Multi-layer diffractive eyepiece with wavelength-selective reflector

1. An eyepiece for projecting an image to an eye of a viewer, the eyepiece comprising:

a planar waveguide having a front surface and a back surface, the planar waveguide being configured to propagate light in a first wavelength range;

a grating coupled to the back surface of the planar waveguide and configured to diffract a first portion of the light propagating in the planar waveguide out of a plane of the planar waveguide toward a first direction and to diffract a second portion of the light propagating in the planar waveguide out of the plane of the planar waveguide toward a second direction opposite to the first direction; and

a wavelength-selective reflector coupled to the front surface of the planar waveguide and configured to reflect light in the first wavelength range and transmit light outside the first wavelength range, such that the wavelength-selective reflector reflects at least part of the second portion of the light back toward the first direction.

2. The eyepiece of claim 1 wherein the front surface of the planar waveguide faces away from the eye of the viewer, the back surface of the planar waveguide faces toward the eye of the viewer, the first direction is toward the eye of the viewer, and the second direction is away from the eye of the viewer.

3. The eyepiece of claim 1 wherein the wavelength-selective reflector is characterized by a reflectance spectrum having a reflectance peak in the first wavelength range.

4. The eyepiece of claim 3 wherein the first wavelength range corresponds to one of red light, green light, or blue light.

5. The eyepiece of claim 4 wherein the reflectance peak is characterized by a full-width-at-half-maximum that substantially matches a spectral band width of the light propagating in the planar waveguide.

6. The eyepiece of claim 4 wherein the reflectance peak is characterized by a full-width-at-half-maximum that is greater than a spectral band width of the light propagating in the planar waveguide.

7. The eyepiece of claim 1 wherein the wavelength-selective reflector comprises one of a multilayer thin film, a metasurface, or a volume phase hologram.

8. The eyepiece of claim 1 wherein the grating is optimized for diffracting light in a first polarization state toward the first direction and for diffracting light in a second polarization state orthogonal to the first polarization state toward the second direction, and the wavelength-selective reflector is optimized for reflecting light in the second polarization state.

9. An eyepiece for projecting an image to an eye of a viewer, the eyepiece comprising:

a first planar waveguide having a first front surface and a first back surface, the first planar waveguide being configured to propagate first light in a first wavelength range;

a second planar waveguide disposed substantially parallel to and in front of the first planar waveguide, the second planar waveguide having a second front surface and a second back surface and being configured to propagate second light in a second wavelength range;

a third planar waveguide disposed substantially parallel to and in front of the second planar waveguide, the third planar waveguide having a third front surface and a third back surface and being configured to propagate third light in a third wavelength range;

a first grating coupled to the first back surface of the first planar waveguide and configured to diffract a first portion of the first light propagating in the first planar waveguide out of a plane of the first planar waveguide toward a first direction and to diffract a second portion of the first light out of the plane of the first planar waveguide toward a second direction opposite to the first direction;

a second grating coupled to the second back surface of the second planar waveguide and configured to diffract a first portion of the second light propagating in the second planar waveguide out of a plane of the second planar waveguide toward the first direction and to diffract a second portion of the second light out of the plane of the second planar waveguide toward the second direction;

a third grating coupled to the third back surface of the third planar waveguide and configured to diffract a first portion of the third light propagating in the third planar waveguide out of a plane of the third planar waveguide toward the first direction and to diffract a second portion of the third light out of the plane of the third planar waveguide toward the second direction;

a first wavelength-selective reflector coupled to the first front surface of the first planar waveguide and configured to reflect light in the first wavelength range and transmit light outside the first wavelength range, such that the first wavelength-selective reflector reflects at least part of the second portion of the first light back toward the first direction;

a second wavelength-selective reflector coupled to the second front surface of the second planar waveguide and configured to reflect light in the second wavelength range and transmit light outside the second wavelength range, such that the second wavelength-selective reflector reflects at least part of the second portion of the second light back toward the first direction; and

a third wavelength-selective reflector coupled to the third front surface of the third planar waveguide and configured to reflect light in the third wavelength range and transmit light outside the third wavelength range, such that the third wavelength-selective reflector reflects at least part of the second portion of the third light back toward the first direction.

