Coherent LiDAR Pixel Array for Speckle-Resistant Detection
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Solution Overview
Problem
Existing coherent lidar systems face challenges in achieving high-resolution imaging with a large number of pixels while minimizing speckle noise and beam routing issues, particularly due to speckle grains smaller than the pixel size, which attenuate the interference signal and require higher power consumption or larger apertures.
Innovation Solution
An integrated detector for coherent lidar with a pixel matrix comprising evanescently coupled waveguides and diffraction gratings, where each pixel includes a photodiode and electronic circuit for beat frequency calculation, allowing for parallel detection and speckle grain alignment through deflection elements to enhance signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels is increased to achieve high-resolution imaging, then the imaging resolution is improved, but the beam routing complexity and speckle noise increase
Solution Approach 1:
The detection device is divided into multiple independent pixel elements, each with its own photodetector and electronic circuit. This segmentation allows parallel processing of light signals from different spatial locations, enabling high-resolution imaging without requiring complex centralized beam routing for each pixel.
Solution Approach 2:
The patent transitions from sequential or centralized beam routing to a two-dimensional array of photodetectors that simultaneously detect light across the entire field of view. This dimensional change from 1D scanning to 2D parallel detection eliminates the need for complex beam routing while maintaining high imaging resolution.
2Measurement precision
If the pixel size is decreased to increase the number of pixels, then the imaging resolution is improved, but the speckle noise increases and signal attenuation occurs
Solution Approach 1:
A diffuser element is introduced as an intermediary between the scattering medium and the pixel array. This diffuser randomizes the phase of the speckle pattern, causing speckle grains to be larger than individual pixels and reducing speckle noise through spatial averaging across multiple pixels.
Solution Approach 2:
The patent changes the optical parameters of the system by introducing a diffuser that modifies the speckle grain size. This parameter change ensures that speckle grains are larger than the pixel size, transforming the harmful speckle noise into a beneficial spatial averaging effect that reduces noise while maintaining high imaging resolution.
3Reliability
If external amplification electronics are used to amplify the beat signal, then the signal-to-noise ratio is improved, but the power consumption increases
Solution Approach 1:
The electronic amplification and signal processing circuits are merged directly into each pixel element on the same substrate. This integration eliminates the need for external amplification electronics, reducing power consumption while maintaining signal-to-noise ratio through localized signal processing close to the photodetector.
Solution Approach 2:
Each pixel element is self-sufficient with its own photodetector, amplification circuit, and signal processing electronics integrated on the same substrate. This self-service architecture allows each pixel to process its own signal independently without requiring external power-hungry amplification systems.
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 solution enables high-resolution lidar imaging with a large number of pixels, reducing speckle noise and beam routing problems, and optimizing power consumption by integrating processing electronics within each pixel, thus enhancing detection efficiency.
Implementation Method 1
The interference of these two waves is detected by a photodetector PD
Implementation Method 2
Each pixel element also includes a diffraction grating configured to couple an incoming beam into the waveguide
Implementation Method 3
The coupling between the reference guide and the N column guides, as well as the coupling between each column guide and its associated M row guides, is passive and of the evanescent type
Implementation Method 4
coherent emission nature of a laser source to amplify the useful signal reflected by the scene
Implementation Method 5
The technique is very insensitive to ambient light interference, such as sunlight. The interference of these two waves is detected by a photodetector PD, and the electrical signal at the detector's output has an oscillating term called the beat signal
Data Source
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AI summary
The invention relates to a detection device (10, 10A, 10B) for a coherent lidar imaging system comprising an integrated detector (Det) comprising a pixel array (Pi,j) distributed over N columns and M rows and comprising: - an optical guide called the reference guide (OGref) configured to receive a laser beam called the reference beam, - N optical guides (OGC(i)), called column guides coupled to the reference guide, - each column guide being coupled to M optical guides (OGL(i,j)), called row guides, the M row guides being configured to direct a portion of the reference beam into each pixel of the column, called the reference pixel beam (Lref(i,j)), - each pixel (Pi,j) of the integrated detector comprising: - a guided photodiode (PhD(i,j)) coupled to a detection optical guide (OGD(i,j)), - a diffraction grating, called the pixel grating (Rpix(i,j)), configured to couple a portion of an illuminating beam the pixel towards the guided photodiode, - a coupler,said pixel coupler (Coup(i,j)), configured to couple, in the detection guide, the coupled pixel beam and at least a fraction (Lref'(i,j)) of the pixel reference beam, -an electronic reading and preprocessing circuit.