

a polarized light management layer sized and shaped to reduce any difference in the relative transmission intensities of the first and second colors at off-axis viewing angles to reduce the color shift of the optical system

wherein the screen includes glass beads, and the screen exhibits an off-axis color shift of less than about 0.010 at off-axis viewing angles of sixty (60) or more degrees when measured according to the Color Shift Test.

10. A rear projection screen according to claim 9 wherein the polarized light management layer comprises a color compensation coating that reduces the color shift of the optical system due to light being provided with a first polarization state associated with a first color and a second polarization state associated with a second color that is distinct from the first polarization state.

11. A rear projection screen according to claim 10 wherein the color compensation coating is a ¼

wave coating.

12. A rear projection screen according to claim 10 wherein the color compensation coating has a non-uniform thickness.

13. A rear projection screen according to claim 10 wherein the color compensation coating has a portion whose thickness is less than a ¼

wave thickness.

14. A rear projection screen according to claim 9 wherein the screen includes glass beads, and the screen exhibits an off-axis color shift of less than about 0.010 at off-axis viewing angles of sixty (60) or more degrees when measured according to the Color Shift Test.

15. A rear projection screen according to claim 9 wherein the screen exhibits an off-axis color shift of less than about 0.005 at off-axis viewing angles of forty-five (45) or more degrees when measured according to the Color Shift Test.

16. A rear projection screen according to claim 9 wherein the polarized light management layer comprises a coating for at least partially altering the polarization state of at least one color.

17. A rear projection screen according to claim 16, further including a ¼

wave coating.

18. A rear projection screen according to claim 9, wherein the plurality of refractive elements comprises glass beads and the polarized light management layer receives light prior to the glass beads.

19. A rear projection screen according to claim 9, wherein the polarized light management layer comprises more than one layer.

20. A rear projection screen according to claim 9, wherein the screen includes a light absorbing layer associated with the light transmmitting substrate for controlling ambient light rejection and a light transmitting substrate.

21. An optical system comprising:

an illumination source for providing light having a first polarization state associated with a first color and a second polarization state associated with a second color;

the first polarization state being distinct from the second polarization state,

a screen comprising;

a plurality of refractive elements arranged to provide the optical system with predetermined optical properties,

a light transmitting substrate,

a light absorbing layer associated with the light transmitting substrate for controlling ambient light rejection wherein the screen is a beaded screen that exhibits an off-axis color shift of about 0.010 or less at off-axis viewing angles of sixty (60) or more degrees when measured according to the Color Shift Test;

the illumination source and screen defining an optical path for the optical system; and

a polarized light management element, disposed in the optical path, for reducing the color shift of the optical system.

22. An optical system comprising:

an illumination source for providing light having a first polarization state associated with a first color and a second polarization state associated with a second color;

the first polarization state being distinct from the second polarization state,

a screen comprising;

a plurality of refractive elements arranged to provide the optical system with predetermined optical properties,

a light transmitting substrate,

a light absorbing layer associated with the light transmitting substrate for controlling ambient light rejection;

the illumination source and screen defining an optical path for the optical system; and

a polarized light management element, disposed in the optical path, for reducing the color shift of the optical system

wherein the optical system exhibits an off-axis color shift of about 0.005 or less at off-axis viewing angles of forty-five (45) or more degrees when measured according to the Color Shift Test.

23. A rear projection screen for use in an optical system having off-axis viewing angles and utilizing an illumination source that provides light having a first polarization state associated with a first color and a second polarization state associated with a second color;

the first polarization state being distinct from the second polarization state, the first and second colors having transmission intensities at off-axis viewing angles, the rear projection screen comprising;

a plurality of refractive elements; and

a polarized light management layer sized and shaped to reduce any difference in the relative transmission intensities of the first and second colors at off-axis viewing angles to reduce the color shift of the optical system wherein the optical system exhibits an off-axis color shift about 0.005 or less at off-axis viewing angles of forty-five (45) or more degrees when measured according to the Color Shift Test.