Devices, systems, and methods using wearable time domain-based activity tracker

1. A wearable optical measurement device for use by a user, the wearable optical measurement device comprising:

a light source configured to emit light pulses directed at a target;

a detector configured to detect arrival times for photons of the light pulses after the photons are scattered by the target; and

a processing unit configured to:

generate, based on the arrival times of the photons at the detector, histogram data associated with the target;

determine, based on the histogram data, an absolute optical property associated with the target;

determine, based on the absolute optical property, a blood oxygenation level of the user;

perform an operation based on the blood oxygenation level;

determine, based on the histogram data, at least one of a heart rate, a heart rate variability, or a respiratory rate of the user; and

access inertial measurement unit (IMU) data associated with the user;

wherein the performing the operation comprises determining a sleep stage of the user based on the blood oxygenation level, the IMU data, and the at least one of the heart rate, the heart rate variability, or the respiratory rate.

2. The wearable optical measurement device of claim 1 , wherein the performing the operation comprises outputting data representative of the blood oxygenation level.

3. The wearable optical measurement device of claim 1 , wherein the performing the operation comprises providing content associated with the blood oxygenation level for presentation to the user.

4. The wearable optical measurement device of claim 3 , wherein the content comprises a recommendation based on the blood oxygenation level.

5. The wearable optical measurement device of claim 3 , wherein the providing the content for presentation comprises displaying, on a screen of the wearable optical measurement device, the blood oxygenation level.

6. The wearable optical measurement device of claim 3 , wherein the providing the content for presentation comprises providing an alert based on the blood oxygenation level meeting a predetermined threshold blood oxygenation level.

7. The wearable optical measurement device of claim 3 , wherein the providing the content for presentation comprises directing an image projection unit of the wearable optical measurement device to project the content.

8. The wearable optical measurement device of claim 7 , wherein the directing the image projection unit to project the content comprises directing the image projection unit to project the content on a ground surface in a vicinity of the user.

9. The wearable optical measurement device of claim 7 , wherein the directing the image projection unit to project the content comprises directing the image projection unit to project the content at an approximate eye level of the user.

10. The wearable optical measurement device of claim 7 , wherein the directing the image projection unit to project the content comprises directing the image projection unit to project the content on a hand or arm of the user.

11. The wearable optical measurement device of claim 1 , further comprising a housing configured to fit on an appendage of the user and house the light source and the detector.

12. The wearable optical measurement device of claim 11 , wherein the housing is further configured to house the processing unit.

13. The wearable optical measurement device of claim 1 , further comprising a housing configured to be worn on a wrist of the user and house the light source and the detector.

14. The wearable optical measurement device of claim 13 , wherein the housing is further configured to house the processing unit.

15. A wearable optical measurement device configured to be worn on an appendage of a user, the wearable optical measurement device comprising:

a light source configured to emit light pulses directed at the appendage;

a detector configured to detect arrival times for photons of the light pulses after the photons are scattered by tissue within the appendage;

a housing configured to house the light source and the detector; and

a processing unit configured to:

generate, based on the arrival times of the photons at the detector, histogram data associated with the appendage;

determine, based on the histogram data, an absolute optical property associated with the appendage;

determine, based on the absolute optical property, a blood oxygenation level of the user;

determine, based on the histogram data, at least one of a respiratory rate of the user, a heart rate of the user, or a heart rate variability of the user;

access inertial measurement unit (IMU) data associated with the user; and

determine, based on the IMU data, and the at least one of the heart rate, the heart rate variability, or the respiratory rate, a sleep stage of the user.

16. The wearable optical measurement device of claim 15 , wherein the housing is further configured to house the processing unit.

17. The wearable optical measurement device of claim 15 , wherein:

the light source comprises two lasers and a prism;

the lasers are configured to direct light pulses at the prism; and

the prism is configured to direct the light pulses at the appendage.

18. The wearable optical measurement device of claim 15 , wherein the light source comprises a vertical-cavity surface-emitting laser (VCSEL).

19. The wearable optical measurement device of claim 15 , wherein the housing is configured to fit on the appendage and comprises:

a first portion configured to house the light source and contact a first side of the appendage; and

a second portion configured to house the detector and contact a second side of the appendage, the second side opposite the first side.

20. The wearable optical measurement device of claim 15 , wherein the housing is configured to fit on the appendage and the light source and the detector are configured to be positioned on a same side of the appendage of the user.

21. The wearable optical measurement device of claim 15 , further comprising:

a disposable head-portion configured to fit on the appendage;

a first optical conduit from the light source to the disposable head-portion, the first optical conduit configured to direct the light pulses at the appendage; and

a second optical conduit from the disposable head-portion to the detector, the second optical conduit configured to direct the photons scattered by the tissue within the appendage to the detector.

22. The wearable optical measurement device of claim 15 , wherein the processing unit is further configured to perform an operation based on the blood oxygenation level.

23. The wearable optical measurement device of claim 22 , wherein the performing the operation comprises providing content associated with the blood oxygenation level for presentation to the user.

24. A wearable optical measurement device configured to be worn on a wrist of a user, the wearable optical measurement device comprising:

a light source configured to emit light directed at the wrist;

a detector configured to detect arrival times for photons of the light after the photons are scattered by tissue within the wrist;

a housing configured to house the light source, the detector, and a processing unit;

a strap coupled to the housing and configured to hold the housing against the wrist; and

the processing unit configured to:

generate, based on the arrival times of the photons at the detector, histogram data associated with the wrist;

determine, based on the histogram data, an absolute optical property associated with the wrist;

determine, based on the absolute optical property, a blood oxygenation level of the user;

determine, based on the histogram data, at least one of a respiratory rate of the user, a heart rate of the user, or a heart rate variability of the user;

access inertial measurement unit (IMU) data associated with the user; and

determine, based on the IMU data, and the at least one of the heart rate, the heart rate variability, or the respiratory rate, a sleep stage of the user.