Dual-Beat Optical Measurement for Phase-Noise-Free FMCW LiDAR
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Solution Overview
Problem
FMCW LiDAR systems face limitations in maximum measurement distance due to laser coherence, and existing methods for reducing non-linear chirp and phase noise either complicate the device configuration or are not suitable for real-time processing.
Innovation Solution
An optical measurement device using a multi-frequency laser that generates a frequency-fixed carrier and at least one frequency-modulated subcarrier, with a dual frequency beat signal generator and arithmetic processing unit to eliminate phase noise by generating a difference signal from two complex beat signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FMCW LiDAR uses coherent detection with laser light, then measurement sensitivity and resolution are improved, but phase noise from the laser limits the maximum measurement distance
Solution Approach 1:
The patent segments the laser light into multiple frequency components (carrier wave and subcarrier waves) and processes them separately through dual beat signal generation. By segmenting the frequency spectrum and processing different frequency components independently, the system can eliminate phase noise through differential calculation while maintaining the coherent detection advantages for sensitivity and resolution.
2Adaptability or versatility
If FMCW LiDAR uses frequency modulation of laser, then distance and speed measurement capabilities are improved, but non-linear chirp deteriorates measurement accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the system measures the actual beat frequencies from multiple frequency components and uses this information to calculate and correct for non-linear chirp effects. The arithmetic processing unit uses the measured beat signal characteristics to compensate for deviations from ideal linear frequency modulation, thereby maintaining measurement accuracy despite non-linear chirp in the laser.
3Measurement precision
If existing methods reduce phase noise using negative feedback control, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates phase noise through mathematical processing rather than physical feedback control. By generating beat signals from multiple frequency components and performing differential calculations in the arithmetic processing unit, the system extracts and removes phase noise components computationally, avoiding the need for complex physical feedback control hardware while achieving phase noise reduction.
4Length of stationary object
If FMCW LiDAR extends measurement distance beyond laser coherence length, then measurement range is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent merges multiple beat signal measurements from different frequency components (carrier and subcarriers) into a unified measurement result. By combining information from multiple frequency channels and performing differential processing, the system achieves coherent integration that improves signal-to-noise ratio, enabling extended measurement distances beyond the traditional laser coherence length limitation.
Data Source
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AI summary
An optical measurement device includes at least a multi-frequency laser configured to simultaneously generate a frequency-fixed carrier and at least one frequency-modulated subcarrier, an optical branching element, a dual frequency beat signal generator, a difference signal generator, and an arithmetic processing unit. Either the carrier or the subcarrier within the output light of the multi-frequency laser is used as first measurement light and either the carrier or the subcarrier having a frequency different from that of the first measurement light is used as second measurement light. The dual frequency beat signal generator separates and outputs a first complex beat signal derived from the first measurement light and a second complex beat signal derived from the second measurement light. The difference signal generator outputs a difference signal between the first complex beat signal and the second complex beat signal.