Metasurfaces with asymmetric gratings for redirecting light and methods of fabrication

Abstract

To provide metasurfaces with asymmetric gratings for redirecting light, and methods of fabricating the same.SOLUTION: An optical system is provided, comprising an optically transmissive substrate having a metasurface with a grating comprising a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width, and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. A pitch of the unit cells is 10 nm to 1 μm. Heights of the first and second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is greater than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] (Priority Claim) This application claims the benefit of priority under 35 USC § 119(e) of U.S. Provisional Application No. 62 / 333,067, filed May 6, 2016, and U.S. Patent Application No. 62 / 474,432, filed March 21, 2017. The entire disclosure of each of these priority documents is incorporated herein by reference.

[0002] (Incorporated by reference) This application incorporates by reference the entireties of U.S. Application Publication No. 2015 / 0016777, U.S. Application Publication No. 2015 / 0178939, and U.S. Application Publication No. 2015 / 0346490.

[0003] The present disclosure relates to display systems, including augmented reality imaging and optical devices. [Background technology]

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or may be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an extension to the visualization of the real world around the user. Mixed reality or "MR" scenarios are a type of AR scenario that typically involve virtual objects that are integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is perceived to otherwise interact with objects in the real world.

[0005] Referring to FIG. 1, an augmented reality scene 10 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, and buildings in the background, and a concrete platform 30. The user also perceives that they are "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30, and a flying cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The human visual perception system is complex, making it difficult to create AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0007] In some embodiments, an optical system includes an optically transmissive substrate including a metasurface including a grating including a plurality of unit cells, each unit cell including a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width, the height of the first and second nanobeams being between 10 nm and 450 nm, the refractive index of the substrate being greater than 3.3 and between 10 nm and 1 μm, and the refractive index being 3.3 or less.

[0008] In some other embodiments, the optical system includes an optically transmissive substrate including a metasurface including a grating including a plurality of unit cells. Each unit cell includes a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced apart from the first nanobeam by a gap. The second nanobeam has a second width greater than the first width. The optical system also includes a reflector. The reflector and the substrate are on opposite sides of the grating.

[0009] In yet another embodiment, a method for forming a metasurface includes providing an optically transmissive substrate, providing an optically transmissive layer over the substrate, and patterning the optically transmissive layer to define a lattice including a plurality of unit cells, each unit cell including a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width, the height of the first and second nanobeams being between 10 nm and 450 nm, the refractive index of the substrate being greater than 3.3 and between 10 nm and 1 μm, and the refractive index being 3.3 or less.

[0010] In some other embodiments, a method for forming a metasurface includes providing an optically transmissive substrate and forming a grating including a plurality of unit cells, each unit cell including a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. The method also includes providing a layer of reflective material in the gaps and between the unit cells.

[0011] In some other embodiments, a method for forming a metasurface includes providing an optically transmissive substrate and forming a grating including a plurality of unit cells, each unit cell including a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. The method further includes depositing a layer of optically transmissive spacer material in the gaps and between the unit cells and depositing a reflective layer on the layer of spacer material, the spacer material separating the grating from the reflective layer.

[0012] In yet another embodiment, an optical system includes an optically transmissive substrate including a metasurface including a grating including a plurality of unit cells. Each unit cell includes a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. The pitch of the unit cells is between 10 nm and 1 μm.

[0013] In some other embodiments, a method for forming a metasurface includes providing an optically transmissive substrate, providing an optically transmissive layer over the substrate, and patterning the optically transmissive layer to define a lattice including a plurality of unit cells. Each unit cell includes a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. The pitch of the unit cells is between 10 nm and 1 μm.

[0014] In yet another embodiment, an optical system includes an optically transmissive substrate including a multilevel metasurface. The multilevel metasurface includes a grating including a plurality of multilevel unit cells. Each unit cell includes, at a bottom level of the unit cell, a first laterally extending bottom level nanobeam having a first width and a second laterally extending bottom level nanobeam having a second width, the second width being greater than the first width. At a top level of the unit cell, there is a first laterally extending top level nanobeam above the first bottom level nanobeam and a second laterally extending top level nanobeam above the second bottom level nanobeam.

[0015] In some other embodiments, a method for forming a metasurface includes providing an optically transmissive substrate, providing an optically transmissive layer over the substrate, and patterning the optically transmissive layer to define a plurality of repeating units. Each repeating unit includes a laterally extending first nanobeam having a first width and a laterally extending second nanobeam spaced from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width. The method also includes depositing an optically transmissive material on the first and second nanobeams and in the gap between the nanobeams to form spaced apart plateaus of optically transmissive material above the nanobeams.

[0016] Additional exemplary embodiments are provided below. 1. An optical system comprising: An optically transparent substrate comprising a metasurface, the metasurface comprising, as seen in top and bottom views: A lattice comprising a plurality of unit cells, each unit cell comprising: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and the height of the first and second nanobeams is 10 nm to 450 nm, and the refractive index of the substrate is greater than 3.3; 10 nm to 1 μm, and the refractive index is 3.3 or less. Including, a substrate an optical system comprising: 2. The optical system of embodiment 1, wherein the unit cells are laterally elongated and mutually parallel. 3. The optical system of embodiment 1, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. 4. The optical system of embodiment 1, wherein the second width is between 10 nm and 1 μm. 5. The optical system of embodiment 4, wherein the second width is between 10 nm and 300 nm. 6. The optical system of embodiment 1, wherein the pitch of the unit cells is between 10 nm and 1 μm. 7. The optical system of embodiment 6, wherein the pitch of the unit cells is between 10 nm and 500 nm. 8. The optical system of embodiment 1, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. 9. The optical system of embodiment 8, wherein the gap is between 10 nm and 300 nm wide. 10. The optical system of embodiment 1, wherein the optically transmissive substrate comprises glass. 11. The optical system of embodiment 1, wherein the first and second nanobeams comprise silicon. 12. The optical system of embodiment 11, wherein the first and second nanobeams comprise silicon nitride. 13. The optical system of embodiment 1, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. 14. The optical system of embodiment 1, wherein the optically transmissive substrate is a waveguide plate. 15. The optical system of embodiment 14, further comprising a stack of optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. 16. The optical system of embodiment 1, wherein the metasurface is an internal coupling optical element, and further comprising an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. 17. The optical system of embodiment 1, wherein the metasurface is an outcoupling optical element, the metasurface being configured to extract light from the substrate. 18. An optical system comprising: 1. An optically transmissive substrate comprising a metasurface, the metasurface comprising: A lattice containing a number of unit cells, each of which, as shown in the top and bottom diagrams, has the following structure: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; Including, lattice A substrate comprising: a reflector, the reflector and the substrate being on opposite sides of the grating; an optical system comprising: 19. The optical system of embodiment 18, wherein the reflector is spaced apart from the grating. 20. The optical system of embodiment 19, wherein the grating is embedded within an optically transmissive material. 21. The optical system of embodiment 20, wherein an optically transmissive material spaces the reflector from the grating. 22. The substrate is a second metasurface on a side of the substrate opposite the metasurface, the second metasurface comprising: A second lattice including a plurality of second unit cells, each of the second unit cells having, as seen in the top and bottom views, a laterally extending third nanobeam; and a laterally extending fourth nanobeam separated from the third nanobeam by a gap, the fourth nanobeam being wider than the third nanobeam; The second lattice, A second metasurface comprising 19. The optical system of embodiment 18, comprising: 23. The optical system of embodiment 18, wherein the unit cells are laterally elongated and mutually parallel. 24. The optical system of embodiment 18, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. 25. The optical system of embodiment 18, wherein the second width is between 10 nm and 1 μm. 26. The optical system of embodiment 25, wherein the second width is between 10 nm and 300 nm. 27. The optical system of embodiment 18, wherein the pitch of the unit cells is between 10 nm and 1 μm. 28. The optical system of embodiment 27, wherein the pitch of the unit cells is between 10 nm and 500 nm. 29. The optical system of embodiment 18, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. 30. The optical system of embodiment 29, wherein the gap is between 10 nm and 300 nm wide. 31. The optical system of embodiment 18, wherein the optically transmissive substrate comprises glass. 32. The optical system of embodiment 18, wherein the first and second nanobeams comprise silicon. 33. The optical system of embodiment 32, wherein the first and second nanobeams comprise silicon nitride. 34. The optical system of embodiment 18, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. 35. The optical system of embodiment 27, wherein the optically transmissive substrate is a waveguide plate. 36. The optical system of embodiment 35, further comprising a stack of optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. 37. The optical system of embodiment 18, wherein the metasurface is an internal coupling optical element and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. 38. The optical system of embodiment 18, wherein the metasurface is an outcoupling optical element, the metasurface being configured to extract light from the substrate. 39. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over a substrate; patterning the optically transmissive layer to define a lattice comprising a plurality of unit cells, each unit cell comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and the height of the first and second nanobeams is 10 nm to 450 nm, and the refractive index of the substrate is greater than 3.3; 10 nm to 1 μm, and the refractive index is 3.3 or less. A method comprising: 40. Patterning an optically transmissive layer includes: providing a resist layer over an optically transparent layer; Defining a pattern in a resist layer; Transferring a pattern from the resist layer to the optically transparent layer. 40. The method of embodiment 39, comprising: 41. The method of embodiment 40, further comprising depositing an optically transmissive material between and across the gratings. 42. The method of embodiment 41, further comprising forming a reflective layer on the optically transmissive material. 43. The method of embodiment 40, wherein the transferring comprises performing anisotropic etching. 44. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; forming a lattice including a plurality of unit cells, each unit cell being, as shown in the top and bottom views, a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and providing a layer of reflective material in the gaps and between the unit cells; A method comprising: 45. The method of embodiment 44, wherein providing a layer of reflective material includes depositing a reflective material between and across the first and second nanobeams. 46. ​​The method of embodiment 45, wherein the reflective material comprises aluminum. 47. Forming a lattice is depositing an optically transmissive layer over a substrate; patterning the optically transmissive layer to define a grating; 45. The method of embodiment 44, comprising: 48. Patterning an optically transparent layer may include providing a resist layer over an optically transparent layer; Defining a pattern in a resist layer; Transferring a pattern from the resist layer to the optically transparent layer. 48. The method of embodiment 47, comprising: 49. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; forming a lattice including a plurality of unit cells, each unit cell being, as shown in the top and bottom views, a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and depositing a layer of optically transmissive spacer material in the gaps and between the unit cells; depositing a reflective layer onto the layer of spacer material, the spacer material separating the grating from the reflective layer; A method comprising: 50. The method of embodiment 49, wherein the spacer material has a refractive index between 1 and 2. 51. An optical system comprising: 1. An optically transmissive substrate comprising a metasurface, the metasurface comprising: A lattice containing a number of unit cells, each of which, as shown in the top and bottom diagrams, has the following structure: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; The pitch of the unit cell is 10 nm to 1 μm. Including, a substrate an optical system comprising: 52. The system of embodiment 51, wherein the pitch is between 300 nm and 500 nm. 53. The system of embodiment 51, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. 54. The optical system of embodiment 51, wherein the unit cells are laterally elongated and mutually parallel. 55. The optical system of embodiment 51, wherein the second width is between 10 nm and 1 μm. 56. The optical system of embodiment 55, wherein the second width is between 10 nm and 300 nm. 57. The optical system of embodiment 51, wherein the pitch of the unit cells is between 10 nm and 1 μm. 58. The optical system of embodiment 57, wherein the pitch of the unit cells is between 10 nm and 500 nm. 59. The optical system of embodiment 51, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. 60. The optical system of embodiment 59, wherein the gap is between 10 nm and 300 nm wide. 61. The optical system of embodiment 51, wherein the optically transmissive substrate comprises glass. 62. The optical system of embodiment 51, wherein the first and second nanobeams comprise silicon. 63. The optical device of embodiment 62, wherein the first and second nanobeams comprise silicon nitride. system. 64. The optical system of embodiment 51, wherein the optically transparent substrate and the metasurface form a polarizing beam splitter. 65. The optical system of embodiment 51, wherein the optically transmissive substrate is a waveguide plate. 66. The optical system of embodiment 65, further comprising a stack of optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. 67. The optical system of embodiment 51, wherein the metasurface is an internal coupling optical element and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. 68. The optical system of embodiment 51, wherein the metasurface is an outcoupling optical element, the metasurface being configured to extract light from the substrate. 69. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over a substrate; patterning the optically transmissive layer to define a lattice comprising a plurality of unit cells, each unit cell comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; The pitch of the unit cells is 10 nm to 1 μm; A method comprising: 70. The method of embodiment 69, wherein the pitch is between 300 nm and 500 nm. 52. The method of embodiment 51, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. 71. An optical system comprising: 1. An optically transmissive substrate comprising a multilevel metasurface, the multilevel metasurface comprising: A lattice including a plurality of multi-level unit cells, each of which, as shown in the top and bottom views, has the following structure: At the lowest level of the unit cell, a laterally extending first, bottom level nanobeam having a first width; a laterally extending second bottom level nanobeam having a second width, the second width being greater than the first width; and At the top level of the unit cell, a first uppermost-level nanobeam extending laterally above the first lowermost-level nanobeam; a second uppermost-level nanobeam extending laterally above the second lowermost-level nanobeam; Including, lattice Including, a substrate an optical system comprising: 72. The optical system of embodiment 71, wherein the first and second top-level nanobeams comprise a different material than the first and second bottom-level nanobeams. 73. The optical system of embodiment 71, wherein the first and second bottom level nanobeams comprise photoresist. 74. The optical system of embodiment 73, wherein the first and second bottom level nanobeams comprise silicon. 75. The optical system of embodiment 74, wherein the first and second bottom level nanobeams comprise silicon nitride. 76. The optical system of embodiment 73, wherein the first and second bottom level nanobeams comprise an oxide. 77. The optical system of embodiment 76, wherein the first and second bottom level nanobeams comprise titanium oxide. 78. The optical system of embodiment 71, wherein the first and second bottom-level nanobeams of the multiple unit cells extend parallel to each other. 79. The optical system of embodiment 71, wherein the first width is between 10 nm and 250 nm. 80. The optical system of embodiment 79, wherein the second width is between 10 nm and 300 nm. 81. The optical system of embodiment 71, wherein the pitch of the unit cells is between 300 nm and 500 nm. 82. The optical system of embodiment 71, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 300 nm. 83. The optical system of embodiment 71, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. 84. The optical system of embodiment 71, wherein the optically transmissive substrate is a waveguide plate. 85. The optical system of embodiment 71, further comprising an image injection device configured to project light onto the incoupling optical element, the metasurface configured to redirect light and propagate light through the substrate by total internal reflection. 86. The optical system of embodiment 84, further comprising a stack of optically transmissive substrates, the dimensions of the features of the unit cell vary between the substrates, the metasurface is an incoupling optical element, the image injection device configured to project light onto the incoupling optical element, the metasurface configured to redirect light and propagate light through the substrate by total internal reflection. 87. The optical system of embodiment 71, wherein the metasurface is an outcoupling optical element, the metasurface being configured to extract light from the substrate. 88. The optical system of embodiment 71, wherein the grating is embedded within an optically transmissive material. 89. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over a substrate; patterning the optically transmissive layer to define a plurality of repeating units, each repeating unit comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and depositing an optically transmissive material over the first and second nanobeams and in the gaps between the nanobeams to form spaced apart plateaus of optically transmissive material above the nanobeams; A method comprising: 90. The method of embodiment 89, wherein the optically transmissive material has a higher refractive index than either the patterned resist or the substrate. 91. The method of embodiment 89, wherein patterning the optically transmissive layer comprises patterning a resist. 92. The method of embodiment 91, wherein patterning the resist comprises imprinting a pattern into the resist. 93. The method of embodiment 91, wherein depositing the optically transmissive material comprises spin-coating the optically transmissive material onto the patterned resist. 94. The method of embodiment 91, wherein depositing the optically transmissive material includes performing conformal or directional deposition of the optically transmissive material. 95. The method of embodiment 94, wherein the conformal deposition comprises chemical vapor deposition or atomic layer deposition of an optically transparent material. 96. The method of embodiment 95, wherein the directional deposition comprises evaporation or sputtering of the optically transparent material. 97. The method of embodiment 89, wherein the first width is between 10 nm and 250 nm. 98. The method of embodiment 97, wherein the second width is between 10 nm and 300 nm. 99. The method of embodiment 89, wherein the pitch of the unit cells is between 300 nm and 500 nm. 100. The optical system of embodiment 89, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 300 nm. 101. The method of embodiment 89, wherein the optically transparent substrate is a waveguide.

