Time of flight sensor
Time of Flight Sensor A method of measuring optical crosstalk in a time of flight sensor, which comprises a substantially transparent cover covering a light emitter and one or more photodetectors. The method comprises emitting a series of pulses of light from the light emitter; and using the one or more photodetectors to obtain a distribution of times at which at least one photodetector of the one or more photodetectors detected photons after each emission of the series of pulses of light. The method further comprises recording one or more parameters of the earliest peak if the distribution comprises two or more separate peaks.
1 . A method of measuring optical crosstalk in a time of flight sensor comprising a substantially transparent cover covering a light emitter and one or more photodetectors, the method comprising:
emitting a series of pulses of light from the light emitter;
using the one or more photodetectors to obtain a distribution of times at which at least one photodetector of the one or more photodetectors detected photons after each emission of the series of pulses of light,
wherein the distribution is obtained over a plurality of detection periods, each detection period containing an emission of one of the pulses of light and being divided into an identical series of time intervals relative to the emission, by counting a total number of photons detected by the at least one photodetector during instances of each time interval across the plurality of detection periods; and
if the distribution comprises two or more separate peaks, recording one or more parameters of the earliest peak.
2 . A method according to claim 1 wherein the distribution of times is a distribution of times at which at least one photodetector of the one or more photodetectors detected photons before, during and after each emission of the pulses of light.
3 . A method according to claim 1 wherein the times at which the at least one photodetector detected photons are relative to an emission of one of the series of pulses of light during or immediately preceding a detection period in which the photon was detected.
4 . A method according to claim 1 wherein a counted number of photons detected by the one or more photodetectors during all of the time intervals at each of the plurality of times are or contribute to values of the distribution for time intervals at the plurality of times.
5 . A method according to claim 4 wherein each time interval of the plurality of time intervals has a substantially equal duration.
6 . A method according to claim 1 wherein the series of pulses of light comprises at least 75,000 light pulses.
7 . A method according to claim 1 wherein the distribution is a histogram.
8 . A method according to claim 1 wherein peaks are parts of the distribution above a predetermined threshold.
9 . A method according to claim 8 wherein two peaks are determined to be separate if the earliest peak is within a predetermined cover reflection peak window and the later peak is separated from the earlier peak by at least a predetermined length of time.
10 . A method according to claim 1 wherein the one or more recorded parameters comprise at least one of the time in the distribution at which the peak occurs, the area of the peak, the height of the peak, the width in time of the peak, the full width of the peak at half its maximum height, the shape of the peak.
11 . A method according to claim 1 comprising the additional step of, if the distribution comprises two or more separate peaks, determining the separation in time between the earliest peak and at least one of the one or more other peaks.
12 . A method according to claim 1 wherein the light emitter is a vertical-cavity surface-emitting laser.
13 . A method according to claim 1 wherein each of the one or more photodetectors is a single photon avalanche diode.
14 . A method according to claim 1 wherein the one or more photodetectors are a plurality of photodetectors, and are used to obtain a plurality of distributions, each distribution being the distribution of times at which at least one photodetector of the plurality of photodetectors detected photons after each emission of the emissions of the pulses of light.
15 . A method according to claim 1 , wherein the light emitter forms part of an optical stack and where the method calibrates the time of flight sensor in conjunction with the optical stack.
16 . A time of flight sensor configured to perform a method comprising:
emitting a series of pulses of light from the light emitter;
using the one or more photodetectors to obtain a distribution of times at which at least one photodetector of the one or more photodetectors detected photons after each emission of the series of pulses of light, wherein the distribution is obtained over a plurality of detection periods, each detection period containing an emission of one of the pulses of light and being divided into an identical series of time intervals relative to the emission, by counting a total number of photons detected by the at least one photodetector during instances of each time interval across the plurality of detection periods, and
if the distribution comprises two or more separate peaks, recording one or more parameters of the earliest peak.
17 . A device comprising a sensor according to claim 16 .
18 . A non-transitory storage medium comprising computer instructions executable by one or more processors comprised by or in communication with a time of flight sensor comprising a substantially transparent cover covering a light emitter and one or more photodetectors, the computer instructions when executed by the one or more processors causing the time of flight sensor to perform a method comprising:
emitting a series of pulses of light from the light emitter;
using the one or more photodetectors to obtain a distribution of times at which at least one photodetector of the one or more photodetectors detected photons after each emission of the series of pulses of light, wherein the distribution is obtained over a plurality of detection periods, each detection period containing an emission of one of the pulses of light and being divided into an identical series of time intervals relative to the emission, by counting a total number of photons detected by the at least one photodetector during instances of each time interval across the plurality of detection periods, and
if the distribution comprises two or more separate peaks, recording one or more parameters of the earliest peak.