Variable Optical Filter Stack for Low-Loss Wavelength Selection
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Solution Overview
Problem
Existing linearly variable optical filters face a tradeoff between optical performance and thickness, leading to increased internal stresses and optical loss, as they require many layers for effective blocking and passband performance.
Innovation Solution
The use of different materials in the bandpass and blocking regions, with high index contrast in the blocking region and low-loss, low-index materials in the bandpass region, along with additional layers in areas of local optical minima, to create a thin, low-stress optical filter with minimal optical loss and strong out-of-band rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of layers in the thin film stack is increased to improve blocking performance and passband performance, then optical performance is improved, but the thickness of the filter increases leading to increased internal stresses and potential breakage
Solution Approach 1:
The patent applies different material combinations with different refractive indices to different regions of the filter: high-index material combinations (e.g., TiO2/SiO2) in the blocking regions and low-index material combinations (e.g., fluoropolymer/oxide) in the passband region. This local differentiation allows the blocking regions to achieve effective wavelength blocking with fewer layers while the passband region maintains low optical loss, thereby reducing overall filter thickness and internal stresses without sacrificing optical performance
Solution Approach 2:
The patent uses composite material structures combining organic fluoropolymer layers with inorganic oxide layers. The fluoropolymer layers provide low refractive index and low optical loss for the passband, while the oxide layers provide high refractive index contrast for effective blocking. This composite approach enables achieving both blocking performance and passband performance with reduced layer count and thickness compared to traditional single-material systems
2Length of stationary object
If high-index materials are used to reduce the number of layers, then the thickness is reduced, but optical loss increases
Solution Approach 1:
The patent strategically places low-loss fluoropolymer materials in the passband region where light transmission is critical, while confining high-index but higher-loss oxide materials to the blocking regions where their primary function is wavelength rejection. This spatial separation of material functions minimizes optical loss in the transmission path while maintaining effective blocking performance
Solution Approach 2:
The patent extracts the low-loss property from the material system by using fluoropolymer materials specifically in the passband region, separating the functions of blocking (handled by oxide layers) and transmission (handled by fluoropolymer layers). This extraction allows the passband to achieve minimal optical loss independent of the blocking region's material choices
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
This approach results in a compact, reliable optical filter with reduced thickness, improved spectral resolution, and enhanced reliability by minimizing light leakage and mechanical stress, while maintaining low optical loss and strong wavelength selectivity.
Implementation Method 1
A filter having the transmission wavelength varying linearly with distance is called a linearly variable filter (LVF)... a thin film interference LVF
Implementation Method 2
a photodetector array coupled to the LVF via an array of gradient-index lenses or an array of microlenses
Data Source
Figure 1A~1B
Figure 2~3C
Figure 4A~4B
AI summary
An optical filter is described having a laterally variable transmission wavelength within a wavelength range, the optical filter comprising: a bandpass filter comprising a stack of alternating first and second layers comprising first and second materials, respectively; a blocking filter comprising a stack of alternating third and fourth layers, comprising third and fourth materials, respectively; wherein the first, second and fourth materials each comprise different materials, so that a refractive index of the first material is smaller than a refractive index of the second material, the refractive index of the second material is smaller than a refractive index of the fourth material, and an absorption coefficient of the second material is smaller than an absorption coefficient of the fourth material.