Light-guiding structures

1. An apparatus comprising:

a first light-guiding structure configured to guide optical waves, having a first surface and a second surface which is opposite to the first surface;

a second light-guiding structure configured to guide optical waves, having a first surface and a second surface which is opposite to the first surface;

a first in-coupling element disposed on the first surface of the first light-guiding structure and configured to receive an input optical beam;

a second in-coupling element disposed on the first surface of the second light-guiding structure and configured to receive the input optical beam; wherein

the input optical beam is configured to be controlled by an optical engine comprising at least one lens; and wherein the optical engine comprises

a first shutter placed such that it is aligned with the first in-coupling element and a second shutter placed such that it is aligned with the second in-coupling element;

a first out-coupling element disposed on the second surface of the first light-guiding structure and being offset from the first in-coupling element and configured to output an output optical beam out of the first light-guiding structure to be viewed by a user;

a second out-coupling element disposed on the second surface of the second light-guiding structure and being offset from the second in-coupling element and configured to output the output optical beam out of the second light-guiding structure to be viewed by a user;

wherein the first and the second light-guiding structures have different curvature radii and are arranged in a stack; and

wherein the first and the second light-guiding structures are respectively configured to produce virtual images at different viewing distances.

2. The apparatus of claim 1 , wherein the first and the second light-guiding structures are exit-pupil expanders.

3. The apparatus of claim 1 , wherein the input optical beam is generated from a virtual image of a display.

4. The apparatus of claim 3 , wherein the display is a field-sequential display with directional properties.

5. The apparatus of claim 1 , wherein a curvature radius of at least one of the first and the second light-guiding structures is changeable.

6. The apparatus of claim 1 , wherein the first and the second in-coupling elements are diffractive elements.

7. The apparatus of claim 1 , wherein the first light-guiding structure has a flat shape and the second light-guiding structure has a non-flat shape.

8. The apparatus of claim 1 further comprising:

a third light-guiding structure configured to guide optical waves, having a first surface and a second surface which is Opposite to the first surface;

a third in-coupling element disposed, on the first surface of the third light-guiding structure and configured to receive the input optical beam; and

a third shutter placed such that it is aligned with the third in-coupling element; and wherein

the first, the second and the third light-guiding structures have different curvature radii.

9. The apparatus of claim 8 , wherein the first light-guiding structure, the second light-guiding structure and the third light-guiding structure present different two-dimensional content of different focal distance to the user.

10. The apparatus of claim 1 , wherein the optical engine is configured to provide adjustable optical power.

11. A method comprising:

receiving an input optical beam by at least one of a first light-guiding structure and a second light-guiding structure, wherein the first light-guiding structure comprises a first in-coupling element and the second light-guiding element comprises a second in-coupling element;

having a first shutter placed such that it is aligned with the first in-coupling element and a second shutter placed such that it is aligned with the second in-coupling element;

outputting an output optical beam, to be viewed by a user, using the first light-guiding structure when the first shutter is switched on and the second shutter is switched off and using the second light-guiding structure when the first shutter is switched off and the second shutter is switched on, and wherein at least one of the first or the second light-guiding structure has a non-flat shape; and

configuring the first and the second light-guiding structures to have curvature radii that define focal distances such that virtual images are produced at different viewing distances, the first and second light-guiding structures being arranged in a stack.

12. The method of claim 11 , wherein at least one of the light-guiding structures is an exit-pupil expander.

13. The method of claim 11 , wherein the input optical beam is generated from a virtual image of a display.

14. The method of claim 11 , wherein a curvature radius of the non-flat shape of the first light-guiding structure is different to the curvature of the non-flat shape of the second light-guiding structure.

15. The method of claim 11 , wherein the first light-guiding structure is configured to have a flat shape and the second light-guiding structure is configured to have a non-flat shape.

16. The method of claim 11 , comprising a third light-guiding structure configured to guide optical waves, having a first surface and a second surface which is opposite to the first surface, wherein the third light-guiding structure and the second light-guiding structure have different curvature radii.

17. The method of claim 16 , wherein the first light-guiding structure, the second light-guiding structure and the third light-guiding structure present different two-dimensional content of different focal distance to the user.