Planar optical waveguide based on two-dimensional optical grating

Abstract

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.

Claims

1. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, wherein said predetermined angle between said grating directions is 60°.

2. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, wherein the period of the two-dimensional grating is in the range of 200-700 nm.

3. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, 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.

4. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, 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.

5. The augmented reality display, as recited in claim 3, 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.

6. The augmented reality display, as recited in claim 4, 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.

7. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, wherein said two-dimensional grating comprises one or more grating members and each of said one or more grating members 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.

8. An augmented reality display, comprising: a micro-projector for light output; and a planar optical waveguide configured for transporting the light output from said micro-projector, wherein said planar optical waveguide comprises 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 having a predetermined angle therebetween, wherein a refractive index of said parallel waveguide is in the range of 1.4-2.2 and a thickness of said parallel waveguide is in the range of 0.3-2.5 mm, wherein said two-dimensional grating comprises one or more grating members and each of said one or more grating members 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a planar optical waveguide based on two-dimensional grating according to a first preferred embodiment of the present invention.

(2) FIG. 2 is a top-down view illustrating the planar optical waveguide based on two-dimensional grating according to the above first preferred embodiment of the present invention, wherein each of the grating member of the two-dimensional grating is a cylindrical column.

(3) FIG. 3 is a top-down view illustrating light propagation inside the planar optical waveguide based on two-dimensional grating according to the above first preferred embodiment of the present invention.

(4) FIG. 4 is a schematic view illustrating the layout of operation unit of the planar optical waveguide based on two-dimensional grating according to the above first preferred embodiment of the present invention.

(5) FIG. 5 is a schematic view of a planar optical waveguide based on two-dimensional grating according to a second preferred embodiment of the present invention.

(6) FIG. 6 is a top-down view illustrating the planar optical waveguide based on two-dimensional grating according to the above first and second preferred embodiments of the present invention, wherein each of the grating member of the two-dimensional grating is a diamond column where its bottom cross section has a diamond shape.

(7) FIG. 7 is a top-down view illustrating the planar optical waveguide based on two-dimensional grating according to the above first and second preferred embodiments of the present invention, wherein each of the grating member of the two-dimensional grating is an elliptical column.

(8) FIG. 8 is a top-down view illustrating the planar optical waveguide based on two-dimensional grating according to the above first and second preferred embodiments of the present invention, wherein each of the grating member of the two-dimensional grating is a column where its bottom cross section has a side-etched diamond shape.

(9) FIG. 9 is a top-down view illustrating the planar optical waveguide based on two-dimensional grating according to the above first and second preferred embodiments of the present invention, wherein each of the grating member of the two-dimensional grating is a triangular column.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(10) The following description is disclosed to enable any person skilled in the art to make and use the present invention. Preferred embodiments are provided in the following description only as examples and modifications will be apparent to those skilled in the art. The general principles defined in the following description would be applied to other embodiments, alternatives, modifications, equivalents, and applications without departing from the spirit and scope of the present invention.

(11) Referring to FIG. 1 and FIG. 2, a planar optical waveguide based on a two-dimensional grating according to a first preferred embodiment of the present invention includes an optical waveguide substrate 1 and a functional grating element 2.

(12) The optical waveguide substrate 1 is a transparent plane-parallel plate which has two flat surfaces enclosing a volume of an optical material that transmits visible spectrum. The top surface 102 and the bottom surface 103 of the waveguide substrate are parallel. The thickness of the waveguide substrate is in the range of 0.3-2.5 mm, and the refractive index of the waveguide material is in the range of 1.4-2.2. Referring to FIG. 2, the functional grating element 2 is a two-dimensional grating with two grating directions D1 and D2 having an angle of 60° in between. The grating period T is in the range of 200-700 nm. The grating can be modulated in depth and shape in selected areas of the waveguide. The two-dimensional grating comprises a plurality of grating members 201 arranged in an array to define the two grating directions D1 and D2. FIG. 2 illustrates a case in which each grating member is cylindrical. As shown in FIGS. 6, 7, 8, and 9, grating member 201 of the two-dimensional grating may also have other shapes.

(13) Referring to FIG. 3, after the output image of the micro-projector 3 is projected onto any functional area of the grating, light is diffracted by the grating to generate four diffraction orders—b, c, d, and e—that are respectively propagating along four directions inside the plane-parallel waveguide. The incidence angles of the four beams on the waveguide surfaces are all greater than the critical angle required for total internal reflection, ensuring that the beams can propagate inside the plane-parallel waveguide without loss. When the beams of b, c, d and e are incident upon the functional grating element again, a portion of the light will be diffracted and coupled out of the plane-parallel waveguide, and the remaining portion of the light will be diffracted by the two-dimensional grating into three diffraction orders which keep propagating inside the waveguide substrate through total internal reflection. For instance, light b will be diffracted into orders f, g, and h, all three of which continue to propagate inside the planar optical waveguide. In this way, light can eventually be coupled out and the out-coupling footprint covers the entire functional grating area, and as a result the human eye 4 can see a complete and continuous image across a large eye-box.

