Polarization Multiplexing in Coherent LiDAR Systems
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Solution Overview
Problem
Conventional LiDAR systems using wavelength multiplexing to measure distance and speed simultaneously face complexity and performance issues due to sensitivity of optical devices to wavelength changes, requiring two optical sources with different wavelengths.
Innovation Solution
The implementation of polarization multiplexing allows for simultaneous measurement of distance and speed using a single optical beam, eliminating wavelength dependence by combining and separating signals using orthogonal linear polarizations, potentially reducing system complexity and cost by using a single optical source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wavelength multiplexing is used to combine and separate up-chirps and down-chirps, then simultaneous distance and speed measurement is enabled, but system complexity increases due to sensitivity of optical devices to wavelength changes
Solution Approach 1:
The patent changes the multiplexing parameter from wavelength to polarization state. Instead of using different wavelengths (up-chirp and down-chirp separated by wavelength), the invention uses orthogonal linear polarizations to multiplex the same wavelength signals, thereby eliminating wavelength sensitivity issues while maintaining simultaneous measurement capability
Solution Approach 2:
The patent introduces a new dimension for signal separation by using polarization state rather than wavelength. By multiplexing up-chirp and down-chirp signals in the polarization domain (orthogonal linear polarizations) rather than the wavelength domain, the system achieves simultaneous distance and speed measurement without the complexity of handling multiple wavelengths
2Productivity
If two optical sources with different wavelengths are used, then simultaneous distance and speed measurement is achieved, but manufacturing precision requirements increase due to wavelength sensitivity of optical components
Solution Approach 1:
The invention changes the distinguishing parameter from wavelength to polarization state. Both optical sources operate at the same wavelength, but are differentiated by orthogonal linear polarizations. This eliminates the need for wavelength-specific optimization of optical components, thereby reducing manufacturing precision requirements
Solution Approach 2:
The patent makes the optical system universal by designing components to handle a single wavelength with high precision, rather than requiring separate optimizations for multiple wavelengths. The polarization multiplexing approach allows the same optical components to be used for both up-chirp and down-chirp signals without wavelength-specific design considerations
3Reliability
If optical devices are designed for specific wavelengths, then performance is optimized for that wavelength, but adaptability to handle multiple wavelengths decreases
Solution Approach 1:
The patent changes the multiplexing approach from wavelength-based to polarization-based. By using orthogonal linear polarizations to distinguish between up-chirp and down-chirp signals at the same wavelength, the system allows optical devices to be optimized for a single wavelength while maintaining the ability to handle both signal types through polarization separation
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 effective optimization of photonics and optics at a single nominal frequency, providing accurate real-time measurements of range, velocity, azimuth, and elevation with reduced polarization crosstalk, suitable for various environments.
Implementation Method 1
the optical beam is frequency modulated to generate an up-chirp and a down-chirp
Implementation Method 2
a multiplexing method is used to separate the two signals, such as wavelength multiplexing... the two frequency modulation signals are polarization multiplexed
Implementation Method 3
both the distance and the relative radial speed of a target affects the mixing frequency between the Local Oscillator (LO) and the return signal
Implementation Method 4
the mixing frequency between the Local Oscillator (LO) and the return signal
Data Source
AI summary
A light detection and ranging (LiDAR) system that includes a first beam splitter to multiplex a first optical beam and a second optical beam into a combined beam having orthogonal linear polarizations. The system also includes lensing optics to emit the combined beam towards a target and collect light returned from the target in a return optical beam to be received by the first beam splitter. The first beam splitter demultiplexes the return optical beam into a first return beam and a second return beam having orthogonal linear polarizations. The system also includes an optical element to generate a first beat frequency from the first return beam and to generate a second beat frequency from the second return beam. The system also includes a signal processing system to determine a range and velocity of the target from the first beat frequency and the second beat frequency.