Diffractive Optical Element for Non-Spherical Surface Measurement
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Solution Overview
Problem
Current methods for measuring optical surfaces, especially non-spherical surfaces without rotational symmetry, face challenges in achieving high accuracy due to limitations in the measurement accuracy of computer-generated holograms (CGHs) and the need for complex measurement configurations.
Innovation Solution
A diffractive optical element with a single substrate and a diffractive structure pattern that generates at least four separate output waves, including a non-spherical measurement wave and multiple calibration waves, allowing for improved measurement accuracy by compensating for manufacturing errors through calibration corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single diffractive optical element is used to generate multiple output waves including calibration waves, then measurement accuracy is improved through error compensation, but device complexity increases due to the need for multiple wave generation and calibration procedures
Solution Approach 1:
The single diffractive optical element is designed to perform multiple functions simultaneously: generating the measurement wave adapted to the intended shape and generating multiple calibration waves with different wavefront characteristics. This multi-functionality allows one element to replace what would traditionally require multiple separate optical components, enabling error compensation without proportionally increasing system complexity
Solution Approach 2:
The calibration waves are generated in advance during a calibration phase before actual measurement. By performing the calibration action preliminarily, the measurement errors caused by manufacturing imperfections are identified and compensated beforehand, improving measurement accuracy without adding complexity to the actual measurement process
2Measurement precision
If multiple calibration waves are generated to compensate for manufacturing errors, then measurement accuracy improves, but loss of time increases due to additional calibration steps
Solution Approach 1:
The calibration waves are generated continuously alongside the measurement wave in a single interferometric measurement process. Rather than performing separate calibration and measurement steps, the system continuously generates all necessary waves simultaneously, maintaining useful action throughout and reducing total measurement time while preserving accuracy improvements
3Measurement precision
If the diffractive structure pattern generates at least four separate output waves including non-spherical and spherical waves, then measurement of non-spherical surfaces improves, but manufacturing precision requirements increase
Solution Approach 1:
The diffractive structure pattern is designed with asymmetric characteristics to generate both non-spherical measurement waves and spherical calibration waves from a single element. This asymmetric design allows the element to handle complex non-spherical surface measurements while the spherical waves provide reference for calibration, reducing the overall manufacturing precision burden compared to using multiple specialized elements
Solution Approach 2:
The calibration waves create optical copies or references of ideal wavefronts that can be used to compare against and correct deviations in the measurement wave. By generating these reference copies within the same optical element, the system compensates for manufacturing errors without requiring the element itself to be manufactured with ultra-high precision
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 enhances the measurement accuracy of optical surfaces by generating additional calibration waves, enabling precise calibration and correction of manufacturing errors, thereby improving the measurement of non-spherical optical surfaces.
Implementation Method 1
The diffractive structure pattern is configured to convert an input wave into at least three separate output waves by diffraction at the structure pattern
Data Source
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AI summary
A diffractive optical element (50) with a substrate (52) and a diffractive structure pattern (54) arranged thereon is provided. The diffractive structure pattern is configured to convert a plane or spherical input wave (42) radiated thereon into at least four separate output waves, wherein at least one of the output waves is a non-spherical wave (56), at least a further one of the output waves is a spherical wave (58; 70) and at least two further ones of the output waves respectively are a plane wave (60) or a spherical wave (72, 74)