Optical Property Calibration Using Pupil Spot Shift Decoupling
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Solution Overview
Problem
Existing methods for determining optical properties of optical systems, such as apodisation and diattenuation, are prone to errors due to manufacturing tolerances, drift, and placement inaccuracies, making it difficult to accurately separate illumination system effects from projection system effects.
Innovation Solution
A method involving an optical element with shifting optical areas, such as wedges or gratings, is used to calibrate individual direction shifts, allowing direct measurement of pupil spot shifts and enabling accurate calculation of optical properties by decoupling illumination and projection system effects, with optional inclusion of a Ronchi test and polarizers for enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing methods are used to determine optical properties, then the measurement process is simple, but the measurement precision deteriorates due to manufacturing tolerances and drift
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement before the actual optical property measurement. The calibration step determines calibration factors that compensate for manufacturing tolerances and drift in the optical element. These calibration factors are stored and used during subsequent measurements to correct for systematic errors, thereby improving measurement precision without adding complexity to the main measurement process.
Solution Approach 2:
The patent implements feedback by using the calibration measurement results to generate correction factors that are applied to subsequent measurements. The system continuously references the calibration data to compensate for drift and manufacturing variations, creating a closed-loop correction mechanism that maintains high measurement precision over time and across different optical elements.
2Reliability
If calibration with multiple pupil spots is performed, then the reliability of optical property determination improves, but the measurement time increases
Solution Approach 1:
The patent applies segmentation by dividing the pupil into multiple discrete pupil spots rather than using a continuous or single-point measurement approach. Each pupil spot is measured separately to determine its specific calibration factor. This segmentation allows parallel processing of multiple measurement points and enables more comprehensive sampling of the optical element's performance across the pupil, improving reliability while the structured approach keeps measurement time manageable.
Solution Approach 2:
The patent uses partial action by measuring a sufficient number of pupil spots to achieve the required reliability without measuring every possible point. The method determines an appropriate number of pupil spots and field points that provides adequate statistical reliability for the application, avoiding unnecessary measurements that would waste time while ensuring enough data points are collected for accurate calibration factor determination.
3Manufacturing precision
If manufacturing tolerances of optical elements are considered, then the accuracy of optical property measurement improves, but the device complexity increases
Solution Approach 1:
The patent implements self-service by allowing each optical element to calibrate itself through the measurement process. The calibration procedure uses the optical element's own performance characteristics to generate correction factors specific to that element's manufacturing variations. This self-calibration approach eliminates the need for external reference standards or complex adjustment mechanisms, improving manufacturing precision compensation while keeping the device relatively simple.
Solution Approach 2:
The patent applies parameter changes by transforming the physical manufacturing variations of the optical element into measurable parameter deviations through the calibration process. The system measures actual performance parameters (pupil spot positions, intensities) and converts them into calibration factors that parameterize the manufacturing deviations. This allows the system to account for manufacturing precision issues through software-based parameter adjustment rather than hardware complexity.
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 errors from manufacturing and drift, providing precise measurements of optical properties like apodisation and diattenuation, independent of system effects, and allows for automatic calibration and calculation of optical properties.
Implementation Method 1
providing an optical element with an optical surface comprising a plurality of shifting optical areas which effect an individual direction shift, depending on the respective shifting optical area, of an illumination beam entering the respective shifting optical area
Data Source
AI summary
A method of determining optical properties of an optical system having an illumination system to illuminate an object field and a projection system to image the object field into an image field, comprises: providing an illumination of the object field via an illumination pupil comprising a plurality of pupil spots; providing an optical element with an optical surface comprising a plurality of shifting optical areas which effect an individual direction shift, depending on the respective shifting optical area, of an illumination beam entering the respective shifting optical area; calibrating the individual direction shift by measuring a pupil spot shift resulting from the shifting optical areas via a measuring pupil in the illumination beam path after the optical element for each of the pupil spots for a plurality of separate field points within the object field; and calculating the optical properties to be determined from the measured pupil spot shift.