Diffractive Wave Shaping for Large Aspherical Surface Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current interferometric measuring apparatuses face limitations in accurately measuring large aspherical optical surfaces, particularly those with convex or raised shapes, due to the size constraints of computer-generated holograms (CGHs) used for generating aspherical wave fronts.
Innovation Solution
The method involves using two diffractive wave-shaping elements with diffractive measurement structures, where each element is aligned relative to the other through an alignment light that has interacted with a diffractive alignment structure, allowing for precise alignment and measurement of optical surfaces larger than a single CGH can cover, using a cascaded arrangement and tilted surface normals to improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single computer-generated hologram (CGH) is used to generate aspherical wave fronts, then measurement precision is improved for small optical surfaces, but the measurable surface area is limited by the CGH size
Solution Approach 1:
The patent divides the measurement task into multiple segments by using a plurality of CGHs instead of a single CGH. Each CGH is responsible for measuring a specific portion of the large optical surface. The wave shaping elements are segmented across multiple components, allowing the system to cover a larger total area while maintaining the measurement precision that would be achievable with a single CGH for its designated region.
2Area of stationary object
If multiple wave shaping elements are used to measure large optical surfaces, then measurable surface area is improved, but alignment uncertainty increases
Solution Approach 1:
The patent introduces alignment markers as intermediary reference structures that are formed together with the CGHs on the same substrates. These alignment markers serve as mediators between the multiple wave shaping elements, providing fixed reference points that enable precise relative positioning. By using these intermediary markers, the system can accurately align multiple CGHs without introducing significant alignment uncertainty, thus maintaining measurement precision while measuring large surfaces.
3Measurement precision
If conventional interferometer optics are used, then spherical wave fronts can be generated with high precision, but aspherical wave fronts cannot be generated accurately
Solution Approach 1:
The patent changes the fundamental parameter of wave front shaping from conventional optics to diffractive optics. Instead of using conventional interferometer optics that are limited to spherical wave fronts, the system employs computer-generated holograms that can generate arbitrary aspherical wave fronts by controlling the diffraction pattern. This parameter change enables the system to adapt to different aspherical surface measurements while maintaining high precision, as the CGHs can be computationally designed to match any target aspherical geometry.
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 high-accuracy measurement of deviations in large aspherical optical surfaces by ensuring precise alignment of wave shaping elements, allowing for the measurement of surfaces that would otherwise be beyond the size limit of individual CGHs, thereby improving the measurement accuracy and reducing alignment uncertainties.
Implementation Method 1
each of which wave shaping elements comprises a diffractive measurement structure for adapting part of a wave front of incoming light to a respective portion of the target shape
Implementation Method 2
deviations between the shape of the surface under test and its target shape are determined from a resulting interference pattern
Data Source
AI summary
A method of measuring a deviation of an optical surface from a target shape and a method of manufacturing an optical element. This method of measuring the deviation includes: performing a first interferometric measurement using a first diffractive measurement structure, which is arranged to cover a first area of the optical surface, to provide a first interferometric measurement result, performing a second interferometric measurement using a second diffractive measurement structure, which is arranged to cover a second area of the optical surface different from the first area, to provide a second interferometric measurement result, and determining a deviation of the optical surface from the target shape.