Off-axis Three-mirror Freeform Imaging Design
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Solution Overview
Problem
Conventional methods for designing off-axis imaging systems with freeform surfaces face challenges in achieving ultra-wide field-of-view due to uncorrectable off-axis aberrations and limited field consideration, which affects the size and position of the aperture stop, and results in poor imaging quality.
Innovation Solution
A method for designing an off-axis three-mirror imaging system with freeform surfaces involves establishing an initial system, tracking feature rays to calculate data points for the tertiary mirror, and then the primary mirror, while maintaining the secondary mirror unchanged, allowing for the optimization of freeform surfaces to improve image quality and field curvature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional designing methods are used with spherical or aspheric surfaces, then the structure is simple, but off-axis aberrations cannot be corrected and field-of-view is limited
Solution Approach 1:
The patent applies freeform surfaces with asymmetric geometry to the primary and tertiary mirrors, breaking the rotational symmetry of conventional spherical or aspheric surfaces. This asymmetric design enables correction of off-axis aberrations while maintaining structural feasibility, achieving both improved imaging quality and ultra-wide field-of-view coverage
Solution Approach 2:
The patent transforms the mirror surfaces from conventional spherical or aspheric parameters to freeform surface parameters with higher degrees of freedom. By changing the surface parameterization from rotationally symmetric to asymmetric freeform forms, the system achieves superior aberration correction capability while maintaining manufacturing feasibility through advanced fabrication techniques
2Manufacturing precision
If freeform surfaces are used to reduce aberrations, then imaging quality improves, but the designing process becomes complex and aperture stop positioning is affected
Solution Approach 1:
The patent establishes the aperture stop position and the secondary mirror configuration in advance before optimizing the freeform surfaces of the primary and tertiary mirrors. This preliminary action fixes critical system parameters, reducing the design variables and simplifying the subsequent freeform surface optimization process while ensuring consistent aperture stop positioning
Solution Approach 2:
The patent divides the design process into distinct stages: first establishing the aperture stop and secondary mirror configuration, then separately optimizing the primary and tertiary mirror freeform surfaces. This segmentation of the design process reduces complexity by breaking down the overall optimization into manageable sub-problems with fixed boundary conditions
3Ease of operation
If the primary mirror is traced before the aperture stop in conventional methods, then the designing sequence is simple, but the aperture stop size and position are affected by optical power changes
Solution Approach 1:
The patent inverts the conventional design sequence by first establishing the aperture stop position and size, then tracing the primary mirror and optimizing its freeform surface. This reversed sequence ensures that the aperture stop parameters remain fixed reference points throughout the optimization process, eliminating the coupling effect between optical power changes and aperture stop positioning
4Device complexity
If conventional methods with limited fields are used, then the designing process is manageable, but the field-of-view remains small and cannot achieve ultra-wide coverage
Solution Approach 1:
The patent changes the surface parameters from conventional spherical or aspheric forms to freeform surfaces with higher degrees of freedom. This parameter transformation enables the system to correct off-axis aberrations across ultra-wide field angles, achieving field-of-view coverage exceeding 60 degrees while maintaining imaging quality through advanced surface parameterization and optimization
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 enables the design of off-axis three-mirror imaging systems with improved imaging quality, increased field-of-view, and reduced aberrations, allowing for the fabrication of continuous and smooth primary and tertiary mirrors, enhancing the system's ability to achieve ultra-wide field-of-view imaging.
Implementation Method 1
an off-axis three-mirror imaging system with freeform surfaces includes a primary mirror, a secondary mirror, and a tertiary mirror. Light from an object is reflected by the primary mirror, the secondary mirror, and the tertiary mirror, and then forms an image on an image detector
Data Source
AI summary
A method for designing an off-axis three-mirror imaging system with freeform surfaces is provided. A primary mirror initial structure, a secondary mirror initial structure, and a tertiary mirror initial structure are established. A number of first feature rays are selected, while the primary mirror initial structure and the secondary mirror initial structure unchanged. The first feature rays are forward ray tracked from an object space to an image detector. A number of first feature data points are calculated to obtain a tertiary mirror. A number of fields and a number of second feature rays are selected, while the secondary mirror initial structure and the tertiary mirror unchanged. The second feature rays are reverse ray tracked from the image detector to the object space. A number of second feature data points are calculated to obtain the primary mirror.