Immersed hot mirrors for imaging in eye tracking
Disclosed herein are techniques for imaging in eye tracking. An imaging system for eye tracking includes a camera configured to detect light in a first wavelength range, a substrate configured to be placed in front of an eye of a user, and at least one reflector located within the substrate. The at least one reflector is configured to receive light in the first wavelength range reflected by the eye of the user, reflect at least a portion of the received light in the first wavelength range to the camera, and transmit light in a second wavelength range different from the first wavelength range to the eye of the user. The substrate is transparent to both the light in the first wavelength range and the light in the second wavelength range.
1. An imaging system for eye tracking comprising:
a camera configured to detect light in a first wavelength range;
a substrate configured to be placed in front of an eye of a user; and
a plurality of reflectors located at different locations within the substrate, each reflector of the plurality of reflectors configured to:
receive light in the first wavelength range reflected by the eye of the user, wherein the light in the first wavelength range received by each reflector of the plurality of reflectors includes light reflected by a same area of the eye of the user;
reflect at least a portion of the received light in the first wavelength range to the camera to form a respective image of a plurality of images of the same area of the eye of the user from a different respective perspective, wherein the plurality of images is in a same image frame; and
transmit light in a second wavelength range different from the first wavelength range to the eye of the user,
wherein the substrate is transparent to both the light in the first wavelength range and the light in the second wavelength range.
2. The imaging system of claim 1 , wherein:
the first wavelength range comprises a near infrared range;
the second wavelength range comprises a visible range for a human eye; and
the plurality of reflectors comprises at least one hot mirror, the at least one hot mirror configured to reflect light in the near infrared range and transmit light in the visible range.
3. The imaging system of claim 1 , wherein the plurality of reflectors is located within a 40° viewing cone in a field of view of the eye of the user when the imaging system is in use.
4. The imaging system of claim 1 , wherein at least one reflector of the plurality of reflectors is located within a 20° viewing cone in a field of view of the eye of the user when the imaging system is in use.
5. The imaging system of claim 1 , wherein each of the plurality of reflectors is configured to reflect at least 30% of the received light in the first wavelength range to the camera.
6. The imaging system of claim 1 , wherein at least one reflector of the plurality of reflectors is configured to reflect at least 70% of the received light in the first wavelength range to the camera.
7. The imaging system of claim 1 , wherein at least one reflector of the plurality of reflectors has a photopically weighted transmission rate greater than 95% for light in the second wavelength range.
8. The imaging system of claim 1 , wherein:
each of the plurality of reflectors comprises a reflecting surface; and
the reflecting surface comprises a flat surface, a concave surface, a convex surface, a cylindrical surface, an aspherical surface, an anamorphic spherical surface, an anamorphic aspherical surface, a freeform surface, or a combination thereof.
9. The imaging system of claim 8 , wherein each of the plurality of reflectors comprises a plurality of dielectric layers, a diffractive optical element, or a reflective material layer at the reflecting surface.
10. The imaging system of claim 1 , wherein each of the plurality of reflectors is different from other reflectors of the plurality of reflectors in at least one of surface curvature, surface orientation, size, or location in the substrate.
11. The imaging system of claim 1 , wherein the substrate comprises at least one of a glass, quartz, plastic, polymer, ceramic, or crystal.
12. The imaging system of claim 1 , wherein at least one reflector of the plurality of reflectors is configured to focus the portion of the received light in the first wavelength range.
13. An eye-tracking unit for a near-eye display device, the eye-tracking unit comprising:
a light source;
a camera;
a substrate configured to be placed in front of an eye of a user; and
a plurality of reflectors located at different locations within the substrate,
wherein:
the light source is configured to emit light in a first wavelength range to illuminate the eye of the user;
each reflector of the plurality of reflectors is configured to:
receive light in the first wavelength range reflected by the eye of the user, wherein the light in the first wavelength range received by each reflector of the plurality of reflectors includes light reflected by a same area of the eye of the user;
reflect at least a portion of the received light in the first wavelength range to the camera; and
transmit light in a second wavelength range from a display panel of the near-eye display device to the eye of the user, the second wavelength range different from the first wavelength range;
the camera is configured to receive light in the first wavelength range and reflected by each reflector of the plurality of reflectors to form a respective image of a plurality of images of the same area of the eye of the user from a different respective perspective, wherein the plurality of images is in a same image frame; and
the substrate is transparent to both the light in the first wavelength range and the light in the second wavelength range.
14. The eye-tracking unit of claim 13 , wherein the light source and the camera are coupled to or embedded in a body of the near-eye display device.
15. The eye-tracking unit of claim 13 , wherein the substrate is a part of the display panel of the near-eye display device.
16. The eye-tracking unit of claim 13 , further comprising an illumination reflector located within the substrate, the illumination reflector configured to:
receive light in the first wavelength range from the light source;
reflect at least a portion of the light in the first wavelength range from the light source to the eye of the user; and
transmit the light in the second wavelength range from the display panel of the near-eye display device to the eye of the user.
17. The eye-tracking unit of claim 13 , wherein at least one reflector of the plurality of reflectors is configured to focus or diverge the portion of the received light in the first wavelength range.
18. The eye-tracking unit of claim 13 , wherein:
each of the plurality of reflectors comprises a reflecting surface; and
the reflecting surface comprises a flat surface, a concave surface, a convex surface, a cylindrical surface, an aspherical surface, an anamorphic spherical surface, an anamorphic aspherical surface, a freeform surface, or a combination thereof.
19. A method of tracking an eye of a user of a near-eye display device, the method comprising:
illuminating, by light in a first wavelength range emitted from a light source, the eye of the user;
receiving, by a plurality of reflectors at different locations within a substrate in front of the eye of the user, light in the first wavelength range reflected by the eye of the user, wherein the light in the first wavelength range received by each reflector of the plurality of reflectors includes light reflected by a same area of the eye of the user;
reflecting, by each reflector of the plurality of reflectors, at least a portion of the received light in the first wavelength range to a camera to form a respective image of a plurality of images of the same area of the eye of the user from a different respective perspective, wherein the plurality of images is in a same image frame; and
transmitting light in a second wavelength range from a display panel of the near-eye display device through the substrate and the plurality of reflectors and to the eye of the user, wherein the second wavelength range is different from the first wavelength range.
20. The method of claim 19 , wherein illuminating the eye of the user comprises:
illuminating, by the light in the first wavelength range emitted from the light source, an eye illumination reflector within the substrate;
reflecting, by the eye illumination reflector, at least a portion of the light in the first wavelength range from the light source to the eye of the user; and
transmitting the light in the second wavelength range from the display panel of the near-eye display device through the substrate and the eye illumination reflector to the eye of the user.