Diffraction Gratings With Tunable Efficiency

• US 20090296218A1
• Filed: 02/27/2006
• Published: 12/03/2009
• Est. Priority Date: 02/27/2006
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Ryytty, Pasi
• Granted Patent: US 8,363,298 B2
• Time in Patent Office: Days
• US Class Current: 359/573
• CPC Class Codes: G02B 26/005 based on electrowetting
• CPC Class Codes: G02B 5/1828 having means for producing variable diffraction controlling the direction of light by means of one or more diffracting elements G02B26/0808; acousto-optical elements G02F1/11, G02F1/33; electro- or magneto-optical diffraction G02F1/292, G02F1/2955

Abstract

The specification and drawings present a new method, apparatus and software product for modulation of the optical intensity using electro-wetting (EW) diffraction gratings in the electronic devices with an electrical control signal. The EW diffraction gratings can be components of an element (e.g., a display) of the electronic device. Applications may include but are not limited to color displays, projection displays, front illuminating displays, field sequential displays, auto-stereoscopic displays, etc. Also, applications in areas other than displays are possible.

Claims

1. An apparatus comprising:

a diffraction grating made of 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 an 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, for creating said electric field.

2. The apparatus of claim 1, wherein said electric field or said predetermined 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 or said predetermined 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 periodic lines of said diffraction grating have a rectangular, 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 the 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 an 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 an electric field, created in said uniform liquid layer, is smaller than a threshold electric field, and wherein said 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 is not removable from said air pocket area, and said air pocket area is filled by said uniform liquid layer by a predetermined value when an 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 said optical beam by an optical device, wherein said optical device comprises;

a diffraction grating made of 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 the 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 or said predetermined 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 or said predetermined 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 code, 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 periodic lines of said diffraction grating have a rectangular, 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.

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 an 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 an electric field, created in said uniform liquid layer, is smaller than a threshold electric field, and wherein said 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 is not removable from said air pocket area, and said air pocket area is filled by said uniform liquid layer by a predetermined value when an 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 made of 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 is configured not to enter an air pocket area formed below a top of said structure when there is no the 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

a component comprising said at least one optical device.

29. The electronic device of claim 28, wherein said element is a display, said optical device is a pixel of said display, and said optical intensity modulation signal is a video signal.

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

31. The electronic device of claim 28, further comprising:

at least one voltage driver, responsive to an intensity selection/modulation signal, configured to provide an electro-wetting control signal to an optical device in said component 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 desired level of the optical intensity; and

an optical intensity selector/switch, responsive to an optical intensity modulation/instruction signal, for providing an intensity selection signal in response to said optical intensity modulation instruction signal, wherein said intensity selection signal indicates a desired level of the optical intensity of reflected from or transmitted through said diffraction grating.

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

33. An apparatus, comprising:

diffraction means made of 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;

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 uniform liquid layer is disposed on said first surface of said diffraction means, wherein parameters of said apparatus are chosen such that;

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

said liquid means 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 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 electrical conducting formed on said second surface, for creating said electric field.

34. The apparatus of claim 33, wherein said liquid means is a uniform liquid layer, said diffraction means is a diffraction grating and said means for electrical conducting is a uniform liquid layer.