Near-Infrared Cut Filter Incident Angle Dependence
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Solution Overview
Problem
Conventional near-infrared cut filters face challenges in suppressing incident angle dependence, leading to inadequate spectral correction for solid-state imaging devices, particularly in digital cameras and videos, due to insufficient refractive index differences between high and low refractive index layers, resulting in unsuitable transmission and stop bands.
Innovation Solution
A near-infrared cut filter with an optical multilayer structure comprising high and low refractive index layers, where the refractive index of the high layer is 2.0 or more and the low layer is 1.6 or less, with a specific repeating structure of (anQH, bnQL, cnQH, dnQL) that averages coefficients within specific ranges to minimize incident angle dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an optical multilayer is used to cut near-infrared light, then near-infrared light can be effectively blocked, but the spectral waveform shifts to the ultraviolet region when the incident angle of light increases
Solution Approach 1:
The patent changes the refractive index parameters of the optical multilayer materials. By selecting materials with higher refractive indices and optimizing their thickness ratios, the patent reduces the incident angle dependence of the spectral waveform, preventing the unwanted shift to the ultraviolet region while maintaining effective near-infrared blocking.
Solution Approach 2:
The patent uses a composite optical multilayer structure combining multiple materials with different refractive indices. This composite structure allows for optimized control of light transmission characteristics at different incident angles, resolving the contradiction between near-infrared blocking effectiveness and spectral stability.
2Reliability
If the refractive index difference between high and low refractive index layers is increased, then incident angle dependence is reduced, but the transmission and stop bands become unsuitable for solid-state imaging devices
Solution Approach 1:
The patent optimizes the refractive index parameters by selecting high-refractive-index materials (such as TiO2 with n>2.0) and carefully controlling their thickness ratios in the multilayer structure. This parameter optimization achieves both reduced incident angle dependence and suitable transmission/stop bands for solid-state imaging devices.
Solution Approach 2:
The patent creates a dynamic balance in the optical multilayer design, where the refractive index difference and layer thickness ratios are adjusted to simultaneously satisfy multiple requirements: reducing incident angle dependence while maintaining appropriate transmission and stop band characteristics for imaging applications.
3Manufacturing precision
If a color glass filter is used to cut near-infrared light, then the spectral waveform remains stable, but ultraviolet light cannot be sufficiently blocked
Solution Approach 1:
The patent merges the advantages of color glass filters (spectral stability) with optical multilayers (ultraviolet blocking capability). The optical multilayer is designed to work in conjunction with the color glass filter, with the multilayer providing ultraviolet stop band while the filter maintains spectral stability, achieving both requirements 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
The solution effectively suppresses incident angle dependence, securing wide transmission and stop bands, thereby improving image quality by maintaining spectral characteristics aligned with human visibility standards across varying incident angles.
Implementation Method 1
an optical multilayer formed on a transparent substrate... formed of a high-refractive index layer and a low-refractive index layer
Implementation Method 2
spectral characteristics... transmission band... stop band... incident angle dependence of the wavelength region cut by the optical multilayer
Data Source
AI summary
A near-infrared cut filter has an optical multilayer provided on at least one main surface of a transparent substrate, in which the optical multilayer is formed of a high-refractive index layer having a refractive index of 2.0 or more, and a low-refractive index layer having a refractive index of 1.6 or less at a wavelength of 500 nm, and the optical multilayer has a repeating structure of (anQH, bnQL, cnQH, dnQL)^n when a QWOT at the wavelength of 500 nm of the high-refractive index layer is set to QH, and a QWOT at the wavelength of 500 nm of the low-refractive index layer is set to QL, in which an average value of the an is not less than 1.5 nor more than 2.5, and a value obtained by averaging average values of the respective bn, cn, and dn is 1.0 or less.