Multispectral LiDAR Spectral Delay Unit for Single-Detector Ranging
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Solution Overview
Problem
Multispectral LiDAR systems face challenges in discriminating spectral information while maintaining sensitivity and cost efficiency, as existing methods either reduce spectral information through filtering or require complex and costly detector arrays.
Innovation Solution
A multispectral LiDAR device that transforms a broadband laser beam pulse into a pulse-train using a spectral delay unit, such as a superstructured Fiber Bragg Grating, allowing spectral discrimination with a single detector and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If spectral filtering is used to identify wavelengths, then a single detector can be used, but spectral information is reduced by the number of wavelength channels
Solution Approach 1:
The broadband laser pulse is segmented into multiple wavelength components using a dispersive element, with each wavelength component delayed by a different time period. This temporal segmentation allows a single detector to distinguish between different wavelengths by detecting the time of arrival of each pulse component, thereby preserving spectral information while using only one detector.
Solution Approach 2:
The patent transforms spectral information from the frequency domain to the time domain by introducing wavelength-dependent time delays. Instead of separating wavelengths spatially (which would require multiple detectors), the invention uses the time dimension to encode spectral information, allowing a single detector to capture all spectral data sequentially over time.
2Loss of information
If a dispersive element and detector array are used, then spectral information is preserved, but sensitivity is reduced and cost increases
Solution Approach 1:
The detection function is segmented temporally rather than spatially. Each wavelength component is assigned a unique time slot through differential delays, allowing a single high-sensitivity detector to process all spectral information sequentially without the sensitivity loss associated with dividing light across multiple detector elements.
Solution Approach 2:
A single detector is made universal by using time-multiplexed detection. The detector processes all wavelength channels sequentially at different time periods, eliminating the need for multiple specialized detectors and thereby maintaining maximum detection sensitivity while preserving full spectral information.
3Measurement precision
If single pulse measurement is used, then distance can be determined, but high signal to noise ratio is required
Solution Approach 1:
The broadband laser pulse is converted into a periodic train of sub-pulses, each corresponding to a different wavelength component with a unique time delay. By detecting the time of flight of multiple periodic pulse components rather than a single pulse, the system achieves more reliable distance measurement with improved signal-to-noise ratio through temporal averaging and pattern recognition.
Solution Approach 2:
The system uses the temporal pattern of returned pulse components as feedback to verify distance measurements. By analyzing the consistent time delays and relative intensities of multiple wavelength components across successive pulses, the system can distinguish true signals from noise, thereby reducing the minimum signal-to-noise ratio requirement for accurate distance determination.
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
Enables accurate distance measurement with improved robustness and reduced complexity by using a single detector, enhancing spectral classification and reducing costs compared to array detectors.
Implementation Method 1
a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb
Implementation Method 2
an optical detector configured to detect a time-of-flight and an optical power of at least part of the reflection of the broadband laser beam pulse
Data Source
AI summary
A multispectral laser detection and ranging device including a spectral delay unit configured for delaying the broadband laser beam pulse depending on the wavelength, to give a wavelength comb selected in the spectral range, such that the broadband laser beam pulse is transformed into a pulse-train wherein each pulse in the train is at a different wavelength of the wavelength comb.