METASURFACES WITH ASYMMETRIC GRATINGS FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING

• US 20170322418A1
• Filed: 05/05/2017
• Published: 11/09/2017
• Est. Priority Date: 05/06/2016
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Magic Leap, Inc.
• Inventors: Lin, Dianmin, Melli, Mauro, St. Hilaire, Pierre, Peroz, Christophe, Poliakov, Evgeni
• Granted Patent: US 10,527,851 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 1/002 made of materials engineered to provide properties not available in nature, e.g. metamaterials
• CPC Class Codes: G02B 2005/1804 Transmission gratings
• CPC Class Codes: G02B 2027/0109 comprising details concerning the making of holograms
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 30/35 using reflective optical elements in the optical path between the images and the observer
• CPC Class Codes: G02B 5/1809 with pitch less than or comparable to the wavelength
• CPC Class Codes: G02B 5/30 Polarising elements light-modulating devices with active elements G02F1/00
• CPC Class Codes: G02B 5/3058 comprising electrically conductive elements, e.g. wire grids, conductive particles
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: H04N 13/344 with head-mounted left-right displays
• CPC Class Codes: H04N 13/349 Multi-view displays for displaying three or more geometrical viewpoints without viewer tracking for viewing without the aid of special glasses using fly-eye lenses H04N13/307

Abstract

An optical system comprises an optically transmissive substrate comprising a metasurface which comprises 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 larger than the first width. A pitch of the unit cells is 10 nm to 1 μm. The heights of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less.

Claims

1. An optical system comprising:

an optically transmissive substrate comprising a metasurface, the metasurface comprising, as seen in a top-down view;

a grating comprising a plurality of unit cells, each unit cell comprising;

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 larger than the first width,

wherein heights of the first and the second nanobeams are;

10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and

10 nm to 1 μ

m where the refractive index is 3.3 or less.

2. The optical system of claim 1, wherein the unit cells are laterally-elongated and are parallel to each other.

3. The optical system of claim 1, wherein the metasurface is configured to diffract incident light of a visible wavelength into a first diffraction order.

4. The optical system of claim 1, wherein the second width is 10 nm to 1 μ

m.

5. The optical system of claim 4, wherein the second width is 10 nm to 300 nm.

6. The optical system of claim 1, wherein a pitch of the unit cells is 10 nm to 1 μ

m.

7. The optical system of claim 6, wherein the pitch of the unit cells is 10 nm to 500 nm.

8. The optical system of claim 1, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μ

m.

9. The optical system of claim 8, wherein the gap is 10 nm to 300 nm wide.

10. The optical system of claim 1, wherein the optically transmissive substrate comprises a glass.

11. The optical system of claim 1, wherein the first and second nanobeam comprises silicon.

12. The optical system of claim 11, wherein the first and second nanobeam comprises silicon nitride.

13. The optical system of claim 1, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter.

14. The optical system of claim 1, wherein the optically transmissive substrate is a waveguide plate.

15. The optical system of claim 14, further comprising a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the substrates.

16. The optical system of claim 1, wherein the metasurface is an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection.

17. The optical system of claim 1, wherein the metasurface is an outcoupling optical element, wherein the metasurface is configured to extract light out of the substrate.

18. An optical system comprising:

an optically transmissive substrate comprising a metasurface, the metasurface comprising;

a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width; and

a reflector, wherein the reflector and the substrate are on opposite sides of the grating.

19. The optical system of claim 18, wherein the reflector is spaced apart from the grating.

20. The optical system of claim 19, wherein the grating is embedded in an optically transmissive material.

21. The optical system of claim 20, wherein the optically transmissive material spaces the reflector apart from the grating.

22. The optical system of claim 18, wherein the substrate comprises:

a second metasurface on a side of the substrate opposite the metasurface, the second metasurface comprising;

a second grating comprising a plurality of second unit cells, each second unit cell comprising, as seen in a top-down view;

a laterally-elongated third nanobeam; and

a laterally-elongated fourth nanobeam spaced apart from the third nanobeam by a gap, wherein the fourth nanobeam is wider than the third nanobeam.

