FMCW LIDAR Frequency Shifting for Low-Speed Imaging
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Solution Overview
Problem
Current FMCW LIDAR systems require high-speed detector arrays for full-field imaging, which are expensive and impractical, due to the need for mechanical scanning and high-speed data processing, limiting their speed and accessibility.
Innovation Solution
A detection approach that modifies the frequencies of signals to enable the use of low-cost, low-speed photodetector arrays like CCD or CMOS cameras by modulating the optical frequency of one arm in the interferometer, allowing for parallel measurement of FMCW LIDAR signals across an array of pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed detector arrays are used for full-field FMCW LIDAR imaging, then imaging speed and resolution are improved, but system cost and complexity increase significantly
Solution Approach 1:
The patent introduces an optical frequency shifter as an intermediary device that shifts the frequency of the local oscillator beam. This frequency shifting enables the use of low-speed photodetector arrays by creating a frequency difference that allows standard cameras to capture the beat signal, thereby eliminating the need for expensive high-speed detector arrays while maintaining full-field imaging capability
Solution Approach 2:
The patent changes the frequency parameter of the local oscillator beam using an optical frequency shifter. By adjusting this frequency parameter, the system creates a beat frequency that can be detected by low-speed photodetectors, transforming the detection requirement from high-speed to low-speed while preserving the ability to perform full-field FMCW LIDAR imaging
2Measurement precision
If mechanical scanning is used to translate one-pixel measurement laterally, then 3-D imaging is achieved, but acquisition speed is severely limited
Solution Approach 1:
The patent segments the imaging task by using a detector array where each pixel independently measures the beat signal for its specific lateral position. This segmentation eliminates the need for mechanical scanning across pixels, as all pixels simultaneously capture information from different lateral positions, thereby achieving full-field 3-D imaging at high speed without mechanical movement
Solution Approach 2:
The patent transitions from a one-dimensional scanning approach (moving a single pixel across the target) to a two-dimensional parallel measurement approach (using an array of pixels to simultaneously measure different lateral positions). This dimensional change enables full-field imaging by capturing multiple lateral positions at once, dramatically increasing acquisition speed while maintaining 3-D imaging capability
3Measurement precision
If each detector measures beat signal in MHz regime, then axial resolution is maintained, but data processing requirements become impractical
Solution Approach 1:
The optical frequency shifter acts as an intermediary that creates a frequency offset between the local oscillator and the reflected beam. This frequency offset enables the beat signal to be shifted to a lower frequency range that can be processed by standard electronics, reducing the data processing rate requirement from impractical THz levels to manageable levels while preserving axial resolution through the FMCW measurement principle
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 fast, real-time, full-field three-dimensional imaging without the need for mechanical scanning or high-speed detectors, making the system robust, inexpensive, and capable of imaging moving targets with low-speed photodetectors.
Implementation Method 1
The optical frequency of a single mode laser is varied linearly with time, with a slope ξ
Implementation Method 2
The output of the laser impinges on a target and the reflected signal is mixed with a part of the laser output in a photodetector (PD)
Implementation Method 3
The reflected target beam is combined with the reference beam and received as input to a photodetector (PD)
Data Source
AI summary
A detection apparatus and method for FMCW LIDAR employ signals whose frequencies are modified so that low-cost and low-speed photodetector arrays, such as CCD or CMOS cameras, can be employed for range detection. The LIDAR is designed to measure the range z to a target and includes a single mode swept frequency laser (SFL), whose optical frequency is varied with time, as a result of which, a target beam which is reflected back by the target is shifted in frequency from a reference beam by an amount that is proportional to the relative range z to the target. The reflected target beam is combined with the reference beam and detected by the photodetector array. By first modulating at least one of the target and reference beams such that the difference between the frequencies of the reflected target beam and the reference beam is reduced to a level that is within the bandwidth of the photodetector array, the need for high-speed detector arrays for full-field imaging is obviated.