Coherent LiDAR Reference Channel for Doppler Shift Suppression
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Solution Overview
Problem
Existing LIDAR systems face challenges in managing the Doppler frequency shift induced by the movement of objects relative to the device, which complicates signal processing and increases system complexity, size, and cost, especially in multi-channel architectures.
Innovation Solution
A LIDAR system that utilizes a reference channel and imaging channels with optical IQ receivers and local oscillators to measure and cancel or reduce Doppler frequency shift through mathematical signal mixing in the time domain, allowing for simplified electronics and reduced data throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection is used in LIDAR systems, then optical gain and single-photon sensitivity are improved, but Doppler frequency shift complicates signal processing and increases system complexity
Solution Approach 1:
The patent introduces a reference channel as an intermediary element that does not directly process the Doppler-shifted imaging signals. Instead, it generates a reference signal that is mathematically combined with the imaging channel signals to cancel Doppler effects. This intermediary approach allows the system to maintain coherent detection capabilities while simplifying the processing of Doppler-shifted signals through reference signal subtraction.
2Adaptability or versatility
If Doppler frequency shift is present in multi-channel LIDAR systems, then the bandwidth of detected signals expands significantly, but this increases the cost, size and complexity of the final system
Solution Approach 1:
The patent implements a universal reference channel that serves all imaging channels simultaneously. Instead of requiring separate Doppler compensation circuits for each channel, a single reference channel generates a reference signal that can be mathematically combined with signals from multiple imaging channels. This multi-functional reference approach enables Doppler suppression across all channels without proportionally increasing system complexity or size.
3Reliability
If Doppler frequency shift is not suppressed, then the frequency shift variable and unknown expands the bandwidth of detected signals, but managing this requires complex electronics readout circuitry
Solution Approach 1:
The patent employs a feedback mechanism where the reference channel continuously monitors and generates a reference signal that is mathematically combined with the imaging channel signals. This feedback loop allows the system to adapt to varying Doppler shifts in real-time by adjusting the reference signal to match the current Doppler conditions, thereby suppressing frequency shifts without requiring complex fixed-frequency electronics.
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 system effectively suppresses or eliminates Doppler frequency shift, reducing system complexity, cost, and enabling scalable multi-channel implementations by moving frequency information to baseband, thus simplifying signal processing and reducing hardware requirements.
Implementation Method 1
Some LIDAR's make use of what is known as coherent detection. In this detection scheme, the light reflected on the sample is mixed with a local oscillator that is coherent with the reflected light.
Implementation Method 2
The local oscillator light is mixed with the reflected light in an optical IQ receiver to produce an interference signal.
Implementation Method 3
A common problem that appears when making use of this type of LIDARs is the frequency shift induced by the movement of the objects in the scene relative to the device, an effect known as Doppler frequency shift.
Data Source
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Figure 1B
AI summary
A LIDAR system which reduces or suppress the frequency shift induced by the movement of objects in a scene relative to the LIDAR, and which comprises a light source, an input aperture (101), a splitter (2) configured to split a reflected light into a reference channel (4) and a first imaging channel (3), a first imaging optical IQ receiver (5) configured to obtain a first interference signal, a reference optical IQ receiver (6) configured to obtain a reference interference signal, an imaging oscillator (111), configured to be temporarily coherent with the reflected light, at least a mixer (12), connected to the first imaging optical IQ (5) and to the reference optical IQ (6) and configured to obtain a first intermodulation product with a higher frequency and an intermodulation product of interest with its Doppler Shift scaled.