23. The optical system of claim 18, wherein the unit cells are laterally-elongated and are parallel to each other.

24. The optical system of claim 18, wherein the metasurface is configured to diffract incident light of a visible wavelength into a first diffraction order

25. The optical system of claim 18, wherein the second width is 10 nm to 1 μ

m. will

26. The optical system of claim 25, wherein the second width is 10 nm to 300 nm.

27. The optical system of claim 18, wherein a pitch of the unit cells is 10 nm to 1 μ

m.

28. The optical system of claim 27, wherein the pitch of the unit cells is 10 nm to 500 nm.

29. The optical system of claim 18, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μ

m.

30. The optical system of claim 29, wherein the gap is 10 nm to 300 nm wide.

31. The optical system of claim 18, wherein the optically transmissive substrate comprises a glass.

32. The optical system of claim 18, wherein the first and second nanobeam comprises silicon.

33. The optical system of claim 32, wherein the first and second nanobeam comprises silicon nitride.

34. The optical system of claim 18, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter.

35. The optical system of claim 27, wherein the optically transmissive substrate is a waveguide plate.

36. The optical system of claim 35, further comprising a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the substrates.

37. The optical system of claim 18, wherein the metasurface is an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection.

38. The optical system of claim 18, wherein the metasurface is an outcoupling optical element, wherein the metasurface is configured to extract light out of the substrate.

39. A method for forming a metasurface, the method comprising:

providing an optically transmissive substrate;

providing an optically transmissive layer over the substrate; and

patterning the optically transmissive layer to define a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width,

wherein heights of the first and the second nanobeams are;

10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and

10 nm to 1 μ

m where the refractive index is 3.3 or less.

40. The method of claim 39, wherein patterning the optically transmissive layer comprises:

providing a resist layer over the optically transmissive layer;

defining a pattern in the resist layer; and

transferring the pattern from the resist layer to the optically transmissve layer.

41. The method of claim 40, further comprising depositing an optically transmissive material between and over the grating.

42. The method of claim 41, further comprising forming a reflective layer on the optically transmissive material.

43. The method of claim 40, wherein transferring comprises performing an anisotropic etch.

44. A method for forming a metasurface, the method comprising:

providing an optically transmissive substrate;

forming a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width, and

providing a layer of reflective material in the gap and between the unit cells.

45. The method of claim 44, wherein providing the layer of reflective material comprises depositing reflective material between and over the first and second nanobeams.

46. The method of claim 45, wherein the reflective material comprises aluminum.

47. The method of claim 44, wherein forming the grating comprises:

depositing an optically transmissive layer over the substrate; and

patterning the optically transmissive layer to define the grating.

48. The method of claim 47, wherein patterning the optically transmissive layer comprises:

providing a resist layer over the optically transmissive layer;

defining a pattern in the resist layer; and

transferring the pattern from the resist layer to the optically transmissve layer.

49. A method for forming a metasurface, the method comprising:

providing an optically transmissive substrate;

forming a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width,

depositing a layer of optically transmissive spacer material in the gap and between the unit cells; and

depositing a reflective layer on the layer of spacer material, wherein the spacer material separates the grating from the reflective layer.

50. The method of claim 49, wherein the spacer material has a refractive index of 1 to 2.

51. An optical system comprising:

an optically transmissive substrate comprising a metasurface, the metasurface comprising;

a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width,

wherein a pitch of the unit cells is 10 nm to 1 μ

m.

52. The system of claim 51, wherein the pitch is 300 nm to 500 nm.

53. The system of claim 51, wherein the metasurface is configured to diffract incident light of a visible wavelength into a first diffraction order.

54. The system of claim 51, wherein the unit cells are laterally-elongated and are parallel to each other.

55. The system of claim 51, wherein the second width is 10 nm to 1 μ

m.

56. The system of claim 55, wherein the second width is 10 nm to 300 nm.

57. The system of claim 51, wherein a pitch of the unit cells is 10 nm to 1 μ

m.

58. The system of claim 57, wherein the pitch of the unit cells is 10 nm to 500 nm.

59. The system of claim 51, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 μ

m.

60. The system of claim 59, wherein the gap is 10 nm to 300 nm wide.

61. The system of claim 51, wherein the optically transmissive substrate comprises a glass.

62. The system of claim 51, wherein the first and second nanobeam comprises silicon.

63. The system of claim 62, wherein the first and second nanobeam comprises silicon nitride.

64. The system of claim 51, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter.

65. The system of claim 51, wherein the optically transmissive substrate is a waveguide plate.

66. The system of claim 65, further comprising a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the substrates.

67. The system of claim 51, wherein the metasurface is an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection.

68. The system of claim 51, wherein the metasurface is an outcoupling optical element, wherein the metasurface is configured to extract light out of the substrate.

