Optical Wavefront Measurement Using Pupil Subaperture Illumination
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Solution Overview
Problem
Existing methods for determining the imaging quality of an optical system require illuminating the entire pupil, which is impractical and limits the flexibility in measuring unconventional pupil shapes, such as elliptical or free-form pupils.
Innovation Solution
A method that illuminates the optical system using subapertures within the pupil, allowing sequential measurement and combination of results, using phase retrieval methods and basis functions like Zernike polynomials to determine the wavefront, and a metrology system with an elliptical stop to measure elliptical pupils directly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the entire pupil is illuminated for measuring imaging quality, then measurement accuracy is improved, but measurement complexity and device requirements worsen
Solution Approach 1:
The pupil is divided into multiple subapertures that can be illuminated and measured sequentially. Each subaperture measurement captures a portion of the wavefront information, and these partial measurements are later combined through computational algorithms to reconstruct the complete wavefront and determine imaging quality. This segmentation allows using simpler measurement setups for each subaperture while achieving accurate overall measurement through data fusion.
2Ease of manufacture
If conventional circular pupils are used for measurement, then measurement simplicity is improved, but adaptability to unconventional pupil shapes worsens
Solution Approach 1:
The method transforms the measurement approach by changing from requiring the entire pupil to be illuminated simultaneously to illuminating and measuring individual subapertures sequentially. This parameter change in the measurement strategy enables the system to handle various pupil shapes (circular, elliptical, free-form) by appropriately selecting and positioning subapertures, without requiring complex customization of the measurement setup for each pupil shape.
3Adaptability or versatility
If subapertures are used instead of full pupil illumination, then measurement flexibility is improved, but measurement time increases
Solution Approach 1:
The measurement process maintains continuity by systematically scanning through multiple subapertures and accumulating wavefront information from each measurement. Rather than performing separate independent measurements, the method continuously builds up the complete wavefront data set by combining results from sequential subaperture measurements, optimizing the measurement sequence to minimize total measurement time while ensuring complete coverage of the pupil.
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
Enables flexible and accurate determination of imaging quality for various pupil shapes, reducing measurement complexity and improving precision by eliminating test structure contributions.
Implementation Method 1
measuring an intensity of the illumination light in an image plane of the optical system using a spatially resolving detection device for the purposes of determining a measured aerial image of the test structure
Implementation Method 2
determining a wavefront of the optical system on the basis of the result of the minimized difference between the measured aerial image and the simulated aerial image
Data Source
AI summary
To determine an imaging quality of an optical system when illuminated by illumination light within an entrance pupil or exit pupil, a test structure is initially arranged in an object plane of the optical system and an illumination angle distribution for illuminating the test structure with the illumination light is specified. The test structure is illuminated at different distance positions relative to the object plane. An intensity of the illumination light is measured in an image plane of the optical system, the illumination light having been guided by the optical system when imaging the test structure at each distance position. An aerial image measured in this way is compared with a simulated aerial image and fit parameters of a function set for describing the simulated aerial image are adapted and a wavefront of the optical system is determined on the basis of the result of a minimized difference.