Anamorphic Reflecting Optical System for Wide-Angle Imaging
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Solution Overview
Problem
Conventional optical systems fail to maintain good ground resolution when viewing at large angles from the nadir direction, particularly in aerospace applications requiring wide area surveillance, due to the elongation of square FPA pixels, which reduces image quality and lacks practical anamorphism for maintaining image quality over a large field of view.
Innovation Solution
An anamorphic optical system comprising a plurality of rotationally symmetric mirrors with tilted and decentered configurations to achieve a focal length ratio greater than 1.5 between the along-scan and cross-scan directions, forming an intermediate image and relaying it to a detector, ensuring effective anamorphism and maintaining image quality across a wide field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional optical systems with square FPA pixels are used, then the system structure is simple, but the ground sample distance becomes elongated when viewing at large angles from nadir, reducing image resolution
Solution Approach 1:
The patent introduces anamorphic optical components that create asymmetric focal lengths in different directions. Specifically, the focal length in the along-scan direction is made different from the focal length in the cross-scan direction, causing the optical system to compensate for the elongation effect of square pixels at large viewing angles. This asymmetric design maintains square pixel footprints across the field of view while preserving image resolution.
Solution Approach 2:
The patent changes the focal length parameter of the optical system to be direction-dependent. By making the focal length vary with direction (anisotropic focal length), the system dynamically adjusts the mapping between angular space and detector pixels to maintain constant ground sample distance across different viewing angles, thereby resolving the elongation problem without changing the detector geometry.
2Measurement precision
If the focal length is doubled in the along-scan direction to maintain resolution at large angles, then the ground sample distance is improved, but the optical system becomes more complex with anamorphic components
Solution Approach 1:
The patent segments the optical system into distinct functional components: anamorphic optical elements (such as cylindrical lenses or curved mirrors) that introduce the focal length variation, and standard optical components that handle image formation. This segmentation allows the anamorphic function to be isolated and optimized separately, making the overall system design more manageable despite the added complexity.
Solution Approach 2:
The anamorphic optical components are designed to serve multiple functions: they correct the pixel footprint distortion, maintain constant ground sample distance across the field of view, and can be integrated with various detector configurations. This multi-functionality justifies the added optical complexity by delivering multiple performance benefits from a single design modification.
3Measurement precision
If cylindrical surfaces are used on mirrors or lenses to achieve anamorphism, then the focal length ratio is improved, but the manufacturing and testing difficulty increases
Solution Approach 1:
The patent introduces intermediate optical elements (such as anamorphic lenses or beam expanders) between the main optical components and the detector. These intermediary components handle the focal length ratio adjustment separately, allowing the primary mirrors and lenses to be manufactured with standard precision while the anamorphic function is implemented through dedicated intermediary elements that are easier to characterize and test.
Solution Approach 2:
The patent explores replacing complex mechanical anamorphic mirror configurations with optical elements (lenses) that provide the same focal length ratio effect through refraction rather than reflection. This substitution can simplify manufacturing by using standard lens fabrication techniques instead of precision mirror figuring, and the optical elements can be more easily tested using conventional optical alignment procedures.
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 solution maintains a smaller ground sample distance and achieves good image quality with a 2:1 anamorphism ratio, providing improved resolution and image quality across a 3-degree by 9-degree field of view, suitable for aerospace applications without wavelength restrictions, and ensuring 100% cold-shielding for cold IR FPAs.
Implementation Method 1
a plurality of mirrors, each mirror having a rotational axis of symmetry; each axis being such that a rotation or a spin of each mirror around its axis of symmetry does not change a ray path of reflected rays from the mirror
Data Source
Figure 1A~1B
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AI summary
Various embodiments provide an optical system including a plurality of mirrors, each mirror having a rotational axis of symmetry; and a detector configured to detect an image formed by the plurality of mirrors. The plurality of mirrors are configured to scan an object space along a first direction. The plurality of mirrors are configured and arranged so that a focal length of the plurality of mirrors along the first direction is greater than a focal length of the plurality of mirrors in a second direction perpendicular to the first direction so as to obtain a ratio of anamorphism greater than approximately 1.5.