Coherent Mechanical LiDAR ADC Switching for Scanner Angle Lag
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Solution Overview
Problem
Mechanical LiDAR systems face challenges in accurately detecting returning light due to scanner-induced angle offset, which affects the precision of range measurement and image definition, especially when multiple pulses are in flight, leading to increased noise and reduced signal strength.
Innovation Solution
The implementation of a photonic integrated circuit (PIC) chip with spatially separate detection channels and advanced signal processing techniques, such as optical mixers and analog-to-digital converters, to compensate for angle lag and improve signal processing efficiency, allowing for precise alignment and efficient detection of overlapping light pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple light pulses are transmitted at different angles to increase accuracy by triangulation calculations, then measurement precision is improved, but scanner-induced angle offset increases leading to noise and reduced signal strength
Solution Approach 1:
The patent replaces mechanical alignment methods with optical phase modulation and electronic signal processing. The PIC chip modulates the phase of transmitted light pulses and processes the phase of received light to calculate range, eliminating the need for mechanical alignment between transmitter and detector elements despite scanner-induced angle offsets.
Solution Approach 2:
The patent changes the parameter of light modulation from intensity-based to phase-based encoding. By modulating the phase of light pulses and measuring phase differences upon return, the system can accurately determine range even when the scanner introduces angle offsets that would otherwise cause misalignment.
2Area of stationary object
If the laser light beam is moved rapidly back and forth to scan a wide field of view, then field of view coverage is improved, but alignment precision between transmitter and detector deteriorates due to mechanical movement
Solution Approach 1:
The patent eliminates mechanical alignment between transmitter and detector by using phase modulation and electronic processing. The PIC chip modulates the phase of transmitted light and measures the phase of returned light, allowing accurate range measurement without precise mechanical alignment even during rapid scanning movements.
Solution Approach 2:
The PIC chip performs multiple functions: it modulates the phase of transmitted light pulses, receives and detects the phase of returned light, and processes signals to calculate range. This multi-functionality allows the system to maintain measurement accuracy while the mechanical scanner covers a wide field of view.
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 enhances the accuracy of range measurement and image definition by reducing noise and increasing signal strength, enabling higher resolution and longer detection ranges while maintaining cost and power efficiency.
Implementation Method 1
a photodetector to convert the received light into electrical signals
Implementation Method 2
optical mixers and analog-to-digital converters, to compensate for angle lag and improve signal processing efficiency
Data Source
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AI summary
A LiDAR system (400) includes a light source (410) to generate light pulses, a mechanical scanner (402), a detector (414) including an array of discrete detector channels to convert light input into electrical signals, a lens (412) that focuses both light pulses generated at the light source onto the mechanical scanner and returning light (432) reflected from the mechanical scanner for reception in sequence by the detector channels, a first analog to digital converter, ADC (454), connected to each of the detector channels in the array and to convert the electrical signals from the detector channels into digital data signals, and a signal processor (456) coupled to the ADC to receive the digital data signals therefrom and to generate images of targets in a field of view of the LiDAR system from the digital data signals. The LiDAR system counteracts the effect of angle offset on detection induced by the rotating scanning mirror. Moreover, the lens transforms the reflection angle offset into a positional offset on the detector face. This positional offset becomes larger as the range to a target increases and cannot be tolerated. A fast-scanning mechanical LiDAR system may use a switch architecture to reduce the required number of ADC channels while overcoming angle lag. For example, if two laser pulses are emitted such that returning light may overlap on the detector due to the angle lag, two pairs of ADC channels may be used to detect returning light on two pairs of adjacent receive channels simultaneously.