Variable Aberrator for Aspheric Wavefront Stitching
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Solution Overview
Problem
Current subaperture wavefront measurement techniques for aspheric optical elements face limitations due to the need for large, costly measurement optics and are prone to systematic errors from wavefront modifying optics, especially when measuring test objects with significant departures from spherical forms, leading to increased measurement time, noise, and errors.
Innovation Solution
The use of a variable optical aberrator that reshapes the measurement wavefront to match the aspheric characteristics of the test object, allowing for subaperture measurements to be collected independently of the test object's size, with compensators to account for systematic errors introduced by the aberrator, enabling high-accuracy wavefront measurements over a wide range of aspheric surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional subaperture wavefront measurement techniques are used for aspheric optical elements, then measurement coverage can be achieved, but the measurement optics must be large and costly, and systematic errors increase when measuring objects with significant departures from spherical forms
Solution Approach 1:
The measurement process is divided into multiple overlapping subaperture measurements that are later stitched together to form a complete measurement of the entire optical element. This segmentation allows the use of smaller, simpler measurement optics while still achieving full-aperture coverage through computational synthesis of the subaperture data.
Solution Approach 2:
The patent changes the reference wavefront parameters to match the aspheric characteristics of the test object. By using an aspheric reference wavefront instead of a spherical one, the measurement system can accurately measure objects with significant departures from spherical forms without requiring large, complex optics, thereby reducing systematic errors.
2Area of stationary object
If the number of subapertures is increased to cover the desired area of the test surface, then measurement coverage is improved, but measurement time, calculation complexity, noise, and other sources of error increase
Solution Approach 1:
The patent performs preliminary characterization of the aspheric test object to determine the optimal subaperture configuration and overlap regions. This preliminary action allows for efficient planning of the measurement sequence, reducing the total number of subaperture measurements required while ensuring complete coverage and minimizing measurement time and computational complexity.
3Productivity
If wavefront modifying optics are used to match curvature variations within larger annular zones, then the number of measurements required is reduced, but systematic errors are introduced that are indistinguishable from test object errors
Solution Approach 1:
The patent creates a computational model (copy) of the aspheric reference wavefront that accurately represents the test object's expected form. This virtual reference is then used in the stitching algorithm to correct for systematic errors, allowing the measurement system to achieve both high productivity and reliability without introducing indistinguishable errors from physical wavefront modifying optics.
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 reduces the number of subaperture measurements required, minimizes uncertainties associated with aspheric wavefront shaping, and improves measurement accuracy by maintaining the measurement wavefront within the capture range of the wavefront-measuring gauge, while allowing for simpler, more predictable optics and larger measurement areas.
Implementation Method 1
a variable optical aberrator that reshapes the measurement wavefront to match the aspheric characteristics of the test object
Implementation Method 2
Various techniques are available for comparing the shape of the test wavefront against the original reference wavefront, such as by forming interference patterns
Data Source
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AI summary
A metrology system for measuring aspheric test objects by subaperture stitching. A wavefront-measuring gauge having a limited capture range of wavefront shapes collects partially overlapping subaperture measurements over the test object. A variable optical aberrator reshapes the measurement wavefront with between a limited number of the measurements to maintain the measurement wavefront within the capture range of the wavefront-measuring gauge. Various error compensators are incorporated into a stitching operation to manage residual errors associated with the use of the variable optical aberrator.