[0017] Additional and other objects, features, and advantages of the present invention are set forth in the detailed description, drawings, and claims. The present invention provides, for example, the following: (Item 1) 1. An optical system comprising: 1. An optically transparent substrate comprising a metasurface, the metasurface comprising, as seen in the top and bottom views: A lattice comprising a plurality of unit cells, each unit cell comprising: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; wherein the heights of the first and second nanobeams are: 10 nm to 450 nm, the refractive index of the substrate is greater than 3.3, 10 nm to 1 μm, and the refractive index is 3.3 or less. Including, a substrate an optical system comprising: (Item 2) 2. The optical system of claim 1, wherein the unit cells are laterally elongated and mutually parallel. (Item 3) 2. The optical system of claim 1, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. (Item 4) 2. The optical system according to item 1, wherein the second width is from 10 nm to 1 μm. (Item 5) 5. The optical system according to item 4, wherein the second width is 10 nm to 300 nm. (Item 6) 2. The optical system according to item 1, wherein the pitch of the unit cells is 10 nm to 1 μm. (Item 7) 7. The optical system according to item 6, wherein the pitch of the unit cells is 10 nm to 500 nm. (Item 8) Item 2. The optical system of item 1, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. (Item 9) 9. The optical system according to item 8, wherein the gap is 10 nm to 300 nm wide. (Item 10) Item 2. The optical system of item 1, wherein the optically transmissive substrate comprises glass. (Item 11) Item 12. The optical system of item 1, wherein the first and second nanobeams comprise silicon. Item 12. The optical system of item 11, wherein the first and second nanobeams comprise silicon nitride. (Item 13) 2. The optical system of claim 1, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. (Item 14) Item 15. The optical system of item 1, wherein the optically transmissive substrate is a waveguide plate. Item 15. The optical system of item 14, further comprising a stack of the optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. (Item 16) 2. The optical system of claim 1, wherein the metasurface is an internal coupling optical element, and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. (Item 17) 2. The optical system of claim 1, wherein the metasurface is an outcoupling optical element, the metasurface being configured to extract light from the substrate. (Item 18) 1. An optical system comprising: 1. An optically transmissive substrate comprising a metasurface, the metasurface comprising: A lattice containing a number of unit cells, each of which, as shown in the top and bottom diagrams, has the following structure: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; Including, lattice A substrate comprising: a reflector, the reflector and the substrate being on opposite sides of the grating; an optical system comprising: (Item 19) 20. The optical system of claim 18, wherein the reflector is spaced from the grating. (Item 20) 20. The optical system of claim 19, wherein the grating is embedded within an optically transmissive material. (Item 21) 21. The optical system of claim 20, wherein the optically transmissive material spaces the reflector from the grating. (Item 22) The substrate is a second metasurface on a side of the substrate opposite the metasurface, the second metasurface comprising: A second lattice including a plurality of second unit cells, each of the second unit cells having, as seen in the top and bottom views, a laterally extending third nanobeam; and a laterally extending fourth nanobeam separated from the third nanobeam by a gap, the fourth nanobeam being wider than the third nanobeam; The second lattice, A second metasurface comprising 19. The optical system according to item 18, comprising: (Item 23) Item 19. The optical system of item 18, wherein the unit cells are laterally elongated and mutually parallel. (Item 24) Item 19. The optical system of item 18, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. (Item 25) Item 19. The optical system according to item 18, wherein the second width is from 10 nm to 1 μm. (Item 26) 26. The optical system according to item 25, wherein the second width is 10 nm to 300 nm. (Item 27) Item 19. The optical system according to item 18, wherein the pitch of the unit cells is 10 nm to 1 μm. (Item 28) 28. The optical system according to item 27, wherein the pitch of the unit cells is 10 nm to 500 nm. (Item 29) Item 19. The optical system of item 18, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. (Item 30) 30. The optical system according to item 29, wherein the gap is between 10 nm and 300 nm wide. (Item 31) 20. The optical system of claim 18, wherein the optically transmissive substrate comprises glass. (Item 32) Item 19. The optical system of item 18, wherein the first and second nanobeams comprise silicon. (Item 33) Item 33. The optical system of item 32, wherein the first and second nanobeams comprise silicon nitride. (Item 34) 20. The optical system of claim 18, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. (Item 35) 28. The optical system of claim 27, wherein the optically transmissive substrate is a waveguide plate. (Item 36) Item 36. The optical system of item 35, further comprising a stack of the optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. (Item 37) 20. The optical system of claim 18, wherein the metasurface is an internal coupling optical element, and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. (Item 38) 20. The optical system of claim 18, wherein the metasurface is an outcoupling optical element, the metasurface configured to extract light from the substrate. (Item 39) 1. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over the substrate; patterning the optically transmissive layer to define a lattice comprising a plurality of unit cells, each unit cell comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; wherein the heights of the first and second nanobeams are: 10 nm to 450 nm, the refractive index of the substrate is greater than 3.3, 10 nm to 1 μm, and the refractive index is 3.3 or less. A method comprising: (Item 40) Patterning the optically transmissive layer comprises: providing a resist layer over the optically transparent layer; Defining a pattern in the resist layer; transferring the pattern from the resist layer to the optically transmissive layer; 40. The method according to item 39, comprising: (Item 41) Item 41. The method of item 40, further comprising depositing an optically transmissive material between and across the gratings. (Item 42) Item 42. The method of item 41, further comprising forming a reflective layer on the optically transmissive material. (Item 43) Item 41. The method of item 40, wherein the transferring comprises performing anisotropic etching. (Item 44) 1. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; forming a lattice including a plurality of unit cells, each unit cell being, as shown in the top and bottom views, a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; Including, providing a layer of reflective material in said gaps and between said unit cells; A method comprising: (Item 45) Item 45. The method of item 44, wherein providing the layer of reflective material comprises depositing a reflective material between and across the first and second nanobeams. (Item 46) Item 46. The method of item 45, wherein the reflective material comprises aluminum. (Item 47) Forming the lattice comprises: depositing an optically transmissive layer over the substrate; patterning the optically transmissive layer to define the grating; 45. The method according to item 44, comprising: (Item 48) Patterning the optically transmissive layer comprises: providing a resist layer over the optically transparent layer; Defining a pattern in the resist layer; transferring the pattern from the resist layer to the optically transmissive layer; 48. The method according to item 47, comprising: (Item 49) 1. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; forming a lattice including a plurality of unit cells, each unit cell being, as shown in the top and bottom views, a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and depositing a layer of optically transmissive spacer material in the gaps and between the unit cells; depositing a reflective layer over the layer of spacer material, the spacer material separating the grating from the reflective layer; A method comprising: (Item 50) 50. The method according to claim 49, wherein the spacer material has a refractive index of 1 to 2. (Item 51) 1. An optical system comprising: 1. An optically transmissive substrate comprising a metasurface, the metasurface comprising: A lattice containing a number of unit cells, each of which, as shown in the top and bottom diagrams, has the following structure: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; The pitch of the unit cell is 10 nm to 1 μm. Including, a substrate an optical system comprising: (Item 52) Item 52. The system according to item 51, wherein the pitch is 300 nm to 500 nm. (Item 53) Item 52. The system of item 51, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. (Item 54) Item 52. The optical system of item 51, wherein the unit cells are laterally elongated and mutually parallel. (Item 55) Item 52. The optical system according to item 51, wherein the second width is 10 nm to 1 μm. (Item 56) Item 56. The optical system according to item 55, wherein the second width is 10 nm to 300 nm. (Item 57) Item 52. The optical system according to item 51, wherein the pitch of the unit cells is 10 nm to 1 μm. (Item 58) Item 58. The optical system according to item 57, wherein the pitch of the unit cells is 10 nm to 500 nm. (Item 59) Item 52. The optical system of item 51, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μm. (Item 60) Item 60. The optical system according to item 59, wherein the gap is between 10 nm and 300 nm wide. (Item 61) Item 52. The optical system of item 51, wherein the optically transmissive substrate comprises glass. (Item 62) Item 52. The optical system of item 51, wherein the first and second nanobeams comprise silicon. (Item 63) Item 63. The optical system of item 62, wherein the first and second nanobeams comprise silicon nitride. (Item 64) 52. The optical system of claim 51, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. (Item 65) Item 52. The optical system of item 51, wherein the optically transmissive substrate is a waveguide plate. (Item 66) Item 66. The optical system of item 65, further comprising a stack of the optically transmissive substrates, wherein dimensions of the features of the unit cell vary between the substrates. (Item 67) 52. The optical system of claim 51, wherein the metasurface is an internal coupling optical element, and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. (Item 68) 52. The optical system of claim 51, wherein the metasurface is an outcoupling optical element, the metasurface configured to extract light from the substrate. (Item 69) 1. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over the substrate; patterning the optically transmissive layer to define a lattice comprising a plurality of unit cells, each unit cell comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; The pitch of the unit cells is 10 nm to 1 μm. A method comprising: (Item 70) Item 70. The method according to item 69, wherein the pitch is 300 nm to 500 nm. Item 52. The method of item 51, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order. (Item 71) 1. An optical system comprising: 1. An optically transmissive substrate comprising a multilevel metasurface, the multilevel metasurface comprising: A lattice including a plurality of multi-level unit cells, each of which, as shown in the top and bottom views, has the following structure: At the lowest level of the unit cell, a laterally extending first, bottom level nanobeam having a first width; a laterally extending second bottom level nanobeam having a second width, the second width being greater than the first width; and At the top level of the unit cell, a first uppermost-level nanobeam extending laterally above the first lowermost-level nanobeam; a second uppermost-level nanobeam extending laterally above said second lowermost-level nanobeam; Including, lattice Including, a substrate an optical system comprising: (Item 72) Item 72. The optical system of item 71, wherein the first and second top-level nanobeams comprise a different material than the first and second bottom-level nanobeams. (Item 73) Item 72. The optical system of item 71, wherein the first and second bottom level nanobeams include photoresist. (Item 74) Item 74. The optical system of item 73, wherein the first and second bottom level nanobeams comprise silicon. (Item 75) Item 75. The optical system of item 74, wherein the first and second bottom level nanobeams comprise silicon nitride. (Item 76) Item 74. The optical system of item 73, wherein the first and second bottom level nanobeams comprise an oxide. (Item 77) Item 77. The optical system of item 76, wherein the first and second bottom level nanobeams comprise titanium oxide. (Item 78) Item 72. The optical system of item 71, wherein the first and second bottom-level nanobeams of the plurality of unit cells extend parallel to each other. (Item 79) Item 72. The optical system according to item 71, wherein the first width is 10 nm to 250 nm. (Item 80) 80. The optical system according to item 79, wherein the second width is 10 nm to 300 nm. (Item 81) Item 72. The optical system according to item 71, wherein the pitch of the unit cells is 300 nm to 500 nm. (Item 82) Item 72. The optical system of item 71, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 300 nm. (Item 83) 72. The optical system of claim 71, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. (Item 84) Item 72. The optical system of item 71, wherein the optically transmissive substrate is a waveguide plate. (Item 85) 72. The optical system of claim 71, wherein the metasurface forms an internal coupling optical element and further comprises an image injection device configured to project light onto the internal coupling optical element, the metasurface configured to redirect the light and propagate the light through the substrate by total internal reflection. (Item 86) 85. The optical system of claim 84, further comprising a stack of optically transmissive substrates, wherein dimensions of features of the unit cell vary between the substrates, and wherein the metasurface is an internal coupling optical element, further comprising an image injection device configured to project light onto the internal coupling optical element, wherein the metasurface is configured to redirect the light and propagate the light through the substrates by total internal reflection. (Item 87) Item 72. The optical system of item 71, wherein the metasurface is an outcoupling optical element, the metasurface configured to extract light from the substrate. (Item 88) Item 89. The optical system of item 71, wherein the grating is embedded within an optically transmissive material. 1. A method for forming a metasurface, the method comprising: Providing an optically transmissive substrate; providing an optically transmissive layer over the substrate; patterning the optically transmissive layer to define a plurality of repeating units, each repeating unit comprising, as seen in the top and bottom views: a laterally extending first nanobeam having a first width; a laterally extending second nanobeam separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width; and depositing an optically transmissive material over the first and second nanobeams and in gaps between the nanobeams to form spaced apart plateaus of the optically transmissive material above the nanobeams; A method comprising: (Item 90) 90. The method of claim 89, wherein the optically transmissive material has a higher refractive index than either the patterned resist or the substrate. (Item 91) 90. The method of claim 89, wherein patterning the optically transmissive layer comprises patterning a resist. (Item 92) Item 92. The method of item 91, wherein patterning the resist comprises imprinting the pattern into the resist. (Item 93) 94. The method of claim 91, wherein depositing the optically transmissive material comprises spin-coating the optically transmissive material onto the patterned resist. Item 92. The method of item 91, wherein depositing the optically transmissive material comprises performing conformal or directional deposition of the optically transmissive material. (Item 95) 95. The method of claim 94, wherein the conformal deposition comprises chemical vapor deposition or atomic layer deposition of the optically transparent material. (Item 96) 96. The method of claim 95, wherein the directional deposition comprises evaporation or sputtering of the optically transparent material. (Item 97) Item 89. The method according to item 89, wherein the first width is 10 nm to 250 nm. (Item 98) Item 98. The method according to Item 97, wherein the second width is 10 nm to 300 nm. (Item 99) Item 89. The method according to item 89, wherein the pitch of the unit cells is 300 nm to 500 nm. (Item 100) Item 90. The optical system of item 89, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 300 nm. (Item 101) 90. The method of claim 89, wherein the optically transmissive substrate is a waveguide. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0019] [Diagram 2] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0020] [Diagram 3] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus.

