Abstract: An illustrative optical measurement system includes a light source configured to emit light directed at a target, an array of photodetectors configured to detect photons of the light after the light is scattered by the target, and a processing unit configured to measure a noise level of a photodetector included in the array of photodetectors, the noise level comprising a dark count rate that measures a dark count divided by a time period, determine that the noise level meets a predetermined threshold comprising a dark count rate threshold, and prevent, based on the determining that the noise level meets the predetermined threshold, an output of the photodetector from being used in generating a histogram based on a temporal distribution of photons detected by the array of photodetectors, the preventing comprising switching the output to a monitoring circuit that monitors a characteristic of the optical measurement system separate from the photodetector.

Abstract: An illustrative multimodal measurement system includes a wearable assembly configured to be worn by a user; and a module configured to be removably inserted into the wearable assembly and comprising: a housing, a printed circuit board (PCB) and a light guide assembly configured to emit light directed at a target within the user. The light guide assembly comprises: a lower light guide portion housed within the housing and having a proximal end attached to the PCB, a conductive spring member housed within the housing and comprising a coil positioned around an external surface of the lower light guide portion, and a conductive upper light guide portion connected to the lower light guide portion and configured to protrude from an upper surface of the housing and be in contact with a surface of a body of the user.

Abstract: An illustrative optical measurement system includes a light source configured to emit light directed at a target, an array of photodetectors configured to detect photons of the light after the light is scattered by the target, and a processing unit. The processing unit is configured to measure a noise level of a photodetector included in the array of photodetectors and determine that the noise level meets a predetermined threshold. The processing unit is further configured to prevent, based on the determining that the noise level meets the predetermined threshold, an output of the photodetector from being used in generating a histogram based on a temporal distribution of photons detected by the array of photodetectors.

Abstract: An illustrative optical measurement system includes a light source configured to emit light directed at a target. The optical measurement system further includes a photodetector configured to detect a photon of the light after the light is scattered by the target. The optical measurement system further includes a control circuit configured to receive a first input voltage that is a temperature-dependent voltage. The control circuit is further configured to receive a second input voltage that is a temperature-invariant voltage. The control circuit is further configured to output, based on a combination of the first input voltage and the second input voltage, a bias voltage for the photodetector, wherein the combination of the first and second input voltages is configured to cause the bias voltage to vary based on temperature.

Abstract: An illustrative multimodal measurement system includes a wearable assembly configured to be worn by a user and comprising a plurality of light sources each configured to emit light directed at a target within the user, a plurality of detectors configured to detect arrival times for photons of the light after the light is scattered by the target, and a plurality of electrodes configured to be external to the user and detect electrical activity of the target.

Abstract: An illustrative system may include a memory storing instructions and a processor communicatively coupled to the memory and configured to execute the instructions to: cause a signal to be applied to a component within an optical measurement system; generate, based on a response of the component to the signal, characterization data representative of a timing uncertainty associated with the component; and perform, based on the characterization data, an action associated with the component.

Abstract: An exemplary optical measurement system includes a signal generator configured to generate a signal and a processing unit configured to direct the signal generator to apply the signal to a component within the optical measurement system, generate, based on a response of the component to the signal, characterization data representative of a timing uncertainty associated with the component, and perform, based on the characterization data, an action associated with the component.

Abstract: An exemplary optical measurement system includes a light source configured to emit light directed at a target. The optical measurement system further includes a photodetector configured to detect a photon of the light after the light is scattered by the target. The optical measurement system further includes a control circuit configured to receive a first input voltage that is a temperature-dependent voltage. The control circuit is further configured to receive a second input voltage that is a temperature-invariant voltage. The control circuit is further configured to output, based on a combination of the first input voltage and the second input voltage, a bias voltage for the photodetector, wherein the combination of the first and second input voltages is configured to cause the bias voltage to vary based on temperature.

Abstract: An exemplary photodetector system includes a plurality of photodetectors connected in parallel and a processor communicatively coupled to the plurality of photodetectors. The processor is configured to receive an accumulated output from the plurality of photodetectors. The accumulated output represents an accumulation of respective outputs from each of the plurality of photodetectors detecting photons during a predetermined measurement time period that occurs in response to a light pulse being directed toward a target within a body. The processor is further configured to determine, based on the accumulated output, a temporal distribution of photons detected by the plurality of photodetectors, and generate, based on the temporal distribution of photons, a histogram representing a light pulse response of the target within the body.

Abstract: An illustrative system may include a component configured to be worn on a body of a user, the component comprising a time-to-digital converter (TDC) configured to: receive, during a predetermined event detection time window that commences in response to an application of a light pulse to a target within the body, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target; and measure, based on the receiving the signal, a time interval between when the event occurred and an end of the predetermined event detection time window. The system may further include a processor configured to determine, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.

