Prismatic Plate Multispectral Filter Ghost Image Elimination
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Solution Overview
Problem
Off-axis telescopes with multispectral imagers suffer from ghost images due to multiple reflections at the focal plane, which interfere with image interpretation, and existing solutions either fail to completely eliminate these reflections or are complex to produce.
Innovation Solution
A multispectral filter with parallel faces and thin layers for spectral bands, positioned at a specific distance from detectors, and optimized prism angles to reject all parasitic reflections without the need for absorbent materials between bands, simplifying production and eliminating ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multispectral filter with parallel faces and thin layers is used, then spectral band separation is achieved, but ghost images appear due to multiple reflections at filter interfaces
Solution Approach 1:
A prismatic plate is introduced as an intermediary element between the multispectral filter and the detectors. This plate refracts the light beams at its entry face, causing parasitic reflections to be directed away from the detector active areas, thereby eliminating ghost images while preserving spectral band separation functionality
Solution Approach 2:
The solution moves the problem from the spectral domain to the spatial domain by using the prismatic plate to spatially separate the useful light beams from parasitic reflections. The refraction angle and plate positioning create different spatial paths for different beam types, allowing detection of useful signals while rejecting reflections
2Object-generated harmful factors
If absorbent materials are deposited between spectral bands to eliminate reflections, then ghost images are reduced, but manufacturing complexity increases significantly
Solution Approach 1:
The harmful reflections are extracted and redirected away from the detection path using the prismatic plate, rather than attempting to absorb them at the filter interfaces. This removes the need for complex absorbent material deposition between spectral bands, simplifying manufacturing while effectively eliminating ghost images
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 effectively eliminates all ghost images at the focal plane, improving image quality and simplifying filter production by eliminating the need for absorbent materials between spectral bands.
Implementation Method 1
characterized in that the prismatic plate refracts the light beams at their entry face
Implementation Method 2
multiple reflections occur both within the filter bands and between the filter bands
Implementation Method 3
a multispectral filter allowing the images to be observed in different spectral windows
Data Source
Figure 1a~2a
Figure 2b
Figure 3a~3b
AI summary
The multispectral filter for image detection devices comprises a prismatic plate (85) having a first inner face (86) and a second outer face (87), the first and second faces (86, 87) being inclined relative to each other at an angle β, and having at least two different spectral bands (91, 92, 93, 94) deposited indifferently on the first or second face (86, 87) of the prismatic plate (85), the different spectral bands (91, 92, 93, 94) being spaced from each other by a predetermined distance (D). Application to multispectral imagers, in particular off-axis imagers. This filter allows the suppression of ghost images (or spurious echoes) generated at the focal plane of a multispectral imager.