[0021] [Figure 4A] FIG. 4A illustrates a representation of the accommodation-vergence response of the human visual system.

[0022] [Figure 4B] FIG. 4B illustrates examples of different accommodation and convergence states of a pair of a user's eyes.

[0023] [Figure 4C]FIG. 4C illustrates an example of a top-down view representation of a user viewing content through a display system.

[0024] [Figure 4D] FIG. 4D illustrates another example of a top-down view representation of a user viewing content through a display system.

[0025] [Diagram 5] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence.

[0026] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0027] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0028] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0029] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an embodiment of a set of stacked waveguides, each of which includes an incoupling optical element.

[0030] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0031] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0032] [Figure 9D]FIG. 9D illustrates an example of a wearable display system.

[0033] [Figure 10] 10A and 10B illustrate cross-sectional side and top-down view examples of metasurfaces, respectively.

[0034] [Figure 11A] FIG. 11A illustrates an example of a cross-sectional side view of a metasurface configured to function in a reflective mode.

[0035] [Figure 11B] FIG. 11B illustrates an example of a cross-sectional top-down view of the metasurface of FIG. 11A as viewed on plane 11B of FIG. 11A.

[0036] [Figure 12] FIG. 12 illustrates a cross-sectional side view example of another metasurface configured to function in a reflective mode.

[0037] [Figure 13] FIG. 13 illustrates an example of a cross-sectional top-down view of the metasurface of FIG. 12 as viewed on plane 13 of FIG.

[0038] [Figure 14A] FIG. 14A illustrates an example of a cross-sectional side view of a substrate having both a transmissive and a reflective metasurface.

[0039] [Figure 14B] FIG. 14B illustrates an example of a top-down view of the metasurface of FIG. 14A.

[0040] [Figure 14C] FIG. 14C illustrates an example of a top-down view of the metasurface of FIG. 14A as viewed on plane 14C of FIG. 14A.

[0041] [Figure 15]15A-15E illustrate an example of a process flow for forming a metasurface.

[0042] [Figure 16] 16A and 16B illustrate scanning electron micrographs of the metasurface.

[0043] [Figure 17] FIG. 17 illustrates an example of a plot showing diffraction efficiency versus angle of incidence of light for a transmissive metasurface.

[0044] [Figure 18] 18A-18C illustrate example plots showing diffraction efficiency versus angle of incidence of light for a reflective metasurface. The wavelength of the incident light is different for each of FIGS. 18A-18C.

[0045] [Figure 19] 19A and 19B illustrate example plots showing the polarization sensitivity of the metasurfaces of FIGS. 10A and 10B.

[0046] [Figure 20] FIG. 20 illustrates plots of amplitude and phase shift versus nanobeam width for the metasurfaces of FIGS. 10A and 10B.

[0047] [Figure 21A] FIG. 21A illustrates an example of a cross-sectional side view of a multilevel metasurface.

[0048] [Figure 21B] FIG. 21B illustrates an example of a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in FIG. 21A.

[0049] [Figure 22A] FIG. 22A illustrates an example of a cross-sectional side view of a multilevel metasurface.

[0050] [Figure 22B] FIG. 22B illustrates an example of a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in FIG. 22A.

[0051] [Diagram 23] 23A-23D illustrate an example of a process flow for forming a multilevel metasurface.

[0052] The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the present disclosure. It should be understood that the drawings are schematic and are not necessarily drawn to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Metasurfaces, i.e., metamaterial surfaces, offer the opportunity to achieve virtually flat, aberration-free optics at much smaller scales compared to geometric optics. Without being limited by theory, in some embodiments, metasurfaces include a dense array of surface structures that act as resonant optical antennas. The resonant nature of light-surface-structure interaction provides the ability to manipulate optical wavefronts. In some cases, metasurfaces may enable the replacement of bulky or difficult to manufacture optical components with thin, planar elements formed by simple patterning processes.

[0054] One type of conventional optical element is a blazed grating, which can be desirable in some applications because it has high selectivity in redirecting light. However, these gratings typically have tilted surfaces and can be difficult to manufacture. Advantageously, in some embodiments, metasurfaces are disclosed that are capable of redirecting light in the visible range in a similar manner to blazed gratings, while providing structures that have a relatively flat response over a wide range of angles of incidence and are more easily manufactured.

[0055] The metasurface may take the form of an asymmetric lattice formed by a plurality of repeating unit cells. Each unit cell includes two lateral elongated protrusions, which may also be referred to as nanobeams or nanowires, one protrusion being wider than the other. As used herein, a protrusion, nanobeam, or nanowire is an elongated volume of material, e.g., a single substantially homogenous material. It should be understood that these elongated structures are not limited to any particular cross-sectional shape. In some embodiments, the cross-sectional shape is rectangular. Preferably, the nanobeams have a sub-wavelength width and spacing from one another. For example, the width of the nanobeams may be less than a wavelength of light that the metasurface is configured to redirect. In some embodiments, the unit cells formed by the nanobeams may be on or adjacent to a surface of an optically transparent substrate, e.g., a waveguide.

[0056] In some embodiments, the metasurface may function in a transmission mode, where light is incident on the metasurface from a first side of the metasurface, propagates through the metasurface, and then propagates away from the metasurface on the opposite side of the metasurface in a direction different from the direction of light incidence on the first side.

