Dielectric Optical Filter for Low NIR Reflectance at Wide Angles
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Solution Overview
Problem
Existing vehicular sensor modules face issues with high near-infrared light reflectance, which leads to noise and reduced sensor sensitivity, particularly when light enters at large incident angles.
Innovation Solution
An optical filter with a substrate and two dielectric multilayer films, each comprising low, medium, and high refractive index films, designed to maintain high near-infrared transmittance while suppressing reflectance, even at large incident angles, by employing specific spectral characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional transparent substrate with simple antireflection film is used, then the manufacturing process is simple, but the near infrared light reflectance increases at large incident angles
Solution Approach 1:
The patent uses a composite multilayer film structure combining three different refractive index materials (high: 2.4-3.6, medium: 1.8-2.3, low: 1.4-1.9) to achieve superior optical performance. This composite structure suppresses near infrared light reflectance at large incident angles while maintaining high transmittance, resolving the contradiction between manufacturing simplicity and optical performance.
Solution Approach 2:
The antireflection coating is divided into multiple discrete layers with different refractive indices rather than using a single uniform material. Each layer segment (high, medium, low refractive index) performs a specific function in controlling light reflection, collectively achieving low reflectance across various incident angles while maintaining manufacturing feasibility.
2Loss of energy
If the incident angle of light increases, then the reflectance naturally increases, but the transmittance must be maintained high
Solution Approach 1:
The patent optimizes specific parameters including refractive index values (high: 2.4-3.6, medium: 1.8-2.3, low: 1.4-1.9), film thickness ratios (50-200 nm for high, 30-150 nm for medium, 50-200 nm for low), and layer configuration to achieve wavelength-selective transmission. These parameter changes enable high transmittance (≥90%) at 0° incidence and low reflectance (≤1%) at 50° incidence in the 800-1600 nm range.
Solution Approach 2:
Different regions of the optical filter (different layers) have locally optimized properties - each layer is designed with specific refractive index and thickness to handle particular aspects of light interaction. The high refractive index layer handles initial reflection, the medium layer provides transition, and the low refractive index layer manages final interface reflection, collectively solving the angle-dependent reflectance problem.
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 optical filter effectively reduces near-infrared light reflectance while maintaining high transmittance, enhancing sensor sensitivity and reducing external disturbances, suitable for use as a cover in vehicular sensor modules.
Implementation Method 1
each of the first dielectric multilayer film and the second dielectric multilayer film is a laminate in which one or more low refractive index films, one or more medium refractive index films, and one or more high refractive index films are laid
Implementation Method 2
each of the first dielectric multilayer film and the second dielectric multilayer film is a laminate in which one or more low refractive index films, one or more medium refractive index films, and one or more high refractive index films are laid
Data Source
AI summary
An optical filter including: a substrate having a first major surface and a second major surface; a first dielectric multilayer film laid on or above the first major surface; and a second dielectric multilayer film laid on or above the second major surface, in which: each of the first dielectric multilayer film and the second dielectric multilayer film is a laminate in which one or more low refractive index films, one or more medium refractive index films, and one or more high refractive index films are laid; each of the first dielectric multilayer film and the second dielectric multilayer film includes two or more medium refractive index films; each of the first dielectric multilayer film and the second dielectric multilayer film includes a structure that the low refractive index film, the medium refractive index film, and the high refractive index film are laid in order; and the optical filter satisfies both of the spectral characteristics (i-1) and (i-2).