Time of Flight Depth Mapping with Single-Photon Detection
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Solution Overview
Problem
Time-of-flight (ToF) depth mapping systems face challenges in accurately distinguishing between reflections from objects fixed to the device and those from nearby objects due to the high intensity of reflected light pulses and stray reflections, which can mask signals from actual objects at short distances, making it difficult to resolve temporal differences.
Innovation Solution
The system uses an array of single-photon detectors and processing circuitry to compare variations in electrical pulse counts from successive light pulses, leveraging the static nature of reflections from objects fixed to the device versus the varying speckle patterns from separate objects, allowing for the differentiation between fixed and separate objects by analyzing pulse count differences and thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional ToF measurement is used for close-range objects, then measurement speed is maintained, but measurement precision deteriorates due to high intensity reflections and stray light masking signals
Solution Approach 1:
The system dynamically adjusts the time interval window for integrating photon counts based on the measured depth value. For close-range objects with high intensity reflections, the integration window is shifted to exclude the immediate high-intensity period, allowing the detector to capture reflections from actual objects while avoiding masking from stray light and fixed reflections.
Solution Approach 2:
The patent changes the temporal parameter of measurement by using multiple time intervals following each light pulse. Instead of a single fixed integration window, the system measures photon counts across multiple time bins and selectively integrates those that correspond to the object's actual distance, thereby separating true object reflections from near-field interference.
2Measurement precision
If multiple time intervals are used for measurement, then measurement precision improves, but device complexity increases due to additional processing requirements
Solution Approach 1:
The measurement process is segmented into multiple discrete time intervals following each light pulse. Each time interval captures reflections from different distance ranges, allowing the system to separate close-range objects from fixed reflections by analyzing which time bins contain valid object signals versus interference signals.
Solution Approach 2:
The system uses feedback from the measured depth values to dynamically adjust the integration time window. The processing circuitry analyzes the distribution of photon counts across time intervals and uses this information to select appropriate integration windows for subsequent measurements, creating a closed-loop system that adapts to varying scene conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively identifies objects less than 10 cm away from the device, distinguishing between reflections from objects that are fixed to the device and those that are separate, thereby improving the accuracy of depth mapping and detecting malfunctions such as smudges or internal reflections.
Implementation Method 1
an array of single-photon detectors, which are configured to output electrical pulses in response to photons that are incident thereon
Implementation Method 2
a light source, such as a pulsed laser, directs pulses of optical radiation toward the scene that is to be mapped, and a high-speed detector senses the time of arrival of the radiation reflected from the scene
Implementation Method 3
The depth value at each pixel in the depth map is derived from the difference between the emission time of the outgoing pulse and the arrival time of the reflected radiation from the corresponding point in the scene, which is referred to as the 'time of flight' of the optical pulses
Data Source
AI summary
An optical sensing device includes a light source, which emits one or more beams of light pulses toward a scene. An array of single-photon detectors output electrical pulses in response to photons that are incident thereon. Light collection optics form an image of the scene on the array. Processing circuitry counts the electrical pulses output by the single-photon detectors during multiple time intervals following each of the light pulses, detects, responsively to the counted pulses, an object located less than 10 cm away from the array, makes a comparison between respective counts of the electrical pulses output by the single-photon detectors group during a specified time interval immediately following each of a plurality of the light pulses, and ascertains, responsively to the comparison, whether the object reflecting the at least one of the beams is fixed to the device or separate from the device.