[0057] In some other embodiments, the metasurface may function in a reflective mode, where light enters a first side of the metasurface, is reflected back to the first side, and propagates away from the metasurface. In the reflective mode, the metasurface may include a nanobeam embedded within a reflective layer. In some other embodiments, the nanobeam may be embedded within a spacer layer, and a reflective layer may be provided directly on the spacer layer, on the side of the metasurface opposite the first side.

[0058] Preferably, the features forming the metasurface are configured to redirect light, for example by diffraction. In some embodiments, the light is visible light, having a wavelength in the range of 350 nm to 800 nm. In some embodiments, the metasurface is configured to diffract incident light of visible wavelength into a first diffraction order.

[0059] In some embodiments, the width of the nanobeams forming the unit cells is in the range of 10 nm to 1 μm, including 10 nm to 300 nm or 10 nm to 250 nm. The nanobeams may be separated by gaps that are in the range of 5 nm to 1 μm wide, including 10 nm to 1 μm wide or 10 nm to 300 nm wide. The pitch of the unit cells (i.e., the distance between the same points in directly adjacent unit cells) may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. In some embodiments, the height of the nanobeams may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 10 nm to 450 nm.

[0060] It has been found that the dimensions of the features of the unit cells can vary depending on the nature of the materials used to form the metasurface. For example, the height of the nanobeams can vary depending on the nature of the materials used for those nanobeams. In some embodiments, the height of the nanobeams can be between 10 nm and 450 nm, and the refractive index of the material is greater than 3.3, between 10 nm and 1 μm, and the refractive index is 3.3 or less. As another example, the height of the nanobeams can be between 10 nm and 450 nm, and the nanobeams are formed from silicon (e.g., amorphous or polysilicon).

[0061] In some embodiments, the metasurface is a multi-level (e.g., bi-level) structure having unit cells with relatively narrow and relatively wide nanobeams on the bottom level and a second optically transmissive material between the nanobeams on the bottom level, as described above. The metasurface may also include a second level formed by a second optically transmissive material disposed on the top surface of the nanobeams. The material on the second level may be localized on the top surface of the nanobeams and may form spaced apart plateaus of material as seen in a cross-sectional view taken along a plane orthogonal to the length axis of the nanobeams. In some embodiments, the height of the material on the second level may be in the range of 10 nm to 1 μm, including 10 nm to 600 nm.

[0062] It should be appreciated that in some embodiments, metasurfaces selectively redirect some wavelengths of light while being transparent to other wavelengths of light. While such properties are typically engineered with structures at the micron scale (e.g., in photonic crystal fibers or distributed Bragg reflectors), various embodiments herein include geometries at the nanoscale (e.g., 10-100 times smaller scale) to provide selective redirection of light within the visible portion of the electromagnetic spectrum. In some embodiments, the nanobeams may be formed at a single level on the surface of the substrate, thereby providing a simply fabricated structure. Advantageously, the metasurfaces may be formed using patterning and deposition processes, such as lithography and chemical etching. In some embodiments, the metasurfaces may be patterned using nanoimprinting, thereby avoiding costly lithography and etching processes.

[0063] The metasurfaces formed according to various embodiments provide one or more of the following advantages. For example, the metasurfaces may have a relatively large angular bandwidth over which light can be redirected or diffracted. In addition, the metasurfaces may have good diffraction efficiency over this bandwidth. For example, the diffraction efficiency may be 25% or more, 30% or more, or 40% or more over an angular bandwidth (FWHM) of 40° or 50° (measured from the normal direction to the surface). Furthermore, the diffraction efficiency over the angular bandwidth may advantageously be flat, e.g., varying less than 25%, 20%, 15%, or 10% over the angular bandwidth. The metasurfaces may also have a large deflection angle, which may be advantageously applied to incouple light within the angular bandwidth by redirecting the light to propagate at an angle suitable for total internal reflection (TIR). In addition, the advantages described above may be realized at some wavelengths of light corresponding to different primary colors for forming an image. For example, the wavelengths may correspond to the colors red, green, and blue (e.g., wavelengths of 455 nm, 520 nm, and 638 nm). In reflective mode, the metasurface may provide color-selective beam shaping with high extinction ratios (e.g., 5 or more, 10 or more, 20 or more). In some embodiments, the metasurface may exhibit strong polarization dependence and act as a polarizing beam splitter. For example, for light of different polarizations, the metasurface may exhibit extinction ratios of 5 or more, 7 or more, or 9 or more.

[0064] In some embodiments, the waveguides supporting the metasurface may form a direct-view or eyepiece display device, where the waveguides are configured to receive input image information and generate an output image based on the input image information. These devices may be wearable and constitute eyewear in some embodiments. The input image information received by the waveguides can be encoded into multiplexed light streams of different wavelengths (e.g., red, green, and blue light) that are incoupling into one or more waveguides. The incoupling light may propagate through the waveguides due to total internal reflection. The incoupling light may be outcoupling (or output) from the waveguides by one or more outcoupling optical elements.

[0065] In some embodiments, the metasurface is an in-coupling optical element and / or an out-coupling optical element. The compactness and planarity of the metasurface allows for compact waveguides and stacks of compact waveguides where multiple waveguides form a stack. In addition, the high wavelength selectivity of the metasurface allows for high precision in the in-coupling and / or out-coupling light, which can provide high image quality in applications where the light contains image information. For example, the high selectivity can reduce channel crosstalk in configurations where a full color image is formed by simultaneously outputting light of different colors or wavelengths.

[0066] Reference is now made to the drawings, in which like reference numbers refer to like features throughout.

[0067] Exemplary Display Systems Various embodiments disclosed herein may be implemented in optical devices to steer or redirect light, and may be particularly advantageously employed as part of a display system. In some embodiments, the display system takes the form of eyewear (e.g., they are wearable), which may advantageously provide a highly immersive VR or AR experience. For example, a display containing a waveguide to display multiple depth planes, e.g., a stack of waveguides (one waveguide or set of waveguides for each of the depth planes), may be configured to be positioned in front of and worn by a user or viewer's eyes. In some embodiments, multiple waveguides, e.g., two stacks of waveguides (one for each eye of the viewer), may be utilized to provide different images to each eye.

[0068] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that when the user's eyes are spaced apart and looking at a real object in space, each eye may have a slightly different view of the object and form an image of the object at a different location on the retina of each eye. This may be referred to as binocular disparity and may be exploited by the human visual system to provide a perception of depth. Conventional display systems simulate binocular disparity by presenting two distinctly different images 190, 200 with slightly different views of one and the same virtual object to each eye 210, 220, corresponding to the view of the virtual object as it would appear by each eye as if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system interprets to derive a perception of depth.

[0069] Continuing with reference to FIG. 2, the images 190, 200 are spaced from the eyes 210, 220 by a distance 230 on the z-axis, which is parallel to the optical axis of the viewer when the eye is fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on slightly different views of the virtual object in the images presented to the eyes 210, 220, respectively, the eyes may necessarily rotate such that the image of the object falls on a corresponding point on the eye's respective retina to maintain single binocular vision. This rotation may cause the line of sight of each of the eyes 210, 220 to converge on a point in space where the virtual object is perceived to reside. As a result, providing three-dimensional images traditionally involves manipulating the convergence and divergence movements of the user's eyes 210, 220 to provide binocular cues that the human visual system interprets to provide the perception of depth.

[0070] However, creating a realistic and comfortable perception of depth is difficult. It should be understood that light from an object at different distances from the eye has a wavefront with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, the light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature depending on how far the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Although only a single eye 210 is illustrated in Figures 3A-3C and various other figures herein for clarity of illustration, the discussion regarding the eye 210 may apply to both eyes 210 and 220 of a viewer.

[0071] 3A-3C, light from an object that a viewer's eye is fixating on may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which in turn may require the lens to assume a different shape and form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as an accommodative cue, causing the shape of the eye's lens to change until a focused image is formed on the retina. For example, an accommodative cue may trigger the relaxation or contraction of the ciliary muscles surrounding the eye's lens, thereby modulating the force applied to the suspensory ligaments that hold the lens, thus changing the shape of the eye's lens, thereby forming a focused image of the object being fixated on the eye's retina / fovea, until retinal blur is eliminated or minimized. The process by which the eye lens changes shape may be referred to as accommodation, and the shape of the eye lens required to form a focused image of the object being gazed upon on the retina / fovea of ​​the eye may be referred to as the state of accommodation.

[0072] Referring now to FIG. 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. Movement of the eyes to fixate on an object causes the eyes to receive light from the object, which forms an image on each of the eye's retinas. The presence of retinal blur in the image formed on the retina may provide a cue for accommodation, and the relative location of the image on the retina may provide a cue for vergence. The cue for accommodation causes accommodation, resulting in a particular accommodation state in which the eye's lens forms a focused image of the object on the eye's retina / fovea. On the other hand, the cue for vergence causes a vergence movement (eye rotation) such that the image formed on each retina of each eye is at a corresponding retinal point maintaining single binocular vision. In these positions, the eyes may be said to be in a particular vergence state. Continuing with reference to FIG. 4A, accommodation can be understood to be the process by which the eye achieves a particular accommodation state, and convergence can be understood to be the process by which the eye achieves a particular convergence state. As shown in FIG. 4A, the accommodation and convergence state of the eye can change if the user gazes at a different object. For example, the accommodated state can change if the user gazes at a new object at a different depth on the z-axis.

[0073] Without being limited by theory, it is believed that a viewer of an object may perceive the object as being "three-dimensional" due to a combination of vergence and accommodation. As previously mentioned, vergence movement of the two eyes relative to one another (e.g., rotation of the eyes such that the pupils move toward or away from one another, converging the line of sight of the eyes to fixate on an object) is closely coupled to accommodation of the eye's lenses. Under normal conditions, changing the shape of the eye's lenses and shifting focus from one object to another at a different distance will automatically produce a matching change in vergence to the same distance, in a relationship known as the "accommodation-vergence reflex." Similarly, a change in vergence will trigger a matching change in lens shape under normal conditions.

[0074] 4B, an example of different accommodation and convergence states of the eyes is illustrated. The pair of eyes 222a gazes at an object at optical infinity, while the pair of eyes 222b gazes at an object 221 at less than optical infinity. Notably, the convergence states of each pair of eyes are different, with the pair of eyes 222a pointing straight ahead, while the pair of eyes 222 converge on the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

[0075] Unfortunately, many users of conventional "3-D" display systems may find such conventional systems uncomfortable or may not perceive any depth sensation due to a mismatch between accommodation and vergence states in these displays. As previously mentioned, many stereoscopic or "3-D" display systems display a scene by providing a slightly different image to each eye. Such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of a scene, causing changes in the vergence states of the eyes, but without a corresponding change in the accommodation states of those eyes. Rather, images are presented by the display at a fixed distance from the eyes, such that the eyes view all image information in a single accommodation state. Such an arrangement counters the "accommodation-vergence-divergence reflex" by causing changes in vergence states without a matching change in accommodation state. This mismatch is believed to cause viewer discomfort. By providing better matching between accommodation and convergence-divergence movements, display systems may form a more realistic and comfortable simulation of three-dimensional images.

[0076] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both vergence cues and matching cues for accommodation, thereby providing physiologically correct accommodation-vergence divergence matching.

[0077] 4B, two depth planes 240 are illustrated, corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, vergence-divergence cues may be provided by displaying appropriately different perspective images to each eye 210, 220. In addition, for a given depth plane 240, the light forming the image provided to each eye 210, 220 may have a wavefront divergence corresponding to the light field generated by a point at the distance of that depth plane 240.

