Tracking system using a differential camera with a co-aligned light source assembly

1. A co-aligned light source camera assembly (LSCA) comprising:

a light source configured to emit light that is directed along an optical path towards an eye box including an eye of a user;

a differential camera sensor configured to detect a change in brightness of the eye caused in part by the emitted light, and asynchronously output data samples corresponding to the detected change in brightness, wherein the optical path is substantially co-aligned with an optical path of the differential camera sensor;

an aperture in a sensor housing that is positioned between the differential camera sensor and the eye box; and

a second light source configured to emit one or more pulses of light along a second optical path towards the eye box, the second light source positioned adjacent to the aperture such that the one or more pulses of light are substantially co-aligned with the optical path of the differential camera sensor, and

wherein a controller is configured to:

identify a pupil of the eye based on data samples output from the differential camera sensor resulting from the emitted light, and

determine a gaze location of the user based in part on the identified pupil.

2. The co-aligned LSCA of claim 1 , further comprising:

an off-axis light source that is off-axis relative to the optical path, the off-axis light source configured to emit light towards the eye box of the user, the eye reflecting the light along the optical path towards the differential camera sensor.

3. The co-aligned LSCA of claim 1 , further comprising a lens that is positioned within the aperture, wherein the light source is positioned adjacent to the lens, and the light source has an optical path that is substantially co-aligned with the optical path of the differential camera sensor.

4. The co-aligned LSCA of claim 1 , further comprising:

an optical waveguide that optically couples light from the light source to an emission location, wherein the emission location is positioned adjacent to the aperture, and the emission location emits light that that is substantially co-aligned with the optical path of the differential camera sensor.

5. The co-aligned LSCA of claim 3 , wherein the aperture is a pinhole.

6. The co-aligned LSCA of claim 1 , wherein the aperture is a pinhole.

7. A co-aligned light source camera assembly (LSCA) comprising:

a light source configured to emit light that is directed along an optical path towards an eye box including an eye of a user;

a differential camera sensor configured to detect a change in brightness of the eye caused in part by the emitted light, and asynchronously output data samples corresponding to the detected change in brightness, wherein the optical path is substantially co-aligned with an optical path of the differential camera sensor;

an aperture in a sensor housing that is positioned between the differential camera sensor and the eye box;

a second light source configured to emit one or more pulses of light along a second optical path towards the eye box, the second light source positioned adjacent to the aperture such that the one or more pulses of light are substantially co-aligned with the optical path of the differential camera sensor; and

a pinhole reflector comprising a reflective surface that reflects light from the light source towards the eye box, and a pinhole through which light from the eye box passes through to reach the differential camera sensor, wherein the pinhole reflector is positioned at a 45-degree angle with respect to the optical path of the differential camera sensor, and

wherein a controller is configured to:

identify a pupil of the eye based on data samples output from the differential camera sensor resulting from the emitted light, and

determine a gaze location of the user based in part on the identified pupil.

8. The co-aligned LSCA of claim 1 , further comprising:

a beam splitter configured to:

redirect at least a portion of the emitted light such that it propagates substantially along the optical path towards the eye box, and

transmit light reflected from the eye back along the optical path toward the differential camera sensor.

9. The co-aligned LSCA of claim 1 , further comprising:

a waveguide configured to incouple the light from the light source; and

a grating coupled to the waveguide that is configured to outcouple the incoupled light towards the eye box.

10. The co-aligned LSCA of claim 1 , further comprising:

a holographic coupler configured to redirect light from the light source towards the eye box.

11. A tracking system comprising:

a co-aligned light source camera assembly (LSCA) comprising:

a light source configured to emit light, the emitted light that is directed along an optical path towards an eye box including an eye of a user, and

a differential camera sensor configured to detect a change in brightness of the eye caused in part by the emitted light, and asynchronously output data samples corresponding to the detected change in brightness, wherein the optical path is substantially co-aligned with an optical path of the differential camera sensor; and

a controller that is configured to:

identify a pupil of the eye based on data samples output from the differential camera sensor resulting from the emitted light,

determine a gaze location of the user based in part on the identified pupil,

instruct the differential camera sensor to obtain one or more data samples, the data samples describing a movement of an eye of a user,

calculate metrics of the movement of the eye based on the data samples,

apply a model to the calculated metrics of the movement of the eye to predict a time to obtain a next data sample, and

instruct the differential camera sensor to obtain the next data sample at the predicted time.

12. The tracking system of claim 11 , further comprising:

an aperture in a sensor housing that is positioned between the differential camera sensor and the eye box.

13. The tracking system of claim 11 , further comprising:

an off-axis light source that is off-axis relative to the optical path, the off-axis light source configured to emit light towards the eye box of the user, the eye reflecting the light along the optical path towards the differential camera sensor.

14. The tracking system of claim 12 , wherein the co-aligned LSCA further comprises a lens that is positioned within the aperture, wherein the light source is positioned adjacent to the lens, and the light source has an optical path that is substantially co-aligned with the optical path of the differential camera sensor.

15. The tracking system of claim 11 , wherein the metrics of the movement of the eye comprise at least one of: a velocity of the eye, an acceleration of the eye, and a pupil jitter.

16. The tracking system of claim 13 , wherein the controller is further configured to:

compute attributes of a plurality of data samples obtained by the tracking system over a time interval; and

determine a state of the tracking system based on the computed attributes.

17. The tracking system of claim 11 , wherein the co-aligned LSCA further comprises:

a pinhole reflector comprising a reflective surface that reflects light from the light source towards the eye box, and a pinhole through which light from the eye box passes through to reach the differential camera sensor.

18. The tracking system of claim 15 , wherein the co-aligned LSCA further comprises:

a beam splitter configured to:

redirect at least a portion of the emitted light such that it propagates substantially along the optical path towards the eye box, and

transmit light reflected from the eye back along the optical path toward the differential camera sensor.