Optical Filter Density Gradient for Weather Resistance
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Solution Overview
Problem
Near-infrared cut filters used in imaging devices face challenges with weather resistance, as they tend to deform, discolor, or deteriorate over time, especially under high-temperature and high-humidity conditions, leading to issues like haze and film cracks.
Innovation Solution
An optical filter design featuring a transparent substrate with an optical multilayer film composed of alternately stacked low-refractive index silicon oxide (SiO2) and high-refractive index films, where the density of the low-refractive index film near the interface with the high-refractive index film is lower than in other areas, improving weather resistance through controlled vacuum deposition methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optical multilayer film is used to sufficiently cut near-infrared rays, then the spectral correction performance is improved, but the weather resistance deteriorates due to haze and film cracks under high-temperature and high-humidity conditions
Solution Approach 1:
The patent applies local quality by creating a density gradient within the low-refractive index film layer. The density of the low-refractive index film is made lower at the interface with the high-refractive index film compared to other portions. This localized variation in density prevents haze and film cracks at the critical interface region while maintaining the optical filtering performance of the multilayer structure.
2Ease of manufacture
If the low-refractive index film density is made uniform, then the manufacturing process is simpler, but weather resistance deteriorates due to haze and film cracks at the film interface
Solution Approach 1:
The patent implements local quality by specifying that the density of the low-refractive index film varies locally - being lower at the interface with the high-refractive index film and higher in other portions. This localized density variation targets the specific problem area (film interface) without requiring complete redesign of the entire manufacturing process.
Solution Approach 2:
The patent applies parameter changes by controlling the density parameter of the low-refractive index film to vary within the film structure. Specifically, the density is made lower at the interface region compared to other portions, which prevents haze and film cracks while maintaining manufacturing feasibility through controlled deposition conditions.
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 significantly enhances the weather resistance of the optical filter, reducing spectral characteristic changes, preventing haze, and minimizing film cracks under high-temperature conditions, while maintaining cost-effectiveness by avoiding the need for expensive ion-assisted deposition equipment.
Implementation Method 1
use of an optical multilayer film in combination is proposed for sufficiently cutting the near-infrared ray
Implementation Method 2
an optical multilayer film formed on the transparent substrate
Implementation Method 3
spectral characteristics of the solid-state imaging devices have high sensitivities with respect to an infrared ray
Data Source
AI summary
There are provided an optical filter excellent in weather resistance and a method for manufacturing an optical filter. The optical filter of the present invention includes a transparent substrate, and an optical multilayer film provided on a surface of the transparent substrate. In the optical multilayer film, a low-refractive index film containing silicon oxide (SiO2) and a high-refractive index film higher in refractive index than the low-refractive index film are alternately stacked. A density of a portion of the low-refractive index film close to an interface between the low-refractive index film and the high-refractive index film is lower than a density of a portion of the low-refractive index film other than the portion close to the interface.