Apodized Broadband Partial Reflectors for Uniform Spectral Performance
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Solution Overview
Problem
Broadband polymeric multilayer optical films face challenges in minimizing color issues due to in-band spectral ringing, which results in non-uniform transmission and reflection characteristics across the visible spectrum, particularly in applications like liquid crystal displays and backlights.
Innovation Solution
The implementation of apodized broadband reflectors with graded thickness profiles, where the second plurality of optical repeating units have an average slope at least 5 times greater than the baseline slope, significantly reducing in-band spectral ringing and color variability by terminating the graded layer thickness profile to minimize undesirable spectral features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If broadband polymeric multilayer optical films are designed with graded layer thickness profile to achieve broadband reflection, then the reflection bandwidth is increased, but in-band spectral ringing occurs causing non-uniform transmission and reflection characteristics
Solution Approach 1:
The patent applies apodization techniques to transform the harmful spectral ringing effects into beneficial smooth spectral characteristics. By modifying the layer thickness profile at the boundaries using apodization functions (such as cosine, Gaussian, or exponential profiles), the abrupt transitions that cause spectral ringing are converted into gradual transitions that produce the desired broadband reflection with uniform spectral characteristics.
Solution Approach 2:
The patent changes the parameters of the layer thickness profile by applying apodization functions that modify the thickness distribution at the boundaries of the graded profile. This parameter modification transforms the sharp cutoffs into smooth transitions, eliminating spectral ringing while preserving broadband reflection capability across the visible spectrum.
2Adaptability or versatility
If the number of optical repeating units is increased to enhance broadband reflection performance, then the reflection bandwidth expands, but the spectral ringing and color variability become more pronounced
Solution Approach 1:
By applying apodization to the increased number of optical repeating units, the patent converts the potentially harmful spectral ringing that would result from having many layers with abrupt thickness transitions into beneficial smooth spectral characteristics. The apodization functions modify the boundary regions of the layered structure, transforming the harmful interference patterns into uniform broadband reflection.
3Illumination intensity
If conventional graded thickness profile is used to achieve broadband reflection, then the optical performance is improved, but the color uniformity deteriorates due to in-band spectral features
Solution Approach 1:
The patent changes the thickness profile parameters by applying apodization functions that modify the layer thickness distribution at the boundaries. This parameter transformation maintains the broadband optical performance while eliminating the spectral ringing that causes color non-uniformity, thereby achieving both high optical performance and excellent color uniformity across the visible spectrum.
Solution Approach 2:
The apodization technique converts the harmful color variability caused by spectral ringing into beneficial color uniformity. By modifying the thickness profile using apodization functions, the patent transforms the disruptive spectral features into smooth, uniform spectral characteristics that provide consistent color performance across the broadband reflection range.
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 apodized broadband reflectors substantially eliminate in-band spectral ringing, providing a smoother spectrum for both transmitted and reflected light, thereby reducing undesired color and achieving more uniform optical performance across the visible spectrum.
Implementation Method 1
the reflection and transmission characteristics of the optical film are determined in large part by constructive and destructive interference of light reflected from the layer interfaces
Implementation Method 2
the Brewster angle - the angle at which reflectance of p-polarized light at an interface goes to zero
Data Source
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AI summary
A broadband partial reflector includes a multilayer polymeric optical film having a total number of optical repeating units that monotonically increases in thickness value from a first side to a second side of the multilayer polymeric optical film. A baseline optical repeating unit thickness profile is defined by a first plurality of optical repeating units and having a first average slope, and a first apodized thickness profile of the multilayer polymeric optical film is defined by a second plurality of optical repeating units having a second average slope being at least 5 times greater than the first average slope. The second plurality of optical repeating units define the first side of the multilayer polymeric optical film and join the first plurality of optical repeating units. The second plurality of optical repeating units are in a range from 3-15% of the total number of optical repeating units.