Optical device having a wide field-of-view for multicolor images

• US 6,757,105 B2
• Filed: 04/25/2002
• Issued: 06/29/2004
• Est. Priority Date: 04/25/2002
• Status: Expired due to Fees

• Current Assignee: Mirage Innovations Limited
• Original Assignee: Planop-Planar Optics, Ltd.
• Inventors: Niv, Yehuda, Nivon, Uzia
• Primary Examiner(s): Chang, Audrey
• Assistant Examiner(s): LAVARIAS, ARNEL C
• Application Number:
  US10/131,262
• Publication Number:
  US 20030202247A1
• Time in Patent Office: 796 Days
• Field of Search: 359/569, 359/558.566, 359/572, 359/15, 359/13, 359/34, 359/630, 359/633, 359/603, 345/7, 345/8, 345/9
• US Class Current: 359/569
• CPC Class Codes: G02B 5/1847 Manufacturing methods
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

A diffractive optical element for guiding a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, λ_B, and shorter than a longest wavelength, λ_R, the light striking the diffractive optical element at an angle greater than a first field-of-view angle, α⁻_FOV, and smaller than a second field-of-view angle, α⁺_FOV. The diffractive optical element comprising a linear grating being formed in a light-transmissive substrate. The linear grating is characterized by a pitch, d, selected so as to allow total internal reflection of a light having wavelength of λ_B and a striking angle of α⁻_FOV. The light-transmissive substrate is characterized by an index of refraction, n_s, larger than a minimal index of refraction, n_MIN, which is selected so as to allow total internal reflection of a light having wavelength of λ_R and a striking angle of α⁺_FOV.

Claims

1. A diffractive optical element for trapping and propagating a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, λ

_B, and shorter than a longest wavelength λ

_R, the light striking the diffractive optical element at an angle greater than a first field-of-view angle, α

⁻

_FOV, and smaller than a second field-of-view angle, α

⁺_FOV, the diffractive optical element comprising a linear grating being formed in a light-transmissive substrate, wherein;

(a) said linear grating is characterized by a pitch, d, selected so as to allow total internal reflection of a first light ray having wavelength of λ

_B and a striking angle of α

⁻

_FOV, thereby to trap said first light ray by total internal reflection;

(b) said light-transmissive substrate is characterized by an index of refraction, n_s, larger than a minimal index of refraction, n_MIN, said minimal index of refraction is selected so as to allow total internal reflection of a second light ray having wavelength of λ

_R and a striking angle of α

⁺_FOV, thereby to trap said second light ray by total internal reflection; and

(c) a thickness of said light-transmissive substrate is sufficiently large so as to allow propagation of a light of any wavelength longer than λ

_B and shorter than λ

_R, striking said light-transmissive substrate at any angle larger than α

⁻

_FOV and smaller than α

⁺_FOV.

2. The diffractive optical element of claim 1, wherein λ

_R is larger than λ

_B by at least 30 nm.

3. The diffractive optical element of claim 1, wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 6 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

4. The diffractive optical element of claim 1, wherein λ

_R is larger than λ

_B by at least 30 nm, and further wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 5 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

5. The diffractive optical element of claim 1, wherein said grating pitch, d, is between about 0.5λ

_B to about 0.99λ

_B.

6. The diffractive optical element of claim 1, wherein said grating pitch, d, is selected so that a ratio between said λ

_B and said d has an average value of about 1.5.

7. The diffractive optical element of claim 1, wherein said grating pitch is smaller than or equals λ

_B/[n_A(1−

sin α

⁻

_FOV)], where n_A is an index of refraction of an external medium.

8. The diffractive optical element of claim 7, wherein said index of refraction of said external medium is substantially a unity.

9. The diffractive optical element of claim 7, wherein said external medium is air.

10. The diffractive optical element of claim 1, wherein said minimal index of refraction is larger than λ

_R/d+n_A sin(α

⁺_FOV).

11. The diffractive optical element of claim 1, wherein said total internal reflection is characterized by a predetermined maximal diffraction angle, α

_D^MAX, smaller than 90 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

12. The diffractive optical element of claim 1, wherein said total internal reflection is characterized by a predetermined maximal diffraction angle, α

_D^MAX, selected so as to allow at least one reflection within a predetermined distance, x.

13. The diffractive optical element of claim 12, wherein said predetermined distance is 30 mm to 80 mm.

14. The diffractive optical element of claim 11, wherein said minimal index of refraction equals [λ

_R/d+sin(α

⁺_FOV)]/sin(α

_D^MAX).

15. The diffractive optical element of claim 12, wherein said minimal index of refraction equals [λ

_R/d+sin(α

⁺_FOV)]/sin(α

_D^MAX).

16. The diffractive optical element of claim 1, wherein λ

_B is between about 400 to about 500 nm.

