Dual-Stack Optical Filter Structure for Visible Light Rejection
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Solution Overview
Problem
Existing optical sensing devices face challenges in effectively filtering visible light while achieving high transmittance into infrared light, leading to interference from undesired light waves.
Innovation Solution
An optical structure comprising a first stack of alternately stacked first low-refractive-index films and semiconductor films, and a second stack of alternately stacked second low-refractive-index films and high-refractive-index films, designed to filter visible light and achieve high transmittance into infrared light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional optical filters are used to block visible light, then visible light filtering is achieved, but infrared transmittance is reduced
Solution Approach 1:
The optical filter is divided into two distinct stacks: a first stack with semiconductor films for blocking visible light (300-600nm), and a second stack with high-refractive-index films for blocking visible light (600-800nm). This segmentation allows each stack to target specific wavelength ranges, achieving comprehensive visible light filtering while preserving infrared transmission above 800nm
Solution Approach 2:
Different materials with specific optical properties are used in different regions of the filter structure. The first stack uses semiconductor films (e.g., amorphous silicon) with bandgap properties optimized for visible light absorption, while the second stack uses high-refractive-index materials (e.g., titanium dioxide, niobium oxide) for additional visible light blocking. This local optimization of material properties enables selective wavelength filtering
2Device complexity
If a single-layer filter is used, then the structure is simple, but it cannot effectively filter visible light while maintaining infrared transmittance
Solution Approach 1:
The filter is segmented into two functional stacks with different material compositions and optical characteristics. The first stack targets the blue-green visible spectrum (300-600nm) using semiconductor films, while the second stack targets the red visible spectrum (600-800nm) using high-refractive-index materials. This segmentation enables effective broad-spectrum visible light filtering that a single-layer structure cannot achieve
Solution Approach 2:
The filter employs composite material structures where semiconductor films are combined with low-refractive-index materials in the first stack, and high-refractive-index materials are combined with low-refractive-index materials in the second stack. These composite structures create multiple interfaces for light interaction, enhancing visible light blocking while maintaining infrared transmission
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 structure effectively filters visible light and achieves high transmittance into infrared light, with an average transmittance of less than 10−5 in the visible light range and a cut-on wavelength from 850 nm to 1550 nm.
Implementation Method 1
The first stack and the second stack each includes specific stacked films, which may effectively filter visible light and achieve high transmittance into infrared light
Implementation Method 2
The first stack includes alternately stacked first low-refractive-index films and semiconductor films
Data Source
AI summary
An optical structure is provided. The optical structure includes a substrate and a first stack disposed on the substrate. The first stack includes alternately stacked first low-refractive-index films and semiconductor films. The optical structure further includes a second stack disposed on the first stack. The second stack includes alternately stacked second low-refractive-index films and high-refractive-index films. The refractive index of each first low-refractive-index film and each second low-refractive-index film is less than the refractive index of each high-refractive-index film.