Diffraction gratings with tunable efficiency

1. An apparatus, comprising:

a diffraction grating comprising dielectric optical material with an index of refraction n and comprising a first surface with a structure having a structure height h and a structure period d, and a second surface; wherein the first surface is covered by hydrophobic material which reduces wettability of the diffraction grating for pre-selected liquids;

a uniform liquid layer with the index of refraction k comprised of one of said pre-selected liquids, wherein said indexes of refraction n and k are substantially equal, said uniform liquid layer is disposed on said first surface of said diffraction grating, wherein parameters of said apparatus are chosen such that:

said uniform liquid layer is configured not to enter an air pocket area formed below a top of said structure when there is no electric field created in said uniform liquid layer, and

said uniform liquid layer is configured to enter, by a predetermined value, said air pocket area formed below the top of said structure, due to a capillary effect and increased wettability of said first surface, when there is a predetermined electric field created in said uniform liquid layer, for changing a diffraction efficiency of the diffraction grating for varying an optical intensity of an optical beam transmitted or reflected by said diffraction grating; and

an electrode layer of electrically conducting material formed on said second surface, configured to create said electric field;

and means for varying said predetermined electric field, for further changing the predetermined value by which said uniform liquid layer enters said air pocket area causing a further change of the diffraction efficiency of the diffraction grating, therefore varying the optical intensity of the optical beam propagating through or reflected from the optical device.

2. The apparatus of claim 1 , wherein said electric field is created by applying a voltage between said uniform liquid layer and said electrode layer.

3. The apparatus of claim 1 , further comprising: a further electrode layer of electrically conducting material formed on a uniform liquid layer, wherein said electric field is created by applying a voltage between said further electrode layer and said electrode layer.

4. The apparatus of claim 1 , wherein said parameters of said apparatus comprise: said structure period d, a surface tension of liquid in the uniform liquid layer and the wettability of said hydrophobic material.

5. The apparatus of claim 1 , wherein said diffraction grating has a rectangular profile, a slanted profile or a smoothly varying wall profile according to a predetermined algorithm.

6. The apparatus of claim 1 , wherein said electrode layer is transparent to an optical beam.

7. The apparatus of claim 1 , wherein said uniform liquid layer is dyed with a predetermined optical color or a color filter is used in front of said uniform liquid layer such that the diffraction grating is configured to transmit only the optical beam with said predetermined color.

8. The apparatus of claim 1 , wherein said parameters of said diffraction grating are chosen such that said diffraction grating is configured to support only first and zero order transmission diffraction modes of the transmitted optical beam transmitted through said diffraction grating, wherein the zero order transmission diffraction mode component of said transmitted optical beam is blocked and the first order transmission diffraction mode component of said transmitted optical beam is directed towards a user of said apparatus.

9. The apparatus of claim 8 , wherein the optical intensity of said first order transmission diffraction mode component of said transmitted optical beam is varied by changing the diffraction efficiency of the diffraction grating by said electric field.

10. The apparatus of claim 1 , wherein said optical beam is received by the first surface of the diffraction grating before it is transmitted or reflected by said diffraction grating.

11. The apparatus of claim 1 , wherein air escapes from said air pocket area, and said air pocket area is completely filled by said uniform liquid layer when the electric field created in said uniform liquid layer exceeds a threshold electric field.

12. The apparatus of claim 1 , wherein air escapes from said air pocket area and said air pocket area is filled by said uniform liquid layer by a predetermined value when the electric field created in said uniform liquid layer is smaller than a threshold electric field, and wherein periodic lines of said diffraction grating have a smoothly varying wall profile according to a predetermined algorithm.

13. The apparatus of claim 1 , wherein air in said air pocket area cannot escape from said air pocket area, and said air pocket area is filled by said uniform liquid layer by a predetermined value when the electric field created in said uniform liquid layer is larger than a threshold electric field, and wherein said predetermined value is defined by an equilibrium condition using a pressure provided by said air in said air pocket.