10. The eyepiece of claim 9 wherein the first front surface of the first planar waveguide faces away from the eye of the viewer, the first back surface of the first planar waveguide faces toward the eye of the viewer, the second front surface of the second planar waveguide faces away from the eye of the viewer, the second back surface of the second planar waveguide faces toward the eye of the viewer, the third front surface of the third planar waveguide faces away from the eye of the viewer, the third back surface of the third planar waveguide faces toward the eye of the viewer, the first direction is toward the eye of the viewer, and the second direction is away from the eye of the viewer.

11. The eyepiece of claim 9 wherein each of the first wavelength-selective reflector, the second wavelength-selective reflector, and the third wavelength-selective reflector comprises one of a multilayer thin film, a metasurface, or a volume phase hologram.

12. The eyepiece of claim 9 wherein each of the first wavelength-selective reflector, the second wavelength-selective reflector, and the third wavelength-selective reflector comprises a metasurface or a volume hologram optimized for a predetermined range of angle of incidence.

13. The eyepiece of claim 9 wherein:

the first wavelength range corresponds to red light;

the second wavelength range corresponds to green light; and

the third wavelength range corresponds to blue light.

14. The eyepiece of claim 13 wherein the first wavelength-selective reflector is configured to transmit green light and blue light, and the second wavelength-selective reflector is configured to transmit blue light.

15. The eyepiece of claim 13 wherein each of the first wavelength-selective reflector, the second wavelength-selective reflector, and the third wavelength-selective reflector comprises a metasurface or a volume hologram, and includes a plurality of regions, each region optimized for a respective range of angle of incidence corresponding to light rays reaching the eye of the viewer.

16. The eyepiece of claim 15 wherein the plurality of regions partially overlap with each other.

17. The eyepiece of claim 9 wherein each of the first wavelength-selective reflector, the second wavelength-selective reflector, and the third wavelength-selective reflector comprises a metasurface including a plurality of interleaved regions, each region optimized for a respective range of angle of incidence.

18. An eyepiece for projecting an image to an eye of a viewer, the eyepiece comprising:

a first planar waveguide having a first front surface and a first back surface and configured to propagate first light in a first wavelength range;

a second planar waveguide disposed substantially parallel to and in front of the first planar waveguide, the second planar waveguide having a second front surface and a second back surface and being configured to propagate second light in a second wavelength range;

a third planar waveguide disposed substantially parallel to and in front of the second planar waveguide, the third planar waveguide having a third front surface and a third back surface and being configured to propagate third light in a third wavelength range;

a first grating coupled to the first front surface of the first planar waveguide and configured to diffract a first portion of the first light propagating in the first planar waveguide out of a plane of the first planar waveguide toward a first direction and to diffract a second portion of the first light out of the plane of the first planar waveguide toward a second direction opposite to the first direction;

a second grating coupled to the second front surface of the second planar waveguide and configured to diffract a first portion of the second light propagating in the second planar waveguide out of a plane of the second planar waveguide toward the first direction and to diffract a second portion of the second light out of the plane of the second planar waveguide toward the second direction;

a third grating coupled to the third front surface of the third planar waveguide and configured to diffract a first portion of the third light propagating in the third planar waveguide out of a plane of the third planar waveguide toward the first direction and to diffract a second portion of the third light out of the plane of the third planar waveguide toward the second direction;

a first wavelength-selective reflector coupled to the second back surface of the second planar waveguide and configured to reflect light in the first wavelength range and transmit light outside the first wavelength range, such that the first wavelength-selective reflector reflects at least part of the second portion of the first light back toward the first direction;

a second wavelength-selective reflector coupled to the third back surface of the third planar waveguide and configured to reflect light in the second wavelength range and transmit light outside the second wavelength range, such that the second wavelength-selective reflector reflects at least part of the second portion of the second light back toward the first direction;

a front cover plate disposed substantially parallel to and in front of the third planar waveguide; and

a third wavelength-selective reflector coupled to a surface of the front cover plate, the third wavelength-selective reflector configured to reflect light in the third wavelength range and transmit light outside the third wavelength range, such that the third wavelength-selective reflector reflects at least part of the second portion of the third light back toward the first direction.

19. The eyepiece of claim 18 wherein each of the first wavelength-selective reflector, the second wavelength-selective reflector, and the third wavelength-selective reflector comprises a metasurface or a volume phase hologram, and includes a plurality of regions, each region optimized for a respective range of angle of incidence corresponding to light rays reaching the eye of the viewer.

20. The eyepiece of claim 18 wherein:

the first wavelength range corresponds to red light;

the second wavelength range corresponds to green light; and

the third wavelength range corresponds to blue light.