Systems, devices, and methods for laser eye tracking
Systems, devices, and methods for laser eye tracking are described. Laser eye tracking involves scanning laser light over the eye and detecting diffuse reflections of the laser light with one or more photodetector(s). While conventional camera-based eye tracking techniques rely on detecting and identifying specific reflections (i.e., Purkinje images such as the “glint”), the laser eye tracking techniques described herein detect and identify a reduction in reflection intensity due to transmission of laser light through the pupil and/or increased diffusivity of reflections from the cornea relative to reflections from the sclera. This effect is referred to herein as the “corneal shadow” effect. Laser eye tracking uses considerably less power than conventional camera-based eye tracking techniques. As a result, the laser eye tracking techniques described herein do not add significant power demands to a system and can be implemented in wearable heads-up displays without adding significant volume to the system battery.
1. A method of determining a gaze direction of a user, the method comprising:
scanning a laser light over at least a portion of an eye of the user by a scanning laser device, wherein the portion of the eye of the user includes at least a portion of a pupil of the eye of the user;
detecting reflections of the laser light from the eye by at least one photodetector;
determining a relative intensity of each reflection by a processor;
mapping each reflection to a respective region of the eye by the processor, wherein mapping each reflection to a respective region of the eye by the processor includes associating each reflection with a corresponding scan parameter of the scanning laser device by the processor;
determining, by the processor, a position of the pupil based on the reflections detected by the at least one photodetector; and
determining, by the processor, the gaze direction of the user based on the position of the pupil.
2. The method of claim 1 wherein scanning a laser light over at least a portion of an eye of the user by a scanning laser device includes scanning the laser light in two dimensions over at least a portion of the eye of the user by the scanning laser device.
3. The method of claim 1 wherein scanning a laser light over at least a portion of an eye of the user by a scanning laser device includes scanning the laser light over at least a portion of a holographic optical element by the scanning laser device and redirecting the laser light over the at least a portion of the eye of the user by the holographic optical element.
4. The method of claim 1 wherein scanning a laser light over at least a portion of an eye of the user by a scanning laser device includes scanning an infrared laser light over at least a portion of the eye of the user by the scanning laser device.
5. The method of claim 1 wherein detecting reflections of the laser light from the eye by at least one photodetector includes detecting diffuse reflections of the laser light from the eye by at least one photodetector.
6. The method of claim 1 wherein detecting reflections of the laser light from the eye by at least one photodetector includes detecting specular reflections of the laser light from the eye by at least one photodetector.
7. The method of claim 1 wherein detecting reflections of the laser light from the eye by at least one photodetector includes detecting reflections of the laser light from the eye by at least two photodetectors.
8. The method of claim 1 wherein associating each reflection with a corresponding scan parameter of the scanning laser device by the processor includes associating, by the processor, each reflection with a corresponding scan parameter selected from a group consisting of: a position of at least one scan mirror of the scanning laser device, respective positions of at least two scan mirrors of the scanning laser device, a projection angle of the scanning laser device, and a modulation state of the scanning laser device.
9. The method of claim 1 wherein the scanning laser device, the photodetector, and the processor are respective components of a head-mounted display that further includes a non-transitory processor-readable storage medium, and wherein the non-transitory processor-readable storage medium stores data and/or instructions that, when executed by the processor, cause the processor to:
determine the position of the pupil based on the reflections detected by the at least one photodetector; and
determine the gaze direction of the user based on the position of the pupil.
10. A laser eye tracker comprising:
a scanning laser device to scan a laser light over at least a portion of an eye of a user, wherein the portion of the eye of the user includes at least a portion of a pupil of the eye of the user;
at least one photodetector;
a processor communicatively coupled to both the scanning laser device and the at least one photodetector; and
a non-transitory processor-readable storage medium communicatively coupled to the processor, wherein the non-transitory processor-readable storage medium stores data and/or instructions that, when executed by the processor, cause:
the at least one photodetector to detect reflections of the laser light from the eye; and
the processor to:
map each reflection to a respective region of the eye;
associate each reflection with a corresponding scan parameter of the scanning laser device;
determine a position of the pupil based on the reflections of the laser light detected by the at least one photodetector; and
determine a gaze direction of the user based on the position of the pupil.
11. The laser eye tracker of claim 10 wherein the scanning laser device includes an infrared laser diode, the laser light includes infrared laser light, and the at least one photodetector includes at least one infrared photodetector.
12. The laser eye tracker of claim 10 wherein the scanning laser device, the photodetector, the processor, and the non-transitory processor-readable storage medium are all components of and carried by a head-mounted display.
13. The laser eye tracker of claim 12 , further comprising:
a holographic optical element carried by the head-mounted display and positioned in a field of view of the eye of the user to redirect laser light scanned by the scanning laser device towards the eye of the user.
14. The laser eye tracker of claim 10 wherein the at least one photodetector includes at least two photodetectors.
15. A wearable heads-up display comprising:
a support frame that in use is worn on a head of a user;
a display carried by the support frame;
a scanning laser device carried by the support frame, the scanning laser device including an infrared laser diode to output an infrared light;
an infrared photodetector carried by the support frame;
a processor communicatively coupled to both the scanning laser device and the infrared photodetector; and
a non-transitory processor-readable storage medium communicatively coupled to the processor, wherein the non-transitory processor-readable storage medium stores data and/or instructions that, when executed by the processor, cause:
the scanning laser device to scan an infrared laser light over at least a portion of an eye of the user;
the at least one infrared photodetector to detect reflections of the infrared laser light from the eye; and
the processor to:
map each reflection to a respective region of the eye;
associate each reflection with a corresponding scan parameter of the scanning laser device;
determine a position of the pupil based on the reflections of the infrared laser light detected by the at least one infrared photodetector; and
determine a gaze direction of the user based on the position of the pupil.