Addressable Emitter Array for Time-of-Flight Sensing
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Solution Overview
Problem
Direct Time-of-Flight (ToF) depth mapping systems are limited by low data acquisition rates due to the need for a fixed waiting period equal to the maximum time of flight, leading to low duty cycles and potential aliasing issues.
Innovation Solution
An array of emitters is controlled to emit pulses in a predefined spatio-temporal sequence, allowing for simultaneous or closely spaced pulse emission, and a receiver processes signals to measure times of flight with improved resolution and throughput, using VCSELs and single-photon sensors with TDCs to accumulate histograms and reduce aliasing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed waiting period equal to the maximum time of flight is used in direct ToF depth mapping systems, then the system can avoid aliasing issues, but the data acquisition rate decreases and duty cycle becomes low
Solution Approach 1:
The system segments the emitter array into multiple groups that can be activated in different time sequences. By dividing the emitters into groups and activating them sequentially with different time offsets, the system can process multiple depth ranges simultaneously, thereby increasing the overall data acquisition rate while maintaining reliable aliasing avoidance for each segment.
Solution Approach 2:
The system employs periodic action by cycling through different emitter groups in a predetermined sequence. Each group is activated for a specific duration and then deactivated, allowing the next group to be activated. This periodic activation pattern enables the system to acquire data from multiple depth ranges over time, effectively increasing the data acquisition rate while maintaining reliable measurement for each period.
2Productivity
If multiple emitters are activated simultaneously to increase data acquisition throughput, then the duty cycle improves, but aliasing issues may occur due to overlapping return signals
Solution Approach 1:
The emitter array is divided into multiple groups that are activated in a predetermined sequence rather than all simultaneously. Each group is spatially or temporally segmented from the others, allowing the system to maintain high throughput by processing multiple groups while preventing aliasing through the sequential activation pattern that separates return signals in time.
Solution Approach 2:
The system introduces a temporal dimension to the emitter activation pattern by using different time sequences for different emitter groups. This temporal separation adds a new dimension to the problem solution, allowing multiple emitters to be used effectively without causing aliasing, as the return signals from different groups arrive at different times and can be distinguished through time-of-flight measurement.
3Measurement precision
If the system waits for the maximum time of flight before emitting the next pulse, then accurate depth measurement is ensured, but the measurement resolution and acquisition speed are limited
Solution Approach 1:
The system segments the measurement process by dividing emitters into groups that measure different depth ranges or time windows. Each group operates with its own optimized pulse timing, allowing the system to maintain accurate depth measurement for each segment while reducing the overall acquisition time by processing multiple segments in parallel or rapid succession.
Solution Approach 2:
The system performs preliminary actions by pre-planning and pre-positioning multiple emitter groups in a predetermined activation sequence. This allows the system to prepare multiple measurement windows in advance, so that when data acquisition begins, multiple groups can be activated efficiently without waiting for maximum time of flight between each pulse, thereby reducing total acquisition time while maintaining measurement precision.
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 increases data acquisition throughput and duty cycle, enabling finer resolution and reducing peak power requirements while minimizing aliasing, allowing for efficient and accurate depth mapping across varying distances.
Implementation Method 1
the emitters include vertical-cavity surface-emitting lasers (VCSELs)
Implementation Method 2
the detectors include single-photon sensors
Implementation Method 3
outputs a digital value indicative of a delay between a pulse emitted by one of the emitters and receipt of a photon at a corresponding pixel of the receiver
Data Source
AI summary
Optical sensing apparatus (20) includes an array (28) of emitters (50), which emit pulses of optical radiation at different, respective times in response to a control input applied to the array. A receiver (26) includes a plurality of detectors (40), which output signals indicative of times of arrival of photons at the detectors. Optics (30, 32) project the optical radiation from the emitters onto respective locations in a scene and image the respective locations onto corresponding pixels of the receiver. A controller (44) controls the emitters to emit the output pulses in a predefined spatio-temporal sequence, and collects and processes the signals output by corresponding pixels in synchronization with the spatio-temporal sequence so as to measure respective times of flight of the pulses to and from the respective locations in the scene.