Compact FMCW Heterodyne LiDAR Imaging Without Optical Splitters
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Solution Overview
Problem
Existing FMCW heterodyne-detection lidar imager systems are large in size due to the inclusion of optical splitting and recombining devices, which are necessary for forming reference and object signals for heterodyne detection.
Innovation Solution
The system eliminates the need for optical splitting and recombining devices by directing the primary signal directly to the scene and using a reflector to reflect a portion of the backscattered signal, forming a heterodyne signal through interference between two coherent signals backscattered by the scene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical splitting and recombining devices are used to form reference and object signals for heterodyne detection, then the system can determine distance accurately, but the system size becomes large
Solution Approach 1:
The patent extracts and eliminates the optical splitting and recombining devices from the heterodyne detection system. Instead of using separate reference and object signal paths, the invention uses only the backscattered object signal for distance determination, removing the bulky optical splitting/recombining hardware while maintaining measurement capability through direct detection of the backscattered signal's phase and frequency characteristics
Solution Approach 2:
The patent inverts the conventional heterodyne detection approach by not creating a separate reference signal through optical splitting, but instead using the backscattered signal itself as the measurement carrier. The system inverts the signal path by directing the primary signal directly to the scene and using the returned signal for detection, eliminating the need for complex optical recombining hardware
2Reliability
If optical splitting elements are used to divide the primary signal into reference and object signals, then heterodyne detection can be performed, but photometric losses occur
Solution Approach 1:
The patent removes the optical splitting elements that cause photometric losses by extracting only the necessary function of signal separation. The system directly transmits the primary signal to the scene without dividing it into reference and object components, eliminating insertion losses from beam splitters and cube splitters while maintaining detection reliability through direct backscattered signal analysis
Solution Approach 2:
The patent merges the reference signal function into the object signal path by using the same optical channel for both transmission and reception. Instead of maintaining separate reference and object signal paths that each suffer from splitting losses, the system combines both functions into a single direct path, eliminating redundant optical components and their associated photometric losses
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 design reduces the system size while maintaining the ability to determine distance based on the beat frequency of the heterodyne signal, achieving a compact lidar imager system without photometric losses.
Implementation Method 1
an optical source designed to emit a coherent, continuous and frequency-modulated primary signal
Implementation Method 2
frequency-modulated primary signal
Implementation Method 3
an optical collection element designed to collect a portion, called collected signal, of a signal backscattered by the scene
Implementation Method 4
a photodetector intended to receive a heterodyne signal associated with the collected signal
Implementation Method 5
forming a heterodyne signal through interference between two coherent signals backscattered by the scene
Implementation Method 6
comprises a reflector designed to reflect a portion, called uncollected signal, of the backscattered signal, not collected by the optical collection element, in the direction of the scene
Data Source
AI summary
The invention relates to a reduced-size FMCW lidar imager system. The imager system comprises an optical source 10 for a coherent, continuous and frequency-modulated primary signal Sp in order to illuminate the scene 2; an optical collection element 41 configured to collect a backscattered signal Sret,c; a photodetector 50 intended to receive a heterodyne signal Sh associated with the collected signal Sret,c; and a processing unit 60 configured to determine the distance zsc from the scene based on a beat frequency of the heterodyne signal sh. It is configured to fully direct the primary signal Sp to the scene 2. It additionally comprises a reflector 42 configured to reflect a portion Spr,nc, called uncollected signal Sret,nc, of the backscattered signal Sret, not collected by the optical collection element 41, in the direction of the scene 2.