Symmetric Test Object for Optical PSF Measurement
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Solution Overview
Problem
Existing test objects for measuring the point spread function of optical systems are inadequate in accurately assessing imaging quality due to limitations in inducing symmetrical image aberrations and separating Zernike polynomials, leading to incomplete illumination of the pupil and low radiation transfer.
Innovation Solution
A test object with structure elements having multiple axes of symmetry, designed to ensure orthogonal Zernike polynomials and increased radiation transfer, comprising bar- or slit-shaped elements with dimensions smaller than the Airy diameter in one direction and larger in another, arranged to prevent asymmetrical image aberrations and enhance luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test object with asymmetrical structure elements is used, then the structure can induce specific image aberrations for measurement, but it cannot prevent asymmetrical image aberrations and achieve orthogonal Zernike polynomials
Solution Approach 1:
The patent applies asymmetry principle by designing structure elements with specific symmetry properties (even-order rotational symmetry) that allow controlled generation of asymmetrical image aberrations for measurement purposes, while the overall test object maintains symmetry to enable orthogonal Zernike polynomials. This resolves the contradiction by using asymmetry in a controlled, beneficial way rather than avoiding it entirely.
Solution Approach 2:
The patent applies local quality principle by making different structure elements have different shapes and orientations (e.g., bars, slits, pinholes with varying dimensions) while maintaining overall symmetry. Each local element is optimized to induce specific types of aberrations, while the global symmetry ensures orthogonal Zernike polynomials for accurate measurement.
2Measurement precision
If the structure elements are made small to resolve fine details, then the illumination of the pupil is improved, but the total transmission and signal-to-noise ratio decrease
Solution Approach 1:
The patent applies segmentation principle by dividing the test object into multiple structure elements of different sizes, shapes, and orientations. This allows the optical system to be probed at different spatial frequencies simultaneously, resolving fine details while maintaining sufficient signal strength through the diversity of element sizes and the overall symmetry that ensures orthogonal Zernike polynomials.
3Device complexity
If a simple pinhole structure is used, then the device complexity is low, but the ability to separate Zernike polynomials and measure different aberration types is insufficient
Solution Approach 1:
The patent applies segmentation principle by using multiple structure elements with different orientations and shapes (bars, slits, pinholes) arranged symmetrically. This segmentation provides the diversity needed to separate Zernike polynomials and measure different aberration types independently, while the overall symmetric arrangement maintains manageable device complexity.
Solution Approach 2:
The patent applies universality principle by designing a single test object that can measure multiple types of imaging aberrations (coma, astigmatism, spherical aberration, higher-order coma) simultaneously through its symmetric multi-element structure. This multi-functional design eliminates the need for multiple separate test objects, maintaining device simplicity while achieving comprehensive measurement capability.
4Measurement precision
If the integration time is increased to improve signal-to-noise ratio, then the measurement accuracy improves, but the measurement time and productivity decrease
Solution Approach 1:
The patent applies segmentation principle by using multiple structure elements that generate different diffraction patterns and image characteristics. This allows parallel extraction of multiple aberration parameters from a single image or minimal images, improving productivity without sacrificing measurement precision through the orthogonal Zernike polynomial separation enabled by the symmetric structure.
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 enables precise measurement of imaging aberrations, improved accuracy in determining coma, astigmatism, and spherical aberrations, and increased signal-to-noise ratio, allowing for shorter integration times and more efficient measurement of the point spread function.
Implementation Method 1
The structure is embodied, in particular, in such a way that it leads to an illumination of the pupil of the optical system for which the Zernike polynomials that are to be used for describing this illumination are orthogonal to one another
Data Source
AI summary
A test object for measuring the point spread function (PSF) of an optical system having a given Airy diameter (dAiry) comprises a structure to be imaged having a plurality of structure elements to be imaged, wherein the structure elements are embodied and arranged in such a way that the structure has at least two axes of symmetry.