Efficient illumination system for color projection displays

• US 6,392,806 B2
• Filed: 03/10/1998
• Issued: 05/21/2002
• Est. Priority Date: 10/27/1994
• Status: Expired due to Term

• Current Assignee: Kopin Corporation
• Original Assignee: Kopin Corporation
• Inventors: Swanson, Gary J.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US09/038,197
• Publication Number:
  US 20010053027A1
• Time in Patent Office: 1,533 Days
• Field of Search: 359/567, 359/566, 359/568, 359/569, 359/571, 359/558, 359/900, 349/61, 349/62, 349/104
• US Class Current: 359/571
• 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: Y10S 359/90 Methods

Abstract

A method and system for providing an improved color image wherein a broad spectrum light is supplied to a phase grating which provides dispersed light having multiple diffraction orders. The dispersed light is supplied to a zero-order phase shifter which shifts the phase of the undiffracted (zero order) light relative to the diffracted light. The light from the phase shifter is thereupon concentrated so that the plane of the phase grating is imaged onto a display having a plurality of pixels assigned to transmit different spectral regions. The depths of the grating elements of each of the grating periods of the phase grating and the depth of the zero-order phase element of the phase shifter are selected to maximize the area of chromaticity space spanned by the different spectral regions at the display.

Claims

1. A method for displaying a color image comprising:

illuminating a multi-level optical phase element with light having a spectrum that includes at least three primary color components to disperse each of the primary color components of said light into a plurality of diffraction orders, the optical phase element having a separate level for each of the primary colors;

focusing the diffraction orders from the multi-level optical phase element with a lens onto a phase shift element which phase shifts undiffracted light with respect to diffracted light; and

imaging the plane of the multi-level optical phase element onto a pixellated liquid crystal display having a plurality of pixels such that selected pixels transmit different spectral regions.

2. A method in accordance with claim 1, concentrating different spectral regions of the light which illuminates said multi-level optical phase element at different subpixel regions of each pixel at the display;

and further including

maximizing the area of chromaticity space for the different spectral regions spanned at the display.

3. A method in accordance with claim 2, wherein said multi-level optical phase element includes a plurality of multi-level optical phase element periods each having a plurality of optical phase sub-elements of different selected depths and said phase shift element has a zero-order phase element having a selected depth and said maximizing includes

selecting the depths of the optical phase sub-elements at each of the multi-level optical phase element periods of the multi-level optical phase element and the depth of said zero-order phase element of said phase shift element so that the selected values thereof produce a maximizing of the area of chromaticity space.

4. A method in accordance with claims 3, wherein the depths of said optical phase sub-elements and said zero-order phase element are selected to lie within a range thereof which will permit the practical manufacture of said multi-level optical phase element and said phase shift element.

5. A method in accordance with claim 3, wherein the depths of the optical phase sub-elements at each of the multi-level optical phase element periods of said multilevel optical phase element are selected to approximate a selected fraction of the wavelengths of different spectral regions of the light.

6. A method in accordance with claim 1, wherein different spectral regions are red, green and blue regions of the spectrum and said imaging includes concentrating said red, green and blue spectral regions at different adjacent sub-pixel regions of each pixel at the display.

7. A method in accordance with claim 6, wherein said red, green and blue regions are concentrated at sub-pixel regions each of which occupies one-third of the corresponding overall pixel region.

8. A system for displaying a color image comprising:

a source of light having a spectrum including a plurality of primary color components;

a multi-level optical phase element illuminated by light from said source for dispersing each of the primary color components of said light into a plurality of diffraction orders, the optical element having at least three separate levels to separate the primary colors;

a phase shifter responsive to said dispersed light from said multi-level optical phase element for shifting undiffracted light thereof with respect to diffracted light thereof;

a first lens between the multi-level optical phase element and the phase shifter, the lens focusing light onto the phase shifter; and

a liquid crystal display that provides an image of the light from said source at an imaging plane having a plurality of pixels such that different spectral regions of the light from said source at the plane of said multi-level optical phase element are concentrated at said imaging plane so as to be imaged at different sub-pixel regions of each of said pixels at said imaging plane.

9. A system in accordance with claim 8, said system further including a second lens that receives light from the phase shifter to provide the image at said imaging plane.

10. A system in accordance with claim 8 or 9 wherein said multi-level optical phase element periods corresponding to a plurality of pixels at said imaging plane, each multi-level optical phase element period having a plurality of optical phase sub-elements with selected depths for different spectral regions of the received light and said phase shifter has a zero-order phase shift element of a selected depth, the depths of said optical phase sub-elements and said zero-order phase shift element being selected to maximize the area of chromaticity space spanned at the imaging plane.

11. A system in accordance with claim 10, wherein the depths of said optical phase sub-elements are selected to be selected fractions of the wavelengths of the spectral regions of the received light.

12. A system in accordance with claim 11, wherein optical phase sub-elements of the multi-level optical phase element corresponding to red, green and blue light regions of the spectrum have depths which are selected fractions of the wavelengths of said red, green and blue light regions.

13. A system in accordance with claim 8, wherein said source of light is a single source thereof.

14. A system in accordance with claim 13, wherein said single source is a tungsten halogen bulb.

15. The system of claim 13 wherein the single source comprises a xenon arc lamp.

16. A system in accordance with claim 8, wherein said source of light comprises three sources of red light, green light, and blue light, respectively.

17. A system in accordance with claim 16, wherein said three sources are light emiting diodes.

18. The system of claim 16 wherein the three sources comprise laser sources.