Dielectric Multilayer Optical Member Reducing Incident Angle Dependence
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Solution Overview
Problem
Existing optical filters with dielectric multilayers for imaging devices suffer from incident angle dependence, leading to variations in color tone across the image, particularly due to the shift in cut-off wavelengths when the angle of light changes, which affects color reproducibility and image quality.
Innovation Solution
An optical member with a dielectric multilayer comprising a transparent substrate and a stack of high-refractive index and low-refractive index layers, where the number of unit refractive index layers and their optical thickness ratios are optimized to reduce incident angle dependence, specifically by ensuring a ratio of high-refractive index layer optical thickness to low-refractive index layer optical thickness (nHdH/nLdL) is greater than or equal to 3, with a total number of layers and specific ratios to minimize wavelength shift and transmittance ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric multilayer with high average refractive index is used to reduce incident angle dependence, then the incident angle dependence is reduced, but the width of the reflecting band is narrowed and reflectance is lowered
Solution Approach 1:
The patent divides the dielectric multilayer into multiple groups, where each group consists of alternating high-refractive index layers (nH) and low-refractive index layers (nL). By segmenting the structure into these functional groups with specific thickness ratios (nHdH/nLdL between 0.8-2.0), the patent achieves both incident angle independence and adequate reflecting band width. The segmentation allows different regions of the multilayer to perform different functions: some groups optimize for angle independence while others maintain reflectance.
Solution Approach 2:
The patent systematically varies key parameters including the refractive index ratio (nH/nL between 1.3-2.5), optical thickness ratio (nHdH/nLdL between 0.8-2.0), and the number of layers in each group (3-20 layers per group). By optimizing these parameters, the patent achieves a balance where the multilayer maintains high reflectance in the infrared region while being insensitive to incident angle variations.
2Manufacturing precision
If the number of dielectric layers is increased to improve spectral characteristics, then the spectral transmittance flatness is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the total number of layers into multiple groups, where each group contains a manageable number of alternating high and low refractive index layers (3-20 layers per group). This segmentation allows the complex spectral optimization to be achieved through modular assembly, reducing the practical complexity of manufacturing while maintaining the desired spectral flatness across the visible to near-infrared region.
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 reduces the difference in 50% transmission wavelengths at 0° and 30° incident angles, minimizing color tone variations and improving spectral transmittance flatness, thereby enhancing image quality and color reproducibility across the image field.
Implementation Method 1
a dielectric multilayer in which each of a plurality of high-refractive index layers and each of a plurality of low-refractive index layers are alternately stacked
Implementation Method 2
the filter that shields light in the infrared-wavelength region
Implementation Method 3
a dielectric multilayer in which each of a plurality of high-refractive index layers and each of a plurality of low-refractive index layers are alternately stacked
Data Source
AI summary
An optical member has: a transparent substrate; and a dielectric multilayer on the transparent substrate formed by stacking a plurality of unit refractive index layers each formed of a high-refractive index layer having a refractive index of 2 or more and a low-refractive index layer having a refractive index of 1.6 or less. In the optical member, a total number of the unit refractive index layers is 15 or more, and a number of the unit refractive index layers satisfying a condition of nHdH/nLdL≧3 is 10 or more, nHdH represents an optical thickness of the high-refractive index layer, and nLdL represents an optical thickness of the low-refractive index layer.