Staggered Multi-Layer Optical Filter for Oblique Angle Wavelength Stability
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Solution Overview
Problem
Conventional color-selective filters, such as multi-layer interference filters, experience significant wavelength shifts when light is incident at oblique angles due to changes in effective layer thickness, leading to reduced light quantity, heat generation, and narrowed bandwidth.
Innovation Solution
An optical filter design featuring alternately laminated first and second optical layers with specific refractive indices and thicknesses, arranged in unit structures with a staggered configuration and shift amounts, which reduces the change in reflected wavelength across a desired incident angle range by satisfying specific condition expressions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a multi-layer interference filter is used to select light of a desired wavelength band, then color selectivity is achieved, but the reflected wavelength changes depending on the incident angle due to changes in effective layer thickness
Solution Approach 1:
The filter is divided into multiple unit structures, each comprising a first multi-layer and a second multi-layer with different refractive index distributions. This segmentation allows each unit to handle specific wavelength ranges, and their combined effect maintains the reflected wavelength stable across different incident angles while achieving color selectivity.
Solution Approach 2:
Different regions of the filter have different refractive index distributions. The first multi-layer has a specific refractive index profile optimized for certain angles, while the second multi-layer has a different profile optimized for other angles. This local quality variation ensures that across the entire angular range, the reflected wavelength remains stable.
2Manufacturing precision
If an absorbing layer is introduced to compensate spectral characteristics when light is obliquely incident, then wavelength shift is reduced, but total light quantity is reduced and heat generation occurs
Solution Approach 1:
Instead of using absorbing layers that directly compensate for wavelength shifts (which cause energy loss), the patent introduces an intermediary structural approach: unit structures with alternately laminated multi-layers having different refractive index distributions. This intermediary structure mechanically/optically adjusts the phase and path of light to stabilize the reflected wavelength without absorbing energy, thus avoiding heat generation and light quantity loss.
3Manufacturing precision
If an M layer with intermediate refractive index is introduced in place of an L layer, then incident angle dependency is reduced, but optical path length change due to oblique incidence is not effectively reduced
Solution Approach 1:
The patent employs asymmetric refractive index distribution within the unit structures. The first multi-layer and second multi-layer have deliberately different refractive index profiles, creating an asymmetric optical path that compensates for the symmetric optical path length changes caused by oblique incidence. This asymmetry allows the filter to maintain wavelength stability without requiring precise control of optical path length.
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 proposed optical filter significantly minimizes wavelength shifts and maintains reflectance and transmittance stability across a wide incident angle range, reducing color degradation and light loss, while avoiding heat generation and bandwidth reduction.
Implementation Method 1
a color-selective filter is typically a spectral filter (multi-layer interference filter) utilizing multi-layer interference. The multi-layer interference filter is formed of a laminated periodic structure with its refractive index and layer thickness adjusted in accordance with the desired wavelength band.
Data Source
AI summary
An optical filter includes a first multi-layer having a width W1 and including a first optical layer and a second optical layer that are made of materials different from each other and that are alternately laminated, the first optical layer having a refractive index nH and an average layer thickness dH, and the second optical layer having a refractive index nL lower than nH and an average layer thickness dL, a second multi-layer having a width W2 and including the first and the second optical layers alternately laminated, the first and the second multi-layers are included in each of unit structures arranged being shifted from each other by a shift amount D in a lamination direction of the first and the second optical layers, and predetermined conditions are satisfied.