17. The diffractive optical element of claim 1, wherein λ

_R is between about 600 to about 700 nm.

18. The diffractive optical element of claim 1, wherein said n_MIN is between about 1.6 to about 2.0.

19. The diffractive optical element of claim 1, wherein said light-transmissive substrate is of thickness ranging between about 0.5 mm and about 5 mm.

20. The diffractive optical element of claim 1, wherein said light-transmissive substrate is selected from the group consisting of glass and a transparent polymer.

21. The diffractive optical element of claim 1, wherein said linear diffraction grating is selected from the group consisting of reflection linear diffraction grating and transmission linear diffraction grating.

22. The diffractive optical element of claim 1, wherein said linear diffraction grating is recorded by a procedure selected from a group consisting of holography, computer-generated masks, lithography, embossing, etching and direct writing.

23. An optical device for transmitting a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, λ

_B, and shorter than a longest wavelength λ

_R, the light striking the optical device at an angle greater than a first field-of-view angle, α

⁻

_FOV, and smaller than a second field-of-view angle, α

⁺_FOV, the optical device comprising a first diffractive optical element being formed in a light-transmissive substrate, and a second diffractive optical element, laterally displaced from said first diffractive optical element, and being formed in said light-transmissive substrate, wherein;

(a) said first and said second diffractive optical elements are linear gratings characterized by a pitch, d, selected so as to allow total internal reflection of a first light ray having wavelength of λ

_B and a striking angle of α

⁻

_FOV, thereby to trap said first light ray by total internal reflection;

(b) said light-transmissive substrate is characterized by an index of refraction, n_s, larger than a minimal index of refraction, n_MIN, said minimal index of refraction is selected so as to allow total internal reflection of a second light ray having wavelength of λ

_R and a striking angle of α

⁺_FOV, thereby to trap said second light ray by total internal reflection; and

(c) a thickness of said light-transmissive substrate is sufficiently large so as to allow propagation of a light of any wavelength longer than λ

_B and shorter than λ

_R, striking said light-transmissive substrate at any angle larger than α

⁻

_FOV and smaller than α

⁺_FOV.

24. The optical device of claim 23, wherein λ

_R is larger than λ

_B by at least 30 nm.

25. The optical device of claim 23, wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 6 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

26. The optical device of claim 23, wherein λ

_R is larger than λ

_B by at least 30 nm, and further wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 5 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

27. The optical device of claim 23, wherein said grating pitch, d, is between about 0.5λ

_B to about 0.99λ

_B.

28. The optical device of claim 23, wherein said grating pitch, d, is selected so that a ratio between said λ

_B and said d has an average value of about 1.5.

29. The optical device of claim 23, wherein said grating pitch is smaller than or equals λ

_B/[n_A(1−

sin α

⁻

_FOV)], where n_A is an index of refraction of an external medium.

30. The optical device of claim 29, wherein said index of refraction of said external medium is substantially a unity.

31. The optical device element of claim 29, wherein said external medium is air.

32. The optical device of claim 23, wherein said minimal index of refraction is larger than λ

_R/d+n_A sin(α

⁺_FOV).

33. The optical device of claim 23, wherein said total internal reflection is characterized by a predetermined maximal diffraction angle, α

_D^MAX, smaller than 90 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

34. The optical device of claim 23, wherein said total internal reflection is characterized by a predetermined maximal diffraction angle, α

_D^MAX, selected so as to allow at least one reflection within a predetermined distance, x.

35. The optical device of claim 34, wherein said predetermined distance is 30 mm to 80 mm.

36. The optical device of claim 34, wherein said predetermined distance is defined between a center of said first diffractive optical element and a center of said second diffractive optical element.

37. The optical device of claim 33, wherein said minimal index of refraction equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

38. The optical device of claim 34, wherein said minimal index of refraction equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

39. The optical device of claim 23, wherein λ

_B is between about 400 to about 500 nm.

40. The optical device of claim 23, wherein λ

_R is between about 600 to about 700 nm.

41. The optical device of claim 23, wherein said n_MIN is between about 1.6 to about 2.0.

42. The optical device of claim 23, wherein said light-transmissive substrate is of thickness ranging between about 0.5 mm and about 5 mm.

43. The optical device of claim 23, wherein said light-transmissive substrate is selected from the group consisting of glass and a transparent polymer.

44. The optical device of claim 23, wherein said linear diffraction grating of said first diffractive optical element is substantially parallel to said linear diffraction grating of said second diffractive optical element.

45. The optical device of claim 23, wherein said linear diffraction gratings of said first and second diffractive optical elements are each independently selected from the group consisting of reflection linear diffraction gratings and transmission linear diffraction gratings.

46. The optical device of claim 23, wherein said linear diffraction gratings of said first and said second diffractive optical elements are each independently formed on a surface selected from the group consisting of a first surface of said light-transmissive substrate and a second surface of said light-transmissive substrate.

