Coherent LIDAR Pixel Array Imaging Without Rolling Shutter Distortion
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Solution Overview
Problem
Existing coherent LIDAR imaging systems face challenges in achieving high-resolution, real-time imaging of dynamic scenes due to limitations in data processing rates, speckle interference, and the need for complex optical routing, especially when scaling to large pixel arrays.
Innovation Solution
A coherent LIDAR imaging system with an array of pixels that simultaneously images a scene, using an optical splitter/recombiner to coherently superpose reference and object beams on each pixel, with integrated electronic circuits to calculate beat frequencies, and optimized optical configurations to minimize speckle interference and enable simultaneous data processing across all pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sequential scanning FMCW-type LIDAR imaging is used, then the reference path does not suffer significant losses and serves to amplify the signal, but the image obtained is of the rolling shutter type which is disrupted by image distortion when the scene contains moving objects
Solution Approach 1:
The detector is divided into multiple pixels arranged in an array, with each pixel independently detecting light from different spatial locations simultaneously. This segmentation allows parallel processing of multiple spatial points without sequential scanning, eliminating rolling shutter effects while maintaining signal amplification through the reference path at each pixel.
Solution Approach 2:
The system transitions from sequential scanning in time to simultaneous spatial parallelization across multiple pixels. By adding the spatial dimension of pixel array, the system captures multiple points in the scene at the same instant, converting the temporal limitation into a spatial solution that eliminates image distortion from moving objects.
2Reliability
If sequential scanning FMCW-type LIDAR imaging is used, then the reference path does not suffer significant losses and serves to amplify the signal, but it requires changing point every 260 ns which requires laser modulation frequency of several MHz to tens of MHz
Solution Approach 1:
By dividing the detection function across multiple pixels, each pixel can operate independently with lower modulation frequency requirements. The parallel architecture distributes the temporal resolution burden across spatial dimensions, allowing each pixel to use more relaxed timing parameters while achieving overall high-speed imaging.
Solution Approach 2:
The system resolves the high modulation frequency requirement by adding spatial parallelization. Instead of requiring each pixel to rapidly modulate and detect at high frequencies sequentially, the pixel array simultaneously captures data at lower frequencies, converting the temporal frequency constraint into a spatial distribution problem that is easier to manage.
3Measurement precision
If the photodetector needs to be able to sample the signal in accordance with Shannon's theorem, then measurements must be taken at frequencies higher than tens of GHz, but this imposes high demands on the photodetector in terms of rapidity and also in terms of sensitivity
Solution Approach 1:
The detection function is segmented across multiple pixels, each handling a portion of the total data load. This distribution allows each individual photodetector to operate at lower sampling frequencies while collectively achieving the required measurement precision through parallel processing across the pixel array.
Solution Approach 2:
The system moves from temporal sampling constraints to spatial parallelization. By distributing measurements across multiple pixels in space, each photodetector can satisfy Shannon's theorem at more manageable frequencies, while the collective system achieves high-resolution imaging without imposing extreme rapidity and sensitivity requirements on individual detectors.
4Measurement precision
If FMCW-type LIDAR imaging with optical imaging system is used, then the laser source is wavelength modulated and the object path illuminates the object, but the coherent imager cannot be readily extended to a large number of pixels because 2N waveguides would be needed
Solution Approach 1:
Multiple optical paths (object and reference) are merged and combined at each pixel through coherent superposition. The reference beam is distributed across the pixel array and combined with the object beam at each pixel's photodetector, creating a compact architecture that reduces the number of required waveguides while maintaining range measurement precision through heterodyne detection.
Solution Approach 2:
The optical paths serve multiple functions: the reference beam provides both illumination reference and signal amplification, while the same waveguide structure serves both object and reference paths. This multi-functionality reduces the overall complexity of optical routing compared to separate dedicated paths for each function.
5Reliability
If coherent LIDAR imaging is used, then the laser source emits coherent light, but speckles are generated by the backscattering of the coherent light by the scene which mar the image
Solution Approach 1:
Each pixel detects light from a specific local spatial position, creating localized detection zones. This local quality approach means that while coherent light does generate speckles, each pixel's small detection area reduces the impact of speckle interference compared to a single large detector, allowing coherent detection capability to be maintained with reduced harmful effects.
Solution Approach 2:
The detection function is segmented across multiple pixels, each independently measuring local intensity and phase information. This segmentation allows the system to process coherent light signals while distributing the speckle interference across multiple spatial locations, reducing the impact on any single measurement and enabling effective range imaging despite coherent backscattering.
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
The system achieves high-quality, instantaneous range imaging of dynamic scenes with improved signal intensity and reduced speckle interference, allowing for real-time processing of large-scale data without the need for mechanical scanning.
Implementation Method 1
The heterodyne detection LIDAR imaging of a scene makes use of the coherent emission nature of a laser source to amplify the useful signal reflected by the scene using a signal coming from a reference path and coherent with the useful signal
Implementation Method 2
The two paths interfere on the photodetector and form a heterodyne signal. The interference produces beats of a frequency proportional to the delay between the two paths
Implementation Method 3
an optical recombiner designed to spatially superpose the reference beam on an object beam reflected by said scene, referred to as reflected object beam, so as to form a recombined beam
Implementation Method 4
an optical imager having an optical axis and creating an image of the scene on a detector by focusing the reflected object beam
Implementation Method 5
the optical frequency of the laser source is modulated, for example with a periodic linear ramp
Data Source
AI summary
A coherent LIDAR imaging system includes a laser source; an optical splitter/recombiner designed to split the laser radiation into a reference beam and into an object beam and to superpose the reference beam on a reflected object beam reflected by the scene; and an optical imager creating an image of the scene on a detector. The detector includes an array of pixels designed for detecting the reflected object beam and the reference beam which together form a recombined beam having a beat frequency representative of a range of the illuminated scene. The optical splitter/recombiner is configured to form an intermediate image of the reference beam in an intermediate image plane perpendicular to the optical axis.