Projecting images

• US 6,181,386 B1
• Filed: 12/17/1996
• Issued: 01/30/2001
• Est. Priority Date: 12/29/1995
• Status: Expired due to Fees

• Current Assignee: Duke University
• Original Assignee: Duke University
• Inventors: Knox, Richard M.
• Primary Examiner(s): LEE, MICHAEL
• Application Number:
  US08/767,967
• Time in Patent Office: 1,505 Days
• Field of Search: H04/M.572, H04/M.574, H04/M.931, 348/744, 348/756, 348/779, 348/780, 348/781, 348/786, 348/787, 348/789, 353/78, 353/74, 353/99, 353/77, 353/98, 353/37, 353/119, 353/20, 353/47, 353/50, 349/4, 349/5, 359/494, 359/630
• US Class Current: 348/788
• CPC Class Codes: G03B 21/10 Projectors with built-in or built-on screen
• CPC Class Codes: G03B 21/606 for relief projection
• CPC Class Codes: G06F 1/1601 Constructional details related to the housing of computer displays, e.g. of CRT monitors, of flat displays constructional details related to flat displays integrated in a portable computer, e.g. laptop, handheld computer G06F1/1637; constructional details related to television receivers H04N5/64
• CPC Class Codes: G09F 13/0422 Reflectors
• CPC Class Codes: G09F 2013/145 curved reflectors
• CPC Class Codes: H04N 5/7408 Direct viewing projectors, e.g. an image displayed on a video CRT or LCD display being projected on a screen
• CPC Class Codes: H04N 9/3141 Constructional details thereof details not peculiar to the presence of an electronic spatial light modulator G03B21/14
• CPC Class Codes: H04N 9/3147 Multi-projection systems displays in general H04N9/12; video walls G06F3/1446, G09G2300/026

Abstract

An “extra-folded” projection display system includes a selectively reflective material (e.g., a linear reflecting polarizer) placed immediately behind the system'"'"'s imaging screen. The display system includes an image projector that projects an image beam containing light of a predetermined linear polarization toward the imaging screen. The linear reflecting polarizer reflects the light in the image beam away from the screen. The reflected image beam then encounters a ¼-wavelength achromatic retarder which converts the linear polarization to circular polarization. The image beam next hits a mirror that reflects the light back through the ¼-wavelength achromatic retarder, which converts the circular polarization back to linear polarization, with the polarization director rotated 90° from the original polarization director. The linear reflecting polarizer then allows the light to pass through to the image screen.

Claims

1. An apparatus for displaying an image projected by an image source comprising:

an imaging screen,

a linear reflecting polarizer positioned in parallel with the imaging screen and substantially coextensive with the imaging screen,

an optical image path which reaches the linear reflecting polarizer twice on its way to the imaging screen, the linear reflecting polarizer at one time reflecting the image travelling along the optical path away from the imaging screen and at a different time transmitting the image onto the imaging screen, and

a retarder positioned such that the optical path reaches the retarder twice after the image is reflected from the linear reflecting polarizer, the retarder having an effective retardation of ½

wavelength for the two passes through the retarder.

2. The apparatus of claim 1 wherein the linear reflecting polarizer is affixed to the imaging screen.

3. The apparatus of claim 1 further comprising a linear absorption polarizer interposed across the optical path.

4. The apparatus of claim 1 further comprising a linear absorption polarizer interposed in the optical path between the image source and the linear reflecting polarizer.

5. The apparatus of claim 1 further comprising a reflective device located in the optical path prior to the linear reflecting polarizer.

6. The apparatus of claim 5 wherein the reflective device is a powered optical element.

7. The apparatus of claim 5 further comprising a second reflective device located in the optical path prior to the linear reflecting polarizer.

8. The apparatus of claim 7 wherein the second reflective device is a powered optical element.

9. The apparatus of claim 1 wherein the imaging screen has an outer periphery and the optical device, the optical path, and the image source are located within the outer periphery and behind the imaging screen.

10. The apparatus of claim 1 wherein the image source receives video data in the format of electrical signals.

11. The apparatus of claim 10 further comprising a computer including a video controller providing the video data to the image source.

20. The apparatus of claim 1 wherein the retarder is a ¼

wavelength retarder.

12. A method for displaying images in a projection display system, the method comprising:

projecting an image toward an imaging screen,

reflecting the image from a linear reflecting polarizer positioned in parallel and substantially coextensive with the imaging screen, and thereafter

reflecting the image back toward the imaging screen,

twice passing the image through a retarder, the retarder having an effective retardation of ½

wavelength for the two passes through the retarder, and

passing the image through the linear reflecting polarizer onto an imaging surface.

13. The method of claim 12 further comprising polarizing the image prior to reflection from the linear reflecting polarizer.

14. The method of claim 12 further comprising reflecting the image a first time prior to reflection from the linear reflecting polarizer.

15. The method of claim 14 wherein the first reflection is powered.

16. The method of claim 14 further comprising reflecting the image a second time prior to reflection from the linear reflecting polarizer.

17. The method of claim 16 wherein the second reflection is powered.

18. The method of claim 12 further comprising converting electrical signals providing video data to form the image which is projected.

21. The method of claim 12 wherein the retarder is a ¼

wavelength retarder.

19. A video display system comprising:

an image source that projects an image having light of a first linear polarization,

an imaging screen on which the image is to be displayed, and

along an optical path between the image source and the imaging screen;

a linear reflecting polarizer positioned parallel to, affixed to, and substantially coextensive with the imaging screen to reflect light having the first linear polarization and to transmit light having a second linear polarization orthogonal to the first linear polarization,

a reflective device positioned to redirect light reflected from the linear reflecting polarizer back toward the linear reflecting polarizer, and

a retarder positioned between the linear reflecting polarizer and the reflective device to rotate the polarization of the light reflected from the linear reflecting polarizer from the first linear polarization to the second linear polarization, the retarder having an effective retardation of ½

wavelength for the two passes through the retarder.