Lidar Phase Correction for Longer Coherence Length
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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, which also masks vibrations with sub-micron amplitudes as additive noise, and existing methods fail to correct phase variance across a wide band of frequencies.
Innovation Solution
Implementing source phase correction near the laser source and target phase correction in the reflected signal to reduce phase wandering, thereby increasing coherence length and effective range, using components like optical phase detectors, phase correction estimators, and phase modulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a laser source is tuned across frequencies, then the bandwidth of the lidar system is improved, but the coherence length is reduced
Solution Approach 1:
The patent applies preliminary action by measuring the phase variance of the laser source beforehand and using this measurement to pre-calculate correction factors that are then applied to compensate for phase wandering. This allows the system to maintain coherence length while tuning across frequency bands.
Solution Approach 2:
The patent implements feedback by continuously monitoring the phase variance of the laser source and using this feedback information to adjust and correct the phase errors in real-time, thereby maintaining coherence length during frequency tuning operations.
2Measurement precision
If phase variance is not corrected, then the system complexity is reduced, but the coherence length and measurement precision are reduced
Solution Approach 1:
The patent applies self-service by having the lidar system measure its own laser source's phase variance and automatically correct it using the measured data, eliminating the need for external calibration equipment or complex additional correction hardware.
Solution Approach 2:
The patent replaces complex mechanical phase stabilization systems with a computational approach that uses measured phase variance data to calculate and apply correction factors, substituting physical complexity with mathematical processing.
3Adaptability or versatility
If conventional phase correction methods are used, then the coherence length is improved at a single frequency, but the correction does not work across a wide band of frequencies
Solution Approach 1:
The patent applies parameter changes by measuring phase variance across multiple frequency points and using this data to determine how phase correction parameters vary with frequency, allowing the system to maintain accurate correction across a wide frequency band rather than at a single frequency.
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 coherence length and effective range of lidar systems are significantly enhanced, enabling accurate measurement of vibrations across a broad frequency band, with phase corrected laser outputs improving system sensitivity and noise reduction.
Implementation Method 1
an optical phase detector to detect a phase of the laser output
Implementation Method 2
a phase modulator to modulate the laser output with a phase correction
Data Source
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.