DISPLAY PROJECTORS

• US 20100246004A1
• Filed: 11/11/2008
• Published: 09/30/2010
• Est. Priority Date: 12/18/2007
• Status: Active Grant

• Current Assignee: BAE Systems Plc
• Original Assignee: BAE Systems Plc
• Inventors: Simmonds, Michael David
• Granted Patent: US 8,107,780 B2
• Time in Patent Office: Days
• US Class Current: 359/567
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• CPC Class Codes: G02B 27/0081 with means for altering, e.g. enlarging, the entrance or exit pupil
• CPC Class Codes: G02B 27/0103 comprising holographic elements
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 6/00 Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: G02B 6/4298 coupling with non-coherent light sources and/or radiation detectors, e.g. lamps, incandescent bulbs, scintillation chambers
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

The present invention is directed to a display which presents an image along a line of sight of an observer, such that the image is overlaid on a real world scene has a first waveguide and an image source device to inject the image into the first waveguide. The first waveguide has a first grating to direct the image internally and to output the image from the first waveguide. A second waveguide has a coupling grating to receive the image from the first waveguide and to direct the image along the second waveguide. The second waveguide has an exit grating to diffract the received image out of the second waveguide towards the observer. The exit grating diffracts the image out of the second waveguide off axis to a normal axis of the second waveguide.

Claims

1. A projection display, for displaying an image to an observer, including:

a first waveguide element arranged to be light transmissive;

an image-providing light source device arranged to generate an image and to inject image bearing light into the first waveguide element;

a first grating associated with the first waveguide element arranged to direct the image bearing light internally along the first waveguide element and through which the image bearing light is outputted from the first waveguide element;

a second waveguide element arranged to be light transmissive and transparent that includes a coupling grating arranged to receive the image bearing light from the first waveguide element and to direct the image bearing light along the second waveguide element;

the second waveguide element further includes an exit grating arranged to diffract received image bearing light out of the second waveguide element towards an observer; and

wherein the exit grating is arranged to diffract image bearing light out of the second waveguide element off axis to a normal axis of the second waveguide element.

2. A projection display, as claimed in claim 1, wherein the exit grating is arranged to diffract image bearing light out of the second waveguide such that the image bearing light will form an elevation angle with a normal axis of the second waveguide element.

3. A projection display, as claimed in claim 2, wherein the spatial frequency of the exit grating is arranged to diffract image bearing light out of the second waveguide such that the image bearing light will form an elevation angle with a normal axis of the second waveguide element.

4. A projection display, as claimed in claim 1, wherein the exit grating is arranged to diffract image bearing light out of the second waveguide such that the image bearing light will form an azimuth angle with a normal axis of the second waveguide element.

5. A projection display, as claimed in claim 4, wherein the exit grating is arranged to perform a rotation of image bearing light such that the image bearing light will form an azimuth angle with the normal axis of the second waveguide element.

6. A projection display, as claimed in claim 1, wherein the exit grating is arranged to diffract image bearing light out of the second waveguide such that the image bearing light will form an elevation and an azimuth angle to a normal axis with the second waveguide element.

7. A projection display, as claimed in claim 6, wherein the spatial frequency of the exit grating is arranged to diffract image bearing light out of the second waveguide such that the image bearing light will form an elevation angle to the normal axis of the second waveguide element and the exit grating is arranged to perform a rotation of the image bearing light such that the image bearing light will form an azimuth angle with a normal axis of the second waveguide element.

8. A projection display, as claimed in claim 1, wherein the first grating is arranged such that incident inputted image bearing light is diffracted therefrom with the incidence angle of the diffracted light at internal surfaces of the first waveguide element arranged to be greater that the critical angle for the material from which the first waveguide element is made.

9. A projection display, as claimed in claim 1, wherein the transmission grating is a low efficiency grating.

10. A projection display, as claimed in claim 1, wherein the coupling grating is arranged such that incident image bearing light is diffracted therefrom with the incident angle of the diffracted light at internal surfaces of the second waveguide element arranged to be greater than the critical angle for the material from which the second waveguide element is made.

11. A projection display, according to claim 1, wherein the diffractive power of the coupling grating is rotated through 90°

with respect to the diffractive power of the first grating.

12. A projection display, according to claim 1, wherein the second waveguide element includes a narrow band selective reflection coating provided on a surface of the second waveguide element parallely spaced parallel to the exit grating, which reflective coating is arranged to reflect light diffracted from the exit grating back to the exit grating.

13. A projection display, according to claim 1, wherein the first plate-like waveguide is curved.

14. A projection display, according to claim 1, wherein the second plate-like waveguide is curved.

15. A projection display, according to claim 1, wherein the first waveguide element includes an input region arranged to receive injected image bearing light via reflective, or transmissive, or refractive means.

16. A projection display, as claimed in claim claim 1, wherein the first waveguide element is plate-like, the second waveguide element is plate-like and the first and second waveguide elements are arranged substantially co-planar to one another.

17. A projection display, as claimed in claim 1, wherein the first waveguide element and the second waveguide element are arranged substantially in the same plane.

18. A projection display, as claimed in claim 17, wherein the first waveguide element and the second waveguide element are formed within a single piece of material.

19. A Head Up Display, or Helmet Mounted Display, or Head Mounted Display including a projection display according to claim 1.