Illumination system for transmissive light valve displays

• US 6,560,018 B1
• Filed: 10/20/1995
• Issued: 05/06/2003
• 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:
  US08/545,990
• Time in Patent Office: 2,755 Days
• Field of Search: 359/566, 359/569, 359/571, 359/567, 359/615, 359/894, 359/900, 359/575, 348/761, 348/791, 348/61, 348/62, 348/106, 348/108, 348/110, 348/57, 348/95, 349/61, 349/62, 349/106, 349/108, 349/110, 349/57, 349/95
• US Class Current: 359/569
• CPC Class Codes: G02B 27/0994 Fibers, light pipes optical fibers per se G02B6/02
• CPC Class Codes: G02B 5/02 Diffusing elements; Afocal elements
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• 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 28/55 with a dielectric comprising a perovskite structure material
• CPC Class Codes: H01L 28/60 Electrodes
• CPC Class Codes: H01L 28/75 comprising two or more layers, e.g. comprising a barrier layer and a metal layer
• 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

Binary optics are used in 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 display system comprising:

a light source for generating light along an optical path, said light having at least two spectral components to be employed in forming an image, each spectral component having a different wavelength region;

a masking element along the optical path of the light source having at least one aperture through which light from the light source is transmitted;

a multilevel optical phase element having a periodic structure optically coupled to light transmitted through the aperture, wherein each period has a number of discrete phase levels equal to the number of spectral components, and wherein one level is a reference level and each of the other levels has a physical depth that relates to the wavelength region of each of the spectral components by a set of independent, underdetermined equations that employ a fraction that is about equal to the reciprocal of the number of discrete phase levels, the phase element separating the spectral components of the light into a plurality of diffraction orders, whereby said multilevel optical phase element represents a binary phase grating for each of said spectral components, in which each discrete phase level corresponds to one of said spectral components; and

a display panel that receives the separated spectral components, the display panel having a plurality of controllable pixel elements that generate an image from the spectral components.

2. The display system of claim 1 wherein the masking element is a mask plate having an array of apertures.

3. The display system of claim 1 wherein the phase element is a diffractive optic element.

4. The display system of claim 1 wherein the spectral components comprise blue, green and red wavelength regions.

5. The display system of claim 1 wherein there are three spectral components, each light component corresponding to a different color of light.

6. The display system of claim 5 wherein the pixel elements include subpixels, each subpixel registered to the phase element so as to receive a respective color of light.

7. The display system of claim 1 further comprising a light pipe having the masking element aperture on an entry surface of the light pipe and the phase element optically coupled to an exit surface of the light pipe.

8. A liquid crystal transmission display system comprising:

a light source for generating light having a constant amplitude and a constant phase with a first transverse image plane, said light having at least two spectral components to be employed in illuminating a liquid crystal display panel, each spectral component having a different wavelength region;

a masking element having an array of apertures disposed at the first image plane, a first portion of the light passing through the apertures and a second portion of the light being blocked by he masking element such that the light forms a secondary wavefront having a constant amplitude and a varying phase at a second transverse image plane;

a multilevel optical phase plate disposed in the second image plane, the phase plate having a periodic structure, wherein each period has a number of discrete phase levels equal to the number of spectral components, and wherein one level is a reference level and each of the other levels has a physical depth that relates to the wavelength region of each of the spectral components by a set of independent, underdetermined equations that employ a fraction that is about equal to the reciprocal of the number of discrete phase levels, said phase plate separating the spectral components of the secondary wavefront of light into a plurality of diffractions orders, whereby said multilevel optical phase plate represents a binary phase grating for each of said spectral components, in which each discrete phase level corresponds to one of said spectral components; and

the liquid crystal transmissive display panel having a plurality of pixel elements, each pixel element including a plurality of subpixel elements, the display panel disposed in the path of the separated spectral components so that each spectral component impinges on a plurality of subpixels.

9. The display system of claim 8 further comprising a condenser lens disposed between the light source and the masking element to collimate the light from the light source.

10. The display system of claim 8 wherein the masking element includes a mirrored surface to reflect the second portion of the light.

11. The display system of claim 8 wherein the array of apertures is a one-dimensional array.

12. The display system of claim 11 wherein the apertures extend through at least about one-third of the illuminated area of the masking element.

13. The display system of claim 8 wherein the array of apertures is a two-dimensional array.

14. The display system of claim 13 wherein the apertures extend through at least about one-ninth of the illuminated area of the masking element.

15. A method of fabricating a diffractive optical element for a display panel comprising:

providing a matrix display panel having a plurality of pixel elements, each pixel element having a plurality of sub-pixels having an aperture area;

providing an optically transmissive substrate; and

forming a multilevel optical phase element with the optically transmissive substrate that diffracts light incident upon it into a plurality of diffraction orders and a plurality of spectral components having different wavelength regions within each diffraction order, the plurality of spectral components corresponding to the plurality of sub-pixels in each pixel element, the multilevel optical phase element having a periodic structure wherein each period has a number of discrete phase levels equal to the number of spectral components, and wherein one level is a reference level and each of the other levels has a physical depth that relates to the wavelength region of each of the spectral components by a set of independent, underdetermined equations that employ a fraction that is about equal to the reciprocal of the number of discrete phase levels, whereby said multilevel optical phase element represents a binary phase grating for each of said spectral components, in which each discrete phase level corresponds to one of said spectral components.

16. The method of claim 15 further comprising forming a lithographic mask and etching the optically transmissive substrate to form the periodic structure.

17. The method of claim 15 further comprising depositing material on the optically transmissive substrate to form the periodic structure.

18. The method of claim 15 wherein the forming step further comprises stamping the substrate with a mold.

19. The method of claim 15 wherein the step of providing an optically transmissive substrate comprises providing a plastic material molded to form a two dimensional grating structure.

20. The method of claim 15 further comprising direct writing the periodic structure on the optically transmissive substrate.