Display projectors

1. A projection display, for displaying an image to an observer overlaid on an outside world scene viewed through the display, 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, the second waveguide being a combiner through which the observer can view an outside world scene along a line of sight with the image overlaid on the outside world scene; 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 and along said line of sight.

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 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 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 .