Multilayer Optical Filter to Block Visible Light Without Red Reflection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical filters with dielectric multilayer films struggle to effectively block visible light in the 400 to 680 nm range while maintaining high transmittance for near-infrared light beyond 800 nm, leading to potential red reflection and reduced sensor sensitivity.
Innovation Solution
Designing an optical filter with a dielectric multilayer film on a substrate, where the low- and high-refractive index films have specific extinction coefficient values, ensuring high absorption of visible light and low reflection in the 400 to 680 nm range, and high transmittance in specific near-infrared ranges, using materials like amorphous silicon and SiO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the reflectance in the wavelength range of 600 to 680 nm is increased to lower the transmittance in this wavelength range, then the visible light blocking ability is improved, but the reflection color becomes red and the appearance deteriorates
Solution Approach 1:
The invention changes the optical parameters of the high-refractive index layer by controlling the spin density of silicon atoms to be 1.0×10^12/(nm·cm^2) or more. This parameter change increases the extinction coefficient k600 to 0.18 or more, enabling the layer to absorb visible light through conversion to internal energy rather than reflecting it, thus blocking visible light while avoiding red reflection and maintaining a black appearance.
2Illumination intensity
If an optical filter uses a dielectric multilayer film with high-refractive index layers having small extinction coefficient in the 800 to 1100 nm range, then the near-infrared transmittance is improved, but the visible light blocking ability deteriorates
Solution Approach 1:
The invention applies local quality by creating a dielectric multilayer film where different layers have different optical properties tailored to specific wavelength ranges. The high-refractive index layer has high extinction coefficient k600 for visible light absorption, while the low-refractive index layer has low extinction coefficient k800-1000MIN for near-infrared light transmission. This local differentiation of optical properties enables simultaneous visible light blocking and near-infrared transmission.
Solution Approach 2:
The invention uses composite materials by combining a high-refractive index layer (silicon with spin density ≥1.0×10^12/(nm·cm^2)) and a low-refractive index layer (such as SiO2) in a multilayer structure. The composite structure leverages the complementary optical properties of each material: silicon provides strong visible light absorption through high k600, while the SiO2 layer maintains near-infrared transmission with low k800-1000MIN, achieving both functions 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 filter achieves superior blocking of visible light and transmission of near-infrared light, enhancing sensor sensitivity by minimizing red reflection and maintaining high transmittance in targeted near-infrared bands.
Implementation Method 1
at least one film selected from the group consisting of the low-refractive index film and the high-refractive index film satisfies the following optical characteristics (i-1) and (i-2A): (i-1) an extinction coefficient k600 at a wavelength of 600 nm is 0.12 or larger
Implementation Method 2
at least one film selected from the group consisting of the low-refractive index film and the high-refractive index film satisfies the following optical characteristics (i-1) and (i-2A): (i-2A) a minimum extinction coefficient k1530-1570MIN in a wavelength range of 1530 to 1570 nm is 0.01 or smaller
Implementation Method 3
reflection-type filters that reflect light, which is to be blocked, utilizing light interference of dielectric thin-films having different refractive indices and provided alternately (i.e., forming a dielectric multilayer film) on one surface or both surfaces of a transparent substrate
Data Source
AI summary
An optical filter includes a substrate and a dielectric multilayer film laid as an outermost layer on at least one major surface of the substrate. The dielectric multilayer film includes a low-refractive index film and a high-refractive index film provided alternately. At least one film selected from the group consisting of the low-refractive index film and the high-refractive index film satisfies the following optical characteristics (i-1) and (i-2A): (i-1) an extinction coefficient k600 at a wavelength of 600 nm is 0.12 or larger; and (i-2A) a minimum extinction coefficient k1530-1570MIN in a wavelength range of 1530 to 1570 nm is 0.01 or smaller; and the optical filter satisfies the following optical characteristic (ii-1A): (ii-1A) light in a wavelength range of 400 to 680 nm is blocked and light in the wavelength range of 1530 to 1570 nm is transmitted.