Ultra-compact HUD utilizing waveguide pupil expander with surface relief gratings in high refractive index materials

• US 9,715,067 B1
• Filed: 09/30/2011
• Issued: 07/25/2017
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Brown, Robert D., Stahl, Kurt A., Wood, Robert B., Burns, Lincoln J.
• Primary Examiner(s): Chang, Audrey Y
• Application Number:
  US13/250,858
• Time in Patent Office: 2,125 Days
• Field of Search: 359 15, 359462, 359569, 359571, 359 34, 359630, 359576, 359633, 385 37, 362618, 362622, 362627
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 6/2848 having refractive means, e.g. imaging elements between light guides as splitting, branching and/or combining devices, e.g. lenses, holograms
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: G03H 1/0248 Volume holograms

Abstract

A head up display include an image source, and a waveguide. The waveguide has a first diffraction grating and a first end and a second diffraction grating at a second end. The waveguide is positioned as a combiner and allows viewing of an outside scene and information from the image source. The first and second diffraction gratings are surface relief gratings having a high index of modulation.

Claims

1. A head up display, comprising:

an image source;

a folded catadioptric collimator comprising a fold prism receiving light from the image source, a field lens receiving light from the fold prism, and a beam splitter receiving light from the field lens and redirecting light to a curved reflector, the curved reflector providing collimated light through the beam splitter to an exit surface on the beam splitter, wherein the folded catadioptric collimator is configured to a have a light path from the image source to the exit surface on the beam splitter, the light path having a single bounce within the fold prism as the light travels from the image source to the field lens, wherein the fold prism receives the light directly from the image source;

a bracket; and

a waveguide attached to a planar surface of the bracket, the waveguide having a first diffraction grating at a first end for receiving the collimated light at the exit surface and a second diffraction grating at a second end, the first diffraction grating being an input diffraction grating and the second diffraction grating being an output diffraction grating and the waveguide being positioned as a combiner and allowing viewing of an outside scene and information from the image source, the waveguide having a high index of refraction of greater than 1.6, wherein the first diffraction grating and the second diffraction grating have a period of 330 nm plus or minus 20 percent, wherein the waveguide provides single axis pupil expansion, the single axis pupil expansion provided by the waveguide being on the order of 3 to 8 times, wherein the waveguide comprises a first plate and a second plate and a beam splitting coating disposed between the first plate and the second plate along a line defined by the first plate and the second plate, the line disposed between the first diffraction grating and the second diffraction grating and parallel to main surfaces of the first diffraction grating and the second diffraction grating, the beam splitting coating being configured to cause light entering the waveguide from the image source and traveling from the first diffraction grating to the second diffraction grating via the first and second plates by total internal reflection between the main surfaces to have an increased number of rays propagating to the second diffraction grating.

2. The head up display of claim 1, wherein the folded catadioptric collimator is disposed adjacent the image source and provides the collimated light to the first diffraction grating.

3. The head up display of claim 2, wherein the waveguide is a non-organic material.

4. The head up display of claim 1, wherein the image source is an active matrix liquid crystal display.

5. The head up display of claim 1, wherein the first and second diffraction gratings are etched into the waveguide.

6. The head up display of claim 1, wherein the waveguide has an index of refraction of 1.7 or more.

7. The head up display of claim 1, the first diffraction grating has an area smaller than an area of the second diffraction grating and being located at a position to receive light from the image source.

8. The head up display of claim 7, wherein the first plate and the second plate are equal sized.

9. The head up display of claim 7 wherein the bracket has a same width as the waveguide.

10. The head up display of claim 1, wherein the first diffraction grating has a greater efficiency than the second diffraction grating.

11. A method of providing information to a pilot, the method comprising:

providing light associated with the information from an image source using a folded catadioptric collimator comprising a fold prism receiving light from the image source, a field lens receiving light from the fold prism, a beam splitter receiving light from the field lens and redirecting light to a curved reflector, the curved reflector providing collimated light through the beam splitter to an exit surface on the beam splitter, wherein the substrate waveguide is part of a fixed head up display configuration, wherein the folded catadioptric collimator is configured to a have a light path from the image source to the exit surface on the beam splitter, the light path having a single bounce within the fold prism as the light travels from the image source to the field lens, wherein the fold prism receives the light directly from the image source; and

diffracting the collimated light at an input of the substrate waveguide using a first surface relief grating into the waveguide and diffracting the light out of the waveguide using a second surface relief grating at an output of the waveguide, wherein the substrate waveguide has a high index of refraction greater than 1.6, and wherein the substrate waveguide comprises a first plate and a second plate, wherein the first plate and the second plate are of equal size.

12. The method of claim 11, wherein the first surface relief grating is etched into the waveguide.

13. The method of claim 11, wherein the surface relief gratings are lithographically formed.

14. The method of claim 11, wherein the waveguide is a combiner.

15. The method of claim 11, wherein the input and output are on the same side of the waveguide.

16. An optical system for a head up display including an image source, the optical system comprising:

a combiner, wherein the combiner is positioned to receive light from an image source, wherein the combiner is a waveguide including surface relief diffraction gratings etched into high index of refraction inorganic material, the waveguide having a high index of refraction of greater than 1.6, a first grating of the surface relief diffraction gratings being an input grating and a second grating of the surface relief diffraction gratings being an output grating; and

a folded catadioptric collimator disposed adjacent the first grating, wherein the folded catadioptric collimator provides the light to the first grating, the folded catadioptric collimator having a rectangular exit pupil having dimensions of 4 units by 1 unit, the rectangular exit pupil being extended to dimensions of 4 units by 4 units by the combiner, wherein the folded catadioptric collimator comprises a fold prism receiving light from the image source, a field lens receiving light from the fold prism, a beam splitter receiving light from the field lens and redirecting light to a curved reflector, the curved reflector providing collimated light through the beam splitter to an exit surface of the beam splitter for receipt by the input grating, wherein the field lens is disposed at an output face of the fold prism, wherein the folded catadioptric collimator is configured to a have a light path from the image source to the exit surface on the beam splitter, the light path having a single bounce within the fold prism as the light travels from the image source to the field lens, wherein the fold prism receives the light directly from the image source.

17. The system of claim 16, wherein the combiner is a substrate waveguide.

18. The system of claim 17, wherein a period of the surface relief gratings is 330 nm plus or minus 20 percent and the duty cycle of the surface relief gratings is between 40 and 70 percent.

19. The system of claim 16, wherein the folded catadioptric collimator is disposed in a bracket attached to the waveguide.

20. The system of claim 16, wherein the surface relief gratings are provided on wafers adhered to the combiner.