Stacked IR Filter for 3D Imaging Blue-Shift
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Solution Overview
Problem
Conventional filters in 3D time-of-flight cameras experience blue-shifting when exposed to large inclined incident light, requiring a telecentric lens with 0° or small chief ray angle to maintain signal-to-noise ratio, which limits their application and increases complexity.
Innovation Solution
A stacked filter comprising a first and second filter layer, allowing light transmission within specific bands, including a narrow IR band, to improve signal-to-noise ratio without the need for a telecentric lens, using dye or pigment materials for the double-layered stacked absorption-type filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional filter is used in the image sensor, then the signal-to-noise ratio can be improved, but blue-shifting occurs when large inclined incident light falls on the filter, requiring a telecentric lens with 0° or small chief ray angle
Solution Approach 1:
The patent changes the optical parameters of the filter by stacking multiple filter layers with different spectral characteristics. The first filter layer transmits a first wavelength band, the second filter layer transmits a second wavelength band, and their overlap creates a narrow third wavelength band. This parameter transformation allows the filter to transmit only the specific wavelength band of the modulated light source while blocking other wavelengths, improving signal-to-noise ratio without requiring a telecentric lens.
Solution Approach 2:
The patent uses a composite filter structure consisting of multiple filter layers stacked together. Each layer has different optical properties, and their combination creates a filter with enhanced spectral selectivity. The first filter layer and second filter layer are stacked to form a composite filter that transmits only the narrow third wavelength band, eliminating the need for complex telecentric lens systems while maintaining high signal-to-noise ratio.
2Ease of manufacture
If a conventional filter is used, then filtering can be performed, but the spectrum shifts toward lower wavelengths when exposed to large inclined incident light
Solution Approach 1:
The patent transforms the spectral transmission parameters by stacking multiple filter layers. The first filter layer transmits a first wavelength band, the second filter layer transmits a second wavelength band, and their spectral overlap produces a narrow third wavelength band. This parameter transformation stabilizes the spectral characteristics against blue-shifting caused by large inclined incident light, as the overlapping bands compensate for wavelength shifts.
Solution Approach 2:
The patent converts the harmful effect of blue-shifting into a beneficial outcome. By stacking multiple filter layers with overlapping transmission bands, the filter design accepts that wavelength shifts will occur but ensures that the overlapping region maintains stable transmission characteristics. The harmful blue-shifting is compensated by the overlapping spectral bands, turning a potential defect into a robust design feature.
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 enhances the signal-to-noise ratio for depth information in 3D imaging by allowing narrow-band IR light transmission while avoiding blue-shifting, eliminating the requirement for a telecentric lens and simplifying the image sensor design.
Implementation Method 1
The first filter layer allows light with wavelengths of a first band to be transmitted through. The second filter layer allows light with wavelengths of a second band to be transmitted through.
Data Source
AI summary
A stacked filter for an image sensor including an infrared (IR) pixel is provided. The stacked filter includes a first filter layer disposed at the IR pixel. The first filter layer allows light with wavelengths of a first band to be transmitted through. The stacked filter further includes a second filter layer stacked with the first filter layer. The second filter layer allows light with wavelengths of a second band to be transmitted through. The first band partially overlaps the second band at wavelengths of a third band. The third band is narrower than the first band and the second band. The stacked filter allows light with the wavelengths of the third band to be transmitted through. Furthermore, an image sensor containing a stacked filter is also provided.