Pixel-Scale GMR Filters for Angular-Tolerant Infrared Imaging
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Solution Overview
Problem
Existing multispectral infrared imaging technologies face challenges with fragile components due to temperature variations and parasitic diffraction effects from non-uniform layer thicknesses, leading to performance deterioration and limited angular tolerance on large surfaces.
Innovation Solution
Development of metallo-dielectric guided mode resonance (GMR) filters with subwavelength periodic structuring, optimized for bandpass transmission on the scale of detection pixels, using dielectric materials and metallic gratings to couple incident waves to waveguide modes, ensuring angular acceptance and spectral selectivity even at the edge of the image field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multilayer structures are used for multispectral infrared imaging, then spectral selectivity can be achieved, but the components become fragile and performance deteriorates due to temperature variations and parasitic diffraction effects
Solution Approach 1:
The patent extracts the spectral filtering function from complex multilayer structures and implements it using simple subwavelength metallic gratings. These gratings are suspended structures that can be directly integrated with detectors, eliminating the need for fragile multilayer coatings while maintaining spectral selectivity through their periodic geometry rather than through layer thicknesses that are sensitive to temperature variations.
Solution Approach 2:
The patent replaces the mechanical/optical multilayer filter system with a metallic grating system that uses subwavelength periodic structuring to achieve spectral filtering. This substitution eliminates the mechanical complexity and fragility of multilayer structures while maintaining the spectral selection function through electromagnetic resonance in the metallic grating structures.
2Adaptability or versatility
If multilayer structures with varying thicknesses are used, then different spectral bands can be filtered, but parasitic diffraction effects increase and manufacturing difficulty increases
Solution Approach 1:
The patent applies local quality by varying the period of the metallic grating structures across different spatial locations to achieve different spectral responses. Each region of the filter matrix has a grating with a specific period tailored to its spectral filtering requirements, allowing diverse spectral band coverage without requiring varying layer thicknesses, thus maintaining manufacturing uniformity.
Solution Approach 2:
The patent achieves spectral band coverage by changing the periodicity parameter of the metallic grating structures rather than changing layer thicknesses. By adjusting the grating period from one region to another, the system can filter different spectral bands while maintaining consistent manufacturing conditions and avoiding parasitic diffraction effects associated with thickness variations.
3Device complexity
If subwavelength metallic gratings are used, then the number of layers is reduced, but angular tolerance is limited on large surfaces
Solution Approach 1:
The patent addresses angular tolerance by designing metallic grating structures with subwavelength periods that are optimized for the specific geometry of the imaging system. By carefully controlling the grating period and depth dimensions, the structures maintain their spectral filtering performance across the angular range required for compact imaging systems, effectively extending angular acceptance without increasing the number of layers.
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 compact, instantaneous acquisition of infrared 'color' images with improved angular tolerance and spectral performance, suitable for small detection pixel surfaces, overcoming the limitations of previous technologies.
Implementation Method 1
at least one metallic diffractive grating, structured according to a given pattern repeated with a given period, less than said detection wavelength. At least one diffraction grating is adapted for coupling an incident wave at said detection wavelength to the mode of the waveguide.
Implementation Method 2
elementary metallo-dielectric guided mode resonance filter, optimized for bandpass transmission in a spectral band centered on a given detection wavelength
Data Source
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AI summary
According to one aspect, the present description relates to a device (20) for multispectral imaging in the infrared, suitable for detecting at at least one first and one second detection wavelength. It comprises a detection matrix array (23) comprising a set of elementary detectors (23i) of preset dimensions forming an image field of given dimensions; and an image-forming optic (22) having a given aperture number (N) and a given focal length (F), which aperture number and focal length are suitable for forming, at any point of the image field, an elementary focal spot covering a set of at least two juxtaposed elementary detectors. The device furthermore comprises a matrix array (24) of elementary metal-dielectric guided-resonance filters, which matrix array is arranged in front of the detection matrix array (23) at a distance smaller than a focal depth of the optic (22), the dimensions of the elementary filters being such that each elementary focal spot formed at each point of the image field covers at least two elementary filters; and the elementary filters are optimised for pass-band transmission in spectral bands centred on two different central wavelengths, equal to two of said detection wavelengths.