Dual-bandpass optical filter for angle shift and blocking
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Solution Overview
Problem
Existing optical filters face challenges in achieving a small angle shift and effective blocking of radiation across a wide spectral range, particularly at larger incidence angles, due to limitations in refractive index materials and layer thickness uniformity.
Innovation Solution
A dual-bandpass filter system is implemented, where a primary bandpass filter with high refractive indices and narrow blocking bands minimizes angle shift, and a secondary bandpass filter with a large refractive index difference compensates for blocking deficits, allowing efficient blocking across the desired spectral range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single bandpass filter with high refractive index materials is used, then angle shift is minimized, but blocking efficiency in certain spectral ranges deteriorates
Solution Approach 1:
The filter system is divided into two separate bandpass filters (first and second) with different material compositions and spectral characteristics. The first filter uses high refractive index materials (aSi:H, TiO2) to minimize angle shift, while the second filter uses materials with appropriate absorption properties (aSi:H, SiO2, Si3N4) to provide effective blocking in specific spectral ranges. This segmentation allows each filter to be optimized for its specific function.
Solution Approach 2:
Each bandpass filter is designed with specific local material properties tailored to its function. The first filter employs materials with high refractive indices (aSi:H with n=3.4-3.9, TiO2 with n=2.5-2.7) specifically to reduce angle shift. The second filter uses materials with controlled absorption characteristics (aSi:H layers, SiO2 with n=1.47, Si3N4 with n=1.78) to achieve superior blocking in particular spectral regions.
2Object-affected harmful factors
If material thickness is increased to improve blocking, then blocking efficiency improves, but manufacturing precision requirements worsen
Solution Approach 1:
The filter combines multiple materials with complementary properties in a layered structure. High refractive index materials (aSi:H, TiO2) are combined with low refractive index materials (SiO2, Si3N4) and absorbing materials to achieve both effective blocking and angle shift minimization. This composite approach allows thinner overall layers while maintaining blocking efficiency, thereby reducing manufacturing precision requirements.
3Measurement precision
If high refractive index materials are used, then angle shift is reduced, but blocking in broad spectral ranges deteriorates
Solution Approach 1:
The invention merges two distinct bandpass filters with complementary spectral characteristics into a single optical system. The first filter (with high refractive index materials) addresses angle shift, while the second filter (with absorbing materials) addresses broad spectral blocking. Together, they provide both minimal angle shift and comprehensive spectral blocking that neither filter could achieve alone.
Solution Approach 2:
The invention converts the typically harmful effect of absorption (which limits refractive index material choices) into a beneficial feature by deliberately selecting the second filter with absorbing materials (aSi:H, SiO2, Si3N4) to provide broad spectral blocking. This transforms what would normally be a limitation into the key mechanism for achieving superior blocking 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 dual-filter system achieves a small angle shift of less than 3% of the center wavelength at larger angles, ensuring effective blocking from 300 nm to 1100 nm, with improved transmittance and blocking efficiency.
Implementation Method 1
a primary bandpass filter which, viewed for each incidence angle individually, largely transmits electromagnetic radiation in a primary transmittance wavelength interval and reflects electromagnetic radiation in primary reflection wavelength intervals on both sides of the primary transmittance wavelength interval
Implementation Method 2
a secondary bandpass filter which, viewed for each incidence angle individually, largely transmits electromagnetic radiation in a secondary transmittance wavelength interval and reflects electromagnetic radiation in secondary reflection wavelength intervals
Implementation Method 3
High refractive index materials allow for filters having spectral properties with only weak dependency on the incidence angle
Implementation Method 4
aSi:H absorbs a large part of the radiation in the spectral range below approximately 700 nm and almost the complete radiation typically below 600 nm
Data Source
AI summary
An optical filter having a substrate including a primary bandpass filter at least predominantly on an interference basis and a secondary bandpass filter at least predominantly on an interference basis. Both bandpass filters are designed such that they transmit sufficiently over the entire required angle range in the desired spectral transmittance wavelength interval. The primary bandpass filter contains the small angle shift required by the overall system. It also has a spectral transmittance wavelength interval which is as small as possible according to the requirements of the respective application and restricted by narrow blocking bands. The secondary bandpass filter is designed such that its transmittance wavelength interval is limited by a short-wave edge and a long-wave edge and is adjusted to the primary bandpass filter in such a way that its edges shift over the required angle range only within the blocking bands of the primary bandpass filter.