Time-Delayed LO LiDAR Ranging Without Wideband Reception
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Solution Overview
Problem
Existing LiDAR technologies face challenges in achieving accurate distance measurement at high frequencies due to the need for wideband receivers and the difficulty in implementing low-cost devices using Frequency Modulated Continuous Wave (FMCW) methods, especially at terahertz frequencies, and ToF methods struggle with noise suppression.
Innovation Solution
The use of a time delayed local oscillator (LO) light with an arbitrary chirp waveform for LiDAR devices, involving a method to sweep the delay time of LO light and analyze the beating signal to determine distance, combined with delay interleaving for improved accuracy and speed in distance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Time of Flight (ToF) method is used for distance measurement, then the transmitted pulse covers a wide frequency band enabling distance detection, but a wideband receiver is required which makes it difficult to suppress noise
Solution Approach 1:
The patent segments the frequency spectrum by using a narrowband transmitted pulse instead of a wideband pulse. The distance measurement is achieved by comparing the transmitted narrowband pulse with the received echo pulse at the same frequency, eliminating the need for wideband reception and enabling effective noise suppression through narrowband filtering techniques.
Solution Approach 2:
The patent introduces a local oscillator (LO) signal as an intermediary that is identical to the transmitted pulse. The received echo signal is mixed with this LO signal to produce a beat signal, which allows for coherent detection and noise suppression while maintaining distance measurement capability without requiring a wideband receiver.
2Measurement precision
If Frequency Modulated Continuous Wave (FMCW) method is used for distance measurement, then continuous wave transmission enables range detection, but the accuracy depends on the linearity of frequency chirp which makes it difficult to implement at low cost for terahertz frequencies
Solution Approach 1:
The patent replaces the complex, expensive linear frequency chirp generation required in traditional FMCW systems with simple pulse modulation. Instead of requiring precise terahertz frequency chirp control, the system uses straightforward pulse transmission and correlation techniques that can be implemented at lower cost while maintaining measurement accuracy.
Solution Approach 2:
The patent substitutes the mechanical/electronic frequency chirp modulation system with an optical pulse-based system. By using direct pulse transmission and time-domain correlation with a local oscillator, the system eliminates the need for complex frequency modulation hardware at terahertz frequencies, significantly reducing implementation cost and complexity.
3Measurement precision
If delay time of LO light is swept in small intervals to achieve high distance measurement accuracy, then measurement precision improves, but switching speed increases which may reduce productivity
Solution Approach 1:
The patent implements a dynamic delay sweeping strategy where the delay interval is adaptively adjusted. For routine measurements, larger delay intervals are used to maintain high productivity. When higher precision is required, the system dynamically switches to smaller intervals. This dynamic adaptation allows the system to optimize between measurement speed and accuracy based on actual operational needs.
Solution Approach 2:
The patent changes the delay time parameter in a stepwise manner rather than using fixed small intervals. By implementing a coarse-to-fine sweeping approach where larger steps are used initially and smaller steps are applied only when necessary for precision, the system achieves high measurement accuracy without continuously operating at maximum switching speed, thereby maintaining productivity.
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 enables precise distance measurement with enhanced accuracy and reduced switching speed, allowing for effective LiDAR applications in autonomous driving and other fields without the need for complex frequency domain analysis.
Implementation Method 1
a transmitter configured to transmit continuous wave light
Implementation Method 2
a receiver configured to receive light reflected from the object
Implementation Method 3
a delay circuit configured to time-delay the local oscillator light by changing an amount of a time delay
Implementation Method 4
a detection circuit configured to determine a distance to the object based on the time delayed local oscillator light and the received light
Implementation Method 5
obtaining an interfered light by interfering the time delayed LO light with the received light
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
A light detection and ranging (LiDAR) device includes a transmitter configured to transmit a continuous wave light to an object and provide a local oscillator (LO) light corresponding to the transmitted continuous wave light; a delay circuit configured to time delay the LO light; a receiver configured to receive the continuous wave light reflected from an object; and a detection circuit configured to determine a distance from the LiDAR device to the object based on the time delayed LO light and the received continuous wave light.