14. A method, comprising:

receiving an optical beam by an optical device, wherein said optical device comprises:

a diffraction grating comprising dielectric optical material with an index of refraction n and comprising a first surface with a structure having a structure height h and a structure period d, and a second surface;

wherein the first surface is covered by hydrophobic material which reduces wettability of the diffraction grating for pre-selected liquids;

an electrode layer of electrically conducting material formed on said second surface, for creating an electric field;

a uniform liquid layer with the index of refraction k comprised of one of said pre-selected liquids, wherein said indexes of refraction n and k are substantially equal, said uniform liquid layer is disposed on said first surface of said diffraction grating, wherein parameters of said optical device are chosen such that:

said uniform liquid layer does not enter an air pocket area formed below a top of said structure when there is no electric field created in said uniform liquid layer, and

said uniform liquid layer enters, by a predetermined value, said air pocket area formed below the top of said structure, due to a capillary effect and increased wettability of said first surface, when there is a predetermined electric field created in said uniform liquid layer, for changing a diffraction efficiency of the diffraction grating for varying an optical intensity of an optical beam transmitted or reflected by said diffraction grating; and

varying said predetermined electric field, for further changing the predetermined value by which said uniform liquid layer enters said air pocket area causing a further change of the diffraction efficiency of the diffraction grating, therefore varying the optical intensity of the optical beam propagating through or reflected from the optical device.

15. The method of claim 14 , wherein said electric field is created by applying a voltage between said uniform liquid layer and said electrode layer.

16. The method of claim 14 , wherein said optical device comprises a further electrode layer of electrically conducting material formed on a uniform liquid layer, wherein said electric field is created by applying a voltage between said further electrode layer and said electrode layer.

17. A computer program product comprising: a computer readable storage structure embodying computer program code thereon for execution by a computer processor with said computer program, wherein said computer program code comprises instructions for performing the method of claim 14 .

18. The method of claim 14 , wherein said parameters of said optical device comprises said structure period d, a surface tension of liquid in the uniform liquid layer and the wettability of said hydrophobic material.

19. The method of claim 14 , wherein said diffraction grating has a rectangular profile, a slanted profile or a smoothly varying wall profile according to a predetermined algorithm.

20. The method of claim 14 , wherein said electrode layer is transparent to an optical beam.

21. The method of claim 14 , wherein said uniform liquid layer is dyed with a predetermined optical color or a color filter is used in front of said uniform liquid layer such that the diffraction grating only transmits the optical beam with said predetermined color.

22. The method of claim 14 , wherein said parameters of said diffraction grating are chosen such that said diffraction grating supports only first and zero order transmission diffraction modes of the transmitted optical beam transmitted through said diffraction grating, wherein the zero order transmission diffraction mode component of said transmitted optical beam is blocked and the first order transmission diffraction mode component of said transmitted optical beam is directed towards a user of said optical device.

23. The method of claim 22 , wherein the optical intensity of said first order transmission diffraction mode component of said transmitted optical beam is varied by changing the diffraction efficiency of the diffraction grating by said electric field.

24. The method of claim 14 , wherein said optical beam is received by the first surface of the diffraction grating before it is transmitted or reflected by said diffraction grating.

25. The method of claim 14 , wherein air escapes from said air pocket area and said air pocket area is completely filled by said uniform liquid layer when the electric field created in said uniform liquid layer exceeds a threshold electric field.

26. The method of claim 14 , wherein air escapes from said air pocket area, and said air pocket area is filled by said uniform liquid layer by a predetermined value when the electric field created in said uniform liquid layer is smaller than a threshold electric field, and wherein periodic lines of said diffraction grating have a smoothly varying wall profile according to a predetermined algorithm.

