Compact Edge Illuminated Diffractive Display

Abstract

There is provided a projection display device comprising: a light source, an SBG device comprising a multiplicity of separately SBG elements sandwich between transparent substrate to which transparent electrodes have been applied. The substrates function as a light guide. A least one transparent electrode comprises plurality of independently switchable transparent electrodes elements, each electrode element substantially overlaying a unique SBG element. Each SBG element encodes image information to be projected on an image surface. Light coupled into the light guide, undergoes total internal reflection until diffracted out to the light guide by an activated SBG element. The SBG diffracts light out of the light guide to form an image region on an image surface when subjected to an applied voltage via said transparent electrodes.

1 .- 17 . (canceled) 
     
     
         18 . A backlight unit for illuminating a display panel, said backlight unit comprising:
 a first light source emitting light of a first wavelength;   a waveguide supporting a first plurality of switchable Bragg grating (SBG) elements disposed in a single layer; and   a coupler for directing said first wavelength light into a total internal reflection path within said waveguide, each SBG element having a diffracting state and a non-diffracting state,   wherein when each SBG element is in its diffracting state, the SBG element diffracts said first wavelength light to form an illumination region of predefined geometry and luminance distribution on a surface of the display panel.   
     
     
         19 . The backlight unit of  claim 18 , wherein said waveguide comprises transparent substrates sandwiching said SBG layer, wherein transparent electrodes for applying electric fields across said SBG elements are disposed on opposing faces of said substrates, and wherein at least one of said transparent electrodes comprises a plurality of independently switchable transparent electrode elements, each of independently switchable electrode element substantially overlays a unique SBG element. 
     
     
         20 . The backlight unit of  claim 18 , wherein said diffracting state exists when no electric field is applied across said unique SBG element and said non diffracting state exists when an electric field is applied across said unique SBG element. 
     
     
         21 . The backlight unit of  claim 18 , wherein said SBG element encodes wavefront and phase information corresponding to said geometry and said luminance distribution. 
     
     
         22 . The backlight unit of  claim 21 , wherein said surface of said display panel is at least one selected from the group of: a surface spatially displaced along a direction normal to a total internal reflection surface of said waveguide; a light diffusing surface; and a curved surface. 
     
     
         23 . The backlight unit of  claim 19 , wherein said first plurality of SBG elements contains at least one infrared diffracting SBG element operative to diffract infrared light from said infrared source towards said surface when said infrared diffracting SBG element is switched from its non-diffracting state to its diffracting state. 
     
     
         24 . The backlight unit of  claim 18 , further comprising:
 a second light source emitting light of a second wavelength;   a third light source emitting light of a third wavelength;   a second plurality of SBG elements and a third plurality of SBG elements,   wherein the second plurality of SBG elements and the third plurality of SBG elements are disposed in substantially overlapping layers,   wherein each SBG element of said second plurality of SBG elements diffracts said second wavelength light to form a second illumination region of predefined geometry and luminance distribution on said surface when subjected to an applied voltage,   wherein each SBG element of said third plurality of SBG elements diffracts said third wavelength light to form a third illumination region of predefined geometry and luminance distribution on said surface when subjected to an applied voltage, and   wherein said elements of said second and third pluralities of SBG elements encode wavefront and phase information corresponding to said predefined geometry and luminance distribution.   
     
     
         25 . The backlight unit of  claim 24 , wherein said first, second, and third illumination regions substantially overlap. 
     
     
         26 . The backlight unit of  claim 24 , wherein each of said first, second and third pluralities of SBG elements are configured in rows and columns of a rectangular array and are switched sequentially into their diffracting states in bands comprising at least one row of SBG elements, wherein at least one band of SBG elements in each of said first, second and third pluralities of SBG elements is activated at any instant, wherein no overlap exists between said bands of said first, second and third plurality of SBG elements. 
     
     
         27 . The backlight unit of  claim 18 , further comprising at least one selected from the group consisting of a despeckler or an eye tracker. 
     
     
         28 . The backlight unit of  claim 18 , wherein said first light source is a laser or a light emitting diode. 
     
     
         29 . The backlight unit of  claim 18 , wherein said coupler is a grating or a prism. 
     
     
         30 . The backlight unit of  claim 18 , further comprising at least two SBG elements having differing grating vectors. 
     
     
         31 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least two SBG elements with identical optical characteristics. 
     
     
         32 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least one selected from the group consisting of an SBG element operative to convert incident collimated light into divergent light, an SBG element operative to convert incident light into diffuse light, an SBG element with optical power, or an SBG element that pre-distorts the shape of said illumination region. 
     
     
         33 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least one SBG element with a first phase retarding characteristic under a first voltage and a second phase retarding characteristic under a second voltage. 
     
     
         34 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least one SBG element with a first light diffusing characteristic under a first voltage and a second light diffusing characteristic under a second voltage. 
     
     
         35 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least one SBG element having a first diffraction efficiency under a first voltage and a second diffraction efficiency under a second voltage. 
     
     
         36 . The backlight unit of  claim 18 , wherein the first plurality of SBG elements comprise at least one SBG element operative to diffract light out of said total internal reflection path through one of said substrates into one of a predefined set of output light paths when said at least one SBG element is in its diffracting state. 
     
     
         37 . The backlight unit of  claim 18 , wherein said first light source provides red, green and blue light and the first plurality of SBG elements comprise SBG elements optimized to diffract red, green and blue light.