LIDAR Calibration Using an Optical Fiber Reference Path
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Solution Overview
Problem
Existing LIDAR systems face challenges in accurate distance calibration due to the narcissus signal, which causes detector saturation and inhibits detection of radiation from targets at short distances, and traditional calibration methods are tedious and require external targets, making frequent recalibration difficult.
Innovation Solution
A method involving a reference optical path using optical fiber is coupled to the LIDAR system to provide a known propagation distance reference, allowing for precise and frequent calibration by converting the fiber length into a free-space propagation distance, which is incorporated within the system for ease of use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods using external retroreflective targets are used, then distance calibration can be performed, but the process is tedious and cannot be repeated frequently
Solution Approach 1:
The patent integrates the calibration function inside the LIDAR system by nesting a reference mirror and reference optical path within the system housing. This eliminates the need for external targets and makes calibration as simple as activating an internal component, resolving the contradiction between calibration accuracy and operational simplicity.
Solution Approach 2:
The LIDAR system performs calibration on its own using internally provided reference elements. The system directs laser pulses to the reference mirror and measures the return signal to automatically establish distance reference values without requiring external equipment or manual intervention, making the calibration process both simple and repeatable.
2Measurement precision
If narcissus signal is used for distance calibration, then a distance reference can be obtained, but the signal causes detector saturation and cannot provide accurate reference for short distances
Solution Approach 1:
The patent extracts the calibration function from the problematic narcissus signal path by using a dedicated reference mirror and reference optical path. This separates the calibration function from the main detection channel, allowing accurate distance reference measurement without the detector saturation issues that plague narcissus signal-based calibration.
3Reliability
If LIDAR system is designed to detect backscattered radiation from atmospheric particles, then detection sensitivity is very high, but this high sensitivity causes saturation when detecting narcissus signal
Solution Approach 1:
The patent segments the optical paths into distinct channels: a reference optical path for calibration using the reference mirror, and a main detection path for atmospheric particle detection. This segmentation allows the high-sensitivity detector to operate in its optimal range for particle detection while the calibration function uses a separate, controlled path that avoids saturation issues.
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 enables accurate and frequent calibration of LIDAR systems, improving distance measurement precision and allowing simultaneous calibration with useful measurements, especially for anemometric applications.
Implementation Method 1
coupling the LIDAR system to a reference optical path which is formed from at least one optical fiber efficient for guiding radiation emitted by the LIDAR system
Implementation Method 2
A particle speed value is deduced from a spectral analysis of the backscattered portion of the laser beam which is detected by the LIDAR system, then from a Doppler effect calculation which is applied to a frequency difference identified between this backscattered portion of the laser beam and the laser beam as emitted by the LIDAR system
Implementation Method 3
obtain a measurement value which is representative of a time of radiation propagation in the reference optical path
Data Source
AI summary
A method for calibrating a LIDAR system proposes incorporating in the LIDAR system a reference optical path which is formed from an optical fiber. The length of the optical fiber determines a measurement reference value, which can then be used to evaluate distances of targets to be characterized using the LIDAR system. The calibration method is simple and economical to implement. It may be used in particular for a LIDAR system which is designed to perform air speed measurements, in particular on board an aircraft.