System and method for efficient illumination in color projection displays

• US 6,791,756 B2
• Filed: 06/29/2001
• Issued: 09/14/2004
• Est. Priority Date: 10/27/1994
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Swanson, Gary J.
• Primary Examiner(s): Juba, Jr., John
• Application Number:
  US09/895,865
• Publication Number:
  US 20020093740A1
• Time in Patent Office: 1,173 Days
• Field of Search: 359/565, 359/566, 359/567, 359/569, 359/571, 359/615, 359/900, 348/760, 348/761, 348/781, 348/791, 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

A multilevel optical phase element is illuminated with a light source having a plurality of wavelengths of interest. The multilevel phase element disperses light from the light source by diffraction and focuses the dispersed light onto an imaging plane. A light modulating display in the imaging plane having a plurality of pixel elements is actuated. Each pixel element is assigned to transmit a predetermined spectral region within the near field region of the multilevel display element so as to receive the dispersed and focused light from the multilevel optical phase element. A system for displaying a color image includes a light source emitting a plurality of wavelengths of interest, a multilevel optical phase element, and a light modulating electronic display.

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 of interest, said multilevel phase element dispersing each wavelength of interest from said light source by diffraction into a plurality of diffraction orders and projecting 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, positioned within the near field region of said multilevel optical phase element so as to receive said dispersed and projected light from said multilevel phase element.

2. 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:

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

wherein T is the periodicity of said multilevel optical phase element, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

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

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

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

6. The method of claim 4 further comprising providing a laser as each said subsource.

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

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:

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

wherein T is the periodicity of said multilevel optical phase element, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

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

focusing light, from a light source having a plurality of wavelengths of interest, using a plurality of focusing elements, said plurality of focusing elements including a plurality of lenslets;

illuminating a multilevel optical phase element with light focused by said plurality of focusing elements, said multilevel phase element dispersing each wavelength of interest from said plurality of focusing elements by diffraction into a plurality of diffraction orders and projecting 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,

wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship;

$\frac{2<br><br>T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{long}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}<<br><br>Z<<br><br>\frac{2<br><br>T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{short}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}$

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, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

10. 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 substantially equal to the dimensions of each pixel element in said display.

11. The method of claim 10 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, and 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.

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

focusing light, from a light source having a plurality of wavelengths of interest, using a plurality of focusing elements, said plurality of focusing elements including a plurality of lenslets;

illuminating a multilevel optical phase element with light focused by said plurality of focusing elements, said multilevel phase element dispersing each wavelength of interest from said plurality of focusing elements by diffraction into a plurality of diffraction orders and projecting 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,

wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship;

$\frac{T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{long}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}<<br><br>Z<<br><br>\frac{T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{short}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}$

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, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

13. A apparatus for displaying a color image comprising:

a light source emitting a plurality of wavelengths of interest;

a multilevel optical phase element positioned to receive light from said light source, said multilevel phase element dispersing each wavelength of interest from said light source by diffraction into a plurality of diffraction orders and projecting 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.

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

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

wherein T is the periodicity of said multilevel optical phase element, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

15. The apparatus of claim 14 wherein said light source has a polychromatic spectrum.

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

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

wherein T is the periodicity of said multilevel optical phase element, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

17. The apparatus of claim 13 wherein said light source comprises a plurality of subsources each subsource having a different spectral distribution.

18. The apparatus of claim 17 wherein each said subsource is a light emitting diode.

19. The apparatus of claim 17 wherein each said subsource is a laser.

20. The apparatus of claim 13 wherein said multilevel optical phase element is multilevel in two orthogonal directions.

21. An apparatus for displaying a color image comprising:

a light source having a plurality of wavelengths of interest;

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

a multilevel optical phase element positioned to receive light focused by said plurality of focusing elements, said multilevel phase element dispersing each wavelength of interest from said plurality of focusing elements by diffraction into a plurality of diffraction orders and projecting 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,

wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship;

$\frac{2<br><br>T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{long}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T_s}<<br><br>Z<<br><br>\frac{2<br><br>T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{short}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T_s}$

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, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

22. The apparatus of claim 21 wherein said multilevel optical phase element is constructed such that a magnification produced by said plurality of lenslets produces a dispersion element substantially equal to the dimensions of each pixel element in said display.

23. The apparatus of claim 21 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 said multilevel optical 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.

24. The apparatus of claim 21 wherein said multilevel optical phase element is multilevel in two orthogonal directions.

25. The apparatus of claim 21 wherein said light source comprises a plurality of subsources each subsource having a different spectral distribution.

26. The apparatus of claim 25 wherein each said subsource is a light emitting diode.

27. The apparatus of claim 25 wherein each said subsource is a laser.

32. The apparatus of claim 21 wherein said light source comprises a plurality of subsources each subsource having a different spectral distribution.

33. The apparatus of claim 25 wherein each said subsource is a light emitting diode.

34. The apparatus of claim 25 wherein each said subsource is a laser.

28. An apparatus for displaying a color image comprising:

a light source having a plurality of wavelengths of interest;

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

a multilevel optical phase element positioned to receive light focused by said plurality of focusing elements, said multilevel phase element dispersing each wavelength of interest from said plurality of focusing elements by diffraction into a plurality of diffraction orders and projecting 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,

wherein said display is positioned at a distance Z from said multilevel optical phase element, wherein Z is determined by the relationship;

$\frac{T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{long}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}<<br><br>Z<<br><br>\frac{T^2<br><br>Z_s}{3<br><br>{\mathrm{\lambda <br><br>}}_{\mathrm{short}}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z_s-2<br><br>T^2}$

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, λ

_long is the largest wavelength of said plurality of wavelengths of interest and λ

_short is the shortest wavelength of said plurality of wavelengths of interest.

29. The apparatus of claim 28 wherein said multilevel optical phase element is constructed such that a magnification produced by said plurality of lenslets produces a dispersion element substantially equal to the dimensions of each pixel element in said display.

30. The apparatus of claim 29 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 said multilevel optical 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.

31. The apparatus of claim 28 wherein said multilevel optical phase element is multilevel in two orthogonal directions.