Laser despeckler based on angular diversity
A device for reducing laser speckle using a micro scanner and a holographic diffuser. The micro scanner includes a first transparent optical substrate with an input surface and an output surface and a second transparent optical substrate with an input surface and an output surface and a variable refractive index medium sandwiched between the output surface of the first substrate and the input surface of the second substrate. Transparent electrodes are applied to the output surface of the first substrate and the input surface of the second substrate. The electrodes are coupled to a voltage generator. The input surface of the first substrate is optically coupled to a laser source. The input surface of the second substrate is configured as an array of prismatic elements. At least one of the input surface of the first substrate or the output surfaces of the second substrate is planar.
1. An illumination device comprising:
a first transparent substrate having an output surface;
a variable refractive index layer having an input surface and an output surface,
wherein said input surface of said refractive index layer overlays
said output surface of said first transparent substrate;
a second transparent substrate having an input surface, wherein said input surface of said second transparent layer overlays said output layer of said variable refractive index layer; and
a holographic diffuser,
wherein said output surface of said variable refractive index layer and said input layer of said second transparent substrate are each configured as a multiplicity of ray deflecting features to deflect incident light into a temporally varying random distribution of ray directions in a first predefined range of angles having a plurality of angles of deflection such that the plurality of angles of deflection are varied as a voltage applied across the variable refractive index is iteratively varied,
wherein each point in said holographic diffuser diffracts incident light rays of said first predefined range of angles into output light rays having a second predefined range of angles such that a diffuse illumination patch is produced at any surface intercepting said output light rays.
2. The illumination device of claim 1 , wherein said diffuse illumination patch is disposed in proximity to the surface of a microdisplay.
3. The illumination device of claim 1 , wherein said diffuse illumination patch is disposed in proximity to the surface of a projection screen.
4. The illumination device of claim 1 , wherein said holographic diffuser comprises a hologram of a scattering surface.
5. The illumination device of claim 1 , wherein said holographic diffuser comprises a multiplicity of holograms of scattering surfaces.
6. The illumination device of claim 1 , wherein said holographic diffuser is at least one of a Bragg hologram, a switchable Bragg grating, a computer generated hologram, a transmission hologram or a reflection hologram.
7. The illumination device of claim 1 , wherein said holographic diffuser encodes properties for varying the intensity distribution of incident light.
8. The illumination device of claim 1 , wherein said holographic diffuser encodes properties for shaping the cross sectional geometry of incident light.
9. The illumination device of claim 1 , wherein said holographic diffuser is an array of selectively switchable holographic elements.
10. The illumination device of claim 1 , further comprising a beam steering means.
11. The illumination device of claim 1 , further comprising at least one of a beamsplitter, a beam expander, a polarizer, a light integrator, a light guide, or a projection lens.
12. The illumination device of claim 1 , configured to illuminate a reflective microdisplay.
13. The illumination device of claim 1 , wherein incident light is provided by red, green and blue emitters.
14. The illumination device of claim 1 , wherein said ray deflecting features are polygonal.
15. The illumination device of claim 1 , wherein said ray deflecting features are pyramidic.
16. The illumination device of claim 1 , wherein said ray deflecting features have surface angles defined by a random distribution.
17. The illumination device of claim 1 , wherein said ray deflecting features are characterized by at least two different geometrical prescriptions.
18. The illumination device of claim 17 , wherein said geometrical prescriptions are distributed uniformly across said input surface of said second transparent substrate.
19. The illumination device of claim 1 , wherein said ray deflecting features have at least one light diffusing surface.
20. The illumination device of claim 1 , wherein electrodes are applied to each the output surface of the first substrate and the input surface of the second substrate, with at least one said electrode patterned into electrode elements for providing addressable regions of said variable refractive index layer, wherein the average refractive index of any of said addressable regions is proportional to a voltage applied across electrodes overlapping said regions, wherein said first range of angles is determined by the refractive index of said substrates and the average refractive index of said regions of said variable refractive index layer, wherein the voltage applied across each of said electrode elements is varied temporally.
21. The illumination device of claim 1 , wherein each ray deflecting feature is configured to output a bundle of light rays that overlaps with at least one other bundle of light rays outputted by another prismatic element.
22. The illumination device of claim 1 , wherein each the multiplicity of ray deflecting features is configured as an array of prismatic elements.