System and method for efficient illumination in color projection displays

• US 6,417,967 B1
• Filed: 05/17/1995
• Issued: 07/09/2002
• Est. Priority Date: 10/27/1994
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Swanson, Gary J.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US08/443,180
• Time in Patent Office: 2,610 Days
• Field of Search: 359/566, 359/569, 359/571, 359/567, 359/565, 359/900, 359/615, 348/761, 348/791, 348/760, 348/781, 345/88
• US Class Current: 359/567
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence
• CPC Class Codes: H01L 28/60 Electrodes
• CPC Class Codes: H04N 5/74 Projection arrangements for image reproduction, e.g. using eidophor
• CPC Class Codes: H04N 5/7441 the modulator being an array of liquid crystal cells
• CPC Class Codes: H04N 9/3108 by using a single electronic spatial light modulator
• CPC Class Codes: H04N 9/315 Modulator illumination systems general applications of lighting devices F21V; general optical systems G02B; lamp houses for projectors not peculiar to the presence of an electronic spatial light modulator G03B21/20
• CPC Class Codes: Y10S 359/90 Methods

Abstract

An illumination system for a color projection display. In one embodiment a broad spectrum light source illuminates a multilevel optical phase element which disperses the broad spectrum light from the light source by diffraction. A display having a number of pixel elements, each capable of transmitting a predetermined spectral region, is positioned within the near field region of the multilevel optical phase element so as to receive the light dispersed by the multilevel phase element.

Claims

1. A method for displaying a color image comprising the steps of:

illuminating a multilevel optical phase element with a light source having a plurality of wavelengths, said multilevel phase element dispersing light from said light source by diffraction and focusing the dispersed light onto an imaging plane; and

actuating a light modulating display in the imaging plane having a plurality of pixel elements, each said pixel element assigned to transmit a predetermined spectral region, within the near field region of said multilevel display element so as to receive said dispersed and focused light from said multilevel optical phase element,

said display being positioned at a distance Z from said multilevel optical phase element as determined by the relationship $\frac{T^2}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{2<br><br>T^2}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}$

with T being the periodicity of said multilevel optical phase element, λ

_Long being the longest wavelength of said plurality of wavelengths and λ

_Short being the shortest wavelength of said plurality of wavelengths.

2. The method of claim 1 further comprising providing a light source having a polychromatic spectrum.

3. The method of claim 1 further comprising providing a plurality of subsources each subsource having a different spectral distribution.

4. The method of claim 3 further comprising emitting light from each said subsource with a light emitting diode.

5. The method of claim 3 further comprising providing a laser as each said subsource.

6. The method of claim 1 further comprising providing a multilevel optical phase element that is multilevel in two othogonal directions.

7. The method of claim 1 wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship:

$\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}.$

8. The method of claim 1 wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship:

$\frac{T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}.$

9. A method for displaying a color image comprising the steps of:

focusing light, from a light source having a plurality of wavelengths, using a plurality of focusing elements that include a plurality of lenslets;

illuminating a multilevel optical phase element with light focused by said plurality of focusing elements, said multilevel phase element dispersing light from said plurality of focusing elements by diffraction and focusing the dispersed light onto an imaging plane; and

actuating a light modulating display in the imaging plane having a plurality of pixel elements, each said pixel element assigned to transmit a predetermined spectral region, so as to receive said dispersed light from said multilevel optical phase element, said display being positioned at a distance Z from said multilevel optical phase element as determined by the relationship;

$\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}$

with T being the periodicity of said multilevel optical phase element, Z_s being equal to the distance between said multilevel optical phase element and said lenslets minus the focal length of said lenslets, λ

_Long being the longest wavelength of said plurality of wavelengths, and λ

_Short being the shortest wavelength of said plurality of wavelengths.

10. The method of claim 9 wherein said display is positioned at a distance Z from said multilevel optical phase element as determined by the relationship:

$\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-T^2}<<br><br>Z<<br><br>\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}<br><br>Z_S-T^2}.$

11. The method of claim 9 wherein said multilevel optical phase element is constructed such that a magnification produced by said plurality of lenslets produces a dispersion element of a size substantially equal to the dimensions of each pixel element in said display.