47. The optical device of claim 23, further comprising an input light source for producing said light.

48. The optical device of claim 47, wherein said input light source comprises an input display source, hence said light constitutes an image.

49. The optical device of claim 47, further comprising a collimator for collimating said light produced by said input light source.

50. The optical device of claim 49, wherein said collimator comprises a converging lens.

51. The optical device of claim 49, wherein said collimator comprises a diffractive optical element.

52. The optical device of claim 23, further comprising at least one optical element for redirecting light rays, positioned so as to reduce an overall size of the optical device.

53. The optical device of claim 52, wherein said at least one optical element is a 45 degrees mirror.

54. The optical device of claim 23, wherein said linear diffraction gratings are recorded by a procedure selected from a group consisting of holography, computer-generated masks, lithography, embossing, etching and direct writing.

55. A method of manufacturing a diffractive optical element for trapping and propagating a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, λ

_B, and shorter than a longest wavelength λ

_R, the light striking the diffractive optical element at an angle greater than a first field-of-view angle, α

⁻

_FOV, and smaller than a second field-of-view angle, α

_+FOV, the method comprising;

(a) determining a linear grating pitch, d, so as to allow total internal reflection of a first light ray having wavelength of λ

_B and a striking angle of α

⁻

_FOV, thereby to trap said first light ray by total internal reflection;

(b) determining a minimal index of refraction, n_MIN, so as to allow total internal reflection of a second light ray having wavelength of λ

_R and a striking angle of α

⁺_FOV, thereby to trap said second light ray by total internal reflection; and

(c) forming a linear grating characterized by said grating pitch, d, in a light-transmissive substrate characterized by an index of refraction, n_s, wherein said n_s being larger than said n_MIN, wherein a thickness of said light-transmissive substrate is selected sufficiently large so as to allow propagation of a light of any wavelength longer than λ

_B and shorter and λ

_R, striking said light-transmissive substrate at any angle larger than α

⁻

_FOV and smaller than α

⁺_FOV.

56. The method of claim 55, wherein λ

_R is larger than λ

_B by at least 30 nm.

57. The method of claim 55, wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 6 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

58. The method of claim 55, wherein λ

_R is larger than λ

_B by at least 30 nm, and further wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 5 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

59. The method of claim 55, wherein said determining said grating pitch, d, is done so that said d is between about 0.5λ

_B to about 0.99λ

_B.

60. The method of claim 55, wherein said determining said grating pitch, d, is done so that a ratio between said λ

_B and said d has an average value of about 1.5.

61. The method of claim 55, wherein said determining said grating pitch, d, is done so that said d is smaller than or equals λ

_B/[n_A(1−

sin α

⁻

_FOV)], where n_A is an index of refraction of an external medium.

62. The method of claim 61, wherein said index of refraction of said external medium is substantially a unity.

63. The method element of claim 61, wherein said external medium is air.

64. The method of claim 55, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN is larger than λ

_R/d+n_A sin(α

⁺_FOV).

65. The method of claim 55, further comprising selecting a maximal diffraction angle, α

_D^MAX.

66. The method of claim 65, wherein said total internal reflection is characterized by said maximal diffraction angle.

67. The method of claim 65, wherein said α

_D^MAX is smaller than 90 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

68. The method of claim 65, wherein said selecting a maximal diffraction angle is by calculating an angle corresponding to at least one reflection within a predetermined distance, x.

69. The method of claim 68, wherein said predetermined distance is 30 mm to 80 mm.

70. The method of claim 67, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

71. The method of claim 68, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

72. The method of claim 55, wherein said λ

_B is between about 400 to about 500 nm.

73. The method of claim 55, wherein said λ

_R is between about 600 to about 700 nm.

74. The method of claim 55, wherein said n_MIN is between about 1.6 to about 2.0.

75. The method of claim 55, wherein said light-transmissive substrate is of thickness ranging between about 0.5 mm and about 5 mm.

76. The method of claim 55, wherein said light-transmissive substrate is selected from the group consisting of glass and a transparent polymer.

77. The method of claim 55, wherein said linear diffraction grating is selected from the group consisting of reflection linear diffraction grating and transmission linear diffraction grating.

78. The method of claim 55, wherein said linear diffraction grating is recorded by a procedure selected from a group consisting of holography, computer-generated masks, lithography, embossing, etching and direct writing.

