Diffractive waveguide providing structured illumination for object detection
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. Apparatus for projecting an image onto a surface comprising:
a first light source emitting light of a first wavelength;
first and second multiplicities of separately switchable grating elements;
transparent substrates sandwiching said grating elements providing a first light guide; and
a means for coupling said first wavelength light into a total internal reflection path in said first light guide,
each said grating element having a diffracting state and a non-diffracting state, wherein each element of said first multiplicity of grating elements when in its diffracting state diffracts said first wavelength light to form a focused first image region of predefined geometry and luminance distribution on said image surface,
wherein each element of said first multiplicity of grating elements encodes wave-front amplitude and phase information corresponding to said geometry and luminance distribution,
wherein each said element of said second multiplicity of grating elements provides a first unique speckle state under a first applied voltage and a second unique speckle state under a second applied voltage.
2. The apparatus of claim 1 , further comprising transparent electrodes applied to said substrates, at least one of said transparent electrodes comprising a plurality of independently switchable transparent electrode elements each overlaying a unique grating element, wherein said diffracting state exists when no voltage is applied across said grating element via said transparent electrodes and said non diffracting state exists when a voltage is applied across said grating element via said transparent electrodes.
3. The apparatus of claim 1 , wherein said switchable grating elements are Switchable Bragg Gratings.
4. The apparatus of claim 1 , further comprising second and third light sources emitting light of second and third wavelengths and means for coupling said second and third wavelength light into total internal reflection paths in said first lightguide, wherein said first multiplicity of grating elements comprises a multiplicity of grating elements for diffracting said first wavelength light and a multiplicity of grating elements for diffracting said second wavelength light, wherein said second and third wavelength light is diffracted into second and third focused image regions of predefined geometry and luminance distribution on said image surface.
5. The apparatus of claim 4 , wherein said first, second and third image regions substantially overlap.
6. The apparatus of claim 4 , wherein each of said first, second and third wavelength multiplicities of grating elements are configured in rows and columns of a rectangular array, wherein grating elements in each of said rectangular arrays are switched sequentially into their diffracting states in bands comprising at least one row of grating elements, wherein no overlap exists between first, second and third wavelength grating element bands switched into their diffracting states.
7. The apparatus of claim 1 , wherein said switchable grating elements are disposed in a single layer.
8. The apparatus of claim 1 , wherein said first multiplicity of switchable grating elements is disposed in a first layer and said second multiplicity of switchable grating elements is disposed in a second layer.
9. The apparatus of claim 1 , wherein the image surface is disposed in proximity to said display.
10. The apparatus of claim 1 , wherein the image surface is more than 50 centimeters from said display.
11. The apparatus of claim 1 , wherein one said image region comprises an image of a keyboard.
12. The apparatus of claim 1 , wherein said image region is an image pixel.
13. The apparatus of claim 1 , wherein said grating elements pre-distort the shape of said image region.
14. The apparatus of claim 1 , wherein said image surface is a diffusing material.
15. The apparatus of claim 1 , wherein said image surface is the retina of an eye.
16. The apparatus of claim 1 , wherein said image surface is curved.
17. The apparatus of claim 1 , further comprising: at least one infrared source; means for directing infrared light from said source towards said image surface and at least one infrared sensor operative to detect light scattered from an object disposed in proximity to said image surface.
18. The apparatus of claim 17 , wherein said infrared source is a laser.
19. The apparatus of claim 17 , wherein said infrared sensor comprises an image sensing array and lens.
20. The apparatus of claim 1 , wherein said first multiplicity of grating elements contains at least one infrared diffracting grating element operative to diffract infrared light from said infrared source towards said image surface when said infrared diffracting grating element is in its diffracting state.