Display waveguide with a high-index layer

1. A waveguide for conveying image light to an eyebox, the waveguide comprising:

a substrate of a first refractive index n 1 ;

a high-index layer of a second refractive index n 2 supported by the substrate without an air gap therebetween, wherein n 2 is greater than n 1 ;

an input coupler at a first location along the waveguide; and

an output coupler at a second, different location along the waveguide;

wherein the input coupler is configured to couple a first portion of the image light into the waveguide for propagating toward the output coupler partly in the substrate, and to couple a second portion of the image light into the waveguide for propagating toward the output coupler within the high-index layer; and

wherein the output coupler is configured to couple the image light out of the waveguide toward the eyebox, the output coupler comprising a first grating and a second grating, wherein at least one of the first or second gratings is configured to redirect light propagating in the high-index layer.

2. The waveguide of claim 1 wherein each one of the first and the second gratings is disposed in the high-index layer or at a surface thereof to diffract light propagating in the high-index layer.

3. The waveguide of claim 2 wherein the first grating is disposed at a surface of the high-index layer, and the second grating is disposed at an interface between the substrate and the high-index layer.

4. The waveguide of claim 2 wherein the output coupler further comprises a third grating configured to redirect light propagating in the substrate.

5. The waveguide of claim 4 wherein the third grating is disposed at a surface of the substrate opposite of the high-index layer.

6. The waveguide of claim 1 wherein the input coupler comprises an input grating disposed to couple at least a portion of the image light into the high-index layer.

7. The waveguide of claim 1 wherein the second refractive index is at least 2.2.

8. The waveguide of claim 1 wherein (n 1 -n 2 ) is equal to or greater than 0.3.

9. The waveguide of claim 1 wherein the high-index layer is at least 150 microns thick.

10. A waveguide for conveying image light to an eyebox, the waveguide comprising:

a substrate of a first refractive index n 1 ;

a high-index layer of a second refractive index n 2 supported by the substrate without an air gap therebetween, wherein n 2 is greater than n 1 ;

an input coupler configured to couple the image light into the high-index layer; and

an output coupler configured to couple the image light out of the waveguide toward the eyebox, the output coupler comprising a first grating and a second grating, wherein at least one of the first or second gratings is configured to redirect light propagating in the high-index layer;

wherein the image light comprises a first color channel and a second color channel, wherein the second color channel comprises longer wavelengths than the first color channel, and wherein the input coupler is configured to propagate at least a portion of the second color channel in the high-index layer by total internal reflection (TIR) at an interface between the high-index layer and the substrate.

11. The waveguide of claim 10 wherein the waveguide provides a field of view (FOV) shared by the first and second color channels, the FOV having an angular FOV width Θ in at least one direction, and wherein the high-index layer supports at least 50% of the angular FOV width Θ of at least one of the first or second color channels.

12. The waveguide of claim 10 wherein the first color channel comprises one of green or blue light and the second color channel comprises red light, and wherein the input coupler is configured to propagate at least a portion of the red light in the high-index layer by TIR at the interface between the high-index layer and the substrate.

13. The waveguide of claim 10 wherein the first color channel comprises blue light and the second color channel comprises green light, and wherein the input coupler is configured to propagate at least a portion of the green light in the high-index layer by TIR at the interface between the high-index layer and the substrate.

14. The waveguide of claim 10 wherein the image light further comprises a third color channel, and wherein the input coupler is configured to couple all three color channels into the waveguide for propagating toward the output coupler.

15. The waveguide of claim 10 wherein the input coupler is configured to direct at least a portion of the first color channel into the substrate through the interface of the high-index layer with the substrate.

16. The waveguide of claim 1 wherein the first grating and the second grating cooperate for diffracting the image light propagating in the high-index layer out of the waveguide at an output angle equal to an angle of incidence thereof upon the waveguide.

17. The waveguide of claim 16 comprising a third grating disposed in the substrate or at a surface thereof, wherein at least one of the first grating or the second grating cooperates with the third grating for diffracting the image light propagating in the substrate out of the waveguide at an output angle equal to an angle of incidence thereof upon the waveguide.

18. The waveguide of claim 1 , wherein the input coupler is configured to couple the first portion of the image light into the high-index layer at first propagation angles that are smaller than an angle of total internal reflection (TIR) at an interface with the substrate, and to couple the second portion of the image light into the high-index layer at second propagation angles that are greater than the angle of TIR at the interface with the substrate.

19. The waveguide of claim 18 , wherein the first portion of the image light comprises a first color channel, the second portion of the image light comprises a second color channel, wherein the second color channel comprises longer wavelengths than the first color channel, and wherein the input coupler is configured to propagate at least a portion of the second color channel in the high-index layer by TIR at the interface between the high-index layer and the substrate.

20. The waveguide of claim 18 , wherein the first and second portions of the image light correspond to different angles of incidence of the image light.