79. A method of manufacturing an optical device for transmitting a light having a color spectrum characterized by a plurality of wavelengths longer than a shortest wavelength, λ

_B and shorter than a longest wavelength λ

_R, the light striking the optical device at an angle greater than a first field-of-view angle, α

⁻

_FOV, and smaller than a second field-of-view angle, α

⁺_FOV, the method comprising;

(a) determining a linear grating pitch, d, so as to allow total internal reflection of a first light ray having wavelength of λ

_B and a striking angle of α

⁻

_FOV thereby to trap said first light ray by total internal refection;

(b) determining a minimal index of refraction, n_MIN, so as to allow total internal reflection of a second light ray having wavelength of λ

_R and a striking angle of α

⁺_FOV, thereby to trap said second light ray by total internal reflection; and

(c) positioning a light-transmissive substrate and forming therein a first diffractive optical element and a second diffractive optical element laterally displaced from said first diffractive optical element;

wherein said first and said second diffractive optical elements are linear gratings characterized by said grating pitch, d, and said light-transmissive substrate is characterized by an index of refraction, n_s, which is larger than said n_MIN, and further, wherein a thickness of said light-transmissive substrate is selected sufficiently large so as to allow propagation of a light of any wavelength longer than λ

_B and shorter than λ

_R, striking said light-transmissive substrate at any angle larger than α

⁻

_FOV and smaller than α

⁺_FOV.

80. The method of claim 79, wherein λ

_R is larger than λ

_B by at least 30 nm.

81. The method of claim 79, wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 6 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

82. The method of claim 79, wherein λ

_R is larger than λ

_B by at least 30 nm, and further wherein α

⁻

_FOV and α

⁺_FOV each independently has an absolute value above 5 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

83. The method of claim 79, wherein said determining said grating pitch, d, is done so that said d is between about 0.5λ

_B to about 0.99λ

_B.

84. The method of claim 79, wherein said determining said grating pitch, d, is done so that a ratio between said λ

_B and said d has an average value of about 1.5.

85. The method of claim 79, wherein said determining said grating pitch is done so that said d is smaller than or equals λ

_B/[n_A(1−

sin α

⁻

_FOV)], where n_A is an index of refraction of an external medium.

86. The method of claim 85, wherein said index of refraction of said external medium is substantially a unity.

87. The method element of claim 85, wherein said external medium is air.

88. The method of claim 79, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN is larger than λ

_R/d+n_A sin(α

⁺_FOV).

89. The method of claim 79, further comprising selecting a maximal diffraction angle, α

_D^MAX.

90. The method of claim 89, wherein said total internal reflection is characterized by said maximal diffraction angle.

91. The method of claim 89, wherein said α

_D^MAX is smaller than 90 degrees with respect to an orientation which is perpendicular to said light-transmissive substrate.

92. The method of claim 89, wherein said selecting a maximal diffraction angle is by calculating an angle corresponding to at least one reflection within a predetermined distance, x.

93. The method of claim 92, wherein said predetermined distance is 30 mm to 80 mm.

94. The method of claim 92, wherein said predetermined distance is defined between a center of said first diffractive optical element and a center of said second diffractive optical element.

95. The method of claim 90, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

96. The method of claim 92, wherein said determining said minimal index of refraction, n_MIN, is done so that said n_MIN equals [λ

_R/d+n_A sin(α

⁺_FOV)]/sin(α

_D^MAX).

97. The method of claim 79, wherein λ

_B is between about 400 to about 500 nm.

98. The method of claim 79, wherein λ

_R is between about 600 to about 700 nm.

99. The method of claim 79, wherein said n_MIN is between about 1.6 to about 2.0.

100. The method of claim 79, wherein said light-transmissive substrate is of thickness ranging between about 0.5 mm and about 5 mm.

101. The method of claim 79, wherein said light-transmissive substrate is selected from the group consisting of glass and a transparent polymer.

102. The method of claim 79, wherein said linear diffraction grating of said first diffractive optical element is substantially parallel to said linear diffraction grating of said second diffractive optical element.

103. The method of claim 79, wherein said linear diffraction gratings of said first and second diffractive optical elements are each independently selected from the group consisting of reflection linear diffraction gratings and transmission linear diffraction gratings.

104. The method of claim 79, wherein said linear diffraction gratings of said first and said second diffractive optical elements are each independently formed on a surface selected from the group consisting of a first surface of said light-transmissive substrate and a second surface of said light-transmissive substrate.

105. The method of claim 79, further comprising positioning an input light source for producing said light.

106. The method of claim 105, wherein said input light source comprises an input display source, hence said light constitutes an image.

107. The method of claim 105, further comprising positioning a collimator for collimating said light produced by said input light source.

108. The method of claim 107, wherein said collimator comprises a converging lens.

109. The method of claim 107, wherein said collimator comprises a diffractive optical element.

110. The method of claim 79, further comprising positioning at least one optical element for redirecting light rays, positioned so as to reduce an overall size of the optical device.

111. The method of claim 110, wherein said at least one optical element is a 45 degrees mirror.

112. The method of claim 79, wherein said linear diffraction gratings are recorded by a procedure selected from a group consisting of holography, computer-generated masks, lithography, embossing, etching and direct writing.