Diffractive waveguide providing a retinal image
A projection display device comprising a light source and an SBG device having a multiplicity of separate SBG elements sandwiched between transparent substrates to which transparent electrodes have been applied. The substrates function as a light guide. A least one transparent electrode comprises a plurality of independently switchable transparent electrode 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. A transparent display for projecting image light onto a retina of an eye, said display comprising:
a light source emitting light of a first wavelength;
a lightguide supporting a first multiplicity of separately switchable Bragg grating (SBG) elements disposed in a single layer;
a given multiplicity of SBG elements, each SBG element in the given multiplicity of SBG elements projecting an image region on an image surface viewable through said display by said eye; and
a coupler for directing said first wavelength light into a total internal reflection path within said lightguide, each said switchable grating element of the first multiplicity having a diffracting state and a non-diffracting state;
wherein each said SBG element of the first multiplicity in its diffracting state diffracts said first wavelength light to form a focused image region of predefined geometry and luminance distribution on said retina.
2. The transparent display of claim 1 , wherein said lightguide comprises a pair of transparent substrates sandwiching said single layer of switchable grating elements, wherein at least one transparent electrode for applying electric fields across said SBG elements are applied to each of the opposing faces of said transparent substrates, at least one said transparent electrode comprising a plurality of independently switchable transparent electrode elements, each of said independently switchable electrode elements substantially overlaying a unique SBG element.
3. The transparent display of claim 1 , wherein said diffracting state exists when no electric field is applied across said first multiplicity of SBG elements and said non diffracting state exists when an electric field is applied across said first multiplicity of SBG elements.
4. The transparent display of claim 1 , wherein said first multiplicity of elements encodes wavefront and phase information corresponding to said geometry and said luminance distribution.
5. The transparent display of claim 1 , wherein said image surface is at least one selected from the group of: a surface spatially displaced along a normal to a total internal reflection surface of said lightguide; a surface spatially displaced by more than 50 centimeters along a normal to a total internal reflection surface of said lightguide; a light diffusing surface; a surface tilted relative to a total internal reflection surface of said lightguide; and a curved surface.
6. The transparent display of claim 1 , wherein said image region comprises an image pixel.
7. The transparent display of claim 1 , wherein said image region comprises an image of a keyboard.
8. The transparent display of claim 1 , wherein said first multiplicity of SBG elements pre-distort the shape of said image region.
9. The transparent display of claim 1 , further comprising: at least one infrared source; at least one optical element for directing infrared light from said source towards said retina; and at least one infrared sensor operative to detect light scattered from a surface disposed in proximity to said retina.
10. The transparent display of claim 9 , configured to project structured illumination towards said retina.
11. The transparent display of claim 9 , configured to project illumination towards said retina and detect light scattered from a surface disposed in proximity to said retina and further comprising an image processor containing a tracking algorithm based on analyzing changes in sequential image frames recorded by said infrared sensor.
12. The transparent display of claim 9 , wherein said infrared sensor comprises an array of photodetectors.
13. The transparent display of claim 9 , wherein said first multiplicity of SBG elements contains at least one infrared diffracting SBG element operative to diffract infrared light from said infrared source towards said retina when said infrared diffracting SBG element is subjected to an applied voltage via transparent electrodes.
14. The transparent display of claim 1 , further comprising:
a plurality of light sources emitting light of second and third wavelengths;
second and third multiplicities of SBG elements disposed in substantially overlapping layers;
each SBG element of said second multiplicity of SBG elements diffracting said second wavelength light to form a second focused image region of predefined geometry and luminance distribution on said retina when subjected to an applied voltage,
each SBG element of said third multiplicity of SBG elements diffracting said third wavelength light to form a third focused image region of predefined geometry and luminance distribution on an image surface when subjected to an applied voltage,
wherein said SBG elements of said second and third multiplicities of SBG elements encode wavefront and phase information corresponding to said geometry and said luminance distribution.
15. The transparent display of claim 14 , wherein said first image region, said second focused image region, and said third focused image region substantially overlap.
16. The apparatus of claim 14 , wherein each of said first, second and third multiplicities 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 switchable grating elements, wherein at least one band of SBG elements in each of said given, second and third multiplicities of SBG elements is activated at any instant, wherein no overlap exists between said first, second and third wavelength SBG element bands.
17. The transparent display of claim 1 , further comprising a despeckler.
18. The transparent display of claim 1 , wherein said source is a laser.
19. The transparent display of claim 1 , wherein said coupler is one of either a grating or a prism.