Lidar Frequency Shifter Resolves Doppler Ambiguity
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Solution Overview
Problem
Lidar systems face ambiguity in measuring object parameters due to object movement and acceleration, which complicates navigation and object detection.
Innovation Solution
A Lidar system incorporating a photonic chip with a frequency shifter to generate a frequency-shifted local oscillator beam, combined with a reflected light beam, and using a processor to remove Doppler ambiguity by comparing measurements from shifted and unshifted local oscillator beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Lidar system measures object parameters using a standard local oscillator beam, then the system structure remains simple, but Doppler ambiguity occurs due to object movement and acceleration
Solution Approach 1:
The local oscillator beam path is segmented into two separate paths: one path includes a frequency shifter to generate a frequency-shifted local oscillator beam, while the other path maintains the original local oscillator beam. This segmentation allows simultaneous measurement using both shifted and unshifted beams, enabling Doppler ambiguity resolution without completely redesigning the system architecture.
Solution Approach 2:
A frequency shifter is introduced as an intermediary component in the local oscillator beam path. This frequency shifter modifies the frequency of the local oscillator beam to create a frequency-shifted version, which serves as a reference for resolving Doppler ambiguity. The frequency shifter acts as a mediator that enables the system to distinguish between target motion and system-induced frequency variations.
2Measurement precision
If a frequency shifter is added to resolve Doppler ambiguity, then measurement accuracy improves, but the device complexity and component count increase
Solution Approach 1:
The frequency-shifted local oscillator beam and the original local oscillator beam are combined through interference with the reflected light beam in a unified detection system. By merging the measurement results from both beams, the system resolves Doppler ambiguity while utilizing a single integrated photodetection pathway, thereby limiting the increase in device complexity.
Solution Approach 2:
The frequency parameter of the local oscillator beam is changed by introducing a frequency shifter. This parameter change creates a frequency-shifted local oscillator beam with a distinct frequency offset, enabling the system to differentiate between Doppler shifts caused by target motion and those caused by system dynamics. The controlled modification of the frequency parameter resolves measurement ambiguity.
3Reliability
If Doppler ambiguity is not resolved, then the system operation remains simple, but navigation and object detection accuracy deteriorates
Solution Approach 1:
The system uses feedback by comparing the interference patterns from the frequency-shifted local oscillator beam and the original local oscillator beam. This comparison provides feedback information that enables the system to distinguish between true Doppler shifts from target motion and frequency variations from system movement or acceleration, thereby improving navigation reliability.
Solution Approach 2:
The frequency shifter pre-modifies the local oscillator beam before it interferes with the reflected light beam. This preliminary frequency shifting action prepares the measurement system to handle Doppler ambiguity by establishing a known frequency reference that accounts for system-induced frequency variations, enabling more reliable navigation and detection.
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
Enables accurate navigation and object detection by resolving Doppler ambiguity, improving the precision of range, azimuth, elevation, and velocity measurements.
Implementation Method 1
shifting a frequency of the associated local oscillator beam via a frequency shifter of the photonic chip to obtain a frequency-shifted local oscillator beam
Implementation Method 2
the transmitted light beam and the associated local oscillator beam from a chirp signal
Implementation Method 3
combining, at a combiner of the photonic chip, a reflected light beam with the frequency-shifted local oscillator beam
Implementation Method 4
obtaining a first measurement of a parameter of the object from the combination of the reflected light beam and the frequency-shifted local oscillator beam at a first set of photodetectors
Data Source
AI summary
A vehicle, Lidar system and method of detecting an object is disclosed. The Lidar system includes a photonic chip having a laser, an on-chip frequency shifter, a combiner and a first set of photodetectors. The laser generates a transmitted light beam and an associated local oscillator beam within the photonic chip. The on-chip frequency shifter shifts a frequency of the local oscillator beam. The combiner combines a reflected light beam with the frequency-shifted local oscillator beam, wherein the reflected light beam is a reflection of the transmitted light beam from the object to generate a first electronic signal at the first set of photodetectors. A processor obtains a first measurement of a parameter of the object from the first electronic signal. The vehicle includes a navigation system for navigating the vehicle with respect to the object using at least the first measurement of the parameter.