Scanning LiDAR Spatial Filtering for Ambient Light Reduction
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Solution Overview
Problem
LiDAR detection systems face challenges in simultaneously detecting both bright objects at close range and low-reflectivity objects at long range due to interference from ambient light, which affects the system's dynamic range and signal-to-noise ratio.
Innovation Solution
The implementation of a scanning LiDAR system with spatial filtering, using a mask with slits aligned with the scan pattern and positioned in the focal plane of the receiver lens, reduces ambient light and enhances the signal-to-noise ratio by blocking excess light at close range while allowing sufficient light to reach the detector at long range, utilizing high-sensitivity detectors like avalanche photodiodes or silicon photomultipliers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the receiver aperture is increased to detect low-reflectivity objects at long range, then the detection capability for low-reflectivity objects is improved, but the ambient light interference increases
Solution Approach 1:
The receiver aperture is segmented into multiple independently controllable regions or pixels, allowing selective gating of light from different spatial locations and time intervals. This enables the system to capture weak return signals from long-range objects while blocking ambient light through temporal and spatial discrimination.
Solution Approach 2:
The system employs periodic pulsed laser transmission with corresponding periodic gating of the receiver aperture. The receiver aperture is opened only during specific time windows when the laser return signal is expected, and closed during other periods to block ambient light, creating a time-division multiplexed detection scheme.
2Object-affected harmful factors
If the receiver aperture is reduced to block ambient light, then the ambient light interference is reduced, but the detection capability for low-reflectivity objects deteriorates
Solution Approach 1:
The receiver aperture is made dynamically controllable through electronic gating mechanisms that can rapidly open and close the aperture in synchronization with the pulsed laser transmission. This dynamic control allows the aperture to be large when needed for signal collection and effectively closed when ambient light would interfere, adapting to the temporal structure of the lidar operation.
3Measurement precision
If the integration time is increased to improve signal-to-noise ratio, then the signal-to-noise ratio is improved, but the temporal resolution and range resolution deteriorate
Solution Approach 1:
The system uses periodic pulsed transmission with integration times matched to the pulse duration and round-trip flight time. By synchronizing the receiver gating to the periodic pulse structure, the system accumulates signal energy during the pulse return window while rejecting out-of-time signals, achieving high signal-to-noise ratio without sacrificing temporal or range resolution.
Solution Approach 2:
The receiver aperture gating is pre-synchronized with the expected arrival time of the laser return signal based on the known pulse transmission time and target range. This preliminary timing arrangement ensures that the aperture is open precisely when the signal arrives, maximizing signal capture while minimizing integration of ambient light noise.
4Measurement precision
If the receiver aperture is increased to detect bright objects at close range, then the detection capability for bright objects is improved, but the dynamic range is exceeded
Solution Approach 1:
The receiver aperture is divided into multiple spatial segments or pixels that can be independently gated. For close-range bright objects, only the specific spatial segment corresponding to the object's direction is opened, while other segments remain closed. This spatial segmentation allows the system to detect bright objects without saturation while maintaining the ability to detect faint objects in other directions.
Solution Approach 2:
The aperture gating timing and duration are dynamically adjusted based on the range and brightness of detected objects. For close-range objects, the gating window is shortened and the aperture may be partially closed to prevent saturation. For long-range objects, the gating window is extended and the aperture is fully opened to maximize signal collection, thereby adapting the dynamic range to match the detection requirements.
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 configuration effectively reduces ambient light by a factor of 5 to 500, increasing the dynamic range and signal-to-noise ratio, enabling the detection of both bright and low-reflectivity objects with the same system configuration, even in daytime conditions.
Implementation Method 1
The implementation of a scanning LiDAR system with spatial filtering, using a mask with slits aligned with the scan pattern and positioned in the focal plane of the receiver lens, reduces ambient light by blocking excess light
Implementation Method 2
a laser fixed to a first surface of the substrate, the laser generating output light for transmission along a transmission axis into a region
Implementation Method 3
An optical detection element is fixed to a second surface of the substrate opposite the first surface, the optical detection element receiving input light reflected from the region and converts the reflected light to electrical signals
Data Source
AI summary
According to one aspect, an optical transceiver includes a substrate and a laser fixed to a first surface of the substrate, the laser generating output light for transmission along a transmission axis into a region. An optical detection element is fixed to a second surface of the substrate opposite the first surface, the optical detection element receiving input light reflected from the region along a reception axis through an opening in the substrate between the first and second surfaces of the substrate, the transmission axis and the reception axis being substantially parallel.