Multilayer Optical Filter for LiDAR Sensor Protection
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Solution Overview
Problem
Existing optical filters do not effectively absorb laser beams with a wavelength of 1550 nm, potentially damaging image sensors when used in conjunction with LiDAR systems, as they do not provide sufficient transmittance characteristics to protect the sensors from high-intensity wavelengths used in LiDAR.
Innovation Solution
An optical element with a multilayer film structure on a substrate, designed to maintain high transmittance in the visible range (470 nm to 630 nm) while reducing transmittance to 10% or lower at 1550 nm, using specific refractive index ranges and optical thickness conditions for the materials, ensuring effective filtering of 1550 nm light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optical filter is used to block infrared light for digital camera applications, then the sensitivity in the visible range is improved, but the filter fails to block laser beams at 1550 nm wavelength used in LiDAR
Solution Approach 1:
The patent changes the optical parameters of the multilayer film by specifying precise refractive index ranges (nm: 1.35-1.80, nh: 1.90-2.50, nl: 1.15-1.50) and optical thickness ratios (1.8≤d2i/d2i-1≤2.2) to achieve wavelength-selective transmission. This allows the filter to block 1550 nm laser light while maintaining high transmittance in the visible range, resolving the contradiction between visible light transmission and laser protection.
Solution Approach 2:
The patent employs a composite multilayer film structure with three different materials having distinct refractive index characteristics. This composite structure creates interference effects that selectively block 1550 nm wavelength while transmitting visible light, solving the problem of protecting image sensors from LiDAR damage without compromising digital camera functionality.
2Use of energy by moving object
If a light absorbing material is used instead of dielectric multilayer film, then the transmittance increases from 1100 nm to 1200 nm, but the filter does not effectively absorb 1550 nm wavelength
Solution Approach 1:
The patent transitions from using light-absorbing materials to a dielectric multilayer film with specifically controlled optical parameters. By adjusting the refractive indices and optical thicknesses of the layers, the system achieves high transmittance in certain wavelengths while blocking 1550 nm laser light through constructive and destructive interference, rather than absorption.
Solution Approach 2:
The patent replaces the mechanism of light absorption with optical interference in a dielectric multilayer structure. This substitution allows the system to achieve wavelength-selective blocking without the limitations of absorbing materials, effectively blocking 1550 nm while maintaining high transmittance in the visible range.
3Object-affected harmful factors
If the transmittance at 1550 nm is reduced to protect image sensors, then the protection capability is improved, but the transmittance in the visible range may be compromised
Solution Approach 1:
The patent applies local quality by designing the multilayer film to have different optical characteristics at different wavelengths. The film structure is optimized to specifically target 1550 nm wavelength for blocking while maintaining high transmittance in the visible range (470-630 nm), achieving wavelength-specific functionality rather than uniform behavior across all wavelengths.
Solution Approach 2:
By precisely controlling the refractive indices and optical thicknesses of the multilayer film layers, the patent achieves wavelength-selective optical properties. The parameter optimization ensures that the interference effects occur at 1550 nm for blocking while the visible range experiences minimal interference, maintaining high transmittance for digital camera operations.
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 element effectively cuts light at 1550 nm while maintaining high transmittance in the visible range, protecting image sensors from damage and ensuring optimal performance in both LiDAR and digital camera applications.
Implementation Method 1
a multilayer film provided on the substrate. The multilayer film has an average transmittance of 75% or higher for light having a wavelength of 470 nm to 630 nm incident at an incident angle of 0° and a transmittance of 10% or lower for light having a wavelength of 1550 nm incident at an incident angle of 0°
Implementation Method 2
The multilayer film includes a layer made of a first material and a layer made of a second material alternately layered, and a final layer made of a third material disposed on an outermost side. 1.35≤nm≤1.80, 1.90≤nh≤2.50, 1.15≤nl≤1.50 where nm is a refractive index of the first material, nh is a refractive index of the second material, and nl is a refractive index of the third material
Data Source
AI summary
An optical element includes a substrate, and a multilayer film provided on the substrate. The multilayer film has an average transmittance of 75% or higher for light having a wavelength of 470 nm to 630 nm incident at an incident angle of 0° and a transmittance of 10% or lower for light having a wavelength of 1550 nm incident at an incident angle of 0°. The multilayer film includes a layer made of a first material and a layer made of a second material alternately layered, and a final layer made of a third material disposed on an outermost side, and a predetermined condition is satisfied.