(14) The two-dimensional grating in FIG. 1 is protruded from the top surface 102 of the plane-parallel waveguide. Referring to FIG. 5, the two-dimensional grating of the present invention may also be recessed into the top surface of the waveguide substrate 1.

Example 1

(15) As shown in FIGS. 1 and 2, the planar optical waveguide based on the two-dimensional grating of this example of the present invention includes an optical waveguide substrate 1 and a functional grating element 2.

(16) In this example, the optical waveguide substrate 1 is a plane-parallel glass plate with top surface 102 and bottom surface 103 being in parallel with each other. The thickness of the substrate is 0.5 mm. The refractive index of the substrate is 1.5.

(17) A two-dimensional grating, which comprises a plurality of grating members 201 embodied as cylindrical columns, with an angle of 60° between the two grating directions, a period T of 360 nm, a column diameter R of 100 nm, and a depth of 150 nm, is formed on the surface of the plane-parallel glass plate (optical waveguide substrate 1) to work as the functional structure.

(18) The optical waveguide is divided into 30 areas as shown in FIG. 4 with A to E along the vertical direction and 1 to 6 along the horizontal direction. The image projected out from the micro-projector 3 enters the optical waveguide through C5, and the image intensity is measured in the remaining areas. The normalized intensity results are shown in table 1.

(19) TABLE-US-00001 TABLE 1 Normalized image intensity of Example 1 1 2 3 4 5 6 A 0.5 0.6 0.7 0.8 0.7 0.8 B 0.6 0.65 0.75 1 0.8 1 C 0.65 0.7 0.8 0.9 In- 0.9 coupling D 0.6 0.65 0.75 1 0.8 1 E 0.5 0.6 0.7 0.8 0.7 0.8

Example 2

(20) As shown in FIGS. 1 and 2, the planar optical waveguide based on the two-dimensional grating of this example of the present invention includes an optical waveguide substrate 1 and a functional grating element 2.

(21) In this example, the optical waveguide substrate 1 is a plane-parallel glass plate with top surface 102 and bottom surface 103 being in parallel with each other. The thickness of the substrate is 1.9 mm. The refractive index of the substrate is 1.8.

(22) A two-dimensional grating, which comprises a plurality of grating members 201 embodied as diamond columns whose bottom cross section has a diamond shape, with an angle of 60° between the two grating directions, a period T of 450 nm, a side length of 200 nm, and a depth of 250 nm, is formed on the surface of the plane-parallel glass plate (optical waveguide substrate 1) to work as the functional structure.

(23) The optical waveguide is divided into 30 areas with A to E along the vertical direction and 1 to 6 along the horizontal direction. The image projected out from the micro-projector 3 enters the optical waveguide through C4, and the image intensity is measured in the remaining areas. The normalized intensity results are shown in table 2.

(24) TABLE-US-00002 TABLE 2 Normalized image intensity of Example 2 1 2 3 4 5 6 A 0.65 0.75 0.85 0.75 0.85 0.75 B 0.7 0.75 1 0.85 1 0.75 C 0.75 0.85 0.9 In- 0.9 0.85 coupling D 0.7 0.8 1 0.8 1 0.8 E 0.65 0.75 0.85 0.7 0.85 0.75

Example 3

(25) As shown in FIGS. 1 and 2, the planar optical waveguide based on the two-dimensional grating of this example of the present invention includes an optical waveguide substrate 1 and a functional grating element 2.

(26) In this example, the optical waveguide substrate 1 is a plane-parallel glass plate with top surface 102 and bottom surface 103 being in parallel with each other. The thickness of the substrate is 0.5 mm. The refractive index of the substrate is 1.5.

(27) A two-dimensional grating, which comprises a plurality of grating members 201 embodied as cylindrical columns, with an angle of 60° between the two grating directions, a period T of 360 nm, and a column diameter R of 100 nm, is formed on the surface of the plane-parallel glass plate (optical waveguide substrate 1) to work as the functional structure.

