FMCW LIDAR Dual Laser Offset Noise Reduction
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Solution Overview
Problem
FMCW LIDAR systems are susceptible to noise caused by a zero DC offset between emitted and reflected laser signals, as well as self-mixing noise due to re-reflection, which affects accuracy and reliability.
Innovation Solution
The system employs two laser sources, where one generates a ranging signal and the other a local oscillator signal with a non-zero frequency offset, using feedback control to maintain this offset, thereby isolating the return laser signal and reducing self-mixing noise by ensuring a physical distance between the signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser source is used to generate both reference and local oscillator signals, then device complexity is reduced, but noise and self-mixing occur due to zero DC offset between signals
Solution Approach 1:
The patent divides the single laser source into two separate laser sources: a first laser for generating the reference signal and a second laser for generating the local oscillator signal. This segmentation eliminates the zero DC offset problem and self-mixing noise while maintaining manageable system complexity through modular architecture.
Solution Approach 2:
The patent introduces a feedback control mechanism as an intermediary between the two laser sources. This feedback control maintains a non-zero frequency offset between the reference and local oscillator signals, preventing DC offset and self-mixing noise while enabling the system to operate reliably.
2Reliability
If a non-zero frequency offset is maintained between ranging and local oscillator signals, then self-mixing noise is reduced, but device complexity increases due to feedback control requirements
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the frequency offset between the reference and local oscillator signals and adjusts the second laser accordingly. This feedback mechanism maintains a stable non-zero offset, eliminating self-mixing noise while keeping the system controlled and manageable.
Solution Approach 2:
The patent changes the frequency parameter of the local oscillator signal relative to the reference signal. By maintaining a non-zero frequency offset through feedback control, the system transforms the signal relationship to eliminate DC offset and self-mixing noise, improving reliability without excessive complexity.
3Reliability
If DC offset is eliminated between laser signals, then noise is reduced, but measurement precision may be affected by signal isolation requirements
Solution Approach 1:
The feedback control acts as an intermediary that preserves the essential measurement functionality while eliminating DC offset. It maintains the frequency offset necessary to prevent noise while ensuring the signals remain properly correlated for accurate distance measurement through the correlation processor.
Solution Approach 2:
The patent changes the frequency parameter relationship between signals to eliminate DC offset while preserving measurement precision. The non-zero frequency offset maintained by feedback control allows the system to distinguish between true distance information and noise, improving both reliability and measurement accuracy simultaneously.
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 significantly reduces noise and self-mixing, enhancing the accuracy of distance measurements by eliminating DC signals and minimizing cross-correlation between the ranging and local oscillator signals.
Implementation Method 1
a receiver photodetector configured to combine the return laser signal and the local oscillator signal
Data Source
AI summary
A frequency-modulated continuous wave (FMCW) LIDAR can be configured to reduce re-reflection and cross-coupling in the FMCW LIDAR. A first laser can be configured to generate a ranging signal, and a second laser can be configured to generate a local oscillator signal. A feedback control can be configured to maintain an offset between the ranging signal and the local oscillator signal. The offset can be a non-zero value. A transmit portion configured to emit a reference laser signal based on the ranging signal into an environment. A receiver portion can be configured to receive a return laser signal from the environment. The return laser signal can be a reflected version of the reference laser signal. A receiver photodetector can be configured to combine the return laser signal and the local oscillator signal.