Planar optical waveguide based on two-dimensional optical gratings having 60° grating directions
A planar optical waveguide based on two-dimensional grating includes an optical waveguide substrate which is a transparent plane-parallel plate, and a functional grating element which includes a two-dimensional grating having two grating directions with an angle of 60° in between. The two-dimensional grating is either protruded or recessed into the top surface of the optical waveguide substrate. The output image from a micro-projector can enter the optical waveguide and then gets projected to cover the entire area of the functional grating element, enabling a human eye to view the output image across a large eye-box.
1. A planar optical waveguide, comprising:
an optical waveguide substrate which is a transparent plane-parallel waveguide, and
a functional grating element coupled to said optical waveguide substrate, wherein said functional grating element is a two-dimensional grating having two grating directions, wherein an angle between said two grating directions is 60°.
2. The planar optical waveguide, as recited in claim 1 , wherein said functional grating element is integrally formed on top of said optical waveguide substrate.
3. The planar optical waveguide, as recited in claim 1 , wherein said optical waveguide substrate has a top surface, wherein said two-dimensional grating is integrally protruded from said top surface of said optical waveguide substrate.
4. The planar optical waveguide, as recited in claim 3 , wherein the refractive index of said parallel waveguide is in the range of 1.4-2.2, and the thickness thereof is in the range of 0.3-2.5 mm.
5. The planar optical waveguide, as recited in claim 4 , wherein the period of the two-dimensional grating is in the range of 200-700 nm.
6. The planar optical waveguide, as recited in claim 1 , wherein said optical waveguide substrate has a groove at a top thereof, wherein said two-dimensional grating is formed in said groove of said optical waveguide substrate.
7. The planar optical waveguide, as recited in claim 1 , wherein the refractive index of said parallel waveguide is in the range of 1.4-2.2, and the thickness thereof is in the range of 0.3-2.5 mm.
8. The planar optical waveguide, as recited in claim 1 , wherein the period of the two-dimensional grating is in the range of 200-700 nm.
9. The planar optical waveguide, as recited in claim 1 , wherein said two-dimensional grating comprises a plurality of grating members arranged in an array, wherein each of said plurality of grating members of the two-dimensional grating is a cylindrical column.
10. The planar optical waveguide, as recited in claim 9 , wherein the diameter of said cylindrical column of each of said plurality of grating members of said two-dimensional grating is in the range of 50-650 nm, and the height thereof is in the range of 80-650 nm.
11. The planar optical waveguide, as recited in claim 1 , wherein said two-dimensional grating comprises a plurality of grating members arranged in an array, wherein each of said plurality of grating members of the two-dimensional grating is a diamond column, wherein the bottom cross section of said diamond column has a diamond shape.
12. The planar optical waveguide, as recited in claim 11 , wherein the side length of said diamond column of each of said plurality of grating members of said two-dimensional grating is in the range of 50-650 nm, and the height thereof is in the range of 80-650 nm.
13. The planar optical waveguide, as recited in claim 1 , wherein said functional grating element is preset with a fixed in-coupling position and have a plurality of out-coupling positions around said fixed in-coupling position, wherein each of said fixed in-coupling position and said plurality of coupling out pints comprises one or more grating members.
14. The planar optical waveguide, as recited in claim 13 , wherein each of said one or more grating members of said in-coupling position is a cylindrical column, wherein the diameter of each cylindrical column is in the range of 200-650 nm, and the height thereof is in the range of 200-650 nm.
15. The planar optical waveguide, as recited in claim 13 , wherein each of said one or more grating members of said in-coupling position is a diamond column, wherein the bottom cross section of said diamond column has a diamond shape, wherein the side length of each diamond column at said in-coupling position is in the range of 200-650 nm, and the height thereof is in the range of 200-650 nm.
16. The planar optical waveguide, as recited in claim 13 , wherein each of said one or more grating members of said in-coupling position is a cylindrical column, wherein the diameter of each of said one or more grating members of said in-coupling position is greater than the diameter of each of said one or more grating members of said out-coupling position, and the height of each of said one or more grating members of said in-coupling position is greater than the height of each of said one or more grating members of said out-coupling position.
17. The planar optical waveguide, as recited in claim 16 , wherein the diameters of said one or more grating members of said out-coupling position increase with the distance of said out-coupling position from said in-coupling position.
18. The planar optical waveguide, as recited in claim 13 , wherein each of said one or more grating members of said in-coupling position is a diamond column, wherein the bottom cross section of said diamond column has a diamond shape, wherein the side length of each of said one or more grating members of said in-coupling position is greater than the side length of each of said one or more grating members of said out-coupling position, and the height of each of said one or more grating members of said in-coupling position is greater than the height of each of said one or more grating members of said out-coupling position.
19. The planar optical waveguide, as recited in claim 18 , wherein the side lengths of said one or more grating members of said out-coupling position increase with the distance of said out-coupling position from said in-coupling position.
20. The planar optical waveguide, as recited in claim 13 , wherein the heights of said one or more grating members of said out-coupling position increase with the distance of said out-coupling position from said in-coupling position.