Systems and methods for calibration of an optical measurement system
An illustrative optical measurement system includes a light source configured to emit light directed at a target. The system further includes a detector configured to detect arrival times for photons of the light after the light is scattered by the target. The system further includes a temperature sensor configured to output a temperature signal representative of a temperature of the light source. The system further includes an optical sensor configured to output a power signal representative of an optical power level of the light emitted by the light source. The system further includes a driver circuit configured to output, based on the temperature signal and the power signal, an input current for the light source.
1. An optical measurement system comprising:
a light source configured to emit light directed at a target;
a first detector configured to detect arrival times for photons of the light after the light is scattered by the target;
a second detector configured to function as both a temperature sensor configured to output a temperature signal representative of a temperature of the light source and an optical sensor configured to output a power signal representative of an optical power level of the light emitted by the light source; and
a driver circuit configured to output, based on the temperature signal and the power signal output by the second detector, an input current for the light source.
2. The optical measurement system of claim 1 , wherein the outputting the input current comprises:
adjusting, based on the temperature, the power signal to determine an actual power level of the light emitted by the light source; and
adjusting, based on the actual power level, a reference power level input to the driver circuit to generate the input current.
3. The optical measurement system of claim 2 , wherein the outputting the input current further comprises:
adjusting, based on the temperature, the reference power level to generate a feedforward current; and
adjusting, based on the adjusting the reference power level based on the actual power level, the feedforward current to generate the input current.
4. The optical measurement system of claim 3 , wherein:
the adjusting the reference power level comprises subtracting the actual power level from the reference power level to determine a power level difference;
the driver circuit is further configured to generate a difference current that corresponds to the power level difference; and
the adjusting the feedforward current comprises adding the difference current to the feedforward current.
5. The optical measurement system of claim 1 , wherein the second detector comprises a single photon avalanche diode (SPAD).
6. The optical measurement system of claim 5 , wherein the outputting the power level comprises generating a histogram based on arrival times of photons of additional light emitted by the light source, the additional light directed at the SPAD.
7. The optical measurement system of claim 1 , further comprising a processing unit configured to:
generate, based on the arrival times of the photons at the first detector, histogram data associated with the target; and
determine, based on the histogram data, a property of the target.
8. The optical measurement system of claim 7 , wherein the processing unit comprises a portion of the driver circuit.
9. The optical measurement system of claim 1 , further comprising a wearable assembly configured to be worn by a user, the wearable assembly configured to house the light source, the first detector, the second detector, and the driver circuit.
10. The optical measurement system of claim 9 , wherein:
the wearable assembly is configured to be worn on a head of the user; and
the target comprises a brain of the user.
11. The optical measurement system of claim 9 , wherein the wearable assembly is configured to be worn on a finger of the user.
12. The optical measurement system of claim 9 , wherein the wearable assembly is configured to be worn on a wrist of the user.
13. A wearable system for use by a user comprising:
a component configured to be attached to a body of the user, the component comprising:
a light source configured to emit light directed at a target within the body;
an array of photodetectors configured to detect photons of light after the light reflects off the target;
a detector configured to function as both a temperature sensor configured to output a temperature signal representative of a temperature of the light source and an optical sensor configured to output a power signal representative of an optical power level of the light emitted by the light source; and
a driver circuit configured to output, based on the temperature signal and the power signal, an input current for the light source.
14. The wearable system of claim 13 , wherein the outputting the input current comprises:
adjusting, based on the temperature, the power signal to determine an actual power level of the light emitted by the light source; and
adjusting, based on the actual power level, a reference power level input to the driver circuit to generate the input current.
15. The wearable system of claim 14 , wherein the outputting the input current further comprises:
adjusting, based on the temperature, the reference power level to generate a feedforward current; and
adjusting, based on the adjusting the reference power level based on the actual power level, the feedforward current to generate the input current.
16. The wearable system of claim 15 , wherein:
the adjusting the reference power level comprises subtracting the actual power level from the reference power level to determine a power level difference;
the driver circuit is further configured to generate a difference current that corresponds to the power level difference; and
the adjusting the feedforward current comprises adding the difference current to the feedforward current.
17. The wearable system of claim 13 , wherein the detector comprises an additional array of photodetectors.
18. The wearable system of claim 17 , wherein the outputting the power level comprises generating a histogram based on arrival times of photons of additional light emitted by the light source, the additional light directed at the additional array of photodetectors.
19. The wearable system of claim 13 , further comprising a processing unit configured to:
generate, based on an output of the array of photodetectors, histogram data associated with the target; and
determine, based on the histogram data, a property of the target.
20. The wearable system of claim 13 , wherein each photodetector of the array of photodetectors comprises a single photon avalanche diode (SPAD).
21. The wearable system of claim 13 , wherein the component is configured to be worn on a head of the user.
22. The wearable system of claim 13 , wherein the component is configured to be worn on a finger of the user.
23. The wearable system of claim 13 , wherein the component is configured to be worn on a wrist of the user.
24. A method comprising:
receiving, by a driver circuit, a temperature signal representative of a temperature of a light source configured to emit light directed at a target;
receiving, by the driver circuit, a power signal representative of an optical power level of the light emitted by the light source; and
outputting, by the driver circuit, based on the temperature signal and the power signal, an input current for the light source;
wherein the temperature signal and the power signal are both output by a detector configured to function as both a temperature sensor and an optical sensor.
25. The method of claim 24 , wherein the outputting the input current comprises:
adjusting, by the driver circuit, based on the temperature, the power signal to determine an actual power level of the light emitted by the light source; and
adjusting, by the driver circuit, based on the actual power level, a reference power level input to the driver circuit to generate the input current.
26. The method of claim 25 , wherein the outputting the input current further comprises:
adjusting, by the driver circuit, based on the temperature, the reference power level to generate a feedforward current; and
adjusting, by the driver circuit, based on the adjusting the reference power level based on the actual power level, the feedforward current to generate the input current.
27. The method of claim 26 , wherein:
the adjusting the reference power level comprises subtracting the actual power level from the reference power level to determine a power level difference;
the method further comprises generating, by the driver circuit, a difference current that corresponds to the power level difference; and
the adjusting the feedforward current comprises adding the difference current to the feedforward current.