Apparatus for eye tracking
An eye tracker having a waveguide for propagating illumination light towards an eye and propagating image light reflected from at least one surface of an eye, a light source optically coupled to the waveguide, and a detector optically coupled to the waveguide. Disposed in the waveguide is at least one grating lamina for deflecting the illumination light towards the eye along a first waveguide path and deflecting the image light towards the detector along a second waveguide path.
1. An eye tracker waveguide comprising:
a light detector;
an imaging grating comprising an array of switchable grating elements configured along a first waveguide path;
an output grating; and
an image sampling grating overlaying said output grating, comprising an array of switchable grating elements configured along a second waveguide path orthogonal to said first waveguide path,
wherein said switchable grating elements are switchable between a diffracting state and a non-diffracting state and one grating element of each of said imaging grating and said image sampling grating is in said diffracting state at any time,
wherein an instantaneous detection aperture of said waveguide is addressed by an image sampling grating element in said diffracting state and an imaging grating element in said diffracting state,
wherein light reflected from said eye is coupled into said waveguide via said detection aperture into said first waveguide path, is coupled out of said first waveguide path by said output grating, and is coupled into said second waveguide path towards said detector by an image sampling grating element in said diffracting state.
2. The apparatus of claim 1 wherein said grating elements of said imaging grating are elongate with longer dimension aligned perpendicular to said first waveguide path.
3. The apparatus of claim 1 further comprising a source and an input grating for deflecting illumination light from said source into a third waveguide path; and an illumination grating for deflecting said illumination light out of said third waveguide path towards said eye.
4. The apparatus of claim 3 further comprising:
an illumination sampling grating overlaying said input grating,
said illumination grating comprising an array of switchable grating elements,
said illumination sampling grating comprising an array of switchable grating elements configured along a fourth waveguide path orthogonal to said third waveguide path,
wherein one grating element of each of said illumination grating and said illumination sampling grating is in said diffracting state at any time,
wherein an instantaneous illumination aperture of said waveguide is addressed by an illumination sampling grating element in said diffracting state and an imaging grating element in said diffracting state,
wherein light from said source coupled into said waveguide via said input grating is coupled into said fourth waveguide path by an illumination sampling grating element in said diffracting state, is coupled into said third waveguide path and is coupled out of said waveguide towards said eye by an illumination grating element in said diffracting state.
5. The apparatus of claim 4 wherein said illumination sampling grating encodes at least one of optical power or diffusion.
6. The apparatus of claim 3 wherein said illumination grating abuts an upper or lower edge of said waveguide said edge parallel to said first waveguide path.
7. The apparatus of claim 3 wherein said illumination grating comprises first and second gratings disposed adjacent upper and lower edges of said waveguide said edges parallel to said first waveguide path.
8. The apparatus of claim 3 wherein said illumination grating is a linear array of elongate switchable beam deflection elements with longer dimension aligned perpendicular to said first waveguide path.
9. The apparatus of claim 3 wherein said imaging grating and said illumination grating are provided by a common grating, wherein said first waveguide path and said fourth waveguide path are provided by a common waveguide path along which said illumination light and said light reflected from said eye propagate in opposing directions.
10. The apparatus of claim 3 wherein said illumination grating or said illumination sampling grating encodes at least one of optical power or diffusion.
11. The apparatus of claim 1 wherein said imaging grating comprises a first array of switchable elongate beam deflection grating elements and an overlapping second array of switchable elongate beam deflection grating elements, said elements of said first and second arrays being disposed with their longer dimensions orthogonal.
12. The apparatus of claim 1 wherein at least one of said gratings is one of a switchable Bragg grating, a switchable grating recorded in a reverse mode holographic polymer dispersed liquid crystal, or a non switching Bragg grating.
13. The apparatus of claim 1 wherein said light reflected from said eye is speckle.
14. The apparatus of claim 1 wherein said eye surface is at least one of the cornea, lens, iris, sclera and retina.
15. The apparatus of claim 1 wherein said detector is a two dimensional array.
16. The apparatus of claim 1 wherein at least one of said imaging grating or said image sampling grating encodes at least one of optical power or light diffusion.
17. The apparatus of claim 1 wherein said detector is connected to an image processing apparatus for determining at least one spatio-temporal characteristic of an eye movement.
18. The apparatus of claim 1 wherein said light is in the infrared band.
19. The apparatus of claim 1 wherein said eye is illuminated by one of a laser or a light emitting diode.
20. The apparatus of claim 1 wherein said image sampling grating, comprises a one dimensional array of switchable grating elements.