[0078] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing the point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured with the zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupil of the user's eye on the optical axis of those eyes. As an approximation, the depth or distance along the z-axis may be measured from the display (e.g., the surface of the waveguide) in front of the user's eye, and a value for the distance between the device and the exit pupil of the user's eye may be added. That value may be called the pupil distance and may correspond to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the pupil distance may be a normalized value that is generally used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0079] 4C and 4D, examples of matched and mismatched accommodation-vergence-divergence distances are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may cause the eyes 210, 220 to assume a convergence-divergence state in which the eyes converge on point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to a real object in that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is focused on the retinas of those eyes. Thus, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0080] It should be appreciated that each of the accommodation and convergence states of the eyes 210, 220 is associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 will cause those eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state is referred to as the accommodation distance A. d Similarly, a particular convergence-divergence distance V associated with the eyes in a particular convergence-divergence state may be referred to as d or positions relative to each other. When the accommodation distance and the vergence distance match, the relationship between accommodation and vergence is said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0081] However, in a stereoscopic display, the accommodation distance and the vergence distance may not always match. For example, as illustrated in FIG. 4D, the images displayed to the eyes 210, 220 may be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 may be in a particular accommodation state in which the points 15a, 15b on the depth plane are in focus. However, the images displayed to the eyes 210, 220 may provide a cue for vergence that causes the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance corresponds in some embodiments to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to a larger distance from the exit pupils of the eyes 210, 220 to the point 15. The accommodation distance is different from the vergence distance. As a result, there is an accommodation-vergence-divergence mismatch. Such a mismatch may be considered undesirable and may cause discomfort to the user. The mismatch may be related to distance (e.g., V d -A d ) and can be characterized in terms of diopters.

[0082] Without being limited by theory, it is believed that a user may still perceive physiologically correct accommodation-vergence-divergence misalignment of up to 0.25 diopters, up to 0.33 diopters, and up to about 0.5 diopters without the misalignment itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) is configured to present images to a viewer using light with wavefront divergence and images with binocular cues that provide an accommodation-vergence-divergence misalignment of 0.5 diopters or less. In some other embodiments, a display system is configured to present images to a viewer using light with wavefront divergence and images with binocular cues that provide an accommodation-vergence-divergence misalignment of 0.33 diopters or less. In yet other embodiments, the display system is configured to present images to a viewer using light with wavefront divergence and images with binocular cues providing an accommodation-vergence-divergence mismatch of 0.25 diopters or less, including about 0.1 diopters or less.

[0083] It should be understood that in some embodiments, a reference point other than the exit pupil of the eye 210, 220 may be used to determine distance, so long as the same reference point is used for accommodation distance and vergence-divergence distance. For example, distance may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide in a display device) to the depth plane, etc.

[0084] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to a user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence that corresponds to the wavefront divergence of a light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, the user's other eye will be illustrated as being provided with image information from a similar waveguide.

[0085] In some embodiments, a single waveguide may be configured to output light with a set wavefront divergence corresponding to a single or limited number of depth planes and / or the waveguide may be configured to output light in a limited range of wavelengths. As a result, in some embodiments, multiple waveguides or stacks of waveguides may be utilized to provide different wavefront divergence for different depth planes and / or to output light in different ranges of wavelengths.

[0086] 6 illustrates an example of a waveguide stack for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that the display system 250 may be considered a light field display in some embodiments. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0087] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for convergence and multiple discrete cues for accommodation. The cues for convergence may be provided by displaying different images to each of the user's eyes, and the cues for accommodation may be provided by outputting light that forms images with discrete amounts of wavefront divergence. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0088] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include a number of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the number of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. The image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to distribute incident light across each individual waveguide for output towards the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed towards the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0089] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information to each of the image input devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0090] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter such as a light emitting diode (LED). The light from the light module 530 may be directed and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may act as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540 and the image may be an image on a depth plane.

[0091] In some embodiments, the display system 250 may be a scanning fiber display including one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of the waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0092] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light module 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) that coordinates the timing and provisioning of image information to the waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. The controller 560 may be part of the processing module 140 or 150 (FIG. 2) in some embodiments.

[0093] Continuing with reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include an out-coupling optical element 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as out-coupled light, and the out-coupling optical element may also be referred to as a light extraction optical element. The extracted beam of light may be output by the waveguide at a location where the light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguide 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top major surface and / or bottom major surface and / or directly within the volume of the waveguide 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0094] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is closer inward toward the person from optical infinity, which was the light from the next upper waveguide 280.

[0095] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0096] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set for each depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0097] Continuing with reference to FIG. 6, the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be volume or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0098] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern or "diffractive optical element" (also referred to herein as "DOE"). Preferably, the DOE has a low enough diffraction efficiency so that only a portion of the light in the beam is deflected towards the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several related exit beams that exit the waveguide at various locations, resulting in a very uniform pattern of exit emission towards the eye 210 for this particular collimated beam bouncing within the waveguide.

[0099] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may include a layer of polymer dispersed liquid crystal in which microdroplets include a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0100] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor a physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 9D) and may be in electrical communication with the processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye to monitor each eye separately.

[0101] 7, an example of an output beam output by a waveguide is shown. Although one waveguide is shown, it should be understood that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly and that the waveguide assembly 260 includes multiple waveguides. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as an output beam 650. The output beam 650 is shown as approximately parallel, but may be redirected to propagate to the eye 210 at an angle (e.g., divergent output beam formation) as discussed herein and depending on the depth plane associated with the waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0102] In some embodiments, a full color image may be formed at each depth plane by overlaying an image on each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or less depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. The different depth planes are indicated in the diagram by different numbers for diopters following the letters G, R, and B. By way of example only, the numbers following each of these letters indicate the diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact location of the depth planes for the different primary colors may be varied to account for differences in the eye's focusing of different wavelengths of light. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0103] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, but it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0104] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or in place of one or more of the red, green, or blue colors.

[0105] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0106] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of visual perception of a viewer, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0107] 9A, in some embodiments, light impinging on a waveguide may need to be redirected to in-couple the light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of a stacked waveguide example of a plurality of stacked waveguides or a set of stacked waveguides 660, each including an in-coupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. The stack 660 may correspond to the stack 260 (FIG. 6), and the illustrated waveguides of the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of the image input devices 360, 370, 380, 390, 400 is launched into the waveguide from a position that requires the light to be redirected for in-coupling.

[0108] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), for example, incoupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, incoupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and incoupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of the incoupling optical elements 700, 710, 720 may be disposed on a bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguide 670, 680, 690 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive deflecting optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the incoupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the incoupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments.

[0109] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400 as shown in FIG. 6 and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to not substantially receive light from others of the in-coupling optical elements 700, 710, 720.

[0110] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0111] The waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid and / or solid layers of material. For example, as shown, layer 760a may separate the waveguides 670 and 680, and layer 760b may separate the waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low index material (i.e., a material having a lower index of refraction than the material forming the immediate neighbors of the waveguides 670, 680, 690). Preferably, the index of refraction of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than the index of refraction of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0112] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or the same, and the materials forming the layers 760a, 760b are similar or the same. In some embodiments, the materials forming the waveguides 670, 680, 690 may differ between one or more of the waveguides, and / or the materials forming the layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0113] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0114] In some embodiments, the light beams 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects the incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0115] For example, incoupling optical element 700 may be configured to deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light beam 780 impinges on and is deflected by incoupling optical element 710, which is configured to deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by incoupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0116] 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the incoupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690 and incouplings the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they strike the corresponding optical dispersive element 730, 740, 750 of the waveguide.

[0117] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, the in-coupled light rays 770, 780, 790 are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the optically dispersive elements 730, 740, 750, respectively. The optically dispersive elements 730, 740, 750 deflect the light rays 770, 780, 790 to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0118] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse the light to the out-coupling optical elements 800, 810, 820, and in some embodiments may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect the light directly to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light to the viewer's eye 210 (FIG. 7). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and an EPE may increase the eyebox in an axis that intersects (e.g., perpendicular to) the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. In response to striking the OPE, again, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, and so on. Similarly, in response to striking the EPE, a portion of the striking light is directed out of the waveguide towards the user, and the remaining portion of the light continues to propagate through the waveguide until it strikes the EP again, at which point another portion of the striking light is directed out of the waveguide, and so on. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0119] Thus, referring to Figures 9A and 9B, in some embodiments, a set of waveguides 660 includes, for each primary color, a waveguide 670, 680, 690, an in-coupling optical element 700, 710, 720, an optically dispersive element (e.g., OPE) 730, 740, 750, and an out-coupling optical element (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical element 700, 710, 720 redirects or deflects the incoming light into its waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated embodiment, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues to bounce back down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, with light ray 780 incident on the in-coupling optical element 710 and being deflected thereby. Light ray 780 will then bounce back down the waveguide 680, via TIR, to its optically dispersive element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light beam 790 so that it propagates by TIR to a light dispersive element (e.g., OPE) 750 and then to an out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light beam 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0120] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690 may be vertically aligned with each waveguide's associated light dispersive element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an arrangement including non-overlapping spatially separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements in these arrangements may correspond to sub-pupils.

[0121] 9D illustrates an example of a wearable display system 60 into which the various waveguide and associated systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which diagrammatically illustrates some portions of the system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0122] 9D , the display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the eye of the user 90. The display 70 may be considered an eyepiece in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker, not shown, may also be optionally positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands to the system 60 (e.g., voice menu command selections, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and mounted on the body of the user 90 (e.g., the head, torso, limbs, etc. of the user 90). The ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0123] 9D, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as wired or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-type configuration, a belt-type configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, such as wired or wireless connectivity. The local processing and data module 140 may include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. Optionally, the local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data includes a) data captured from sensors (such as image capture devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., which may be operatively coupled to the frame 80 or otherwise attached to the user 90)) and / or b) data acquired and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for passing to the display 70 after processing or retrieval. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted to frame 80 or may be a freestanding structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0124] 9D , in some embodiments, remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (GPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, remote data repository 160 may include digital data storage facilities that may be available through the Internet or other networking configurations in a "cloud" resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all computations are performed within the local processing and data module, allowing for fully autonomous use from the remote modules. Optionally, an external system (e.g., one or more processors, one or more computer systems), including a CPU, GPU, etc., may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, e.g., via a wireless or wired connection.

[0125] Metasurface 10A and 10B respectively illustrate cross-sectional side and top-down view examples of a metasurface 2002 according to some embodiments. A substrate 2000 has a surface 2000a on which a metasurface 2002 is disposed, the metasurface 2002 including a plurality of metasurface unit cells 2010. Each unit cell includes a plurality of nanobeams 2020a, 2020b formed from an optically transparent material. The nanobeams 2020a, 2020b may be ridges (or nanowires) that extend laterally into and out of the page to define trenches between adjacent nanobeams. In some embodiments, the nanobeams 2020a, 2020b may be linear. Preferably, the nanobeams 2020a, 2020b are continuous along their length, which can have the advantage of providing high diffraction efficiency. In some other embodiments, the nanobeams 2020a, 2020b may be intermittent along their length, for example, the nanobeams 2020a, 2020b may each extend along a line with gaps in the nanobeams 2020a, 2020b along those lines.

[0126] The unit cells 2010 may be repeated at regular intervals across the surface 2000a and may be parallel to one another such that the nanobeams 2020a, 2020b are also parallel to one another. The unit cells 2010 may have a width P, which is the distance between the same points of immediately adjacent unit cells 2010. In some embodiments, P may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. It should be understood that P may be considered the pitch of the unit cells 2010 and may be substantially constant across the lattice formed by those unit cells. In some other embodiments, P may vary across the surface 2000a.