12. The method of claim 11 wherein said magnification (M) is given by the equation:

$M=1+\frac{Z}{Z_s}$

wherein T is the periodicity of said multilevel optical phase element, Z_s is equal to the distance between said multilevel optical phase element and said lenslets minus the focal length of said lenslets and Z is the distance between said multilevel optical phase element and said display.

13. The method of claim 9 wherein said display is positioned at a distance Z from said multilevel optical phase element as determined by the relationship:

$\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}.$

14. A system for displaying a color image comprising:

a light source emitting a plurality of wavelengths;

a multilevel optical phase element positioned to receive light from said light source, said multilevel phase element dispersing light from said light source by diffraction and focusing the dispersed light onto an imaging plane; and

a light modulating electronic display positioned in the imaging plane and having a plurality of pixel elements, each said pixel element assigned to transmit a predetermined spectral region, positioned within the near field region of said multilevel optical phase element so as to receive said dispersed light from said multilevel phase element,

said display being positioned at a distance Z from said multilevel optical phase element as determined by the relationship;

$\frac{T^2}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{2<br><br>T^2}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}$

with T being the periodicity of said multilevel optical phase element, λ

_Long being the longest wavelength of said plurality of wavelengths, and λ

_Short being the shortest wavelength of said plurality of wavelengths.

15. The system of claim 14 wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship:

$\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}.$

16. The system of claim 14 wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship:

$\frac{T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}}<<br><br>Z<<br><br>\frac{T^2}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}}.$

17. The system of claim 14 wherein said light source has a polychromatic spectrum.

18. The system of claim 14 wherein said light source comprises a plurality of subsources each subsource having a different spectral distribution.

19. The system of claim 18 wherein each said subsource is a light emitting diode.

20. The system of claim 18 wherein each said subsource is a laser.

21. The system of claim 14 wherein said multilevel optical phase element is multilevel in two othogonal directions.

22. A system for displaying a color image comprising:

a light source having a plurality of wavelengths;

a plurality of focusing elements positioned to focus light from said light source;

a multilevel optical phase element positioned to receive light focused by said plurality of focusing elements, said multilevel phase element dispersing light from said plurality of focusing elements by diffraction and focusing the dispersed light onto an imaging plane; and

a light modulating electronic display positioned in the imaging plane and having a plurality of pixel elements, each said pixel element assigned to transmit a predetermined spectral region, positioned so as to receive said dispersed light from said multilevel optical phase element,

said plurality of focusing elements including a plurality of lenslets, said display being positioned at a distance Z from said multilevel optical phase element as determined by the relationship;

$\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}$

with T being the periodicity of said multilevel optical phase element, Z_s being equal to the distance between said multilevel optical phase element and said lenslets minus the focal length of said lenslets, λ

_Long being the longest wavelength of said plurality of wavelengths, and λ

_short being the shortest wavelength of said plurality of wavelengths.

23. The system of claim 22 wherein said display is positioned at a distance Z from said multilevel optical phase element as determined by the relationship:

$\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-T^2}<<br><br>Z<<br><br>\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Short}}<br><br>Z_S-T^2}.$

24. The system of claim 22 wherein said multilevel optical phase element is constructed such that a magnification produced by said plurality of lenslets produces an dispersion element substantially equal to the dimensions of each pixel element in said display.

25. The system of claim 24 wherein said magnification (M) is given by the equation:

$M=1+\frac{Z}{Z_s}$

wherein T is the periodicity of said multilevel optical phase element, Z is the distance between the multilevel phase element and said display and Z_s is equal to the distance between said multilevel optical phase element and said lenslets minus the focal length of said lenslets.

26. The system of claim 22 wherein said multilevel optical phase element is multilevel in two othogonal directions.

27. The system of claim 22 wherein said light source comprises a plurality of subsources each subsource having a different spectral distribution.

28. The system of claim 27 wherein each said subsource is a light emitting diode.

29. The system of claim 27 wherein each said subsource is a laser.

30. The system of claim 22 wherein said display is positioned at a distance Z from said multilevel optical phase element as determined by the relationship:

$\frac{T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}<<br><br>Z<<br><br>\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2<br><br>Z_S}{3<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{Long}}<br><br>Z_S-2<br><br>\text{\hspace{1em}<br><br>}<br><br>T^2}.$