FMCW LiDAR LO Signal Offset for Descan Compensation
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Solution Overview
Problem
The increased scan speed in FMCW LiDAR systems causes spatial misalignment of the target signal with respect to the LO signal at the detector, degrading the spatial mixing efficiency and reducing the signal-to-noise ratio due to descan effects.
Innovation Solution
Implementing descan compensation through vertical displacement of an imaging lens or tilting the LO surface to shift both the LO and target return signals at the detection plane, optimizing their overlap and enhancing coherent mixing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the scan speed of the scanner is increased to increase the frame rate, then the frame rate is improved, but the spatial misalignment between the target signal and LO signal increases, degrading the signal-to-noise ratio
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-positioning the LO signal at a location offset from the optical axis before the scanning occurs. This offset is determined based on the scan speed and scanner characteristics, so that when the scanner operates at high speed, the LO signal is already positioned to compensate for the expected descan effect, maintaining optimal overlap with the target return signal throughout the scan.
Solution Approach 2:
The patent changes the spatial parameter of the LO signal by deliberately offsetting it from the optical axis by a specific distance. This parameter change is calculated based on the scan speed and scanner characteristics, transforming the LO signal position from a fixed central location to a dynamically adjusted offset position that compensates for descan effects at high scan speeds.
2Productivity
If the scan speed is increased to improve frame rate, then the productivity is improved, but the spatial misalignment causes degradation of mixing efficiency
Solution Approach 1:
The system performs preliminary positioning of the LO signal at an offset location before scanning begins. This pre-positioning action ensures that when the scanner operates at high speeds causing descan effects, the LO signal is already located to maintain optimal spatial overlap with the target return signal, thereby preserving mixing efficiency without requiring complex real-time adjustments.
Solution Approach 2:
The patent modifies the spatial parameter of the LO signal by offsetting it from the optical axis by a calculated distance. This parameter change is specifically designed to counteract the descan effect, transforming the mixing efficiency from degraded to optimized at high scan speeds by adjusting the LO signal's position relative to the scanning target.
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
Increases the signal-to-noise ratio and improves the performance of the LiDAR system by maximizing the overlap between the LO and target return signals, particularly in fast-scanning systems.
Implementation Method 1
The photodetector (PD) is configured to mix the target return signal with the LO signal to extract range and velocity information of the target
Implementation Method 2
an optical window aligned with the first optical lens to reflect a first portion of the optical beam to generate a local oscillator (LO) signal
Data Source
AI summary
A LiDAR system includes an optical source to emit an optical beam toward a target, a partially reflective surface to generate a local oscillator (LO) signal from the optical beam, and an optical lens disposed in front of a photodetector (PD), wherein the LO signal is incident at a decenter of the optical lens to shift the LO signal at the photodetector with respect to a return signal received from the target.