Prism for high contrast projection

• US 6,959,990 B2
• Filed: 12/31/2002
• Issued: 11/01/2005
• Est. Priority Date: 12/31/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Penn, Steven M.
• Primary Examiner(s): Dowling, William C.
• Application Number:
  US10/335,342
• Publication Number:
  US 20030151834A1
• Time in Patent Office: 1,036 Days
• Field of Search: 353/31, 353/81, 353/98, 353/99, 348/742, 348/743, 348/771, 359/831, 359/833, 359/834
• US Class Current: 353/81
• CPC Class Codes: G02B 5/04 Prisms
• CPC Class Codes: G02B 7/181 with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10

Abstract

Prism elements having TIR surfaces placed in close proximity to the active area of a SLM device 302 to separate unwanted off-state 324 and/or flat-state 326 light from the projection ON-light bundle 322. The TIR critical angle of these prisms is selected to affect either the off-state light or additionally, any portion of flat-state light reflected from the SLM. These TIR surfaces are placed to immediately reflect the unwanted light as it comes off the SLM, thereby preventing the contamination of light along the projection path, which tends to degrade the system contrast. To further improve the optical performance of the system, these TIR prisms can be attached directly to the SLM package 300, completely eliminating the package window. Also, these TIR prism can be coupled to DMDs having asymmetric mirrors, which tilt through a larger angle for the ON-light to provide high etendue and lumen output, but through near-zero degrees for the OFF-light, thereby improving the separation of any unwanted light from the off/flat states.

Claims

1. A prism assembly for use with projection systems, comprising:

a prism having a first side TIR surface with a critical angle, a second side TIR surface with a critical angle, and a third side;

a display panel mounted in close proximity to said third side of said prism;

incoming illumination entering through said first side of said prism, striking said second TIR surface on said second side of said prism at an angle greater than that of the critical angle of said second TIR surface, reflecting from said second TIR surface to the active surface of said display panel;

reflected light from ON pixels of said display panel passing through said prism, striking said first TIR surface on said first side of said prism at an angle greater than the critical angle of said first TIR surface, and reflecting out of said prism through said second side of said prism along a projection path;

light reflected from OFF pixels of said SLM striking said first TIR surface on said first side of said prism at an angle less than the critical angle of said TIR surface, passing through said first side of said prism into an optical heat sink; and

light reflected from flat-pixels, flat surfaces and edges in, around, and under said pixels of said SLM striking said first TIR surface on said first side of said prism at an angle less than the critical angle of said TIR surface, passing through said first side of said prism into an optical heat sink.

2. The prism assembly of claim 1, wherein said projection illumination passes through a single prism element and one display panel package window.

3. The prism assembly of claim 1, said third side of said prism forming a lid of a package enclosing said display panel.

4. The prism assembly of claim 1, wherein said display panel is a micromirror device.

5. The prism assembly of claim 4, wherein said micromirror device has symmetric micromirrors, which tilt the same number of degrees in both the positive and negative direction about a diagonal axis.

6. The prism assembly of claim 4, wherein said micromirror device has micromirrors which tilt x degrees in the positive direction and less than x degrees in the negative direction.

7. A display system comprising:

a light source providing illumination light along an illumination light path;

a first interface allowing said illumination light to pass and reflecting on state light from a display panel;

a second interface reflecting said illumination light and passing on state light, and

a third face passing said illumination light to said display panel and passing said on state light from said display panel.

8. The display system of claim 7, said first interface allowing off state light to pass.

9. The display system of claim 7, said first interface allowing flat state light to pass.

10. The display system of claim 7, said display panel comprising a micromirror device.

11. The display system of claim 7, said display panel comprising a micromirror device having an on state tilt angle greater than an off state tilt angle.

12. The display system of claim 7, comprising a color splitting prism between said third face and said display panel, wherein said display panel comprises three display panels.

13. The display system of claim 7, said third face forming a portion of a package enclosing said display panel.

14. The display system of claim 7, said third face forming a portion of a package enclosing said display panel comprising a micromirror device.

15. The display system of claim 7, said third face forming a portion of a package enclosing said display panel comprising a micromirror device having an on state tilt angle greater than an off state tilt angle.

16. An illumination prism comprising:

a first interface for allowing illumination light to pass and reflecting on state light from a display panel;

a second interface for reflecting said illumination light and passing on state light; and

a third face for passing said illumination light to said display panel and passing said on state light from said display panel.

17. The illumination prism of claim 16, said first interface allowing off state light from said display panel to pass.

18. The illumination prism of claim 16, said first interface allowing flat state light from said display panel to pass.

19. The illumination prism of claim 16, said third face forming a portion of a package enclosing said display panel.

20. The illumination prism of claim 16, said third face forming a portion of a package enclosing said display panel comprising a micromirror device.