Multispectral Imaging Optical System Stray Light Reduction
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Solution Overview
Problem
Multispectral imaging systems face issues with stray light and ghost images due to the reflection of light spectrum on spectral filters, leading to reduced image quality and increased complexity in acquisition time, especially when dealing with moving objects.
Innovation Solution
The implementation of an optical system with upstream and downstream spectral filters, where upstream filters define sub-beams and filter them before they enter the imaging lens, reducing stray light by ensuring each sub-beam is spectrally filtered before propagation, and downstream filters further refine the spectral bands to minimize ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spectral filters are placed close to the detector to filter sub-beams, then spectral imaging capability is improved, but stray light and ghost images increase due to light reflection on the filters
Solution Approach 1:
The optical system is divided into multiple independent channels, each handling a specific spectral band. The filter assembly is segmented into multiple filter regions (first, second, third spectral bands) that can be independently optimized. Each sub-beam corresponding to a specific field of view is filtered by its dedicated spectral band filter, reducing cross-contamination and stray light interference between different spectral regions.
Solution Approach 2:
A beam splitter is introduced as an intermediary element to separate the light path into multiple sub-beams before they reach the filter assembly. This allows the system to distribute different spectral bands to different detectors through the beam splitter, reducing the need for complex filter arrangements and minimizing stray light paths while maintaining spectral imaging capability.
2Measurement precision
If multiple spectral bands are filtered using separate filters, then spectral resolution is improved, but device complexity increases
Solution Approach 1:
Multiple spectral filtering functions are merged into a single filter assembly that contains multiple filter regions arranged in different orientations. The filter assembly integrates filters for first, second, and third spectral bands in one component, allowing the system to achieve multi-band spectral resolution without requiring separate filter modules for each band, thus reducing overall device complexity.
Solution Approach 2:
The filter assembly utilizes different spatial orientations (first orientation and second orientation perpendicular to each other) to arrange filter regions for different spectral bands. This dimensional arrangement allows multiple spectral filters to be packed efficiently in a compact space, reducing device complexity while maintaining the capability to filter multiple spectral bands simultaneously.
3Measurement precision
If field of view is divided into multiple sub-beams for spectral filtering, then spectral information accuracy is improved, but light intensity is reduced
Solution Approach 1:
The beam splitter performs preliminary action by separating the incoming light into multiple sub-beams before they reach the filter assembly. This early separation ensures that each sub-beam contains only the relevant spectral information for its designated field of view, improving spectral accuracy while maintaining adequate light intensity by avoiding unnecessary filtering of irrelevant wavelengths.
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 configuration significantly reduces noise from diffuse reflections and stray light, improving image quality by ensuring each sub-image represents the intended spectral information with minimal interference from other spectral bands, thus enhancing the accuracy and efficiency of multispectral imaging.
Implementation Method 1
n upstream spectral filters pass band to an upstream spectral band distinct from the others, each upstream spectral filter being arranged so as to filter a sub-beam associated with a diaphragm
Implementation Method 2
an element arranged in the image focal plane of said telescope and comprising n>2 diaphragms, each diaphragm being adapted to define a sub-beam associated with a field of view of the observed scene
Implementation Method 3
an optical system called an imaging lens adapted to form, on the detector, n sub-images corresponding respectively to said n fields of view of the scene associated with the n sub-beams
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 2C
AI summary
Multispectral imaging optical system (1) comprising: - an optical system called a telescope (T) adapted to collect light (L) from a scene to be observed so as to form an intermediate image (It) in an image focal plane (PFim,t) of said telescope, - an optical system called an imaging lens (OI), an object focal plane (PF0,OI) of said imaging lens being coincident with the image focal plane of said telescope - a detector (Det) adapted to acquire an image of the intermediate image by the imaging lens, - a spectral and spatial filtering system called an upstream filter (F1), said upstream filter comprising: - an element (Diaph) disposed in the image focal plane (PFim,t) of said telescope and comprising n > 2 diaphragms (Di), each diaphragm being adapted to define a subbeam (SFi) associated with a field of view (FOV¡) of the observed scene;- n upstream spectral filters (R1i) bandpass to an upstream spectral band (Δλ1i) distinct from the others, each upstream spectral filter being arranged to filter a sub-beam (SFi) associated with a diaphragm (Di); the imaging lens being adapted to form, on the detector, n sub-images (Ii) corresponding respectively to said n fields of view (FOVi) of the scene associated with the n sub-beams (SFi); said imaging optics system further comprising n downstream spectral filters (R2i), located near the detector and bandpass to a downstream spectral band (λ2i) distinct from the others, a downstream spectral filter being arranged to filter a sub-beam (SFi) associated with an upstream spectral filter, a downstream spectral band (Δλ2i) of a downstream spectral filter having a non-zero overlap with the upstream spectral band (Δλ2i) of the associated upstream spectral filter.;