Lidar Phase Correction for Longer Coherence and Vibration Sensing
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Solution Overview
Problem
Conventional frequency modulated, continuous wave lidar systems suffer from reduced coherence length and effective range due to phase wandering, and are unable to accurately measure vibrations with sub-micron amplitudes across a wide band of frequencies, as these vibrations appear as additive noise.
Innovation Solution
Implementing source phase correction near the laser source and target phase correction in the reflected signal to compensate for phase variance, using optical and digital phase correction systems to increase coherence length and improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a tunable laser source is used in frequency modulated lidar systems, then the tuning speed is improved, but the coherence length is reduced
Solution Approach 1:
The patent implements a feedback mechanism where phase noise detected from the laser source is used to generate a correction signal that is fed back to cancel the phase noise. This closed-loop feedback system allows the laser to be tuned rapidly while maintaining coherence by actively compensating for phase variations that would otherwise reduce coherence length.
Solution Approach 2:
The patent introduces an intermediary phase noise cancellation system that mediates between the tunable laser source and the target. This intermediary component detects phase noise and applies corrective phase modulation, allowing the laser to operate at high tuning speeds without directly transmitting phase noise to the target, thus preserving coherence length.
2Productivity
If conventional lidar systems operate at high sampling rates, then the measurement bandwidth is improved, but the ability to detect sub-micron vibrations is reduced due to additive noise
Solution Approach 1:
The patent extracts phase noise from the measurement signal by detecting it separately from the laser source and removing it through phase cancellation. This separation allows the system to operate at high sampling rates for broad bandwidth measurement while eliminating the additive noise that would otherwise mask sub-micron vibrations, thereby maintaining measurement precision.
Solution Approach 2:
The patent converts the harmful phase noise into a useful signal by detecting it and using it to generate a correction signal. The phase noise that would normally degrade measurement precision is instead utilized to improve vibration detection accuracy by canceling itself out in the measurement path, allowing high sampling rates to be maintained without sacrificing 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
The proposed method significantly increases coherence length and effective range of lidar systems, enabling accurate measurement of vibrations across a wide band of frequencies by reducing phase wandering and additive noise.
Implementation Method 1
an optical phase modulator at least partially cancels said phase noise in the optical domain
Implementation Method 2
The intensity noise is converted into an electrical signal by the photodetector
Implementation Method 3
The laser beam and the resonator coupled to the laser beam convert phase noise of light transported by the laser beam prior to the coupling point into intensity noise of light transported by the laser beam immediately after the coupling point
Data Source
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AI summary
Various implementations of the invention compensate for "phase wandering" in tunable laser sources. Phase wandering may negatively impact a performance of a lidar system that employ such laser sources, typically by reducing a coherence length/range of the lidar system, an effective bandwidth of the lidar system, a sensitivity of the lidar system, etc. Some implementations of the invention compensate for phase wandering near the laser source and before the output of the laser is directed toward a target. Some implementations of the invention compensate for phase wandering in the target signal (i.e., the output of the laser that is incident on and reflected back from the target). Some implementations of the invention compensate for phase wandering at the laser source and in the target signal.