Pupil tracking in an image display system

1. A pupil tracking system comprising:

a plurality of light sources for illuminating a pupil of a viewer;

a plurality of first apertures in a first mask, each one of the plurality of the first apertures located along a same direction from the pupil of the viewer as a direction of a corresponding one of the plurality of light sources, to pass retro-reflected light from the plurality of light sources after the light is retro-reflected from a retina of the viewer through the pupil of the viewer, the first apertures sized and shaped to pass the light from the plurality of light sources and block at least a portion of other light arriving at the first apertures;

a light sensor; and

an optical component which produces a spot of retro-reflected light from the pupil of the viewer on the light sensor,

such that tracking movement the spot produced by the retro-reflected light which passed through the pupil of the viewer on the light sensor corresponds to tracking movement of the pupil of the viewer.

2. The system of claim 1 , in which locations of each one of the plurality of first apertures is located so as not to receive retro-reflected light from a non-corresponding one of the plurality of light sources.

3. The system of claim 1 , in which:

the plurality of light sources for illuminating the pupil of the viewer are provided by using one first light source and a second mask comprising a plurality of second apertures for passing light emerging from the one first light source through the plurality of second apertures, thereby providing a plurality of light sources corresponding to the plurality of apertures in the second mask.

4. The system of claim 1 , wherein the optical component for imaging the pupil of the viewer on the light sensor is placed next to the plurality of first apertures.

5. The system of claim 1 comprised in a Head Mounted Display (HMD) and further comprising a computer generated image display system for displaying a computer generated image to an eye of the viewer.

6. The system of claim 5 , wherein the computer generated image display system is a system for displaying a three dimensional (3D) computer generated holographic (CGH) image to the eye of the viewer.

7. The system of claim 5 , in which light from the plurality of light sources forms a plurality of apparent images, relative to the computer generated image, which do not overlap the computer generated image.

8. The system of claim 1 , in which at least a first one of the plurality of light sources emits light at a different spectrum than at least a second one of the plurality of light sources.

9. The system of claim 8 and further comprising at least one of the first aperture passing light from a first light source and a second aperture passing light from a second light source comprises a spectral filter to pass only light from a corresponding one of the first light source and the second light source.

10. The system of claim 1 , wherein the plurality of light sources provide plane-polarized light and further comprising:

a retro-reflected-light plane-polarizing filter located along an optical path after retro-reflection from the pupil of the viewer, polarized at a polarization direction perpendicular to that of a direction of polarization of the plane-polarized light provided by the plurality of light sources.

11. The system of claim 1 wherein each one of the plurality of first apertures is located at an image of a corresponding one of the plurality of light sources.

12. A method for tracking a pupil of a viewer comprising:

using a plurality of light sources to illuminate a pupil of a viewer;

collecting retro-reflected light returning from a retina of the viewer through the pupil of the viewer at a direction opposite to a direction the retro-reflected light entered through the pupil of the viewer;

using a plurality of first apertures in a first mask, each one of the plurality of the first apertures located along a same direction from the pupil of the viewer as a direction of a corresponding one of the plurality of light sources, to pass the retro-reflected light from the pupil of the viewer;

using the first mask to stop at least some of other light arriving at the first mask;

using an optical element to produce a spot of the retro-reflected light from the pupil of the viewer on a light sensor; and

determining locations of the spots by the light sensor,

and further comprising locating the plurality of first apertures each along a same direction from the viewer's pupil as a corresponding direction of the plurality of light sources to the pupil, in the optical path after the retro-reflected light has been retro-reflected from the eye of the viewer through the pupil of the viewer.

13. The method of claim 12 , in which the plurality of light sources are turned on in a time sequential fashion.

14. The method of claim 12 , wherein tracking the pupil of the viewer comprises tracking the pupil of the viewer in a Head Mounted Display (HMD) for displaying a computer generated image.

15. The method of claim 14 , wherein the computer generated image comprises a three dimensional (3D) computer generated holographic (CGH) image.

16. The method of claim 14 , in which an optical path of the light from the plurality of light sources forms an apparent image, relative to the computer generated image, which does not overlap the computer generated image.

17. The method of claim 12 , wherein:

the using the plurality of light sources to illuminate the pupil of the viewer comprises illuminating the pupil of the viewer pupil with plane-polarized light,

and further comprising:

using a retro-reflected-light plane-polarizing filter located along an optical path after retro-reflection through the pupil of the viewer, polarized at a polarization direction perpendicular to that of a direction of polarization of the plane-polarized light provided by the plurality of light sources to filter light after retro-reflection through the viewer's pupil.

18. The method of claim 12 and further comprising using a plurality of second apertures in a second mask for passing light emerging from the plurality of light sources before illuminating the eye of the viewer, and locating the plurality of second apertures next to a corresponding one of the plurality of light sources.

19. The method of claim 12 , in which locations of each one of the plurality of first apertures is located so as not to receive retro-reflected light from a non-corresponding one of the plurality of light sources.

20. The method of claim 12 , wherein the optical element to produce the image of the pupil of the viewer on the light sensor is placed next to the plurality of first apertures.

21. The method of claim 12 , in which at least a first one of the plurality of light sources emits light at a different spectrum than at least a second one of the plurality of light sources.

22. The method of claim 21 in which at least one of a first aperture passing light from the first one of the plurality of light sources and a second aperture passing light from the second one of the plurality of light sources comprises a spectral filter to pass only light from a corresponding one of the first light source and the second light source.

23. The method of claim 12 wherein each one of the plurality of first apertures is located at an image of a corresponding one of the plurality of light sources.

24. The method of claim 12 wherein the plurality of light sources to illuminate the viewer's pupil are located so that the direction of light arriving from the plurality of light sources to the pupil is different from a direction of an image displayed to the viewer.

25. The method of claim 12 wherein the plurality of first apertures is located adjacent to the optical element used to produce the spot of the retro-reflected light on the light sensor.

26. A method for tracking a pupil of a viewer comprising:

using one light source and a first mask comprising a plurality of first apertures for passing light emerging from the one light source to illuminate a pupil of the viewer;

collecting retro-reflected light returning from a retina of the viewer through the pupil of the viewer at a direction opposite to a direction the light entered through the pupil of the viewer;

using a plurality of second apertures in a second mask, each one of the plurality of second apertures located to correspond to images of the plurality of first apertures to pass the retro-reflected light from the pupil of the viewer;

using the second mask to stop at least some of other light arriving at the second mask;

using an optical element to produce a spot of the retro-reflected light from the pupil on a light sensor; and

determining a location of the spot by the light sensor,

and further comprising locating the second apertures along a same direction from the pupil of the viewer as the direction of the first apertures to the pupil of the viewer, in the optical path after the retro-reflected light has been retro-reflected from the eye of the viewer through the pupil of the viewer.