[0127] Preferably, the refractive index of the material forming the nanobeams 2020a, 2020b is higher than that of the substrate 2000. In some embodiments, the substrate 2000 may be a waveguide and may correspond to the waveguides 270, 280, 290, 300, 310 (FIG. 6) and / or the waveguides 670, 680, and 690 (FIG. 9A). In such applications, the substrate preferably has a relatively high refractive index, e.g., 1.5, 1.6, 1.7, 1.8, 1.9, or higher, which may provide the advantage of increasing the field of view of a display that forms an image by outputting light from the substrate 2000. Examples of materials for forming the substrate 2000 include glass (e.g., doped glass), lithium niobate, plastic, polymer, sapphire, or other optically transparent materials. In some embodiments, the refractive index of the material forming the nanobeams 2020a, 2020b may be 2.0 or higher, 2.5 or higher, 3.0 or higher, 3.3 or higher, or 3.5 or higher. Examples of materials for forming the nanobeams 2020a, 2020b include silicon-containing materials (e.g., amorphous or polysilicon, and silicon nitride), oxides, and gallium phosphide. Examples of oxides include titanium oxide, zirconium oxide, and zinc oxide. Preferably, the materials forming the nanobeams 2020a, 2020b are the same, which has the advantage of simplifying the fabrication of the metasurface 2002.

[0128] 10A and 10B, one of the nanobeams 2020b has a width NW2 that is greater than the width NW1 of the other of the nanobeams 2020a shown. In some embodiments, the widths NW1 and NW2 are each in the range of 10 nm to 1 μm, including 10 nm to 300 nm, with NW1 exceeding NW2, as discussed above. As shown, the nanobeams 2020a, 2020b may be separated by a gap in the range of 10 nm to 1 μm width, including 10 nm to 300 nm width. Also as shown, the nanobeams 2020a, 2020b have a height h nw, which may be in the range of 10 nm to 1 μm, including 10 nm to 450 nm. Preferably, the heights of the nanobeams 2020a, 2020b are substantially equal.

[0129] As disclosed herein, the dimensions of the unit cell 2010 and various features of the nanobeams 2020a, 2020b may vary depending on the nature of the materials used to form the metasurface 2002 and the nature of the surrounding structures, such as the substrate 2000. In some embodiments, the height h of the nanobeams 2020a, 2020b may vary depending on the nature of the materials used to form the metasurface 2002 and the nature of the surrounding structures, such as the substrate 2000. nw may vary depending on the refractive index of the material used for those nanobeams. In some embodiments, the height of the nanobeams may be between 10 nm and 450 nm, and the refractive index of the material is greater than 3.3, between 10 nm and 1 μm, and the refractive index is 3.3 or less. As another example, the height of the nanobeams may be between 10 nm and 450 nm, and the nanobeams are formed from silicon (e.g., amorphous or polysilicon).

[0130] 10A and 10B, the metasurface 2002 illustrated therein functions in a transmission mode. Light rays 2021a, 2021b are redirected in response to propagating through the metasurface 2002 formed by the nanobeams 2020a, 2020b. As illustrated, light ray 2021a is incident on the metasurface 2002 at an angle α relative to the normal to the surface 2000a. Preferably, the angle α is within the angular bandwidth for the metasurface 2002 such that the light ray 2021a is redirected by the metasurface 2002 and propagates within the substrate 2000 at an angle that promotes total internal reflection within the substrate 2000. As illustrated, light ray 2021b is incident on the metasurface 2002 at an angle θ relative to the normal to the surface 2000a. TIR Preferably, the angle θ TIRis within the range of angles that promote total internal reflection within the substrate 2000. As disclosed herein, in some embodiments, the metasurface 2002 may be utilized as an incoupling optical element (e.g., as one or more of the incoupling optical elements 700, 710, 720 (FIG. 9A)) to incoupling incident light such that the light propagates through the substrate 2000 via total internal reflection.

[0131] The metasurface 2002 will also deflect light impinging thereon from within the substrate 2000. Taking advantage of this functionality, in some embodiments, the metasurfaces disclosed herein may be applied to form external coupling optical elements, such as one or more of external coupling optical elements 570, 580, 590, 600, 610 (FIG. 6) or 800, 810, 820 (FIG. 9B), instead of or in addition to forming internal coupling optical elements at different locations on the surface 2000a. It should be understood that when different waveguides have different associated primary colors, the external coupling optical elements and / or internal coupling optical elements associated with each waveguide may have a geometric size and / or periodicity specific to the wavelength or color of light that the waveguide is configured to propagate. Thus, different waveguides may have metasurfaces with different geometric sizes and / or periodicities. As an example, a metasurface for incoupling or outcoupling red, green, or blue light may have a geometric size and / or periodicity (pitch) configured to redirect or diffract light at wavelengths of, for example, 638 nm, 520 nm, and 455 nm, respectively. In some embodiments, the geometric size and periodicity of the nanobeams 2020a, 2020b and unit cell 2010 increase as the wavelength becomes longer, and the height or thickness of one or both of the nanobeams 2020a, 2020b also increases as the wavelength becomes longer.

[0132] In some embodiments, when the metasurface 2002 is utilized as an outcoupling optical element, the metasurface 2002 may have a geometric size and / or pitch that causes the metasurface to impart a refractive power to the diffracted light. For example, the metasurface may be configured to cause light to exit the metasurface in divergent or converging directions. Different portions of the metasurface may have different pitches, which, for example, deflect different light rays in different directions, such that the light rays diverge or converge.

[0133] In some other embodiments, the metasurface 2002 may redirect light such that it propagates away from the metasurface 2002 as a ray of collimated light. For example, if collimated light impinges on the metasurface 2002 at a similar angle, the metasurface 2002 may have a consistent geometric size and consistent pitch throughout the metasurface 2002 and redirect the light at a similar angle.

[0134] 11A-11B, the metasurface 2002 may deflect light in a "reflective mode," in which the redirected light remains on the same side of the metasurface 2002 before and after it strikes the metasurface. FIG. 11A illustrates an example of a cross-sectional side view of a metasurface configured to function in a reflective mode, and FIG. 11B illustrates an example of a cross-sectional top-down view of the metasurface of FIG. 11A as viewed on plane 11B. As shown, the nanobeams 2020a, 2020b of the metasurface 2002 may be embedded within a reflective layer 2100. The reflective layer 2100 may be formed from a reflective material, e.g., a metal such as aluminum, silver, gold, and copper. Preferably, the material forming the reflective layer 2100 fills the spaces between the nanobeams 2020a, 2020b and between the unit cells 2010. Additionally, the height or thickness h of the reflective layer 2100 may be 0.1 mm or less. r is the height h of the nanobeams 2020a and 2020b. nw In some embodiments, the height h r The thickness of the reflective layer 2100 may be 150 nm or thicker or 1 μm or thicker. Preferably, the reflective layer 2100 is thick enough to block incident light and rexceeds the optical depth of layer 2100. It should be understood that the range of dimensions of the various features forming unit cell 2010 are similar to those discussed herein with respect to Figures 10A and 10B.

[0135] 12-13, another example of a reflection mode metasurface is illustrated. FIG. 12 illustrates a cross-sectional side view example of a metasurface 2002 configured to function in a reflection mode, and FIG. 13 illustrates a cross-sectional top-down view example of the metasurface of FIG. 12 as viewed on plane 13 of FIG. 13. As shown, the nanobeams 2020a, 2020b are embedded within an optically transmissive spacer layer 2110. In these embodiments, the reflection layer 2100 is disposed directly on the surface of the spacer layer 2110 opposite the substrate 2000. The spacer layer 2110 has a height or thickness h sl which has a height h s The height of the nanobeams 2020a, 2020b is exceeded by the height of the nanobeams 2020a, 2020b, thereby s 2100. In some embodiments, the height h s may be in the range of 5 nm to 1 μm, including 10 nm to 300 nm. It should be appreciated that examples of suitable materials for the spacer layer 2100 can include materials that can be deposited by spin-on coating, including poly(methyl methacrylate) (PMMA), spin-on glass, e-beam resist or photoresist, and polymers. In some embodiments, the spacer layer has a refractive index of 1 to 2.

[0136] In some embodiments, substrate 2000 may include both a transmissive metasurface and a reflective metasurface. FIG. 14A illustrates an example of a cross-sectional side view of substrate 2000 having transmissive and reflective metasurfaces 2002a, 2002b, respectively. In some embodiments, transmissive and reflective metasurfaces 2002a, 2002b may be on opposite sides of the substrate. FIG. 14B illustrates an example of a top-down view of metasurface 2002a of FIG. 14A. FIG. 14C illustrates an example of a top-down view of metasurface 2002b of FIG. 14A as viewed on plane 14C of FIG. 14A.

[0137] 14A, metasurface 2002a includes a plurality of unit cells 2010a that include nanobeams 2020a, 2020b. Similarly, metasurface 2002b includes a plurality of unit cells 2010b that include nanobeams 2020c, 2020d. Like nanobeams 2020a, 2020b, one of nanobeams 2020c, 2020d is wider than the other. As disclosed herein, the dimensions of the features of unit cells 2010a, 2010b may be selected based on the wavelength of light that the metasurface is configured to redirect and the desired degree of redirection. When the metasurface is configured to redirect light of different wavelengths, the widths of nanobeams 2020a and 2020c may differ from one another and / or the widths of nanobeams 2020b and 2020d may also differ from one another. For example, metasurface 2002a may be configured to redirect light corresponding to the color green, while metasurface 2002b may be configured to redirect light corresponding to the color red. In some embodiments, such an arrangement, in which each metasurface is configured to redirect light of a different range of wavelengths, may advantageously reduce the size of a waveguide stack, in which different waveguides are used to propagate light of different wavelengths. Advantageously, metasurfaces 2002a, 2002b may be used as in-coupling and / or out-coupling optical elements to allow a single waveguide to be used to guide light corresponding to different primary colors, thereby avoiding the use of one waveguide.

[0138] As shown, metasurface 2002a functions in a transmission mode, selectively redirecting light ray 2040a while allowing light ray 2040b to propagate through the metasurface without being redirected. Light ray 2040b then impinges on reflection-mode metasurface 2002b, which reflects light ray 2040b to propagate in a desired direction (different from that expected for a specular reflector).

[0139] 15A-15E, an example of a process flow for forming a transmissive metasurface is illustrated. With reference to FIG. 15A, a layer 2020 of optically transmissive material for forming nanobeams 2020a, 2020b is deposited on a substrate 2000. The deposition may be accomplished using a deposition process such as chemical vapor deposition (CVD), including plasma enhanced chemical vapor deposition. Then, with reference to FIG. 15B, a selectively definable material, such as a resist (such as a nanoimprint resist), is deposited on the layer 2022. The resist 2022 may be deposited by jet coating (e.g., inkjet printing), which may offer the advantage of forming very thin layers and also layers with variable composition and / or thickness.

[0140] 15C, an imprint template or master 2024 is brought into contact with resist 2022 to pattern the resist. In some other embodiments, the pattern in the imprint template 2024 may be formed by lithography, including, for example, electron beam lithography or EUV lithography.

[0141] 15D, the pattern formed in resist layer 2022 is transferred to optically transmissive layer 2020. It should be understood that this pattern transfer may be accomplished using etch selectivity for the material forming optically transmissive layer 2020 relative to other exposed materials. In some embodiments, the pattern transfer etch may be an anisotropic etch, such as a reactive ion etch. Subsequently, in some embodiments, resist layer 2022 may be removed using, for example, an ashing process.

[0142] 15E, a plurality of unit cells 2010 are formed that include nanobeams 2020a, 2020b. While shown diagrammatically as having similar widths for ease of illustration, it should be understood that the nanobeams 2020a, 2020b have different widths as disclosed herein.

[0143] 16A and 16B illustrate scanning electron microscope images of the metasurface. The metasurface was formed generally as described with respect to FIGS. 15A-15E, and the resist was patterned by electron beam lithography. Advantageously, highly uniform rows of material corresponding to the nanobeams 2020a, 2020b were formed. As shown in FIG. 16B, each nanobeam has a substantially uniform cross-sectional shape as seen in the illustrated side view.

