Holographic waveguide eye tracker
An eye tracker having a first waveguide for propagating illumination light along a first waveguide path and propagating image light reflected from at least one surface of an eye along a second waveguide path. At least one grating lamina for deflecting the illumination light out of the first waveguide path towards the eye and deflecting the image light into the second waveguide path towards a detector is disposed adjacent an optical surface of the waveguide.
1. An eye tracker comprising:
a first waveguide for propagating illumination light along a first plurality of waveguide paths and propagating image light reflected from at least one surface of an eye along a second plurality of waveguide paths;
a source of said illumination light disposed adjacent an optical surface of said waveguide;
a detector disposed adjacent an optical surface of said waveguide;
at least one grating for deflecting said illumination light out of at least one of said first waveguide paths towards said eye and deflecting said image light into at least one of said second waveguide paths towards said detector;
an input grating for coupling light from said source into said waveguide;
an output grating for coupling light from said waveguide to said detector; and
first and second pluralities of turning grating elements for diffracting light in a plane of said waveguide,
wherein elements of said first plurality of turning grating elements are operative to diffract said illumination light coupled into said waveguide by said input grating into one of said first plurality of waveguide paths,
wherein elements of said second plurality of turning grating elements are operative to diffract image light from one of said second plurality of waveguide paths towards said output grating,
wherein said light from said source coupled into said waveguide is angularly displaced so that at least a portion of light in said first plurality of paths is displaced from at least a portion of light in said second plurality of paths by an angle equivalent to a dimension of a turning grating element.
2. The apparatus of claim 1 wherein at least one of said input and output gratings comprises at least one switchable grating element having a diffracting state and a non diffracting state.
3. The apparatus of claim 1 wherein said at least one grating comprises at least one switchable grating element having a diffracting state and a non diffracting state wherein said element in said diffracting state deflects said illumination light out of said first waveguide path towards said eye and deflects said image light into said second waveguide path towards said detector.
4. The apparatus of claim 3 wherein said at least one grating comprises grating elements elongate with longer dimension aligned perpendicular to at least one of said first and second waveguide paths.
5. The apparatus of claim 1 wherein at least one path from each of said first and second pluralities of waveguide paths are parallel.
6. The apparatus of claim 1 wherein said at least one grating comprises upper and lower gratings disposed adjacent upper and lower edges said waveguide.
7. The apparatus of claim 1 wherein said at least one 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.
8. The apparatus of claim 1 wherein at least one of said input and output gratings is a linear array of elongate switchable beam deflection elements with longer dimension.
9. The apparatus of claim 1 wherein said optical surface is an internal surface or an external surface of said waveguide.
10. 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, a switchable grating recorded in a reverse mode holographic polymer dispersed liquid crystal, a surface relief grating or a non switching Bragg grating.
11. The apparatus of claim 1 wherein said image light is characterized by a statistical distribution of light intensities.
12. The apparatus of claim 1 wherein said eye surface is at least one of a cornea, lens, iris, sclera and retina.
13. The apparatus of claim 1 wherein said detector is a two dimensional array.
14. The apparatus of claim 1 wherein said at least one grating encodes at least one of optical power and diffusing properties.
15. 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.
16. The apparatus of claim 1 wherein said detector is connected to an image processing system including a neural network.
17. The apparatus of claim 1 wherein said turning grating elements are switchable between a diffracting state and a non-diffracting state, wherein one element of each of said first and second pluralities of switchable turning grating elements are switched into a diffracting state simultaneously.
18. The apparatus of claim 1 wherein said gratings are disposed in a single lamina.
19. The apparatus of claim 1 wherein said angular displacement is provided by one of a grating or a prism.
20. The apparatus of claim 1 wherein said angular displacements are a function of the turning grating element positions within the waveguide.