Abstract: An illustrative system may include a TDC configured to monitor for an occurrence of a photodetector output pulse during a measurement time window that is within and shorter in duration than a light pulse time period, the photodetector output pulse generated by a photodetector when the photodetector detects a photon from a light pulse having a light pulse time period; a PLL circuit for the TDC and having a PLL feedback period defined by a reference clock, the PLL circuit configured to: output a plurality of fine phase signals and output one or more signals representative of a plurality of feedback divider states during the PLL feedback period; and a precision timing circuit configured to adjust, based on one or more of the fine phase signals and/or the feedback divider states, a temporal position of the measurement time window within the light pulse time period.

Abstract: An exemplary system includes a photodetector configured to generate a photodetector output pulse when the photodetector detects a photon from a light pulse having a light pulse time period, a TDC configured to monitor for the occurrence of the photodetector output pulse during a measurement time window that is within and shorter in duration than the light pulse time period, a PLL circuit for the TDC, and a precision timing circuit connected to the PLL circuit and configured to adjust, based on at least one signal generated within the PLL circuit, a temporal position of the measurement time window within the light pulse time period.

Abstract: An exemplary system includes a photodetector configured to generate a plurality of photodetector output pulses over time as a plurality of light pulses are applied to and scattered by a target, a TPSF generation circuit configured to generate, based on the photodetector output pulses, a TPSF representative of a light pulse response of the target, and a control circuit configured to direct the TPSF generation circuit to selectively operate in different resolution modes.

Abstract: An exemplary system includes a PLL circuit and a precision timing circuit connected to the PLL circuit. The PLL circuit has a PLL feedback period defined by a reference clock and includes a voltage controlled oscillator configured to lock to the reference clock and having a plurality of stages configured to output a plurality of fine phase signals each having a different phase, and a feedback divider configured to be clocked by a single fine phase signal included in the plurality of fine phase signals and have a plurality of feedback divider states during the PLL feedback period. The precision timing circuit is configured to generate a timing pulse and set, based on a first combination of one of the fine phase signals and one of the feedback divider states, a temporal position of the timing pulse within the PLL feedback period.

Abstract: An exemplary wearable brain interface system includes a head-mountable component and a control system. The head-mountable component includes an array of photodetectors that includes a photodetector comprising a single-photon avalanche diode (SPAD) and a fast-gating circuit configured to arm and disarm the SPAD. The control system is for controlling a current drawn by the array of photodetectors.

Abstract: An illustrative wearable brain interface system includes a headgear configured to be worn on a head of a user and a plurality of photodetector units configured to attach to the headgear, the photodetector units each housing a photodetector included in a plurality of photodetectors configured to be controlled by a master control unit to detect photons of light.

Abstract: An illustrative system may include a component configured to be worn on a body of a user, the component comprising a time-to-digital converter (TDC) configured to: receive, during a predetermined event detection time window that commences in response to an application of a light pulse to a target within the body, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target; and measure, based on the receiving the signal, a time interval between when the event occurred and an end of the predetermined event detection time window. The system may further include a processor configured to determine, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.

Abstract: An illustrative wearable system includes a head-mountable component configured to be worn on a head of a user and a processor. The head-mountable component includes a time-to-digital converter (TDC) configured to receive, during a predetermined event detection time window that commences in response to an application of a light pulse to a target, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target, the signal configured to enable a GRO of the TDC. The TDC is further configured to measure, using the GRO, a time interval between when the event occurred and an end of the predetermined event detection time window. The processor is configured to determine, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.

Abstract: An exemplary system includes a PLL circuit and a precision timing circuit connected to the PLL circuit. The PLL circuit has a PLL feedback period defined by a reference clock and includes a voltage controlled oscillator configured to lock to the reference clock and having a plurality of stages configured to output a plurality of fine phase signals each having a different phase, and a feedback divider configured to be clocked by a single fine phase signal included in the plurality of fine phase signals and have a plurality of feedback divider states during the PLL feedback period. The precision timing circuit is configured to generate a timing pulse and set, based on a first combination of one of the fine phase signals and one of the feedback divider states, a temporal position of the timing pulse within the PLL feedback period.

Abstract: An illustrative optical measurement system includes a light source configured to emit a light pulse directed at a target. The optical measurement system further includes a plurality of photodetectors configured to operate in accordance with an input bias voltage. The optical measurement system further includes a control circuit configured to identify a photodetector subset included in the plurality of photodetectors and that detects, while the input bias voltage has a first value, photons of the light pulse after the light pulse is scattered by the target. The control circuit is further configured to determine, based on the identifying of the photodetector subset, an overvoltage associated with the photodetector subset. The control circuit is further configured to update, based on the overvoltage, the input bias voltage for the plurality of photodetectors to have a second value.