Stereo imaging with Fresnel facets and Fresnel reflections
Techniques for eye-tracking in a near-eye display system are disclosed. One example of a near-eye display system includes a waveguide-based display substrate that is transparent to visible light and configured to be placed in front of a user's eye. The waveguide-based display substrate includes a first surface area configured to specularly reflect a first portion of invisible light reflected by the user's eye to a camera to form a first image of the user's eye in a first area of an image frame, and a light deflector embedded in the waveguide-based display substrate or formed on a second surface area of the waveguide-based display substrate. The light deflector is configured to direct a second portion of the invisible light reflected by the user's eye to the camera to form a second image of the user's eye in a second area of the image frame.
1. An eye-tracking system comprising:
one or more light sources configured to emit light invisible to a user's eye for illuminating the user's eye;
a camera configured to detect the light invisible to the user's eye; and
a substrate transparent to visible light and configured to be placed in front of the user's eye, the substrate comprising:
a first surface area configured to specularly reflect a first portion of illumination light reflected by the user's eye to the camera to form a first image of the user's eye in a first area of an image frame, the first image including one or more glints corresponding to the one or more light sources; and
a light deflector embedded in the substrate or formed on a second surface area of the substrate, the light deflector configured to direct a second portion of the illumination light reflected by the user's eye to the camera to form a second image of the user's eye in a second area of the image frame, the second image including one or more glints corresponding to the one or more light sources,
wherein:
the first surface area and the second surface area are on opposite surfaces of the substrate; or
the first surface area includes an uncoated surface area of the substrate.
2. The eye-tracking system of claim 1 , wherein the substrate includes a curved or a flat surface.
3. The eye-tracking system of claim 1 , wherein the one or more light sources and the camera are positioned in a peripheral region of a field of view of the user's eye.
4. The eye-tracking system of claim 1 , wherein the one or more light sources are configured to emit illumination light in a near infrared range.
5. The eye-tracking system of claim 1 , wherein the light deflector comprises:
a reflective Fresnel lens;
a Fresnel mirror;
a dichroic mirror;
a reflective grating;
a diffractive optical element;
a holographic optical element; or
a reflective thin film coating.
6. The eye-tracking system of claim 1 , wherein:
the first surface area and the second surface area are on the opposite surfaces of the substrate; and
the light deflector includes:
a Fresnel lens formed on the second surface area; and
a reflective coating on the Fresnel lens, the reflective coating configured to reflect the light invisible to the user's eye and transmit the visible light.
7. The eye-tracking system of claim 1 , wherein the first surface area of the substrate includes a reflective coating configured to at least partially reflect invisible light and transmit visible light.
8. The eye-tracking system of claim 1 , wherein the substrate comprises at least one of a glass, quartz, plastic, polymer, ceramic, or crystal.
9. The eye-tracking system of claim 1 , wherein the first surface area and the light deflector are in a field of view of the user's eye.
10. The eye-tracking system of claim 1 , wherein:
the first surface area and the light deflector are on the same surface of the substrate;
the first surface area includes a first plurality of zones;
the light deflector includes a second plurality of zones; and
the first plurality of zones are interleaved with the second plurality of zones.
11. The eye-tracking system of claim 10 , wherein the first plurality of zones and the second plurality of zones include rectangular zones, triangular zones, hexagonal zones, octagonal zones, or ring-shaped zones.
12. The eye-tracking system of claim 1 , wherein:
the eye-tracking system is a part of a near-eye display system that includes a frame; and
the one or more light sources and the camera are positioned in the frame.
13. The eye-tracking system of claim 1 , wherein:
the one or more light sources include at least two light sources; and
each image of the first image and the second image includes at least two glints, each glint of the at least two glints corresponding to a light source of the at least two light sources.
14. A display device comprising:
a waveguide-based display substrate transparent to visible light and configured to be placed in front of a user's eye, the waveguide-based display substrate comprising:
a first surface area configured to specularly reflect a first portion of invisible light reflected by the user's eye to a camera to form a first image of the user's eye in a first area of an image frame; and
a light deflector embedded in the waveguide-based display substrate or formed on a second surface area of the waveguide-based display substrate, the light deflector configured to direct a second portion of the invisible light reflected by the user's eye to the camera to form a second image of the user's eye in a second area of the image frame.
15. The display device of claim 14 , wherein the light deflector comprises:
a reflective Fresnel lens;
a Fresnel mirror;
a dichroic mirror;
a reflective grating;
a diffractive optical element;
a holographic optical element; or
a reflective thin film coating.
16. The display device of claim 14 , wherein the first surface area and the second surface area are on opposite surfaces of the waveguide-based display substrate.
17. The display device of claim 14 , wherein:
the first surface area and the light deflector are on a same surface of the waveguide-based display substrate;
the first surface area includes a first plurality of zones;
the light deflector includes a second plurality of zones; and
the first plurality of zones are interleaved with the second plurality of zones.
18. A method of tracking an eye of a user of a near-eye display system, the method comprising:
illuminating, by invisible light emitted from one or more light sources, the eye of the user;
receiving, by a substrate of the near-eye display system positioned in front of the eye of the user, the invisible light reflected by the eye of the user;
reflecting, specularly by a first surface area of the substrate, a first portion of the invisible light reflected by the eye of the user to a camera to form a first image of the eye of the user in a first area of an image frame, the first image including one or more glints corresponding to the one or more light sources; and
deflecting, by a light deflector embedded in the substrate or formed on a second surface area of the substrate, a second portion of the invisible light reflected by the eye of the user to the camera to form a second image of the eye of the user in a second area of the image frame, the second image including one or more glints corresponding to the one or more light sources,
wherein:
the first surface area and the second surface area are on opposite surfaces of the substrate; or
the first surface area includes an uncoated surface area of the substrate.
19. The method of claim 18 , further comprising:
determining an angular position of the eye of the user with respect to a reference frame of the near-eye display system based on the first image and the second image in the image frame.
20. The method of claim 18 , wherein the light deflector comprises:
a reflective Fresnel lens;
a dichroic mirror;
a Fresnel mirror;
a reflective grating;
a diffractive optical element;
a holographic optical element; or
a reflective thin film coating.