Methods and systems for high efficiency eyepiece in augmented reality devices

1. A display system comprising:

projection optics configured to project a beam of light in a first direction;

an eyepiece unit including:

a first waveguide layer disposed in a first lateral plane and including an incident light surface and an opposing surface opposite the incident light surface;

an incoupling diffractive optical element disposed on the incident light surface, wherein the incoupling diffractive optical element is configured to:

incouple a first portion of the beam of light and to propagate the first portion of the beam of light by total internal reflection in a second direction; and

transmit a second portion of the beam of light along the first direction; and

a retroreflector disposed adjacent the opposing surface, wherein the retroreflector is configured to retroreflect the second portion of the beam of light along a reflected direction opposite to the first direction.

2. The display system of claim 1 wherein the eyepiece unit further comprises:

an orthogonal pupil expander region laterally displaced from the incoupling diffractive optical element; and

an exit pupil expander (EPE) region laterally displaced from the incoupling diffractive optical element.

3. The display system of claim 1 further comprising a projection display configured to direct the beam of light to the projection optics.

4. The display system of claim 1 wherein the beam of light comprises a plurality of colors projected sequentially.

5. The display system of claim 1 wherein the second direction is parallel to the first lateral plane.

6. The display system of claim 1 wherein the retroreflector is disposed on the opposing surface.

7. The display system of claim 1 wherein the retroreflector is disposed parallel to the opposing surface at a predetermined distance from the opposing surface.

8. The display system of claim 1 wherein the incoupling diffractive optical element is further configured to:

incouple a third portion of the second portion of the beam of light and to propagate the third portion by total internal reflection in the second direction; and

transmit a fourth portion of the beam of light along the reflected direction.

9. The display system of claim 1 , further comprising:

a second waveguide layer disposed in a second lateral plane adjacent to the first lateral plane and including a second incoupling diffractive optical element disposed at a second lateral position, a second waveguide optically coupled to the second incoupling diffractive optical element, and a second outcoupling diffractive optical element optically coupled to the second waveguide; and

a third waveguide layer disposed in a third lateral plane and including a third incoupling diffractive optical element disposed at a third lateral position, a third waveguide optically coupled to the third incoupling diffractive optical element, and a third outcoupling diffractive optical element optically coupled to the third waveguide.

10. The display system of claim 9 , wherein the incoupling diffractive optical element is disposed at a first lateral position and the first lateral position and the second lateral position are a same lateral position.

11. An eyepiece unit comprising:

a waveguide layer disposed in a lateral plane and including an incident light surface and an opposing surface opposite the incident light surface;

a first incoupling diffractive optical element disposed on the incident light surface, wherein the first incoupling diffractive optical element is configured to:

incouple a first portion of a beam of light propagating in a first direction and to propagate the first portion of the beam of light by total internal reflection in a second direction; and

transmit a second portion of the beam of light along the first direction;

a second incoupling diffractive optical element disposed on the opposing surface, wherein the second incoupling diffractive optical element is configured to:

receive the second portion of the beam of light along the first direction;

incouple a third portion of the beam of light and to propagate the third portion of the beam of light by total internal reflection in a third direction; and

transmit a fourth portion of the beam of light along the first direction; and

a retroreflector disposed adjacent the opposing surface, wherein the retroreflector is configured to retroreflect the fourth portion of the beam of light along a reflected direction opposite to the first direction.

12. The eyepiece unit of claim 11 , wherein the second incoupling diffractive optical element comprises a metallized retroreflector.

13. The eyepiece unit of claim 11 , wherein the first incoupling diffractive optical element is configured to incouple light in a first spectral band.

14. The eyepiece unit of claim 13 wherein:

the second incoupling diffractive optical element is configured to incouple light in a second spectral band;

the first spectral band includes red wavelengths; and

the second spectral band includes green wavelengths.

15. A method of operating a display system, the method comprising:

directing a beam of light in a first direction;

receiving the beam of light at an incident light surface of a waveguide layer having an opposing surface opposite the incident light surface;

propagating, at a first diffractive optical element, a first portion of the beam of light into the waveguide layer in a second direction;

transmitting, at the first diffractive optical element, a second portion of the beam of light toward the opposing surface; and

retroreflecting the second portion of the beam of light along a reflected direction opposite to the first direction.

16. The method of claim 15 further comprising:

propagating, at the first diffractive optical element, a first fraction of the second portion of the beam of light into the waveguide layer in the second direction; and

transmitting, at the first diffractive optical element, a second fraction of the second portion of the beam of light along the reflected direction.

17. The method of claim 16 further comprising:

reflecting at least a portion of the second fraction in the first direction toward the waveguide layer;

receiving the reflected portion at the incident light surface of the waveguide layer; and

propagating, at the first diffractive optical element, a portion of the reflected portion into the waveguide layer in the second direction.

18. The method of claim 15 wherein the first diffractive optical element is disposed on the incident light surface.

19. The method of claim 15 wherein retroreflecting the second portion of the beam of light comprises retroreflecting light along a reflected direction opposite to the first direction.

20. The method of claim 15 wherein directing the beam of light in the first direction comprises reflecting a time sequential color beam from a display element.