Gradation Optical Filter with Antireflection Layers
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Solution Overview
Problem
Existing ND filters face challenges in achieving low reflectance across different incident light directions and regions, particularly in maintaining antireflection performance and manufacturing ease for gradation ND filters.
Innovation Solution
The optical filter design incorporates an intermediate antireflection layer, an absorption layer with varying thickness for gradation, and a surface antireflection layer, ensuring uniform thickness and refractive index to reduce reflectance independently of light direction and density, using materials like oxygen-deficient TiO2 and Ta2O5 to satisfy specific extinction coefficient conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an ND filter is configured to absorb unnecessary light, then the transmittance is controlled, but the reflectance varies depending on the incident direction of light
Solution Approach 1:
The optical filter is divided into multiple regions with different optical densities (first region with OD 0.1-1.0, second region with OD 1.0-2.0, third region with OD 2.0-3.0). Each region independently controls transmittance while the antireflection structure ensures stable reflectance across all regions regardless of incident light direction.
Solution Approach 2:
The patent changes the optical density parameter across different regions of the filter to achieve varying transmittance levels. By carefully selecting OD ranges for each region, the patent maintains stable reflectance characteristics while providing graduated light attenuation from 0.1 to 3.0 optical density.
2Object-affected harmful factors
If the reflectance is reduced to be not greater than 5% within optical density range 0.1 to 1.0, then ghost and flare are reduced, but it is not easy to manufacture and the antireflection structure may collapse
Solution Approach 1:
The patent applies different optical density values to different local regions of the filter. The first region has OD 0.1-1.0, the second region has OD 1.0-2.0, and the third region has OD 2.0-3.0. This local differentiation allows the antireflection structure to be optimized for each region's specific transmittance requirements, making manufacturing more feasible while maintaining low reflectance (<5%) in the first region to reduce ghost and flare.
Solution Approach 2:
Instead of applying a uniform antireflection treatment across the entire filter, the patent applies partial action by focusing the most stringent reflectance control (≤5%) on the first region with lower optical density, while allowing different reflectance characteristics in regions with higher optical density. This partial approach reduces manufacturing complexity while still achieving the primary goal of reducing ghost and flare where it matters most.
3Manufacturing precision
If a gradation ND filter is used to control brightness and improve edge sharpness, then image quality is enhanced, but the reflectance varies across different regions with different transmittances
Solution Approach 1:
The patent creates a gradation ND filter with locally differentiated optical densities: first region (OD 0.1-1.0) for high transmittance areas, second region (OD 1.0-2.0) for medium transmittance areas, and third region (OD 2.0-3.0) for low transmittance areas. Each region is designed with appropriate antireflection treatment to maintain reliable reflectance characteristics while achieving the desired brightness control and edge sharpness improvement across the image.
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 achieves low reflectance and optical path difference across the entire optical filter region, enhancing antireflection performance and manufacturing simplicity, reducing ghost and flare effects in image pickup apparatuses.
Implementation Method 1
an absorption layer (a first layer) 3, wherein a transmittance changes in a first direction, and in a second direction orthogonal to the first direction, a thickness of the absorption layer 3 changes in the first direction
Implementation Method 2
an intermediate antireflection layer 2, an absorption layer (a first layer) 3, and a surface antireflection layer 4
Implementation Method 3
PTL 2 discloses an ND filter which reduces the reflectance by using an antireflection structure
Data Source
Figure 1A~1C
Figure 2
Figure 3A~4B
AI summary
An optical filter that has a region where a transmittance changes in a first direction and that includes a substrate and a first layer in order along a second direction orthogonal to the first direction, a thickness of the first layer in the second direction changes in the first direction, and an extinction coefficient of the first layer satisfies a predetermined conditional expression.