Near-Infrared Cut Filter Incident Angle Dependence
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Solution Overview
Problem
Conventional near-infrared cut filters exhibit significant incident angle dependence in their spectral characteristics, leading to variations in color reproducibility, particularly on the long wavelength side, which affects the accuracy of color representation in imaging devices.
Innovation Solution
A near-infrared cut filter design featuring an absorption layer and a reflection layer, optimized to maintain a spectral characteristic close to the relative visibility curve, with specific transmittance requirements across different wavelengths and angles, and incorporating a transparent substrate, absorption layer, and reflection layer to minimize incident angle dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric multilayer film is used as the reflection layer, then near-infrared light can be blocked by interference, but incident angle dependence occurs causing color reproducibility to vary
Solution Approach 1:
The patent changes the optical parameters of the dielectric multilayer film by controlling the film thickness to be 1/4 wavelength or less for each layer, and adjusting the refractive index ratio between adjacent layers to be 2.0 or less. These parameter changes reduce the incident angle dependence while maintaining the near-infrared blocking performance through optical interference.
Solution Approach 2:
The patent uses composite dielectric materials with different refractive indexes (such as TiO2, SiO2, Ta2O5, Nb2O5) to construct the multilayer film. By combining materials with appropriate refractive indexes and controlling their layer thickness, the filter achieves both effective near-infrared blocking and reduced incident angle dependence, improving color reproducibility consistency.
2Reliability
If conventional near-infrared cut filters are used, then infrared light is blocked, but spectral characteristic deviates from relative visibility curve particularly on long wavelength side
Solution Approach 1:
The patent optimizes the spectral characteristics by controlling the film thickness parameters of the dielectric multilayer film to be 1/4 wavelength or less, and adjusting the refractive index ratios. These parameter changes shift the transmittance cutoff wavelength and shape the spectral curve to better match the relative visibility curve, particularly improving accuracy on the long wavelength side while maintaining infrared blocking.
3Illumination intensity
If filter with high transmittance in visible range is used, then visible light passes through, but transmittance on long wavelength side is too high affecting red color reproducibility
Solution Approach 1:
The patent carefully controls the film thickness and refractive index parameters of the dielectric multilayer film to achieve a balanced spectral transmittance curve. By setting each layer thickness to 1/4 wavelength or less and controlling the refractive index ratio to 2.0 or less, the filter maintains high visible light transmittance while sufficiently reducing transmittance on the long wavelength side (600-750 nm) to improve red color reproducibility accuracy.
Data Source
AI summary
A near-infrared cut filter has an absorption layer and a reflection layer and satisfies following requirements:average transmittance (R) of 620-750 nm is ≤20%, average transmittance (G) of 495-570 nm is ≥90%, and a ratio (R)/(G) is ≤0.20;|T0(600-725)−T30(600-725)| is ≤3%·nm where T0(600-725) is a transmittance integral value of 600-725 nm in a spectral transmittance curve (0°), and T30(600-725) is a transmittance integral value of 600-725 nm in a spectral transmittance curve (30°);wavelengths λIRT(80), λIRT(50), and λIRT(20) where transmittance becomes 80%, 50%, and 20% respectively in 550-750 nm in the spectral transmittance curve (0°) normalized by maximum transmittance in 450-650 nm satisfy following formulae: 0≤λIRT(80)−λT(80)≤30 nm, 0≤λIRT(50)−λT(50)≤35 nm, and 0≤λIRT(20)−λT(20)≤37 nm where λT(80), λT(50), and λT(20) are wavelengths on a long wavelength side where relative visibility of 0.8, 0.5 and 0.2 is exhibited in a relative visibility curve.