69. A method for forming a metasurface, the method comprising:

providing an optically transmissive substrate;

providing an optically transmissive layer over the substrate; and

patterning the optically transmissive layer to define a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view;

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 larger than the first width,

wherein a pitch of the unit cells is 10 nm to 1 μ

m.

70. The method of claim 69, wherein the pitch is 300 nm to 500 nm.

71. An optical system comprising:

an optically transmissive substrate comprising a multilevel metasurface, the multilevel metasurface comprising;

a grating comprising a plurality of multilevel unit cells, each unit cell comprising, as seen in a top-down view;

on a lowermost level of the unit cell;

a laterally-elongated, first lowermost level nanobeam having a having a first width; and

a laterally-elongated, second lowermost level nanobeam having a having a second width, wherein the second width is larger than the first width; and

on an uppermost level of the unit cell;

a laterally-elongated, first uppermost level nanobeam above the first lowermost level nanobeam; and

a laterally-elongated, second uppermost level nanobeam above the second lowermost level nanobeam.

72. The optical system of claim 71, wherein the first and second uppermost level nanobeams comprise a different material from the first and second lowermost level nanobeams.

73. The optical system of claim 71, wherein the first and second lowermost level nanobeams comprise photoresist.

74. The optical system of claim 73, wherein the first and second lowermost level nanobeams comprise silicon.

75. The optical system of claim 74, wherein the first and second lowermost level nanobeams comprise silicon nitride.

76. The optical system of claim 73, wherein the first and second lowermost level nanobeams comprise an oxide.

77. The optical system of claim 76, wherein the first and second lowermost level nanobeams comprise titanium oxide.

78. The optical system of claim 71, wherein the first and second lowermost level nanobeams of the plurality of unit cells extend parallel to each other.

79. The optical system of claim 71, wherein the first width is 10 nm to 250 nm.

80. The optical system of claim 79, wherein the second width is 10 nm to 300 nm.

81. The optical system of claim 71, wherein a pitch of the unit cells is 300 nm to 500 nm.

82. The optical system of claim 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 claim 71, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter.

84. The optical system of claim 71, wherein the optically transmissive substrate is a waveguide plate.

85. The optical system of claim 71, wherein the metasurface forms an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection.

86. The optical system of claim 84, further comprising a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the substrates, wherein the metasurface is an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection.

87. The optical system of claim 71, wherein the metasurface is an outcoupling optical element, wherein the metasurface is configured to extract light out of the substrate.

88. The optical system of claim 71, wherein the grating is embedded in 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 the substrate; and

patterning the optically transmissive layer to define a plurality of repeating units, each repeating unit comprising, as seen in a top-down view;

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 larger than the first width; and

depositing an optically transmissive material on the first and second nanobeams and into the gaps between the nanobeams to form spaced apart plateaus of the optically transmissive material above the nanobeams.

90. The method of claim 89, wherein the optically transmissive material has a higher refractive index than either the patterned resist or the substrate.

91. The method of claim 89, wherein patterning the optically transmissive layer comprises patterning resist.

92. The method of claim 91, wherein patterning the resist comprises imprinting the pattern into the resist.

93. The method of claim 91, wherein depositing the optically transmissive material comprises spin coating the optically transmissive material on the patterned resist.

94. The method of claim 91, wherein depositing the optically transmissive material comprises performing a conformal deposition or a directional deposition of the optically transmissive material.

95. The method of claim 94, wherein the conformal deposition comprises chemical vapor deposition or atomic layer deposition of the optically transmissive material.

96. The method of claim 95, wherein the directional deposition comprises evaporation or sputtering the optically transmissive material.

97. The method of claim 89, wherein the first width is 10 nm to 250 nm.

98. The method of claim 97, wherein the second width is 10 nm to 300 nm.

99. The method of claim 89, wherein a pitch of the unit cells is 300 nm to 500 nm.

100. The method of claim 89, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 300 nm.

101. The method of claim 89, wherein the optically transmissive substrate is a waveguide.