Lidar Phase Correction Systems for Coherence Length
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Solution Overview
Problem
Conventional frequency modulated, continuous wave lidar systems face reduced coherence length and effective range due to phase wandering in tunable laser sources, which also hinder the detection of sub-micron vibrations as additive noise across a broad band of frequencies.
Innovation Solution
The implementation of source phase correction and target phase correction systems to compensate for phase variance in lidar systems, using optical phase detectors and phase correction estimators to reduce phase wandering and increase coherence length, thereby enhancing the effective range and sensitivity of lidar systems.
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 employs feedback mechanisms where phase detectors continuously monitor the phase of the laser output and feed this information back to phase correction devices (such as phase modulators or acoustic wave devices). This closed-loop feedback system dynamically compensates for phase variations introduced by frequency tuning, thereby maintaining long coherence length while enabling fast tuning speeds.
Solution Approach 2:
The patent utilizes parameter changes in the laser system by dynamically adjusting operational parameters (such as current, temperature, or modulation depth) to achieve frequency modulation. By carefully controlling these parameters and compensating for their side effects on phase, the system maintains long coherence length while achieving the desired tuning speed and frequency modulation capability.
2Reliability
If conventional phase correction methods are used, then phase variance is compensated at limited frequencies, but the correction cannot be applied across a wide band of frequencies
Solution Approach 1:
The patent implements dynamic phase correction systems that can adapt to a wide frequency band. The phase correction devices (such as broadband phase modulators or acousto-optic devices) are designed to operate dynamically across the entire frequency range of interest, allowing phase variance compensation to be applied universally across all frequency components of the modulated laser signal, not just at specific discrete frequencies.
Solution Approach 2:
The patent employs universal phase correction mechanisms that function across the entire frequency spectrum of the lidar system. The phase correction system is designed to handle multiple frequency components simultaneously, making it versatile and applicable to the full bandwidth of frequency-modulated signals, thereby enabling accurate phase compensation regardless of the specific frequency being transmitted.
3Measurement precision
If sampling rates are increased to detect sub-micron vibrations, then measurement precision is improved, but system complexity and cost increase
Solution Approach 1:
The patent replaces mechanical or electronic sampling-based vibration detection with optical phase measurement techniques. By using optical interferometry and phase detection methods, the system can measure sub-micron vibrations directly from the optical signal without requiring high-speed electronic sampling. This substitution of the detection mechanism achieves high measurement precision while avoiding the complexity and cost associated with ultra-high-speed sampling electronics.
Solution Approach 2:
The patent exploits the asymmetry between the optical carrier frequency (which is extremely high) and the vibration frequencies (which are relatively low). By using heterodyne or homodyne detection schemes that down-convert the optical signal to baseband or intermediate frequencies, the system can extract vibration information at low frequencies where simple, low-cost electronics suffice, thereby achieving high measurement precision without requiring high sampling rates.
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 phase correction systems effectively increase the coherence length of lidar systems by a factor of at least two, improving the ability to measure vibrations and extending the effective range, while reducing noise and enhancing sensitivity across a wide band of frequencies.
Implementation Method 1
an optical phase detector to detect a phase difference between the output of the laser source and a delayed output of the laser source
Implementation Method 2
a phase correction estimator to process the phase difference and determine an estimate of a phase correction to be applied to the output of the laser source
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.