Waveguide display with multiple monochromatic projectors

1. A waveguide display comprising:

a waveguide;

three non-overlapping input gratings, wherein each of the three non-overlapping input gratings is configured to couple display light in a respective color into the waveguide;

one or more first middle gratings configured to receive and redirect the display light from the three non-overlapping input gratings;

a second middle grating configured to diffract, at two or more regions of the second middle grating, the display light from the one or more first middle gratings; and

an output grating configured to couple the display light from each of the two or more regions of the second middle grating out of the waveguide at two or more regions of the output grating.

2. The waveguide display of claim 1 , wherein the one or more first middle gratings include three first middle gratings, each first middle grating of the three first middle gratings corresponding to a respective input grating of the three non-overlapping input gratings and configured to receive and redirect the display light of the respective color from the corresponding respective input grating.

3. The waveguide display of claim 1 , wherein the waveguide comprises:

a first substrate;

a second substrate; and

one or more holographic material layers between the first substrate and the second substrate, wherein the one or more first middle gratings and the second middle grating are formed in the one or more holographic material layers.

4. The waveguide display of claim 1 , further comprising three projectors, wherein:

each projector of the three projectors is configured to generate a monochromatic image; and

each input grating of the three non-overlapping input gratings is configured to couple the monochromatic image from a corresponding projector of the three projectors into the waveguide.

5. The waveguide display of claim 4 , wherein each projector of the three projectors includes a two-dimensional array of micro-LEDs.

6. The waveguide display of claim 1 , further comprising a phase structure on the waveguide, the phase structure configured to change a polarization state of the display light incident on the phase structure before or after the display light is redirected by the one or more first middle gratings.

7. The waveguide display of claim 6 , wherein the phase structure comprises a waveplate, a layer of a birefringent material, or a subwavelength structure and an overcoat layer.

8. The waveguide display of claim 6 , wherein the phase structure is in selected regions of the waveguide or is characterized by a spatially varying phase retardation across different regions of the phase structure.

9. The waveguide display of claim 1 , wherein the three non-overlapping input gratings, the one or more first middle gratings, and the second middle grating include multiplexed transmissive volume Bragg gratings or multiplexed reflective volume Bragg gratings.

10. The waveguide display of claim 1 , wherein:

each input grating of the three non-overlapping input gratings is on a respective staircase structure bonded to the waveguide; and

each respective staircase structure is on top of the one or more first middle gratings.

11. The waveguide display of claim 10 , wherein:

each respective staircase structure includes a staircase substrate; and

each input grating of the three non-overlapping input gratings is on a top or a bottom of the staircase substrate of the respective staircase structure.

12. The waveguide display of claim 10 , wherein the respective staircase structure is characterized by a total thickness less than 100 μm.

13. The waveguide display of claim 10 , wherein the respective staircase structure includes two or more holographic material layers, the input grating formed in the two or more holographic material layers.

14. The waveguide display of claim 10 , wherein a shape and a thickness of the respective staircase structure are selected to avoid clipping of a field of view of the waveguide display by the respective staircase structure.

15. A waveguide display comprising:

a waveguide;

three projectors, each projector of the three projector configured to generate display light of a respective color;

three non-overlapping input gratings, each of the three non-overlapping input gratings configured to couple the display light in a respective color into the waveguide;

three first middle gratings, each of the three first middle gratings configured to receive and redirect the display light from a respective input grating of the three non-overlapping input gratings;

a second middle grating configured to receive and redirect the display light from the three first middle gratings; and

an output grating configured to couple the display light from the second middle grating out of the waveguide.

16. The waveguide display of claim 15 , wherein the waveguide comprises:

a first substrate;

a second substrate; and

one or more holographic material layers between the first substrate and the second substrate, wherein the three first middle gratings and the second middle grating are formed in the one or more holographic material layers.

17. The waveguide display of claim 15 , further comprising a phase structure on the waveguide, the phase structure configured to change a polarization state of the display light incident on the phase structure after or before the display light is diffracted by the three first middle gratings.

18. The waveguide display of claim 17 , wherein the phase structure comprises a waveplate, a layer of a birefringent material, or a subwavelength structure and an overcoat layer.

19. The waveguide display of claim 15 , wherein:

each input grating of the three non-overlapping input gratings is on a respective staircase structure bonded to the waveguide; and

each respective staircase structure is on top a first middle grating of the three first middle gratings.

20. The waveguide display of claim 19 , wherein:

each respective staircase structure includes a staircase substrate;

each input grating of the three non-overlapping input gratings is on a top or a bottom of the staircase substrate of the respective staircase structure; and

each respective staircase structure is characterized by a total thickness less than 100 μm.