[0144] Although not shown, it should be understood that a reflective mode metasurface may be formed through additional processing of the structure shown in Figure 15E. For example, a reflective material may be deposited in the open volume between and across the nanobeams 2020a, 2020b to form the structure illustrated in Figures 11A and 11B. In some other embodiments, the nanobeams 2020a, 2020b may be formed by etching trenches into the reflective layer and subsequently filling the trenches with the material of the nanobeams 2020a, 2020b.

[0145] As another example, the structure illustrated in Figure 12 may be formed by depositing a layer of optically transparent spacer material on and between the nanobeams 2020a, 2020b. A reflective layer may then be deposited on the spacer layer. In some embodiments, deposition may be accomplished using a deposition process, such as a chemical vapor deposition (CVD) process and / or a physical vapor deposition (PVD) process.

[0146] As discussed herein, metasurfaces according to various embodiments provide highly uniform diffraction efficiency over a wide range of incidence angles. Figure 17 illustrates an example plot showing diffraction efficiency versus incidence angle of light for a transmissive metasurface. Advantageously, the diffraction efficiency over a range of angles spanning approximately 50° is highly uniform.

[0147] High uniformity is also provided by various embodiments of reflective metasurfaces. Figures 18A-18C illustrate examples of plots showing diffraction efficiency versus angle of incidence of light for reflective metasurfaces. The wavelength of the incident light is different for each of Figures 18A-18C. Advantageously, the plots are very flat over a wide range of angles of incidence. In addition, the plots are advantageously similar for different wavelengths corresponding to the colors red, green, and blue. Such uniformity may be beneficially applied to display systems utilizing different primary colors. Diffraction uniformity may aid in the formation of high quality images with high color accuracy.

[0148] It has also been found that the diffraction efficiency of the metasurface is highly dependent on the polarization of the instantaneous light. Figures 19A and 19B illustrate examples of plots showing the polarization sensitivity of the transmission metasurface of Figures 10A and 10B. As shown in Figure 19A, the diffraction efficiency is high for incident light with polarization parallel to the nanobeams forming the asymmetric grating. However, light with polarization perpendicular to the nanobeams has a low diffraction efficiency. Given this sensitivity to polarization, the metasurfaces, as described herein, may be advantageously utilized as polarizing beam splitters. Preferably, the metasurfaces provide an extinction ratio of 5 or more, 7 or more, or 9 or more for light of different polarizations.

[0149] As discussed herein, the amplitude and phase of the light redirected by the metasurfaces disclosed herein depend on the width of the nanobeam forming the metal surface. Figure 20 illustrates a plot of amplitude and phase shift versus nanobeam width for the metasurfaces of Figures 10A and 10B. As shown by the plot, the width of the nanobeam or nanowire may be adjusted to manipulate the amplitude and phase of the redirected light.

[0150] Referring now to FIG. 21A, in some embodiments, a metasurface may include a multilevel asymmetric grating. FIG. 21A illustrates an example of a cross-sectional side view of a multilevel metasurface 2008 including multiple levels of optically transmissive material. It should be understood that the cross-sectional side view is taken on a plane perpendicular to the elongation axis of the illustrated nanobeams 2020a, 2020b. The nanobeams 2020a, 2020b are formed on a surface 2000a of a substrate 2000. As illustrated, in some embodiments, the metasurface 2008 is a bi-level structure having a bottom and top level 2012, 2014, respectively. The bottom level 2012 includes nanobeams 2020a, 2020b formed from a first optically transmissive material and a mass 2030c of a second optically transmissive material between the nanobeams 2020a, 2020b. The top level 2014 may be directly vertically adjacent to the nanobeams 2020a, 2020b and includes a top level nanobeam 2030a of a second optically transmissive material formed directly on the nanobeam 2020a and a top level nanobeam 2030b of a second optically transmissive material formed directly on the nanobeam 2020b. It should be understood that the top level nanobeam 2030a, 2030b of the second optically transmissive material may contact the nanobeams 2020a, 2020b. As shown, on the top level 2014, the nanobeams 2030a, 2030b of the second optically transmissive material may form plateaus of material that are localized on the surface of the nanobeams 2020a, 2020b and spaced apart from other localized deposits (or plateaus) of the second optically transmissive material.

[0151] 21A , preferably the refractive index of the second optically transmissive material forming nanobeams 2030a, 2030b and mass 2030c is higher than the refractive index of both the first optically transmissive material forming nanobeams 2020a, 2020b and the material forming substrate 2000. In some embodiments, the refractive index of the first optically transmissive material forming nanobeams 2020a, 2020b is lower than or similar to the refractive index of the material forming substrate 2000.

[0152] Continuing with reference to FIG. 21A, the first optically transmissive material of the nanobeams 2020a, 2020b is preferably a material that can be patterned, for example, by lithography and etching processes. More preferably, the first optically transmissive material is a nanoimprint resist that can be patterned by nanoimprinting. As discussed herein, the second optically transmissive material forming the nanobeams 2030a, 2030b and the mass 2030c may have a higher refractive index than both the first optically transmissive material of the nanobeams 2020a, 2020b and the material forming the substrate 2000. In some embodiments, the refractive index of the second optically transmissive material is higher than 1.6, 1.7, 1.8, or 1.9. Examples of materials for the second optically transmissive material include semiconductor materials, including silicon-containing materials and oxides. Examples of silicon-containing materials include silicon nitride and silicon carbide. Examples of oxides include titanium oxide, zirconium oxide, and zinc oxide. In some embodiments, the second optically transmissive material may have a lower optical transmissivity than these oxides. For example, the second optically transmissive material may be silicon or a derivative thereof. In some embodiments, the first and second optically transmissive materials are amorphous solid state materials or crystalline solid state materials. Without being limited by theory, amorphous materials may be desirable in some applications because they can be formed at lower temperatures and over a larger surface area of ​​some crystalline materials. In some embodiments, the first and second optically transmissive materials forming the features 2020a, 2020b, 2030a, 2030b, 2030c may each be one of an amorphous or crystalline semiconductor material.

[0153] As mentioned above, in some embodiments, the widths NW1, NW2 of the nanobeams 2020a, 2020b, respectively, forming the unit cell 2010, may be in the range of 10 nm to 1 μm, including 10 nm to 300 nm or 10 nm to 250 nm. The nanobeams 2020a, 2020b of the unit cell 2010 may be separated by gaps that are in the range of 5 nm to 1 μm wide, including 10 nm to 1 μm wide or 10 nm to 300 nm wide. The pitch P of the unit cells 2010 may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. In some embodiments, the heights h of the nanobeams 2020a, 2020b may be in the range of 10 nm to 1 μm wide, including 10 nm to 300 nm to 500 nm. nw may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 10 nm to 450 nm. m may be in the range of 10 nm to 1 μm, including 10 nm to 600 nm. Preferably, the heights of the nanobeams 2030a, 2030b and mass 2030c are substantially similar.

[0154] It has been found that the dimensions of the features of the unit cells may vary depending on the nature of the materials used to form the metasurface. For example, the height of the nanobeams may vary depending on the refractive index of the material used for those nanobeams. In some embodiments, the height of the nanobeams may be between 10 nm and 450 nm, and the refractive index of the material is greater than 3.3, between 10 nm and 1 μm, and the refractive index is 3.3 or less. As another example, the height of the nanobeams may be between 10 nm and 450 nm, and the nanobeams are formed from silicon (e.g., amorphous or polysilicon). In some embodiments, the height of the material of the nanobeams 2030a, 2030b and mass 2030c may be within the range of 10 nm to 1 μm, including between 10 nm and 600 nm.

[0155] It should be understood that within the aforementioned dimensional ranges, in some embodiments, the metasurface may function primarily in a reflective mode or primarily in a transmissive mode, depending on the appropriate selection of dimensions in conjunction with materials for the features 2030a, 2030b, 2030c. For example, for a given wavelength of light, the thickness of the features 2030a, 2030b, 2030c for a metasurface 2008 functioning in a reflective mode may be lower than the thickness of the features 2030a, 2030b, 2030c for a metasurface functioning in a transmissive mode. Additionally, in either the transmissive or reflective mode, the use of higher refractive index materials for the features 2030a, 2030b, 2030c may allow for a reduction in the thickness of those features while achieving similar light redirecting properties.

[0156] 21A, metasurface 2008 is functioning in a reflection mode, where incident light ray 2200 impinges on metasurface 2008 and is redirected by diffraction at an angle such that it propagates through substrate 2000 by total internal reflection. In some embodiments, the height of features 2030a, 2030b, 2030c may be less than the height of nanobeams 2020a, 2020b, as shown. It should be appreciated that light passes twice through a metasurface functioning in a reflection mode (first time where the incident light impinges on the metasurface and a second time where it is reflected through and away from the metasurface), thereby allowing features 2030a, 2030b, 2030c and nanobeams 2020a, 2020b with heights less than the metasurface to function in a transmission mode with similar light redirecting capabilities.

[0157] Referring now to FIG. 21B, an example of a plot of transmission and reflection as a function of the angle of incidence of light for a metasurface having the general structure shown in FIG. 21A is illustrated. The various diffraction orders of transmitted and reflected light are indicated by "T" and "R", respectively. In this example, the nanobeams 2020a, 2020b are formed from an optically transparent resist, and the features 2030a, 2030b, 2030c are formed from titanium oxide. Titanium oxide advantageously has a high refractive index of 2.6, which may facilitate a reduction in the thickness or height of the features 2030a, 2030b, 2030c and the nanobeams 2020a, 2020b relative to lower refractive index materials. For each unit cell, the width of nanobeam 2020a is 50 nm, the width of nanobeam 2020b is 110 nm, the gap between nanobeams 2020a and 2020b is 40 nm, the height of nanobeams 2020a, 2020b is 100 nm, the height of features 2030a, 2030b, 2030c is 50 nm, and the pitch of unit cells 2010 is 382 nm.

[0158] With continued reference to FIG. 22B, the percentage of light incident on metasurface 2008 that is reflected and undergoes first order diffraction (R1) at angles suitable for TIR is approximately 25% for an angle of incidence of 0°, and varies from 25% to 42% for angles of incidence from about -10° to about 10°. As shown, the zero order reflection is advantageously low. When metasurface 2008 is utilized within a display device, such as display system 250 (FIG. 6), utilizing a reflective spatial light modulator, zero order reflection may be undesirable and cause light to be reflected off the spatial light modulator, which in turn reflects light back to the viewer, thereby causing undesirable image artifacts, such as ghosting. As a result, a low amount of zero order reflection may be desirable in such applications. In addition, as shown, a portion of the incident light is transmitted (T0) and another portion of the incident light undergoes negative first order diffraction (R1). -1 ) will be received.

[0159] 22A, a metasurface 2008 operating in a transmission mode is illustrated. Notably, in this embodiment, the metasurface 2008 is similar to that shown in FIG. 21A, except for the height of the features 2030a, 2030b, 2030c and, optionally, the material from which these features 2030a, 2030b, 2030c are formed. As shown, the height of the mass 2030c (and the corresponding height of the nanobeams 2030a, 2030b) may, in some embodiments, exceed the height of the nanobeams 2020a, 2020b. In the illustrated embodiment, a light ray 2200 propagates through the metasurface 2008 and is diffracted by total internal reflection into an angle such that it propagates through the substrate 2000.

[0160] 22B, an example plot of transmission and reflection as a function of the angle of incidence of light for a metasurface having the general structure shown in FIG. 22A is illustrated. As above, the diffraction orders of transmitted and reflected light are denoted by "T" and "R", respectively. For each unit cell, the width of nanobeam 2020a is 50 nm, the width of nanobeam 2020b is 110 nm, the gap between nanobeams 2020a and 2020b is 50 nm, the height of nanobeams 2020a, 2020b is 150 nm, the height of features 2030a, 2030b, 2030c is 190 nm, and the unit cell pitch 2010 is 382 nm. In this embodiment, the nanobeams 2020a, 2020b are formed from an optically transmissive resist, and the features 2030a, 2030b, 2030c are formed from silicon nitride, which has a refractive index of 2.0.

