Eye-imaging apparatus using diffractive optical elements

1. A optical device comprising: an eyepiece comprising:

a substrate having a first surface proximate to a user and a second surface opposite the first surface;

a first coupling optical element disposed on the first surface and configured to collect light from an eye of the user; and

a second coupling optical element disposed on the first surface or the second surface and laterally offset from the first coupling optical element along a first direction parallel to one of the first surface or the second surface on which the second coupling optical element is disposed,

wherein the first coupling optical element is configured to deflect light at a first angle θ to totally internally reflect (TIR) the light between the first and second surfaces and toward the second coupling optical element, the second coupling optical element configured to deflect light at a second angle out of the substrate,

wherein the first coupling optical element has a first width along the first direction smaller than a stride distance of the light, and

wherein the eyepiece is configured to capture an image of the eye of the user using the light totally internally reflected within the substrate and deflected by the second coupling optical element.

2. The optical device of claim 1 , wherein the second coupling optical element has a second width along the first direction smaller than the stride distance.

3. The optical device of claim 1 , wherein the stride distance is proportional to tan(θ).

4. The optical device of claim 3 , wherein the first coupling optical element is a diffractive optical element comprising a plurality of diffractive features, and wherein the angle θ is dependent at least in part on a period or spatial frequency of the diffractive features.

5. The optical device of claim 1 , wherein the stride distance is determined as a function of the first angle θ and a thickness t of the substrate between the first surface and the second surface.

6. The optical device of claim 5 , wherein the stride distance is equal to 2*t*tan(θ).

7. The optical device of claim 1 , wherein the substrate is transparent to visible light.

8. The optical device of claim 1 , wherein the substrate comprises a polymer.

9. The optical device of claim 8 , wherein the polymer comprises a polycarbonate.

10. The optical device of claim 1 , wherein the first and second coupling optical elements are external to and fixed to at least one of the first and second surfaces of the substrate.

11. The optical device of claim 1 , wherein the eyepiece comprises a waveguide stack including a plurality of waveguides, the substrate comprising at least a portion of one of the plurality of waveguides.

12. The optical device of claim 1 , wherein each of the first and second coupling optical elements are configured to deflect light of a first range of wavelengths while transmitting light of a second range of wavelengths.

13. The optical device of claim 12 , wherein the first range of wavelengths comprises light in at least one of the infrared (IR) or near-IR spectrum and the second range of wavelengths comprises light in the visible spectrum.

14. A method of imaging an object using a virtual camera, the method comprising:

providing an imaging system in front of an eye of a user to be imaged, wherein the imaging system comprises:

a substrate comprising a first coupling optical element and a second coupling optical element, each of the first and second coupling optical element disposed on one of a first surface proximate to the user and a second surface of the substrate distal from the user and offset from each other, the first coupling optical element configured to deflect light at a first angle to totally internally reflect (TIR) the light between the first and second surfaces and toward the second coupling optical element in a propagation direction, the second coupling optical element configured to deflect the light at a second angle out of the substrate, the first angle selected such that a stride distance of the light is greater than a width of the first coupling optical element along the propagation direction of the light;

capturing the light with a camera assembly oriented to receive the light deflected by the second coupling optical element; and

producing an off-axis image of the object eye of the user based on the captured light.

15. The method of claim 14 , wherein the first angle is selected such that 2*t*tan(θ) is greater than the width of the first coupling optical element, where θ is the first angle and t is a thickness of the substrate between the first and second surfaces.

16. The method of claim 14 , wherein the first coupling optical element comprises a plurality of diffractive features that cause deflection of the light, the plurality of diffractive features having a period or spatial frequency selected to determine the first angle.

17. The method of claim 16 , wherein the eyepiece comprises a waveguide stack including a plurality of waveguides, the substrate comprising at least a portion of one of the plurality of waveguides.

18. The method of claim 14 , wherein each of the first and second coupling optical elements deflect light of a first range of wavelengths while transmitting light in a second range of wavelengths.

19. The method of claim 14 , further comprising illuminating the object with a first range of wavelengths emitted by a light source.

20. The method of claim 14 , further comprising:

analyzing the off-axis image, and

performing one or more of: eye tracking; biometric identification; multiscopic reconstruction of a shape of the eye; estimating an accommodation state of the eye;

and imaging a retina, iris, other distinguishing pattern of the eye, and evaluating a physiological state of the user based, in part, on the analyzed off-axis image.