Method and apparatus for generating input images for holographic waveguide displays
An image generation device having: a spatial light modulator; a source of light; a beam deflector; an illumination waveguide and an image transport waveguide, each waveguide containing at least one switchable grating; and a coupler for directing scanned light into a first set of TIR paths in said illumination waveguide. A switchable grating in the illumination waveguide diffracts light onto the SLM, a switchable grating in the image transport waveguide diffracting image-modulated from the SLM into a waveguide path.
1. An image generation device comprising:
a spatial light modulator (SLM) having a light modulating surface;
a source emitting a first wavelength light;
a beam deflector for forming said first wavelength light into a scanned beam having a scanned beam angle;
an illumination waveguide containing at least one switchable grating disposed in at least one layer;
an image transport waveguide overlaying the light modulating surface of said SLM and containing at least one switchable grating disposed in at least one layer; and
a coupler for directing said scanned beam into a first set of total internal reflection (TIR) paths in said illumination waveguide,
said at least one switchable grating in said illumination waveguide diffracting light out of said first set of TIR paths onto said SLM,
said SLM modulating light diffracted from said illumination waveguide with image information that varies with the scanned beam angle to form image-modulated light and reflecting the image-modulated light through said illumination waveguide onto said image transport waveguide, and
said at least one switchable grating in said image transport waveguide diffracting said image-modulated light into a second set of TIR paths in said image transport waveguide.
2. The device of claim 1 wherein the at least one grating along said image transport waveguide defines a coupling aperture, wherein said coupling aperture defines a numerical aperture for each pixel of said SLM.
3. The device of claim 1 wherein at least one grating in said illumination waveguide and at least one grating in said image transport waveguide are switched into their diffracting states simultaneously.
4. The device of claim 1 wherein said switchable grating in said illumination waveguide comprises an array of elements each having a unique angular diffraction characteristic.
5. The device of claim 1 wherein said switchable grating in said image transport waveguide comprises an array of elements each having a unique angular diffraction characteristic.
6. The device of claim 1 wherein regions of said SLM are illuminated and updated with a new image information update corresponding to a field of view region of said image generation device cyclically, wherein at least one grating having high diffraction efficiency in said field of view region in said illumination waveguide and at least one grating having high diffraction efficiency in said field of view region in said image transport waveguide are switched into their diffracting states synchronously with said new image information updates.
7. The device of claim 1 wherein a collimating lens is disposed between said illumination waveguide and said image transport waveguide.
8. The device of claim 1 further comprising a source emitting second wavelength light wherein said illumination grating waveguide and said image transport waveguide each contain at least one grating for diffracting said first wavelength light and at least one grating for diffracting second wavelength light, wherein said SLM displays first wavelength image information when said first wavelength diffracting gratings are in their diffracting states, and wherein said SLM displays second wavelength image information when said second wavelength diffracting gratings are in their diffracting states.
9. The device of claim 1 wherein said image transfer waveguide provides an optical path to a waveguide display device.
10. The device of claim 1 further comprising a lossy grating operative to provide a spatial variation of intensity across said beam.
11. The device of claim 1 wherein said coupler comprises a prism or grating.
12. The device of claim 1 wherein said SLM, said illumination waveguide and said image transport waveguide are configured in a stack.
13. The device of claim 1 further comprising a despeckler.
14. The device of claim 1 wherein said switchable grating layers are recorded in one of a holographic polymer dispersed liquid crystal (HPDLC) reverse mode, or HPDLC uniform modulation.
15. The device of claim 1 wherein said source is a laser or light emitting diode (LED).
16. The device of claim 1 wherein said SLM is a liquid crystal device.
17. A method of generating a wave guided image comprising the steps of:
providing a SLM, an illumination waveguide containing at least one switchable grating layer, an image transport waveguide containing at least one switchable grating layer, a laser module, a micro mirror and a coupler;
said micro-mirror sweeping light from said laser module, through a defined angular range the light being injected into the illumination waveguide;
switching a switchable Bragg grating (SBG) layer in the illumination waveguide to diffract light onto the SLM; and
switching a SBG layer in the image transport waveguide to diffract light reflected from the SLM into a waveguide path in the image transport waveguide.
18. The method of claim 17 wherein at least one grating in said illumination waveguide and at least one grating in said image transport waveguide are switched into their diffracting states simultaneously.
19. A method of generating a wave guided image comprising the steps of:
providing a SLM, an illumination waveguide containing at least one switchable grating layer, an image transport waveguide containing at least one switchable grating layer, a laser module, a micro mirror and a coupler;
the micro-mirror sweeping light from said laser module through a defined angular range the light being injected into the illumination waveguide;
sequentially update regions of the SLM with image information;
switching a switchable Bragg grating (SBG) layer in the illumination waveguide to diffract light onto a region of the SLM; and
switching a SBG layer in the image transport waveguide to diffract light reflected from the SLM into a waveguide path in the image transport waveguide.
20. The method of claim 18 wherein simultaneously at least one grating in said illumination waveguide is switched into a first diffracting state and least one grating in said image transport waveguide is switched into a second diffracting state and a region of said SLM is updated with image information.