Waveguide structure for head up displays

1. An optical waveguide for a head up display, the optical waveguide being configured to provide pupil expansion in two dimensions and having an input end and an output end, the optical waveguide comprising:

first and second input regions positioned at the input end;

first and second optical gratings configured to direct light received through the first and second input regions respectively such that the light propagates towards the output end of the optical waveguide and is trapped in the optical waveguide by total internal reflection, wherein the propagation direction has a lateral component relative to the direction from the input end to the output end;

first and second beam splitters configured to expand the pupil of light propagating in the optical waveguide and received through the first and second input regions respectively, the expansion being in the direction of propagation through the first and second beam splitters;

third and fourth optical gratings configured to direct light received from the first and second beam splitters respectively such that the light propagates in a direction substantially aligned with the direction from the input end to the output end;

third and fourth beam splitters configured to expand the pupil of light propagating in the optical waveguide and received from the third and fourth optical gratings respectively, the expansion being in the direction of propagation through the third and fourth beam splitters; and

an output grating configured to couple light propagating in the optical waveguide and received from the third and fourth beam splitters out of the optical waveguide; wherein the first and second input regions are positioned to the left and right respectively of an axis from the input end to the output end of the optical waveguide, and the first and second input regions are substantially in a first plane, the first plane parallel to the direction of propagation and parallel to the pupil expansion direction.

2. The optical waveguide according to claim 1 , wherein light received through the first input region is coupled out of the optical waveguide by the output grating in a region predominantly to the right of the axis, and light received through the second input region is coupled out of the optical waveguide by the output grating in a region predominantly to the left of the axis.

3. The optical waveguide according to claim 1 , wherein the axis is positioned at the centre of the output region in a lateral direction.

4. The optical waveguide according to claim 1 , further comprising first and second projectors to project light into the first and second input regions.

5. The optical waveguide according to claim 4 , wherein the light received in each of the first and second input regions comprises light to form an image and the light represents the full field of view of the image.

6. The optical waveguide according to claim 4 , wherein the light received in each of the first and second input regions comprises light to form part of the full field of view of the image and these two parts are combined by the optical waveguide to provide the full field of view.

7. The optical waveguide according to claim 1 , wherein light received through the first and second input regions crosses within the optical waveguide in the region of the third and fourth optical gratings.

8. The optical waveguide according to claim 1 wherein the light received at the first input region illuminates a first portion of the output, and the light received at the second input region illuminates a second portion of the output.

9. The optical waveguide according to claim 8 wherein the first portion is equal to the second portion of the output.

10. The optical waveguide according to claim 8 wherein the first portion and the second portion are unequal.

11. The optical waveguide according to claim 1 wherein the light received at the first input region illuminates a first portion of the output, and the light received at the second input region illuminates a second portion of the output.

12. The optical waveguide according to claim 11 wherein the first portion is equal to the second portion of the output.

13. The optical waveguide according to claim 11 wherein the first portion and the second portion are unequal.

14. An optical waveguide having an input end and an output end, the optical waveguide comprising:

first and second input regions positioned at the input end of the optical waveguide and comprising first and second optical gratings respectively, the first and second optical gratings configured to direct light incident on the first and second input regions into the optical waveguide such that the light propagates towards the output end of the optical waveguide;

first and second beam splitters configured to expand the pupil of light propagating from the first and second optical gratings respectively, the expansion being in the direction of propagation through the first and second beam splitters;

third and fourth optical gratings configured to direct light received from the first and second beam splitters respectively;

third and fourth beam splitters configured to expand the pupil of light propagating in the optical waveguide and received from the third and fourth optical gratings respectively, the expansion being in the direction of propagation through the third and fourth beam splitters; and

an output grating configured to couple light propagating in the optical waveguide and received from the third and fourth beam splitters out of the optical waveguide.

15. The optical waveguide according to claim 14 , wherein the first and second input regions are positioned to the left and right respectively of an axis from the input end to the output end of the optical waveguide, and wherein light received through the first input region is coupled out of the optical waveguide by the output grating in a region predominantly to the right of the axis, and light received through the second input region is coupled out of the optical waveguide by the output grating in a region predominantly to the left of the axis.

16. The optical waveguide according to claim 14 , wherein the axis is positioned at the centre of the output region in a lateral direction.

17. The optical waveguide according to claim 14 , further comprising first and second projectors to project light toward the first and second input regions.

18. A head up display system comprising the optical waveguide according to claim 14 .

19. An optical waveguide having an input end and an output end, the optical waveguide comprising:

first and second input regions positioned at the input end of the optical waveguide and comprising first and second optical gratings respectively, the first and second optical gratings configured to direct light incident on the first and second input regions into the optical waveguide such that the light propagates towards the output end of the optical waveguide;

first and second beam splitters configured to expand the pupil of light propagating from the first and second optical gratings respectively, the expansion being in the direction of propagation through the first and second beam splitters;

third and fourth optical gratings configured to direct light received from the first and second beam splitters respectively, wherein light received at the first and second input regions crosses within the optical waveguide in the region of the third and fourth optical gratings;

third and fourth beam splitters configured to expand the pupil of light propagating in the optical waveguide and received from the third and fourth optical gratings respectively, the expansion being in the direction of propagation through the third and fourth beam splitters; and

an output grating configured to couple light propagating in the optical waveguide and received from the third and fourth beam splitters out of the optical waveguide.

20. A head up display system comprising the optical waveguide according to claim 19 .