LiDAR Optical Delay Lines for Long-Range Coherence
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Solution Overview
Problem
Coherent Light Detection and Ranging (LiDAR) systems face signal degradation and loss at long distances due to decoherence, limiting their maximum range and requiring narrow laser linewidths, which are costly and restrictive.
Innovation Solution
Incorporating optical delay lines in the LiDAR system to introduce a predetermined time delay in the local oscillator signal, balancing the coherence between the local oscillator and scattered light, thereby extending the maximum range and reducing decoherence effects without the need for expensive laser linewidth reduction techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection is used in LiDAR systems, then measurement precision is improved, but the detectable range is limited due to signal loss beyond half the coherence length
Solution Approach 1:
The patent applies preliminary action by introducing a predetermined time delay to the local oscillator signal through optical delay lines before detection. This pre-synchronization ensures that the local oscillator signal arrives at the detector at the same time as the scattered light from distant targets, maintaining coherence and enabling detection beyond the conventional coherence length limit.
2Reliability
If narrow laser linewidths are used to maintain coherence at long distances, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the temporal parameter of the local oscillator signal by introducing a predetermined time delay through optical delay lines. This parameter change allows the system to maintain coherence with scattered light from distant targets without requiring narrow laser linewidths, thereby reducing device complexity and cost while improving reliability for long-range detection.
3Length of stationary object
If the local oscillator signal is delayed to match distant target return time, then detectable range is extended, but signal-to-noise ratio deteriorates due to decoherence
Solution Approach 1:
The patent applies preliminary action by pre-delivering the local oscillator signal through optical delay lines with a predetermined time delay that matches the round-trip time for distant targets. This ensures the local oscillator signal is synchronized with the scattered light when they arrive at the detector, maintaining coherence and preventing signal-to-noise ratio deterioration even at extended ranges.
Solution Approach 2:
The system uses feedback by measuring the coherence between the delayed local oscillator signal and the scattered light at the detector. This feedback mechanism allows the system to optimize the predetermined time delay parameter to maintain maximum signal-to-noise ratio across varying target distances, ensuring reliable detection at extended ranges.
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
The optical delay lines enhance the signal-to-noise ratio, allowing LiDAR systems to maintain coherence at longer distances, increasing the detectable range while maintaining signal quality above the noise floor, even with affordable lasers.
Implementation Method 1
routing the second laser signal through an optical delay line of the light detection and ranging system, wherein the optical delay line adds a predetermined time delay to the second laser signal
Implementation Method 2
In some cases, the sensor uses coherent detection, where a portion of the energy from the laser is separated and made to interfere optically with the energy reflected by the target
Data Source
AI summary
The technology disclosed herein includes a system having a light source configured to generate a laser signal, an optical signal splitter circuit configured to split the laser signal into a first laser signal for transmission to a plurality of targets and a second laser signal, an optical signal scanner configured to transmit the first laser signal to the plurality of targets, two or more optical delay lines configured to receive the second laser signal, wherein each of the two or more optical delay lines adds a predetermined time delay to the second laser signal to generate a delayed second laser signal, and a detector configured to receive a reflected laser signal from the plurality of targets, wherein the reflected laser signal includes a reflection of the first laser signal from the plurality of targets, and the delayed second laser signal.