Optics of a display using an optical light guide

Patent metadata

Field	Value
Publication number	US-11656458-B2
Application number	US-202016934536-A
Country	US
Kind code	B2
Filing date	Jul 21, 2020
Priority date	Jan 23, 2019
Publication date	May 23, 2023
Grant date	May 23, 2023

Abstract

A projection display having an optical light guide for a see-though display system using holographic optical element or diffractive optical element as in-coupling optics and combined with Fresnel mirrors as out-coupling optics is disclosed. A display using this light guide enables a wide angle (e.g., over 90 degrees field of view), high resolution, and a large eye-box with a compact size.

First claim

What is claimed is:

1. A display system for providing light rays toward an eye of a viewer, the display system comprising:
a display device comprising an array of pixels;
a set of one or more lenses configured to receive light rays from respective pixels of the display device and project said light rays such that respective angles (θ) of at least two projected light rays are proportional to a respective distance (X), from a center of said array of pixels, of different respective pixels from which the projected light rays are received, where θ is proportional to X such that θ=CX with C being a constant having units of angle divided by distance;
a light pipe;
an in-coupling optical element configured to receive light rays from said set of one or more lenses and redirect said projected light rays into said light pipe having three or more sides and at least a portion of surfaces of the sides of said light pipe are reflective by coating or total internal reflection;
an out-coupling light guide; and
one or more mirrors configured to reflect light rays from an exit portion of said light pipe into said out-coupling light guide; wherein
said one or more mirrors include at least a first Fresnel reflector that comprises a plurality of saw-tooth shaped grating elements configured to reflect rays into said out-coupling light guide, and said out-coupling light guide includes a second Fresnel reflector that comprises a plurality of saw-tooth shaped grating elements.

2. The display system of claim 1 wherein:
said in-coupling optical element comprises a prism, and said set of one or more lenses is telecentric, where principal rays emitted from pixels of the display device are substantially perpendicular to the surface of said display device and the principal rays cross each other within or in proximity to said prism.

3. The display system of claim 1 wherein:
said in-coupling optical element comprises a prism, said prism has a reflective surface configured to receive light rays from said set of one or more lenses and to reflect the light rays into said light pipe, and a normal vector of the reflective surface is between 15 and 45 degrees with respect to an optical axis of said set of one or more lenses.

4. The display system of claim 1 wherein:
said in-coupling optical element comprises a prism, said prism has a reflective surface configured to receive light rays from said set of one or more lenses and to reflect the light rays into said light pipe, and a normal vector of the reflective surface is configured to rotate to form an angle between 30 and 60 degrees with respect to a long side of said light pipe.

5. The display system of claim 1 wherein:
said in-coupling optical element comprises a prism, and a refractive index of said prism is over 1.4, and a refractive index of said light pipe is over 1.4.

6. The display system of claim 1 wherein:
a size of the exit portion varies based at least in part on a location of the exit portion along a long side of said light pipe.

7. The display system of claim 1 wherein:
said grating elements of said first Fresnel reflector are curved on a surface of a triangular prism in saw-tooth shape and said surface is tilted between 15 and 45 degrees with respect to a top surface of said light pipe and a normal vector of the first Fresnel reflector is set so that a light ray parallel to an optical axis of said set of one or more lenses is substantially parallel to a normal vector of the top surface of said light pipe.

8. The display system of claim 1 wherein:
said in-coupling optical element comprises a prism, and a refractive index of said prism is over 1.3, a refractive index of said out-coupling light guide is over 1.3, and the refractive index of said prism is substantially equal to the refractive index of said out-coupling light guide.

9. The display system of claim 1 wherein:
said out-coupling light guide has a slant side forming a prism where light rays are able to enter and a normal vector of the slant side is between 15 and 45 degrees with respect to a top surface of said light pipe to enable light rays from said one or more mirrors to be reflected into said out-coupling light guide.

10. The display system of claim 1 wherein:
said out-coupling light guide has a slant side forming a prism where light rays enter and the normal vector of the slant side is between 15 and 45 degrees with respect to a top surface of said light pipe to enable light rays from said one or more mirrors to be reflected into said out-coupling light guide.

11. The display system of claim 1 wherein:
said second Fresnel reflector includes a grating region that includes multiple saw-tooth shaped grating elements configured to reflect light rays from said one or more mirrors toward the eye of the viewer and flat regions between the saw-tooth shaped grating elements, where no saw-tooth shaped grating elements exist in the flat regions, and the out-coupling light guide reflects the light rays by total internal reflection and is substantially transparent so that external light can reach the eye of the viewer, and the grating region includes a reflective coating.

12. The display system of claim 1 wherein:
said second Fresnel reflector includes a grating region that includes multiple saw-tooth shaped grating elements configured to reflect light rays from said one or more mirrors toward the eye of the viewer and flat regions between the saw-tooth shaped grating elements, where dual reflections by both the flat regions and the saw-tooth shaped grating elements are prevented by light absorbing areas.

13. The display system of claim 1 wherein:
at least one of said light pipe or said out-coupling light guide includes one or more layers that are configured to at least partially reflect light to reduce unilluminated areas.

14. The display system of claim 1 wherein:
a surface of said out-coupling light guide includes a curved envelope of multiple flat surfaces so that internally reflected light beams have the same angles as those of a flat surface.

15. The display system of claim 1 wherein:
angles of multiple saw-tooth shaped grating elements of said second Fresnel reflector of said out-coupling light guide vary by location so that an image is focused at a finite distance.

16. The display system of claim 1 further comprising:
a plurality of sets of the display system overlaid so that images at multiple distances are viewable.

17. The display system of claim 1 further comprising:
a plurality of waveguides integrated into a single waveguide using one or more dichroic filters and at least one dichroic cross prism.

18. The display system of claim 1 wherein:
at least one of said out-coupling light guide or said light pipe is coated with a holographic optical element, a diffractive optical element, or a multi-layer thin film so that a total internal reflection angle is reduced to enlarge a field of view of the display system.

19. The display system of claim 1 wherein:
at least one of said out-coupling light guide or said light pipe comprises a lower refractive index material adjacent to said in-coupling optical element and a higher refractive index material within or in proximity to the out-coupling light guide.

20. The display system of claim 1 wherein:
said out-coupling light guide is laminated with a higher refractive index material than a refractive index of said out-coupling light guide, and
said second Fresnel reflector is formed on the higher refractive index material.

Assignees

• Ishii Fusao
• Ntt Docomo Inc

Inventors

• Ishii Fusao
• Nakanishi Mikiko
• Ichikawa Kazuoki
• Iwamura Mikio

Classifications

• G02B13/16

  for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV} · CPC title

• G02B2027/0125

  Field-of-view increase by wavefront division · CPC title

• G02B6/0006

  Coupling light into the fibre (in general G02B6/4298) · CPC title

• G02B13/22

  Telecentric objectives or lens systems · CPC title

• G02B27/0101 Primary

  characterised by optical features (G02B27/0172 takes precedence) · CPC title