FMCW LiDAR Coherence Extension via Asymmetric Feedback
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Solution Overview
Problem
FMCW LiDAR systems face challenges in achieving desired speed, measurement range, resolution, precision, and accuracy due to limitations in laser coherence length and signal-to-noise ratio, particularly at longer ranges.
Innovation Solution
The implementation of high-closed-loop bandwidth active feedback to control laser frequency chirps, utilizing an asymmetric sideband generator and photonic integrated circuit elements within an active feedback loop, increases the laser coherence length beyond its free-running value, enabling improved distance measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If free-running laser source is used without feedback control, then device complexity is reduced, but coherence length is insufficient for long-range measurements
Solution Approach 1:
The patent implements a feedback loop that uses an asymmetric sideband generator to create optical paths with different lengths, generates interference signals from these paths, and uses the interference signal to control the laser frequency via an actuator. This feedback mechanism extends the coherence length beyond the free-running limit while managing system complexity through integrated photonic circuits.
2Measurement precision
If traditional LiDAR systems are used, then manufacturing cost is lower, but measurement precision and range resolution are insufficient
Solution Approach 1:
The patent replaces traditional mechanical frequency modulation methods with photonic integrated circuit elements and optical feedback mechanisms. The asymmetric sideband generator and photonic integrated circuits enable precise frequency control and coherence extension without complex mechanical assemblies, improving measurement precision while simplifying manufacturing.
3Measurement precision
If laser frequency chirp is applied to improve range resolution, then measurement precision improves, but coherence length decreases due to Schawlow-Townes linewidth limit
Solution Approach 1:
The patent changes the frequency parameter of the laser beam by applying controlled chirp through the feedback loop. The asymmetric sideband generator creates optical paths with different transit times, and the interference signal generated from these paths is used to modulate the laser frequency. This parameter change enables range resolution improvement while the feedback mechanism maintains coherence length beyond the Schawlow-Townes limit.
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 approach enhances the coherence length of FMCW LiDAR systems, leading to increased precision and range resolution, even beyond the Schawlow-Townes linewidth limit, and reduces the complexity and cost of the system by using a shared reference interferometer and photonic integrated circuits.
Implementation Method 1
The feedback loop may have a closed-loop bandwidth selected to cause the laser beam to have an actual coherence length longer than the free-running coherence length... the feedback loop includes splitting the laser beam into at least two optical paths and generating an interference signal based on the at least two optical paths
Data Source
AI summary
Methods and apparatuses are described for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR). Examples are provided where high-closed-loop bandwidth, active feedback applied to laser frequency chirps may provide increases in the free-running laser coherence length for long-range FMCW distance measurements. Examples are provided that use an asymmetric sideband generator within an active feedback loop for higher closed-loop bandwidth. Examples of using a single shared reference interferometer within multiple active feedback loops that may be used for increasing the coherence length of multiple chirped lasers are described. Example calibrators are also described.