Apparatus for eye tracking
An eye tracker comprises a light source; a detector; and first and second waveguides. The first waveguide comprises an input coupler for coupling source light into a waveguide path and a first grating for coupling light out of the waveguide path onto an eye. The second waveguide comprises a second grating for coupling light reflected from the eye into a waveguide path and an output coupler for coupling light out of the waveguide path onto the detector. The second grating is optically configured for imaging the eye onto the detector.
1. A waveguide sensor comprising:
a first waveguide;
a source of light for illuminating an object;
a detector optically coupled to said first waveguide; and
a first grating formed within said first waveguide, comprising a first plurality of grating elements of a first focal length and a second plurality of grating elements of a second focal length, wherein image light reflected from at least one surface of said object is deflected by said grating elements into total internal reflection paths towards said detector.
2. The waveguide sensor of claim 1 , wherein said first grating provides a configuration selected from the group consisting of: said first and second pluralities of elements are uniformly dispersed across said first grating, said first and second pluralities of elements are disposed in a common grating layer within said first grating, and said first grating provides focal lengths varying across said first grating.
3. The waveguide sensor of claim 1 , wherein said first waveguide provides a variable focal length by overlaying at least one of said grating elements having a fixed focal length with a variable refractive index layer.
4. The waveguide sensor of claim 1 , wherein said first waveguide is coupled to said detector by a grating or a prism.
5. The waveguide sensor of claim 1 , wherein said first grating comprises a plurality of electrically switchable elements, each having a diffracting state for coupling light from said eye into said waveguide and a non-diffracting state.
6. The waveguide sensor of claim 1 , wherein said first grating is a linear array of elongated switchable beam deflection elements with longer dimension aligned perpendicular to a principal waveguide path.
7. The waveguide sensor of claim 1 , wherein each of said first plurality of grating elements is one of a switchable Bragg prating, a switchable grating recorded in a reverse mode holographic polymer dispersed liquid crystal, or a non-switching Bragg grating.
8. The waveguide sensor of claim 1 , wherein said first grating encodes diffusing properties.
9. The waveguide sensor of claim 1 , wherein light from said source is directed towards said object by a second grating.
10. The waveguide sensor of claim 9 , wherein said first and second gratings provide a configuration selected from the group consisting of: disposed in a single layer, disposed with said first grating at least partially overlapping said second grating, disposed adjacent to each other, and disposed in separate and at least partially overlapping waveguides.
11. The waveguide sensor of claim 9 , wherein said second grating comprises a second plurality of grating elements for diffracting said light into a plurality of illumination beams providing a configuration selected from the group consisting of: beams substantially normal to said second grating, beams converging onto said object, beams having average directions varying cyclically across said second grating, beams having diffusion distributions around an average direction, and beams having diffusion distributions around an average direction that varies across said second grating.
12. The waveguide sensor of claim 9 , wherein said second grating is formed in a second waveguide, said second waveguide comprising at least one selected from the group consisting of: an input grating or prism for coupling light from said source into a TIR path in said second waveguide, an output grating or prism for deflecting said image light out of a TIR path towards said detector, and a fold grating.
13. The waveguide sensor of claim 9 , wherein said second grating comprises at least one switchable grating element having a diffracting state and a non-diffracting state, wherein said diffracting state of said at least one switchable element in said second grating deflects said light towards said object.
14. The waveguide sensor of claim 9 , wherein said second grating comprises at least one elongated switchable beam deflection element with a longer dimension aligned perpendicular to a principal waveguide path.
15. The waveguide sensor of claim 9 , wherein said second grating is one selected from the group consisting of: a switchable Bragg grating, a switchable grating recorded in a holographic polymer dispersed liquid crystal, a switchable grating recorded in a reverse mode holographic polymer dispersed liquid crystal, a surface relief grating, a non-switching Bragg grating, a grating encoding optical power, and a grating encoding light diffusing properties.
16. The waveguide sensor of claim 1 , wherein said light reflected from said object is a speckle pattern.
17. The waveguide sensor of claim 1 , wherein said source emits in the infrared band.
18. The waveguide sensor of claim 1 , wherein said detector is a two-dimensional array.
19. The waveguide sensor of claim 1 , wherein said detector is connected to an image processor for determining at least one spatio-temporal characteristic of an eye movement.
20. The waveguide sensor of claim 1 , wherein said object is an eye and said image light is reflected from at least one selected from the group consisting of: the cornea, lens, iris, sclera, and retina of said eye.