DMD Modulation for Geiger Mode APD LIDAR Sensitivity Uniformity
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Solution Overview
Problem
Conventional LIDAR systems using Geiger mode Avalanche PhotoDiodes (APDs) suffer from unresponsive 'dead' detectors, continuously triggering 'hot' detectors, and non-uniform sensitivity across the detector array, leading to noise and crosstalk issues that affect image quality and require costly calibration.
Innovation Solution
A Digital Micromirror Device (DMD) is used to modulate light illumination across a Geiger mode APD array, allowing for selective deflection and uniform sensitivity by positioning micromirrors to either direct or block light to individual APD detectors, identifying and masking dead or hot detectors to reduce noise and crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Geiger mode APD detectors are used for LIDAR range finding, then single photon detection capability is improved, but non-uniform sensitivity and detector defects (dead/hot detectors) worsen image quality
Solution Approach 1:
A spatial light modulator is introduced as an intermediary component between the telescope and the Geiger mode APD array. This modulator selectively deflects or blocks light paths to individual detectors, enabling compensation for non-uniform sensitivity and masking of defective detectors without replacing the entire detector array.
Solution Approach 2:
The patent applies local quality by allowing each detector in the APD array to receive a customized amount of light based on its individual sensitivity characteristics. The spatial light modulator creates different illumination conditions for different detectors, with more light directed to less sensitive detectors and less or no light to dead or hot detectors.
2Measurement precision
If calibration lookup tables are generated for each detector to compensate sensitivity variations, then sensitivity uniformity is improved, but noise from hot detectors and dead detectors is not reduced
Solution Approach 1:
The spatial light modulator serves as a physical intermediary that actively controls light distribution to detectors. Unlike software-based calibration tables, the modulator can physically block light from reaching dead or hot detectors, thereby eliminating their harmful effects on image quality while maintaining sensitivity uniformity.
3Measurement precision
If individual bias level adjustment is performed for every APD detector, then sensitivity uniformity is improved, but device complexity and calibration requirements increase
Solution Approach 1:
The spatial light modulator takes over the function of sensitivity equalization from the detector bias control system. By using the modulator to adjust light distribution instead of adjusting individual detector biases, the patent simplifies the detector control architecture while achieving the same sensitivity uniformity goal.
4Ease of manufacture
If APD arrays with non-uniform sensitivity are used to reduce cost, then manufacturing cost is reduced, but image quality and dynamic range deteriorate
Solution Approach 1:
The patent converts the harmful effect of non-uniform detector sensitivity into a benefit by using the spatial light modulator to create complementary non-uniform illumination. This approach allows the use of lower-cost, non-uniform detector arrays while achieving uniform overall system response and high image quality through the coordinated light modulation.
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 enhances image quality by reducing noise, salvaging non-uniform APD arrays, decreasing crosstalk, and increasing the dynamic range of the sensor, while allowing for precise control of light exposure to improve imaging of features with varying reflectivity.
Implementation Method 1
A Digital Micromirror Device (DMD) is used to modulate light illumination across a Geiger mode APD array, allowing for selective deflection and uniform sensitivity by positioning micromirrors to either direct or block light to individual APD detectors
Implementation Method 2
The term 'Geiger mode' refers to an application of a bias voltage which exceeds the breakdown voltage of the APD detector. When the APD detector is over biased, the APD operates in a metastable state where a single photon may cause an avalanche current.
Implementation Method 3
When the APD detector is over biased, the APD operates in a metastable state where a single photon may cause an avalanche current
Data Source
AI summary
Systems (100) and methods (600) for acquiring data relating to an environment of interest. The methods comprise: receiving by a telescope (110) light scattered by an object within the environment; focusing a cone of light towards a spatial light modulator (112) which is placed a certain distance from the telescope on a telescope-focus surface; and deflecting a select amount of the cone of light by the spatial light modulator towards a photodiode array (114), whereby a sensitivity across the photodiode array is made uniform.