Dielectric Multilayer Optical Filter for LiDAR
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Solution Overview
Problem
Existing optical filters face challenges in achieving high shieldability against visible light and high transmissivity of near infrared light, especially at large incident angles, while maintaining a black appearance.
Innovation Solution
The use of a dielectric multilayer film with a specific configuration, comprising a low refractive index film and multiple high refractive index films, optimized for spectral characteristics such as extinction coefficient, spin density, and thickness, to achieve desired transmittance and reflectance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If absorption-type optical filters are used to reduce visible light transmissivity and reflectivity, then visible light shieldability is improved, but near infrared transmissivity deteriorates because materials absorbing visible light also absorb near infrared
Solution Approach 1:
The patent applies local quality by using different dielectric materials with distinct optical properties for different wavelength ranges. Specifically, it employs a first dielectric layer with high visible light absorption (low reflectivity) and a second dielectric layer with high near infrared transmission. This spatial separation of functional layers allows the filter to simultaneously achieve high visible light shieldability and high near infrared transmissivity, resolving the contradiction between these two opposing requirements.
2Object-affected harmful factors
If reflection optical filters are used to interrupt visible light, then visible light shieldability is improved, but design performance deteriorates because the external surface becomes a mirror surface
Solution Approach 1:
The patent applies local quality by differentiating the optical functions of different layers: the first dielectric layer is optimized for visible light absorption with low reflectivity, while the second dielectric layer is optimized for near infrared transmission. This functional differentiation allows the filter to achieve high visible light shieldability without creating a mirror-like external appearance, thus resolving the contradiction between shieldability and aesthetic design performance.
3Reliability
If the extinction coefficient of high refractive index layers is reduced to improve near infrared transmissivity, then near infrared transmissivity is improved, but visible light shieldability deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the optical filter into multiple dielectric layers, each with specific extinction coefficient characteristics. The first dielectric layer has a first extinction coefficient optimized for visible light absorption, while the second dielectric layer has a second extinction coefficient optimized for near infrared transmission. This segmentation allows independent optimization of extinction coefficients for different wavelength ranges, resolving the contradiction between visible light shieldability and near infrared transmissivity.
4Object-affected harmful factors
If multilayer film reflectance is increased to compensate for visible light shielding, then visible light shieldability is improved, but design performance deteriorates due to red reflection color
Solution Approach 1:
The patent applies local quality by optimizing the optical properties of different layers for specific wavelength ranges. The first dielectric layer is designed with low reflectivity in the visible range to prevent red reflection, while the second dielectric layer provides near infrared transmission. This localized optimization of optical properties allows the filter to achieve high visible light shieldability without producing unwanted red reflection colors, thus resolving the contradiction between shieldability and design performance.
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 achieves high shieldability against visible light and high transmissivity of near infrared light even at large incident angles, while maintaining a black appearance, thereby enhancing the design performance and sensitivity of sensors like LiDAR.
Implementation Method 1
Absorption optical filters are also known which employ, as a multilayer film, a material that is optically absorptive
Implementation Method 2
an optical filter that transmits near infrared light of 800 nm or longer and interrupts visible light
Implementation Method 3
reflection optical filters are known in which dielectric thin films having different refractive indices are laid alternately (dielectric multilayer film) on one or both surfaces of a transparent substrate and which reflect light to interrupt utilizing light interference
Data Source
AI summary
An optical filter, including: a substrate; and a dielectric multilayer film laid on or above at least one major surface of the substrate, the dielectric multilayer film including at least two different layers, where: the dielectric multilayer film includes four or more films having a spin density of 5.0×1010/nm·cm2 or larger, each of the four or more films has a minimum thickness of 1.5 nm to 5 nm, a maximum transmittance at an incident angle of 0° in a wavelength range of 400 nm to 680 nm is 6% or lower, a maximum reflectance at an incident angle of 5° in the wavelength range is 20% or lower, and an average transmittance at an incident angle of 0° in at least one wavelength range having a width of 40 nm included in a wavelength range of 800 nm to 1570 nm is 90% or higher.