Optical Filter Layout for High-Contrast Sky and Sun Reproduction
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Solution Overview
Problem
Existing optical filters used to reproduce the natural light of the sky and sun suffer from issues such as low transmission efficiency, high manufacturing complexity and cost, and the creation of spatially modulated luminance patterns, leading to blurred images and reduced contrast.
Innovation Solution
A multilayer optical filter with alternating transparent and absorbing sectors, each sector having refractive power to focus light along orthogonal focal lines, effectively removing straylight and enhancing luminous transmittance, particularly designed to work with Fresnel optics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-dimensional multi-channel spatial filter with absorbing channels (honeycomb filter) is used to remove ghost images and spurious light, then the image quality and contrast are improved, but the transmission efficiency deteriorates to 50%
Solution Approach 1:
The filter is segmented into alternating transparent and absorbing sectors arranged in a one-dimensional pattern rather than a two-dimensional honeycomb structure. This segmentation allows light to pass through transparent sectors while absorbing sectors block straylight, achieving effective ghost image removal with higher transmission efficiency than conventional 2D filters.
Solution Approach 2:
The invention transitions from a two-dimensional honeycomb filter structure to a one-dimensional alternating sector pattern. This dimensional reduction simplifies the filter geometry while maintaining the essential function of separating useful light from straylight, thereby improving transmission efficiency without sacrificing image quality.
2Measurement precision
If the length/diameter ratio of channels is increased to produce a realistic image of the sun, then the image realism is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The filter is divided into alternating transparent and absorbing sectors that can be manufactured as separate components and then assembled. This segmentation allows each sector to be produced using standard manufacturing processes without requiring complex high aspect-ratio channel structures, reducing both manufacturing difficulty and cost while maintaining image realism.
Solution Approach 2:
By reducing the filter structure from 2D honeycomb to 1D alternating sectors, the invention eliminates the need for deep, narrow channels with high length/diameter ratios. The simplified geometry can be manufactured using conventional techniques such as extrusion or lamination, significantly reducing manufacturing complexity and cost.
3Stability of the object's composition
If low angle diffuser filters (frost) are used to remove spatially modulated luminance patterns, then the luminance uniformity is improved, but the contrast deteriorates and the sun image becomes blurred
Solution Approach 1:
Different sectors of the filter have different optical properties: transparent sectors maintain high luminance transmission for the direct sun image, while absorbing sectors remove straylight and spatially modulated patterns. This local differentiation of optical properties achieves both luminance uniformity and high contrast without blurring the sun image.
Solution Approach 2:
The filter is segmented into alternating transparent and absorbing sectors that perform different functions. The transparent sectors preserve the sharp sun image while the absorbing sectors eliminate unwanted spatial modulations. This segmented approach achieves luminance uniformity without the contrast loss and image blurring caused by conventional diffuser filters.
4Volume of moving object
If Fresnel optics are used for collimation to compact and lighten the device, then the device size and weight are reduced, but spurious light is generated that reduces contrast
Solution Approach 1:
The filter extracts and removes the spurious light generated by Fresnel optics through its alternating transparent and absorbing sectors. The absorbing sectors specifically target and block the straylight propagating at angles greater than useful for sun image reproduction, while the transparent sectors allow the useful collimated light to pass through. This extraction of harmful spurious light restores high contrast while maintaining the compact device size enabled by Fresnel optics.
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 filter achieves high luminous transmittance, sharp contrast between sky and sun images, and compact device size, while eliminating ghost images and spurious light, at a lower cost and complexity compared to traditional solutions.
Implementation Method 1
each transparent sector (103) is locally arranged and configured to have such a refractive power that, given a first collimated light (201) which impinges on the inlet surface (101) along an incidence direction (D) at a local region of the inlet surface (101) of the optical filter (100), the transparent sector (103) focuses the first collimated light (201) along a first focal line (203) orthogonal to a local plane of incidence (P)
Implementation Method 2
a plurality of locally planar and mutually locally parallel visible light absorbing sectors (108) extending between the inlet surface (101) and the outlet surface (102)
Data Source
AI summary
The present invention refers to an optical filter (100) comprising an inlet surface (101) and an outlet surface (102) which are substantially flat and parallel, a plurality of locally planar and mutually locally parallel visible light absorbing sectors (108) extending between the inlet surface (101) and the outlet surface (102) for a sector length (L), and a plurality of solid transparent sectors (103) made with at least one solid material transparent to visible light, each transparent sector (103) of the plurality of transparent sectors being interposed between two absorbing sectors (108) to create an alternation of transparent sectors (103) and absorbing sectors (108) adjacent to and in contact with each other, wherein each visible light absorbing sector (108) of the plurality of visible light absorbing sectors (108) borders at most two transparent sectors (103) of the plurality of transparent sectors (103), and/or wherein a distance between adjacent absorbing sectors (108) of the plurality of absorbing sectors (108) is substantially constant, wherein each transparent sector (103) of the plurality of transparent sectors is locally arranged and configured to have such a refractive power that, given a first collimated light (201) which impinges on the inlet surface (101) along an incidence direction (D) at a local region of the inlet surface (101), the transparent sector (103) focuses the first collimated light (201) along a first focal line (203) orthogonal to a local plane of incidence (P), and/or gives a second collimated light (202) which impinges the outlet surface (102) along an incidence direction (D) at a local region of the inlet surface (101), the transparent sector (103) focuses the second collimated light (202) along a second focal line (204) orthogonal to a local plane of incidence (P), wherein a plane orthogonal to the inlet surface (101) and containing a normal (N) to an absorbing sector (108) of the plurality of absorbing sectors D at the local region of the inlet surface (101) defines the local plane of incidence (P), and the intersection between the local plane of incidence (P) and the surface of an absorbing sector (108) defines the incidence direction (D) substantially common to the whole inlet surface (101).