Multilayer Optical Filter Reducing Wavelength Shift at Oblique Incidence
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Solution Overview
Problem
Existing optical filters with multilayer film interference structures suffer from significant wavelength shifts when incident light enters at angles, leading to reduced band width and ineffective reduction of incident angle dependency.
Innovation Solution
The optical filter employs a combination of first and second multilayer film structures with alternating layers of different refractive indices, where the first multilayer film structure has a fine in-plane structure and the second is a typical multilayer film, both shifted in the lamination direction, to reduce wavelength shifts across a desired incident angle range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a multilayer film interference filter is used to achieve color selectivity, then light intensity loss and heat generation are reduced, but wavelength shift occurs when light beam is dispersed with opening angle
Solution Approach 1:
The multilayer film is divided into multiple unit multilayer films with different structures. The first unit multilayer film has a specific layer thickness configuration, while the second unit multilayer film has a different layer thickness configuration. This segmentation allows each unit to contribute differently to the overall spectral characteristics, enabling wavelength compensation for oblique incidence while maintaining the energy efficiency of interference filtering.
Solution Approach 2:
Different regions of the multilayer film structure are assigned different local properties. The first and second unit multilayer films have distinct layer thicknesses and refractive index configurations tailored to specific functions. This local quality differentiation enables the film to simultaneously achieve high reflectance in certain wavelength ranges and compensate for incident angle dependencies in other ranges.
2Reliability
If an alternate structure with in-plane fine structure is used to reduce incidence angle dependency, then wavelength shift is reduced, but reflection wavelength shift at low-angle incidence cannot be sufficiently reduced
Solution Approach 1:
The multilayer film structure incorporates dynamic adaptability to incident angles through its segmented unit film design. The different layer thickness configurations in the first and second unit multilayer films create a structure that dynamically compensates for wavelength shifts across various incident angles, including low-angle incidence, by leveraging interference effects that are sensitive to angle variations.
Solution Approach 2:
The patent combines multiple multilayer film structures with different material compositions and layer thicknesses into a composite filter system. The first unit multilayer film and second unit multilayer film use the same or different refractive index materials but with deliberately different thickness configurations, creating a composite structure that achieves superior angular dependency reduction compared to uniform structures.
3Manufacturing precision
If M-layer with middle refractive index is introduced instead of L-layer with low refractive index, then spectral characteristics are improved, but change of optical path due to oblique incidence cannot be effectively reduced
Solution Approach 1:
The filter structure is segmented into multiple unit multilayer films where each unit contains both M-layers (middle refractive index) and L-layers (low refractive index). By dividing the structure into repeating units with specific thickness ratios, the patent achieves both improved spectral characteristics from the M-layer and reduced optical path variation through the overall segmented architecture.
Solution Approach 2:
The patent systematically varies the layer thickness parameters of the first and second unit multilayer films to optimize performance. By adjusting the thickness of each layer in the segmented structure, the optical path length for oblique incident light is compensated, reducing wavelength shift while maintaining the spectral filtering properties provided by the M-layer materials.
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 configuration effectively minimizes wavelength shifts and maintains reflectance within a predetermined wavelength band, even at varying incident angles, thereby reducing the incident angle dependency and ensuring stable spectral performance.
Implementation Method 1
a spectral filter (multilayer film interference filter) using multilayer film interference is known. The multilayer film interference filter is obtained by laminating periodic structures where a refractive index or a layer thickness has been adjusted in accordance with the desired wavelength band.
Data Source
AI summary
An optical filter includes a first multilayer film structure including first and second optical layers which are constituted by materials different from each other, and a second multilayer film structure including third and fourth optical layers which are constituted by materials different from each other, the first multilayer film structure includes a first unit multilayer film with a width W1 including the first optical layer and the second optical layer, and a second unit multilayer film with a width W2 including the first optical layer and the second optical layer laminated alternately, the first and second unit multilayer films are shifted from each other in a lamination direction of the first and second optical layers, and constitute a unit structure in which the first and second unit multilayer films are arranged adjacent to each other in an arrangement direction orthogonal to the lamination direction.