Pupil steering for a pupil expander
A pupil expander spatially modulates decoupling efficiency of light for pupil steering. The pupil expander can be used in a waveguide display, such as part of an artificial-reality display, to reduce power consumption of an optical source.
1. An apparatus comprising:
a waveguide;
a coupling element configured to couple light into the waveguide; and
a decoupling element configured to:
output light from the waveguide toward an eye of a user of the apparatus from a selected location of the decoupling element and/or in a selected orientation from the decoupling element; and
vary the selected location and/or the selected orientation in response to tracking of the eye of the user.
2. The apparatus of claim 1 , wherein the decoupling element comprises:
a grating; and
an optical element configured to vary polarization of light incident on the grating.
3. The apparatus of claim 2 , wherein the optical element comprises liquid-crystals.
4. The apparatus of claim 1 , wherein an optical element of the decoupling element is configured to vary polarization of light incident on a grating so that there is higher diffraction efficiency for light incident on a first area of the grating than for light incident on a second area of the grating.
5. The apparatus of claim 1 , wherein light outputted by the decoupling element from the selected location and/or in the selected orientation defines an exit pupil that is slightly larger than a pupil of the eye.
6. The apparatus of claim 5 , wherein the exit pupil is equal to or greater than a width of the pupil of the eye and equal to or less than two times the width of the pupil of the eye.
7. The apparatus of claim 1 , wherein light outputted by the decoupling element from the selected location and/or in the selected orientation defines an exit pupil of the apparatus that is substantially smaller than the decoupling element.
8. The apparatus of claim 7 , wherein the exit pupil is less than one fourth of the decoupling element.
9. The apparatus of claim 1 , further comprising an eye-tracking module configured to track a location of a pupil of the eye, and wherein the decoupling element is configured to vary the selected location and/or the selected orientation based on tracking the location of the pupil.
10. The apparatus of claim 1 further comprising an eye-tracking module configured to track an orientation of the eye, and wherein the decoupling element is configured to vary the selected location and/or the selected orientation based on tracking the orientation of the eye.
11. A method comprising:
coupling, using a coupling element, light into a waveguide;
decoupling light, using a decoupling element, from a selected location of the decoupling element and/or in a selected orientation from the decoupling element toward an eye; and
varying the selected location and/or the selected orientation in response to tracking of the eye.
12. The method of claim 11 , further comprising tracking the eye.
13. The method of claim 11 , further comprising varying polarization of light incident on a grating so that there is higher diffraction efficiency for light incident on a first area of the grating than for light incident on a second area of the grating, wherein the first area is the selected location.
14. The method of claim 13 , wherein diffraction efficiency is higher where more light is coupled into a first-order mode of the grating than coupled into a zeroth-order mode of the grating.
15. The method of claim 11 , further comprising modulating electrical signals to a liquid crystal layer to vary polarization of light passing through the liquid crystal layer to vary the selected location and/or the selected orientation.
16. The method of claim 15 , wherein varying polarization comprises rotating light polarization by 30 degrees or more and less than 180 degrees.
17. The method of claim 11 , further comprising:
tracking a location of a pupil of the eye; and
spatially modulating light based on tracking the location the pupil.
18. The method of claim 11 , further comprising:
tracking an orientation of an eye; and
spatially modulating light based on tracking the orientation of the eye.
19. A system comprising:
a source, wherein the source is an optical source;
a waveguide;
a coupling element, wherein the coupling element is configured to couple light from the source into the waveguide; and
a decoupling element, the decoupling element configured to:
couple light out of the waveguide and toward an eye of a user of the system from a selected location of the decoupling element and/or in a selected orientation from the decoupling element; and
vary the selected location and/or the selected orientation in response to tracking of the eye of the user.
20. The system of claim 19 , further comprising a frame, wherein:
the frame is part of glasses to be worn by the user; and
the waveguide, the coupling element, and the decoupling element are part of a lens secured in the frame.