27. The method of claim 14 , wherein air in said air pocket area cannot escape from said air pocket area, and said air pocket area is filled by said uniform liquid layer by a predetermined value when the electric field created in said uniform liquid layer is larger than a threshold electric field, and wherein said predetermined value is defined by an equilibrium condition using a pressure provided by said air in said air pocket.

28. An electronic device, comprising:

at least one optical device, which comprises:

a diffraction grating comprising dielectric optical material with an index of refraction n and comprising a first surface with a structure having a structure height h and a structure period d, and a second surface;

wherein the first surface is covered by hydrophobic material which reduces wettability of the diffraction grating for pre-selected liquids;

an electrode layer of electrically conducting material formed on said second surface, configured to create an electric field;

a uniform liquid layer with the index of refraction k comprised of one of said pre-selected liquids, wherein said indexes of refraction n and k are substantially equal, said uniform liquid layer is disposed on said first surface of said diffraction grating, wherein parameters of said optical device are chosen such that:

said uniform liquid layer is configured not to enter an air pocket area formed below a top of said structure when there is no electric field created in said uniform liquid layer, and

said uniform liquid layer is configured to enter by a predetermined value said air pocket area formed below the top of said structure, due to a capillary effect and increased wettability of said first surface, when there is a predetermined electric field created in said uniform liquid layer, for changing a diffraction efficiency of the diffraction grating for varying an optical intensity of an optical beam transmitted or reflected by said diffraction grating,

and an optical intensity selector/switch configured to, in response to receiving an optical intensity modulation instruction signal, provide an intensity selection/modulation signal to at least one voltage driver, wherein said intensity selection/modulation signal indicates a predetermined level of the optical intensity reflected from or transmitted through said diffraction grating: and

wherein the at least one voltage driver is configured to, in response to receiving the intensity selection/modulation signal, provide an electro-wetting control signal to the optical device for providing an electric field applied between said uniform liquid layer and said electrode layer for varying said predetermined electric field and further changing the predetermined value by which said uniform liquid layer enters said air pocket area causing a further change of the diffraction efficiency of the diffraction grating, for varying the optical intensity of the optical beam propagating through or reflected from the optical device to provide said predetermined level of the optical intensity.

29. The electronic device of claim 28 , wherein said electronic device is a display, and said at least one optical device is a pixel of said display.

30. The electronic device of claim 28 , wherein said electronic device is a projection display, front illuminating display, a field sequential display or an auto-stereoscopic display.

31. The electronic device of claim 28 wherein the optical intensity selector/switch and the at least one voltage driver are combined in one block.

32. An apparatus comprising:

means for receiving an optical beam by an optical device, wherein said optical device comprises:

diffraction means comprising dielectric optical material with an index of refraction n and comprising a first surface with a structure having a structure height h and a structure period d, and a second surface;

wherein the first surface is covered by hydrophobic material which reduces wettability of the diffraction means for pre-selected liquids;

means for electrical conducting formed on said second surface, for creating an electric field;

liquid means with the index of refraction k comprised of one of said pre-selected liquids, wherein said indexes of refraction n and k are substantially equal, said liquid means is disposed on said first surface of said diffraction means, wherein parameters of said optical device are chosen such that:

said liquid means does not enter an air pocket area formed below a top of said structure when there is no electric field created in said liquid means, and

said liquid means enters, by a predetermined value, said air pocket area formed below the top of said structure, due to a capillary effect and increased wettability of said first surface, when there is a predetermined electric field created in said liquid means, for changing a diffraction efficiency of the diffraction means for varying an optical intensity of an optical beam transmitted or reflected by said diffraction means; and

means for varying said predetermined electric field, for further changing the predetermined value by which said liquid means enters said air pocket area causing a further change of the diffraction efficiency of the diffraction means, therefore varying the optical intensity of the optical beam propagating through or reflected from the optical device.

33. The apparatus of claim 32 , wherein said liquid means is a uniform liquid layer, said diffraction means is a diffraction grating and said means for electrical conducting is a an electrode layer of electrically conducting material.