Frequency-Modulated Continuous-Wave Lidar Beat Frequency Minimization
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Solution Overview
Problem
Existing frequency-modulated continuous-wave lidar systems face challenges in achieving high-resolution distance imaging at video rates due to the complexity of detection electronics and noise issues associated with increasing bandwidth, leading to a decrease in signal-to-noise ratio and erroneous measurements.
Innovation Solution
A continuous-wave lidar system with a laser source generating laser radiation over multiple frequency ranges, each with varying durations and widths, and a frequency shifter to minimize the beat frequency, allowing for distance information to be determined from the values of these ranges when the beat frequency is zero or minimized, reducing the complexity of detection electronics and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bandwidth of detection circuits is increased to measure higher beat frequencies for extended distance ranges, then the measurement range is improved, but the noise increases and signal-to-noise ratio decreases
Solution Approach 1:
The detection process is segmented into multiple frequency bands. The detection circuit processes beat frequencies within a limited bandwidth by dividing the overall frequency range into segments, each handled by appropriate circuitry. This allows extended measurement range while maintaining acceptable signal-to-noise ratio in each segment.
Solution Approach 2:
The patent introduces a temporal dimension to the detection process by using multiple detection circuits operating at different frequency bands simultaneously. This multi-dimensional approach allows the system to cover extended distance ranges without requiring a single high-bandwidth circuit that would suffer from noise.
2Adaptability or versatility
If the bandwidth of detection circuits is increased to accommodate higher beat frequencies, then the maximum measurable distance is improved, but the complexity of detection electronics increases
Solution Approach 1:
The detection electronics are segmented into multiple independent circuits, each designed to handle a specific frequency band. This modular segmentation allows the system to achieve extended measurement range without requiring any single circuit to be overly complex, as each circuit operates within a manageable bandwidth.
Solution Approach 2:
Multiple detection circuits are employed that can collectively handle a wide frequency range. Each circuit is optimized for its specific band but together they provide universal coverage for extended distances, avoiding the need for a single complex universal circuit.
3Productivity
If high bandwidth detection circuits are used to achieve video-rate imaging, then the imaging speed is improved, but the noise and erroneous measurements increase
Solution Approach 1:
The detection process is segmented across multiple frequency bands with dedicated circuits for each band. This allows parallel processing of different frequency components, achieving video-rate imaging speeds while each individual circuit operates within a noise-acceptable bandwidth, maintaining measurement accuracy.
Solution Approach 2:
The system employs feedback mechanisms where the detected signals from multiple frequency bands are processed and combined. This feedback approach allows the system to maintain high imaging speed while correcting for noise and measurement errors through coherent integration of results from multiple bands.
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 simplifies the detection electronics, enhances the signal-to-noise ratio, and enables high-resolution distance imaging at video rates by determining distance information from the specific frequency ranges, thereby overcoming the limitations of existing systems.
Implementation Method 1
the backscattered light wave and a portion of the emitted wave that was not transmitted to the scene, called the 'local oscillator', are mixed. The interference of these two waves is detected by the photodetector
Implementation Method 2
a detecting device Det0 comprising at least one pixel P comprising a photodetector component PD
Implementation Method 3
The Doppler frequency shift of the backscattered wave is dependent on the radial velocity of the point that backscattered the wave
Data Source
AI summary
A continuous-wave lidar system includes a laser source configured to generate laser radiation (L) with a laser optical frequency fopt-I varying linearly over a plurality of N successive frequency ranges indexed i, a first optical device configured to spatially separate the laser radiation (L), a detecting device, a second optical device configured to simultaneously deliver, to the pixel, a recombined beam, a frequency shifter placed on the path of the reference beam and configured to shift the laser optical frequency by a shift frequency comprised in the interval [fRmax, fRmin], a processing unit, the continuous-wave lidar imaging system further being configured to determine distance information from a signal detected by the pixel.