Laser illumination device
An Electrically Switchable Bragg Grating (ESBG) despeckler device comprising at least one ESBG element recorded in a hPDLC sandwiched between transparent substrates to which transparent conductive coatings have been applied. At least one of said coatings is patterned to provide a two-dimensional array of independently switchable ESBG pixels. Each ESBG pixel has a first unique speckle state under said first applied voltage and a second unique speckle state under said second applied voltage.
1. An ESBG despeckler apparatus comprising:
a first ESBG element for diffracting a first polarization illumination light incident along an input path and transmitting a second polarization illumination light incident along said input path without substantial deviation;
a second ESBG element for diffracting said first polarization light in a first direction into an output path and transmitting said second polarization light without substantial deviation into said output path;
a first reflecting surface;
a second reflecting surface; and
a third reflecting surface,
wherein, said first reflecting surface and said second reflecting surface reflecting second polarization light transmitted by said first ESBG element onto said second ESBG element in a direction parallel to said output path,
said third reflecting surface reflecting first polarization light diffracted by said first ESBG element into said first direction onto said second ESBG element,
each of said ESBG elements comprising at least one layer,
at least one said ESBG element containing a layer comprising a multiplicity of ESBG pixels, and
each said ESBG pixel having 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 wherein said first ESBG and said second ESBG lie in a common plane parallel to said third reflecting surface and said first and second reflecting surfaces are symmetrically disposed about a normal to said plane.
3. The apparatus of claim 1 wherein said layers are sandwiched between upper and lower transparent substrates, transparent conductive coatings applied to each said substrate, and at least one of said coatings being patterned into independently addressable elements overlapping said pixels.
4. The apparatus of claim 1 wherein at least one of said first, second and third reflecting surfaces each include wavelength selective reflecting layers.
5. The apparatus of claim 1 wherein said first, second and third reflecting surfaces are disposed on faces of a polygonal refractive medium.
6. The apparatus of claim 1 wherein said first polarization is P-polarization and said second polarization is S-polarization.
7. The apparatus of claim 1 wherein said first and second speckle states occur during the integration time of a human eye.
8. The apparatus of claim 1 wherein said first unique speckle state corresponds to a first unique diffracting state of said ESBG pixel and said second unique speckle state corresponds to a second unique diffracting state of said ESBG pixel, wherein said first and second diffracting states have diffraction efficiencies having values in a range extending from zero to unity.
9. The apparatus of claim 1 wherein said first and second voltages are points on a time varying voltage characteristic.
10. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels each having a unique grating vector.
11. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels operative to alter the angular characteristics of incident light.
12. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels with identical optical characteristics.
13. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels with a first phase retarding characteristic under said first voltage and a second phase retarding characteristic under said second voltage.
14. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels with a first light diffusing characteristic under said first voltage and a second light diffusing characteristic under said second voltage.
15. The apparatus of claim 1 wherein at least one ESBG element contains ESBG pixels with optical power.
16. The apparatus of claim 1 wherein said ESBG despeckler apparatus comprises identical first and second ESBG elements and waveforms applied to overlapping pixels of said first and second ESBG elements operate in anti-phase.
17. The apparatus of claim 1 wherein said ESBG despeckler apparatus comprises identical first and second ESBG elements and ESBG pixels from said first and second ESBG elements form an overlapping illumination beam cross section.
18. The apparatus of claim 1 wherein said first and second ESBG elements provide a two-dimensional array of independently switchable ESBG pixels forming a Hadamard diffuser.
19. The apparatus of claim 1 further comprising an external light source providing red, green and blue light, wherein at least one of the first and second ESBG elements comprise an ESBG optimized to diffract red, green and blue light.
20. The apparatus of claim 1 further comprising: a laser, a display panel, a projection lens and an image projection surface, cooperating with one another in an optical train.