Plasmonic Optical Element for High-Transmittance Color Filtering
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Solution Overview
Problem
Current color filters for imaging devices face challenges in achieving sufficient transmittance and color-filter characteristics, especially as pixel sizes decrease, due to the limited sensitivity and periodicity of metal structures, leading to suboptimal performance in capturing light and maintaining color accuracy under various incident angles.
Innovation Solution
The optical element employs a plurality of optical filters with different characteristics, featuring metal structures periodically arranged with uniform optical distances between adjacent metal structures, which are adjusted to be within a specific range (0.75 to 1.25 times) to ensure consistent plasmon resonance conditions and minimize diffraction effects, thereby enhancing transmission spectra and maintaining high-contrast filtering effects across various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If aperture arrays or periodic metal structures are used to achieve color filter characteristics, then plasmon resonance can be excited to enable wavelength-selective transmission, but the transmittance becomes very low (only 5-6% at most) and sensitivity is insufficient
Solution Approach 1:
The optical element is divided into multiple regions, each containing metal structures with different periodic arrangements optimized for specific wavelength bands. This segmentation allows each region to independently optimize for its target wavelength while collectively achieving high transmittance across the visible spectrum through the cumulative effect of multiple transmission paths.
Solution Approach 2:
Multiple metal structure groups with different periodicities are combined within a single optical element. By merging structures optimized for different wavelength ranges (e.g., one group for blue-green, another for red), the system achieves broad-spectrum high transmittance while maintaining wavelength selectivity, overcoming the limitation of single-structure low transmittance.
2Productivity
If the size of pixels is reduced to increase the number of pixels, then the amount of light captured by detector units decreases, but reducing the thickness of microlenses and color filters is necessary to capture sufficient light
Solution Approach 1:
The patent employs extremely thin metal film structures (on the order of nanometers) as the color filter medium. These thin films maintain their plasmon resonance functionality while minimizing light absorption and scattering losses, allowing sufficient light transmission even through reduced-thickness structures in small pixels.
Solution Approach 2:
The optical element utilizes changes in the periodic arrangement parameters of metal structures (period, size, shape) to optimize plasmon resonance conditions for maximum transmittance. By carefully tuning these parameters, the system achieves high transmission efficiency that compensates for the reduced light-capturing area in smaller pixels.
3Adaptability or versatility
If image sensors capture obliquely incident light, then the field of view increases, but color filter characteristics that do not significantly vary with respect to obliquely incident light are desired
Solution Approach 1:
The metal structures are designed with asymmetric geometries and non-uniform periodic arrangements that create plasmon resonance modes less sensitive to incident angle variations. This asymmetric design causes the resonance conditions to remain relatively stable across a range of incident angles, maintaining consistent color filter characteristics even when capturing obliquely incident light.
Solution Approach 2:
The patent introduces complexity in the two-dimensional periodic arrangement of metal structures, using patterns that extend in multiple directions with different periods. This multi-directional periodicity creates resonance conditions that are more robust to angle changes, as the structure responds similarly to light incident from different directions by engaging multiple resonance modes simultaneously.
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 approach results in smooth, sharp peak characteristics in transmission spectra, providing high-contrast filtering effects for specific wavelength regions and enabling the use of thin, efficient color filters compatible with reduced pixel sizes, while maintaining performance across different incident angles.
Implementation Method 1
When light is incident on metal particles or metal structures, a resonance phenomenon is observed in which scattering or absorption increases in a particular wavelength band. This phenomenon is the localized surface plasmon resonance (simply referred to as 'plasmon resonance' hereinafter)
Data Source
AI summary
An optical element includes a plurality of optical filters having different characteristics. The element includes a first optical filter including a first metal-structure group including first metal structures periodically arranged in an in-plane direction of a substrate surface and a second optical filter including a second metal-structure group including second metal structures periodically arranged in the in-plane direction, the second metal-structure group exhibiting a plasmon resonance condition different from that of the first metal-structure group. The optical distance between the first metal structures adjacent to each other is in a range of 0.75 to 1.25 times the optical distance between the second metal structures adjacent to each other.