Lidar Sub-Pulse Modulation for Photon Noise Reduction
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Solution Overview
Problem
Pulse time-of-flight distance measurement devices face limitations in accuracy due to temporal uncertainty of photons and inherent fluctuations in coherent light, leading to noise and jitter in distance estimation, especially at short and mid ranges, which affects their performance in industrial applications.
Innovation Solution
The device employs a light generator emitting pulsed light signals composed of sub-pulses with a high repetition rate, typically above 1GHz, to improve temporal localization of photons and reduce noise, using modulation techniques such as electro-optic beam deflectors or semiconductor devices like comb lasers, which provide low time jitter and photon noise, allowing for precise distance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pulsed light signals are used for distance measurement, then the device structure is simple, but the measurement precision is limited due to temporal uncertainty of photons and inherent fluctuations in coherent light
Solution Approach 1:
The light generator is divided into a first light source generating sub-pulses and a second light source generating envelope pulses. This segmentation allows each light source to be optimized for its specific function, with the sub-pulses providing temporal precision and the envelope pulses providing measurement signal, thereby resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent uses periodic sub-pulses with a repetition rate of at least 1 GHz to create a structured light signal. This periodic action provides temporal reference points that reduce photon temporal uncertainty and improve distance measurement accuracy without requiring complex single-pulse generation systems
2Productivity
If single shot detection mode is used to reduce measurement time, then the productivity is improved, but the measurement precision deteriorates due to distance jitter that cannot be reduced by repeating measurements
Solution Approach 1:
The patent implements feedback by using a portion of the emitted structured light signal as a reference at the receiver. This reference signal provides temporal and phase information that enables real-time correction of distance jitter, allowing single shot detection to achieve both high productivity and high precision
Solution Approach 2:
The patent changes the temporal parameters of the light signal by using sub-pulses with repetition rates of at least 1 GHz. This parameter change creates a dense temporal structure that provides sufficient reference information for accurate distance measurement in single shot mode, resolving the contradiction between measurement speed and 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 enhances the accuracy of distance information by reducing temporal and chromatic errors, enabling precise distance measurement with low jitter and improved signal-to-noise ratio, even at short ranges, and is applicable in various measurement instruments like 3D scanners and laser trackers.
Implementation Method 1
a light generator configured to emit at least one pulsed light signal to a target, wherein the pulsed light signal has a pulse form envelope
Implementation Method 2
using modulation techniques such as electro-optic beam deflectors or semiconductor devices like comb lasers
Implementation Method 3
a receiving circuit having a detector configured for detecting at least part of the light signal returning from the target
Data Source
Figure 1~2a
Figure 2b~3
Figure 4~5
AI summary
Distance measuring device for geodetic or industrial distance measurement according to the pulse time-of-flight principle, the distance measuring device comprising a light generator (1) configured to emit at least one pulsed light signal to a target (5), wherein the pulsed light signal has a pulse form envelope (10), a receiving circuit (8) having a detector configured for detecting at least part of the light signal returning from the target (5), wherein the receive signal is extracted in such a way as to be comparable to the pulse form envelope (10), and an evaluation unit (9) configured for determining the time of flight of the pulsed light signal on the basis of the receive signal, wherein a start time of the pulsed light signal is determined, particularly based on the time of occurrence of a feature in the emitted pulse form envelope of the emitted pulsed light signal, and a stop time is determined based on the time of occurrence of a feature in the receive signal, particularly the same feature as the feature used for determining the start time, wherein the difference between the stop and start time is used for determining the distance to the target, wherein the distance measuring device is configured in such a way that the at least one pulsed light signal generated by the light generator (1) is comprised of sub-pulses (13) provided with a repetition rate of at least 1GHz, wherein the sub-pulses (13) contained in the pulsed light signal preserve the pulse form envelope (10) of the pulsed light signal.