[0161] Continuing to refer to FIG. 22B, the negative first order diffraction (TIR) ​​is applied to the light beam at an angle suitable for TIR. -1The percentage of light incident on the metasurface that undergoes positive first order diffraction (T1) is about 35% for an angle of incidence of 0° and varies from 35% to 56% for angles of incidence from about -10° to about 10°. Zero order reflection advantageously remains low. Also, as shown, a portion of the incident light is not redirected but is transmitted (T0), and another portion of the incident light undergoes positive first order diffraction (T1).

[0162] 23A-23D, an example of a process flow for forming a metasurface 2008 is illustrated. Referring to FIG. 14A, a layer 2020 of a first material, e.g., a resist (such as a nanoimprint resist), is deposited on a substrate 2000. The layer 2020 is preferably optically transparent and may be deposited, for example, by spin coating. In some embodiments, the layer 2020 may be deposited by jet coating (e.g., inkjet printing), which may offer the advantage of forming very thin layers and also layers with variable composition and / or thickness.

[0163] 23B, an imprint template or master 2024 is brought into contact with the resist layer 2020 to pattern the layer. It should be understood that the pattern in the imprint template 2024 may be a negative of the pattern of the nanobeam of the metasurface to be formed. The pattern in the imprint template 2024 may be formed by lithography, including, for example, electron beam lithography or EUV lithography. Advantageously, the same template 2024 may be reused to pattern resist on multiple substrates, thereby reducing the processing cost per unit for the ultimately formed metasurface.

[0164] After contacting the imprint template 2024, the resist 2020 takes on the pattern defined by the openings in the template 2024. In some embodiments, the resist 2020 may be cured, for example by exposure to light (such as UV light) and / or heat to immobilize the resist. The template 2024 may then be retracted to leave the patterned resist with the nanobeams 2020a, 2020b, as shown in FIG. 23C. In some other embodiments, the pattern in the resist layer may be transferred to an underlying layer of material (e.g., as shown in FIGS. 15A-15E), and the resist may be removed, thereby forming the nanobeams 2020a, 2020b in that underlying layer of material.

[0165] Referring now to FIG. 23D, a second material is subsequently deposited on the nanobeams 2020a, 2020b to form nanobeams 2030a, 2030b. Examples of materials for the second material include semiconductor materials, including silicon-containing materials such as silicon nitride, silicon carbide, oxides, including zirconium oxide, zinc oxide, and titanium oxide, and optically transparent resists. As disclosed herein, the second material 2030 is preferably an optically transparent material. The second material 2030 may be deposited by a variety of processes, including blanket deposition, directional deposition, and spin or jet coating. Examples of blanket deposition include chemical vapor deposition (CVD), where a resist is exposed to mutually reactive precursors that are simultaneously present in a deposition chamber containing the substrate 2000, and atomic layer deposition (ALD), where a resist is alternately exposed to precursors. ALD may provide the advantage of precisely controlling the thickness of the deposited layer when high precision is desired, and also depositing the material at low temperatures. Examples of directional deposition include evaporation and sputtering to preferentially deliver the second material onto the nanobeams 2020 a , 2020 b and the top surface of the substrate 2000 .

[0166] It should be understood that the substrate 2000 having a metasurface according to various embodiments disclosed herein may be used to form a display system, such as the system 1000 (FIG. 6) disclosed herein. For example, the metasurface may be utilized as an in-coupling optical element and / or an out-coupling optical element, as described herein. In some embodiments, after processing of the metasurface, the waveguide 2000 may be optically coupled to a light pipe, such as a light pipe, for injecting image information into the waveguide. The light pipe may be an optical fiber, in some embodiments. Examples of light pipes include image injection devices 200, 202, 204, 206, 208 (FIG. 6) and scanning optical fibers. In some embodiments, multiple waveguides, each having a metasurface 2010, may be provided, and each of these waveguides may be optically coupled to one or more image injection devices.

[0167] Various exemplary embodiments of the present invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate the broader and more applicable aspects of the present invention. Various modifications may be made to the invention described, and equivalents may be substituted without departing from the true spirit and scope of the invention.

[0168] For example, although advantageously utilized with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by systems that provide images on a single depth plane and / or with virtual reality displays. In some embodiments where multiplexed image information (e.g., light of different colors) is directed into the waveguide, multiple metasurfaces may be provided on the waveguide, e.g., one active metasurface for each color of light. In some embodiments, the pitch or periodicity and / or geometric size of the nanobeams or nanobeams that form the metasurface may vary across the metasurface. Such metasurfaces may be active in redirecting light of different wavelengths depending on the geometry and pitch at which the light impinges on the metasurface. In some other embodiments, the geometry and pitch of the metasurface features are configured to vary such that deflected light rays, even of similar wavelengths, propagate away from the metasurface at different angles. It should also be understood that multiple separated metasurfaces may be disposed across the substrate surface, with each metasurface having the same geometry and pitch in some embodiments, and at least some of the metasurfaces having a different geometry and / or pitch than other metasurfaces in some other embodiments.

[0169] Various terms that define orientation are utilized herein. For example, a nanobeam may be described as residing on or across a substrate and may be described as having a height (or thickness). It should be understood that these terms refer to the nanobeam and substrate when placed in a reference orientation where the substrate is vertically below the nanobeam. In such an orientation, the height describes the vertical dimension, while the gap, pitch, or width describes the lateral dimension, e.g., extending in a plane facing (e.g., substantially parallel to) the surface of the substrate on which the nanobeam is disposed. It should be understood, however, that the nanobeam and substrate are not limited to that relative orientation and may be positioned in other orientations relative to one another.

[0170] Although advantageously applied to displays, such as wearable displays, metasurfaces may also be applied to a variety of other devices where a compact and thin light redirecting element is desired. For example, metallic surfaces may be applied to form the light redirecting portions of optical plates (e.g., glass plates), optical fibers, microscopes, sensors, watches, cameras, and image projection devices in general.

[0171] In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process acts, or steps to the objective, spirit, or scope of the present invention. Moreover, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein has discrete components and features that can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

[0172] The present invention includes methods that may be performed using the device. The method may include the act of providing such a suitable device. Such providing may be performed by a user. In other words, the act of "providing" merely requires the user to obtain, access, approach, locate, configure, activate, power on, or otherwise act to provide the required device in the method. The methods described herein may be carried out in any order of the described events that is logically possible, and in the described order of events.

[0173] Exemplary aspects of the invention, together with details regarding material selection and manufacturing, are described above. As for other details of the invention, these will be understood in conjunction with the patents and publications referenced above and will generally be known or understood by those skilled in the art. The same may be true with respect to method-based aspects of the invention in terms of additional acts as generally or logically adopted.

[0174] For ease of description, various words are used herein to indicate the relative location of features. For example, various features may be described as being "on" another feature, "across" it, on the "side" of it, "higher" than it, or "lower" than it. Other words of relative location may also be used. All such words of relative location assume that the aggregate structure or system formed by the features as a whole is in a particular orientation as a reference point for purposes of description, but it should be understood that when used, the structures may be positioned side-by-side, inverted, or in any number of other orientations.

[0175] In addition, although the present invention has been described with reference to several embodiments that optionally incorporate various features, the present invention is not limited to those described or indicated as being considered with respect to each variation of the present invention. Various modifications may be made to the invention described, and equivalents may be substituted (whether described herein or not included for some brevity) without departing from the true spirit and scope of the invention. In addition, when a range of values ​​is provided, it is understood that all intervening values ​​between the upper and lower limits of that range, and any other stated or intervening values ​​within that stated range, are encompassed within the present invention.

[0176] It is also contemplated that any optional feature of the inventive variations described herein may be described and claimed independently or in combination with any one or more of the features described herein. Reference to a singular item includes the possibility that there are multiple identical items. More specifically, as used herein and in the claims associated therewith, the singular forms "a," "an," "said," and "the" include plural referents unless specifically stated otherwise. In other words, the use of articles allows for "at least one" of the subject item in the above description and in the claims associated with this disclosure. Furthermore, it is noted that such claims may be drafted to exclude any optional element. Thus, this statement is intended to serve as a predicate for the use of such exclusive terms, such as "only," "only," and the like, in connection with the description of claim elements, or the use of "negative" limitations.

[0177] Without using such exclusive language, the term "comprising" in the claims associated with this disclosure is intended to permit the inclusion of any additional elements, regardless of whether a given number of elements are recited in such claims or whether the addition of features can be considered as changing the nature of the elements recited in such claims. Except as specifically defined herein, all technical and scientific terms used herein are to be given their broadest possible commonly understood meanings while maintaining the validity of the claims.

[0178] The scope of the present invention is not intended to be limited to the examples provided and / or this specification, but rather is to be limited only by the scope of the claims associated with this disclosure.

Claims

1. 1. A head mounted system, comprising: a spatial light modulator configured to output light encoded with image information; an image input device configured to receive and output light encoded with said image information; a display including a stack of a plurality of waveguides, each waveguide being formed by an optically transmissive substrate including optical elements on a major surface of the optically transmissive substrate, each waveguide being configured to receive light encoded with the image information; Equipped with the optical element includes a metasurface, the metasurface including a plurality of unit cells; Each unit cell is a first nanobeam elongated laterally of the optically transmissive substrate, the first nanobeam having a first width and a first height; a second nanobeam elongated in a transverse direction of the optically transparent substrate, the second nanobeam being separated from the first nanobeam by a gap, the second nanobeam having a second width greater than the first width and a first height; a reflector, the reflector and the optically transmissive substrate being on opposite sides of the first nanobeam and the second nanobeam; Including, A head-mounted system, wherein the optical element is configured to direct incident light from the image capture device to propagate the light through the optically transmissive substrate by total internal reflection.

2. The head mounted system of claim 1 , wherein the reflector is spaced apart from the first nanobeam and the second nanobeam.

3. The head mounted system of claim 2 , wherein the first nanobeam and the second nanobeam are embedded in an optically transparent material.

4. The head mounted system of claim 3 , wherein the optically transmissive material spaces the reflector from the first nanobeam and the second nanobeam.

5. the optically transmissive substrate includes a second metasurface on a side of the optically transmissive substrate opposite the metasurface; the second metasurface comprises a plurality of second unit cells; Each second unit cell comprises: a third nanobeam elongated laterally of the optically transmissive substrate; a fourth nanobeam elongated in a lateral direction of the optically transparent substrate, the fourth nanobeam being separated from the third nanobeam by a gap, the fourth nanobeam being wider than the third nanobeam; The head mounted system of claim 1 , comprising:

6. The head mounted system of claim 1 , wherein the unit cells are parallel to one another.

7. 10. The head mounted system of claim 1, wherein the metasurface is configured to diffract incident light of visible wavelengths into a first diffraction order.

8. The head mounted system of claim 1 , wherein the second width is equal to or greater than 10 nm and equal to or less than 300 nm.

9. The head mounted system of claim 1 , wherein the pitch of each of the plurality of unit cells is between 10 nm and 500 nm.

10. The head mounted system of claim 1 , wherein the gap between the first nanobeam and the second nanobeam is between 10 nm and 300 nm wide.

11. The head mounted system of claim 1 , wherein the optically transmissive substrate comprises glass.

12. The head mounted system of claim 1 , wherein the first nanobeam and the second nanobeam comprise silicon.

13. The head mounted system of claim 12 , wherein the first nanobeam and the second nanobeam comprise silicon nitride.

14. The head mounted system of claim 1 , wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter.

15. The head-mounted system of claim 1, wherein the geometric sizes and periodicities of the first and second nanobeams and some of the unit cells of the plurality of unit cells vary among a plurality of substrates forming the stack of the plurality of waveguides, and the geometric sizes and periodicities of the first and second nanobeams and some of the unit cells of the plurality of unit cells are configured to direct incident light corresponding to a plurality of different colors into associated waveguides.

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