(28) The intensity of light propagating inside the optical waveguide gradually decreases along with continuous out-coupling by the two-dimensional grating, and thus the brightness of the output image gradually decreases along the direction of exit pupil expansion if the grating structure is non-variant. In order to solve the above problem, the column depths of the plurality of grating members 201 of the two-dimensional grating in different areas are controlled and modulated so that the brightness of the output image across the grating area is relatively uniform. More specifically, the optical waveguide is divided into 30 areas with A to E along the vertical direction and 1 to 6 along the horizontal direction, in which gratings are manufactured with column depths shown in table 3.

(29) TABLE-US-00003 TABLE 3 Column depths of two-dimensional gratings of Example 3 1 2 3 4 5 6 A 250 nm 200 nm 170 nm 140 nm 120 nm 140 nm B 200 nm 170 nm 140 nm 120 nm 100 nm 120 nm C 200 nm 170 nm 140 nm 120 nm 250 nm 120 nm D 200 nm 170 nm 140 nm 120 nm 100 nm 120 nm E 250 nm 200 nm 170 nm 140 nm 120 nm 140 nm

(30) The image projected out from the micro-projector 3 enters the optical waveguide through C5, and the image intensity is measured in the remaining areas. The normalized intensity results are shown in table 4.

(31) TABLE-US-00004 TABLE 4 Normalized image intensity of Example 3 1 2 3 4 5 6 A 0.85 0.88 0.95 0.96 0.7 0.96 B 0.9 0.92 0.95 1 0.8 1 C 0.9 0.92 0.95 0.97 In- 0.97 coupling D 0.9 0.92 0.95 1 0.8 1 E 0.85 0.88 0.95 0.97 0.7 0.97

Example 4

(32) As shown in FIGS. 1 and 2, the planar optical waveguide based on the two-dimensional grating of this example of the present invention includes an optical waveguide substrate 1 and a functional grating element 2.

(33) In this example, the optical waveguide substrate 1 is a plane-parallel glass plate with top surface 102 and bottom surface 103 being in parallel with each other. The thickness of the substrate is 0.5 mm. The refractive index of the substrate is 1.5.

(34) A two-dimensional grating, which comprises a plurality of grating members 201 embodied as cylindrical columns, with an angle of 60° between the two grating directions, a period T of 360 nm, and depth of 150 nm, is formed on the surface of the plane-parallel glass plate (optical waveguide substrate 1) to work as the functional structure.

(35) The intensity of light propagating inside the optical waveguide gradually decreases along with continuous out-coupling by the two-dimensional grating, and thus the brightness of the output image gradually decreases along the direction of exit pupil expansion if the grating structure is non-variant. In order to solve the above problem, the diameter R of the plurality of grating members 201 of the two-dimensional grating in different areas are controlled and modulated so that the brightness of the output image across the grating area is relatively uniform. More specifically, the optical waveguide is divided into 30 areas with A to E along the vertical direction and 1 to 6 along the horizontal direction, in which gratings are manufactured with column diameters R shown in table 5.

(36) TABLE-US-00005 TABLE 5 Column diameters R of two-dimensional gratings of Example 4 1 2 3 4 5 6 A 260 nm 240 nm 210 nm 170 nm 130 nm 170 nm B 240 nm 210 nm 170 nm 130 nm 100 nm 130 nm C 240 nm 210 nm 170 nm 130 nm 220 nm 130 nm D 240 nm 210 nm 170 nm 130 nm 100 nm 130 nm E 260 nm 240 nm 210 nm 170 nm 130 nm 170 nm

(37) The image projected out from the micro-projector 3 enters the optical waveguide through C5, and the image intensity is measured in the remaining areas. The normalized intensity results are shown in table 6.

(38) TABLE-US-00006 TABLE 6 Normalized image intensity of Example 4 1 2 3 4 5 6 A 0.82 0.88 0.91 0.94 0.94 0.94 B 0.88 0.91 0.95 1 0.96 1 C 0.88 0.91 0.93 0.96 In- 0.96 coupling D 0.88 0.91 0.93 1 0.96 1 E 0.82 0.88 0.91 0.94 0.94 0.94

(39) The present invention realizes in-coupling, exit pupil expansion and out-coupling of light through a two-dimensional grating optical waveguide with a fixed period. After light output from the micro-projector 3 passes through any area of the functional grating element 2, it gets diffracted by the two-dimensional grating to produce multiple diffraction orders which enter the optical waveguide substrate 1, and gets out-coupled from the waveguide after various numbers of bounces inside the optical waveguide substrate 1, and as a result, the output image can be seen across the entire area of the functional grating element 2. The invention involves a monolithic structure, which is suitable for mass-production as well as for application adaption.

(40) One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

(41) It will thus be seen that the objects of the present invention have been fully and effectively accomplished. The embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.