Methods and systems for forming images of eye features using a non-imaging, scanning-MEMS-based eye-tracking system
Aspects of the present disclosure describe systems, methods, and structures that provide eye-tracking by 1) steering a beam of light through the effect of a microelectromechanical system (MEMS) onto a surface of the eye and 2) detecting light reflected from features of the eye including corneal surface, pupil, iris—among others. Positional/geometric/feature/structural information pertaining to the eye is determined from timing information associated with the reflected light.
1. An apparatus comprising:
a first microelectromechanical system (MEMS) scanner for steering a first input light signal in a two-dimensional pattern over a scan region, wherein the first MEMS scanner has a first scanning axis characterized by a first resonant frequency and a second scanning axis characterized by a second resonant frequency;
a detector configuration that is non-imaging and includes at least one discrete detector, wherein the detector configuration is configured to provide a first detector signal based a first reflected light signal from the scan region, the first reflected light signal comprising at least a portion of the input light signal;
a comparator configured to provide a first comparator signal based on a first comparison of the first detector signal and a first threshold; and
a processor configured to estimate the position of the MEMS scanner and generate a first contour plot based on a spatiotemporal correlation of the first comparator signal and the estimated position of the MEMS scanner over the first time period.
2. The apparatus of claim 1 wherein the processor is further configured to estimate at least one of the size and location of a first feature in the scan region based on the first contour plot.
3. The apparatus of claim 1 wherein the scan pattern is a Lissajous pattern.
4. The apparatus of claim 3 wherein the processor is further configured to drive the first scanning axis with a first periodic signal having a first drive frequency and the second scanning axis with a second periodic signal having a second drive frequency, and wherein the first and second drive frequencies give rise to a precession of the Lissajous pattern.
5. The apparatus of claim 1 wherein the processor comprises the comparator.
6. The apparatus of claim 1 wherein the first detector signal comprises a combination of a plurality of second detector signals, each of the plurality of second detector signals being based on a different reflected light signal of a plurality of reflected light signals that includes the first reflected light signal.
7. The apparatus of claim 1 wherein the first input light signal is modulated at a modulation frequency, and wherein the detector configuration includes a detector circuit that is tunable to the modulation frequency.
8. The apparatus of claim 1 further comprising a plurality of MEMS scanners for steering a plurality of input light signals, the plurality of MEMS scanners including the first MEMS scanner and the plurality of input light signals including the first input light signal, wherein each of the plurality of light signals is directed at the scan region from a different position and a different orientation with respect to the scan region.
9. The apparatus of claim 1 wherein the processor is further configured to generate a plurality of contour plots that includes the first contour plot, wherein each of the plurality of contour plots is based on a spatiotemporal correlation of a different comparator signal of a plurality of comparator signals that includes the first comparator signal, and wherein each of the plurality of comparator signals is based on a comparison selected from the group consisting of:
(i) a comparison of the first detector signal and a different threshold of a plurality of thresholds that includes the first threshold;
(ii) a comparison of a plurality of detector signals and the first threshold, wherein the plurality of detector signals includes the first detector signal and each of the plurality of detector signals corresponds to a different gain for the at least one discrete detector; and
(iii) a comparison of a plurality of detector signals and the first threshold, wherein the plurality of detector signals includes the first detector signal and each of the plurality of detector signals corresponds to a different intensity of the input light signal.
10. The apparatus of claim 9 wherein the processor is further configured to form a reflected-intensity map based on the plurality of contour plots.
11. A method comprising:
scanning a first input light signal in a two-dimensional scan pattern over a scan region through the effect of a microelectromechanical system (MEMS) scanner that has a first scanning axis characterized by a first resonant frequency and a second scanning axis characterized by a second resonant frequency, wherein the light signal is scanned by driving the first axis with a first periodic signal having a first drive frequency and driving the second axis with a second periodic signal having a second drive frequency;
providing a first detector signal based on reflected light from the scan region at a detector configuration that is non-imaging and includes at least one discrete detector, wherein the reflected light comprises at least a portion of the input light signal;
generating a first comparator signal based on a first comparison of the first detector signal and a first threshold; and
generating a first contour plot based on a spatiotemporal correlation between the first comparator signal and an estimate of the position of the MEMS scanner over a first time period.
12. The method for claim 11 further comprising estimating at least one of the size and location of a first feature in the scan region based on the first contour plot.
13. The method for claim 11 wherein the two-dimensional scan pattern is a Lissajous pattern.
14. The method for claim 13 further comprising selecting at least one of the first drive frequency and second drive frequency to give rise to a precession of the Lissajous pattern.
15. The method for claim 11 further comprising:
modulating the first input light signal at a modulation frequency; and
configuring a detector circuit to detect the modulation frequency.
16. The method for claim 11 further comprising:
generating a plurality of comparator signals that includes the first comparator signal, wherein each comparator signal of the plurality thereof is based on a comparison of the first detector signal and a different threshold of a plurality of thresholds that includes the first threshold; and
generating a plurality of contour plots that includes the first contour plot, wherein each contour plot of the plurality thereof is based on a spatiotemporal correlation between a different comparator signal of the plurality thereof and an estimate of the position of the MEMS scanner over a first time period.
17. The method for claim 11 further comprising:
generating a plurality of comparator signals that includes the first comparator signal, wherein each comparator signal of the plurality thereof is based on a comparison of the first threshold and a different detection signal of a plurality of detector signals that includes the first detector signal, wherein each of the plurality of detector signals is generated using a different gain for the at least one discrete detector; and
generating a plurality of contour plots that includes the first contour plot, wherein each contour plot of the plurality thereof is based on a spatiotemporal correlation between a different comparator signal of the plurality thereof and an estimate of the position of the MEMS scanner over a first time period.
18. The method for claim 11 further comprising:
generating a plurality of comparator signals that includes the first comparator signal, wherein each comparator signal of the plurality thereof is based on a comparison of the first threshold and a different detection signal of a plurality of detector signals that includes the first detector signal, wherein each of the plurality of detector signals corresponds to a different intensity of the first input light signal; and
generating a plurality of contour plots that includes the first contour plot, wherein each contour plot of the plurality thereof is based on a spatiotemporal correlation between a different comparator signal of the plurality thereof and an estimate of the position of the MEMS scanner over a first time period.
19. The method for claim 11 further comprising generating a multibit reflected-intensity map of the scan region using a successive approximation method selected from the group consisting of successive-approximation analog-to-digital conversion (ADC), counter-type ADC, and servo-tracking ADC.
20. The method for claim 19 wherein the successive approximation method is successive-approximation ADC based on a binary search.