Multilayer Optical Film Overlapping Harmonics
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Solution Overview
Problem
Multilayer optical films struggle to achieve uniform reflection and transmission characteristics over a wide spectral range, particularly in broadband applications, often resulting in undesirable color appearances due to spectral non-uniformities and material inefficiencies.
Innovation Solution
The development of multilayer optical films that utilize overlapping harmonic reflection bands, specifically a 2nd order reflection band overlapping with a 1st and/or 3rd order reflection band, to create a single wide reflection band covering visible and infrared wavelengths, achieved through tailored refractive index differences and layer thickness profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single packet of microlayers with carefully tailored layer thickness profile is used, then manufacturing precision and control of layer thickness are improved, but the spectral coverage and bandwidth of reflection are limited
Solution Approach 1:
The patent combines multiple harmonic reflection bands (1st, 2nd, and 3rd order bands) from a single microlayer packet into one unified wide reflection band. By carefully designing the layer thickness profile to generate overlapping harmonics, the invention merges these bands to achieve broad spectral coverage from visible to infrared wavelengths while maintaining precise control through a single manufacturing process without layer multiplier devices.
Solution Approach 2:
The invention utilizes parameter changes in the layer thickness profile, specifically employing an apodized graded thickness profile where the optical thickness of optical repeat units varies continuously. This parameter variation enables the generation of multiple overlapping harmonic reflection bands within a single packet, expanding spectral coverage while maintaining manufacturing precision.
2Adaptability or versatility
If broadband reflectors with graded layer thickness profile are designed, then spectral coverage is improved, but color appearance and spectral uniformity deteriorate
Solution Approach 1:
The patent applies local quality by implementing an apodized graded thickness profile where the optical thickness of optical repeat units varies continuously across the packet. This localized variation in thickness is carefully controlled to generate specific harmonic relationships, ensuring that reflection is distributed uniformly across the spectrum while maintaining a neutral color appearance without unwanted spectral non-uniformities.
Solution Approach 2:
The invention employs parameter changes in the optical thickness of optical repeat units, using an apodized gradient that continuously varies the thickness. This controlled parameter change enables the generation of overlapping harmonic bands that cover broad spectrum while maintaining spectral uniformity and avoiding color artifacts through careful optimization of the thickness profile.
3Adaptability or versatility
If multiple packets of microlayers are used to expand spectral coverage, then bandwidth is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges multiple harmonic reflection bands within a single microlayer packet to achieve the spectral coverage that would traditionally require multiple separate packets. By designing the layer thickness profile to generate overlapping 1st, 2nd, and 3rd order harmonics, the invention consolidates what would be multiple discrete optical elements into one integrated structure, reducing overall device complexity.
Solution Approach 2:
The invention makes a single microlayer packet universal by enabling it to perform multiple functions simultaneously - generating 1st order, 2nd order, and 3rd order harmonic reflection bands that overlap to provide broad spectral coverage. This multi-functionality eliminates the need for separate packets for different spectral regions, simplifying the overall device architecture.
4Adaptability or versatility
If intermediate amounts of reflection and transmission are provided, then adaptability is improved, but spectral uniformity and color control become more difficult
Solution Approach 1:
The patent employs parameter changes in the optical thickness of optical repeat units using an apodized graded profile. This enables continuous adjustment of the reflection and transmission characteristics across the spectrum, providing intermediate amounts of both while maintaining spectral uniformity. The apodization function carefully controls the distribution of optical thickness to achieve desired reflectivity levels without creating color artifacts.
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 enhances reflective efficiency, reduces material costs, and provides a smooth spectral response with minimal color distortion, enabling high reflectivity over a broad spectral range while optimizing material usage.
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
Figure 1~2
Figure 3~4
Figure 5A~5B
AI summary
A broadband mirror, polarizer, or other reflector includes at least one stack of microlayers. Microlayers in the stack are arranged into optical repeat units. At a design angle of incidence such as normal incidence, the stack provides a 1st order reflection band, a 2nd order reflection band, and optionally a 3rd order reflection band. The 2nd order reflection band overlaps, or substantially overlaps, the 1st and/or 3rd order reflection bands to form a single wide reflection band. The wide reflection band may include the 2nd and 1st but not a 3rd order reflection band, or the 2nd and 3rd but not the 1st order reflection band, or it may include the 1st, 2nd, and 3rd order reflection bands, as well as still higher order reflection bands. The wide reflection band may cover at least a portion of visible and infrared wavelengths.