IR Neutral Filter Layer Design for Stray Light Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing IR imaging optical systems face challenges in reducing broadband scattered light noise while maintaining sufficient signal strength and quality, particularly due to stray light from components and environmental sources, which hinders high-contrast imaging.
Innovation Solution
An IR neutral filter with a specific layer structure comprising a metallic absorbing layer between non-absorbing layers with differing refractive indices, optimized for low reflectivity and constant transmissivity across a given spectral range, is designed to reduce stray light and maintain signal detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a filter is used to reduce stray light, then the signal-to-noise ratio is improved, but the reflectivity increases causing signal loss
Solution Approach 1:
The patent applies parameter changes by precisely controlling the layer thicknesses of the filter structure. The first layer has a thickness of 0.028-0.03 μm and the second layer has a thickness of 0.04-0.045 μm, which are optimized to achieve both low reflectivity (1.76-5%) and adequate stray light reduction (damping factor 0.17-0.2). This precise parameter control allows the filter to simultaneously improve signal-to-noise ratio while minimizing signal loss.
Solution Approach 2:
The patent uses composite materials by combining titanium as the absorbing layer material and titanium oxide as the antireflection layer material. This composite structure creates a multi-layer filter where each material contributes specific properties: titanium provides absorption characteristics while titanium oxide provides antireflection properties, achieving both stray light reduction and low reflectivity requirements.
2Use of energy by moving object
If the transmissivity is increased to retain signal strength, then the signal detection capability is improved, but the stray light reduction capability deteriorates
Solution Approach 1:
The patent resolves this contradiction through parameter changes in the layer thicknesses. By optimizing the first layer thickness to 0.028-0.03 μm and the second layer thickness to 0.04-0.045 μm, the filter achieves a balance where sufficient signal transmissivity is maintained while adequate stray light reduction is accomplished, as evidenced by the damping factor of 0.17-0.2.
Solution Approach 2:
The patent applies local quality by creating different layer structures with specific properties at different positions. The first titanium layer provides absorption functionality while the second titanium oxide layer provides antireflection functionality. Each layer is locally optimized for its specific function, allowing the overall filter to maintain signal strength while reducing stray light.
3Loss of energy
If the reflectivity is reduced to maintain signal, then the signal transmissivity is improved, but the stray light reduction capability worsens
Solution Approach 1:
The patent uses parameter changes to resolve this contradiction. The specific thickness parameters (first layer: 0.028-0.03 μm, second layer: 0.04-0.045 μm) are optimized to achieve low reflectivity (1.76-5%) while maintaining adequate stray light reduction (damping factor 0.17-0.2), thus improving signal transmissivity without sacrificing stray light reduction capability.
Solution Approach 2:
The patent employs composite materials where titanium and titanium oxide layers work together. The titanium layer provides absorption properties for stray light reduction, while the titanium oxide layer provides antireflection properties. This composite structure enables the filter to simultaneously achieve low reflectivity and adequate stray light reduction.
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 filter achieves low reflectivity and stable transmissivity, effectively reducing scattered light noise and enhancing signal detection in IR imaging systems, with adjustable transmissivity between 20% and 60% and minimal fluctuation, suitable for various operating conditions.
Implementation Method 1
The metal layer minimizes the transmissivity of IR radiation
Implementation Method 2
an antireflection layer of titanium oxide with a layer thickness between 0.04 and 0.045 μm
Implementation Method 3
a substrate that is transparent in the spectral range from 0.4 to 0.7 μm
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The infrared (IR) neutral density filter comprises a substrate (1) transparent for IR radiation, and layers having different refractive indices and absorption coefficients stacked on the substrate, where one of the layers is a metallic IR radiation absorbing layer (3), and two IR radiation non-absorbing layers (2.1, 2.2, 2.3, 2.4, 2.5) are stacked on each side of the absorbing layer. The non-absorbing layers comprise alternating low-index materials and high-index materials. The refractive indices of the non-absorbing layers differ by 0.3. The infrared (IR) neutral density filter comprises a substrate (1) transparent for IR radiation, and layers having different refractive indices and absorption coefficients stacked on the substrate, where one of the layers is a metallic IR radiation absorbing layer (3), and two IR radiation non-absorbing layers (2.1, 2.2, 2.3, 2.4, 2.5) are stacked on each side of the absorbing layer. The non-absorbing layers comprise alternating low-index materials and high-index materials. The refractive indices of the non-absorbing layers differ by 0.3. The refractive indices of the low-index materials are 1.3-1.6 and the high-index materials are 1.6-4.2. The refractive indices of the layers, materials and layer thicknesses are adjusted so that the filter over a partial region of a given spectral range has an adjustable transmissivity of 20-60% with a variation of less than +- 3%, where the spectral range has a wavelength of 2-15 mu m.