Interferometer Path-Matching for Radius-of-Curvature Precision
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Solution Overview
Problem
Interferometric measurements of the radius of curvature require two measurements, one in the cateye and one in the confocal configuration, making them susceptible to external environmental factors and impractical for high-throughput environments where precision is needed for production tolerance, often leading to inaccurate production and discarded components.
Innovation Solution
An interferometer with internal path-matching configuration using a short-coherence source and a beam splitter produces two beams for a single cateye measurement that is stored as a calibration, allowing subsequent ROC measurements to be taken with a single confocal position measurement, independent of external factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two measurements (cateye and confocal) are taken externally to determine ROC, then measurement can be performed, but measurement precision deteriorates due to environmental factors and mechanical stresses
Solution Approach 1:
The patent combines the cateye and confocal measurements into a single integrated measurement process. By using a single interferometric setup to perform both measurements simultaneously or in sequence without external repositioning, the system eliminates the need for separate external measurement devices that are susceptible to environmental interference. The internal path-matching mechanism ensures both measurements reference the same stable optical path, thereby improving precision while reducing exposure to harmful external factors.
Solution Approach 2:
The patent performs a preliminary cateye measurement to establish a reference position before performing the confocal measurement. This preliminary action allows the system to calculate ROC from the difference between the two positions within the same stable optical setup. By establishing the reference internally beforehand, the system eliminates the need for repeated external cateye measurements that would be affected by environmental changes, thereby maintaining high measurement precision.
2Measurement precision
If two measurements are required for ROC determination, then accuracy can be achieved, but productivity decreases due to repositioning time and cycle time constraints
Solution Approach 1:
The patent merges the cateye and confocal measurements into a single operational cycle using one interferometric instrument. The system performs both measurements on the same optical path without requiring the test article to be removed or repositioned externally. This integration maintains measurement accuracy while dramatically improving productivity by eliminating repositioning time and enabling high-throughput inline measurements in production environments.
Solution Approach 2:
The patent enables continuous measurement operations by performing both cateye and confocal measurements in an uninterrupted sequence within the same optical setup. The test article remains in place throughout the measurement process, allowing the interferometer to continuously acquire data without downtime for repositioning. This continuity of useful action maintains measurement accuracy while maximizing productivity for high-volume production inspection.
3Productivity
If cateye position is used as reference for multiple samples, then productivity improves, but reliability decreases due to environmental shifts affecting the reference position
Solution Approach 1:
The patent performs a preliminary cateye measurement to establish an internal reference position that is stored for subsequent confocal measurements. By capturing this reference internally within the interferometer's stable optical path and storing it for reuse, the system enables rapid repetitive measurements without repeatedly exposing the reference to environmental changes. This preliminary action maintains reference position stability while improving productivity for measuring multiple samples.
Solution Approach 2:
The patent transitions from external spatial referencing to internal optical path referencing. Instead of relying on the physical position of the test article in external space (which is affected by environmental factors), the system uses the internal optical path length within the interferometer as the reference dimension. This dimensional shift from external mechanical positioning to internal optical path measurement ensures reference stability while enabling efficient repetitive measurements.
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 accurate and efficient repetitive measurements of the radius of curvature by internalizing the path-matching mechanism, reducing the impact of environmental changes and allowing for inline measurements in production settings, thereby reducing production errors and increasing efficiency.
Implementation Method 1
a beam splitter are used to produce two beams propagated along respective shorter-path and longer-path arms
Implementation Method 2
mirrors that reflect them back to the beam splitter for injection into an interferometric setup
Implementation Method 3
Interference fringes are produced only when the time of flight is the same for both the test and reference beams
Implementation Method 4
a short-coherence source and a beam splitter are used to produce two beams
Data Source
AI summary
An interferometer includes a short-coherence source and an internal path-matching assembly contained within its housing. Because path matching occurs within the housing of the interferometer, it is removed from external environmental factors that affect measurements. Therefore, a single cateye measurement of an exemplary surface can be performed in advance and stored as a calibration for subsequent radius-of-curvature measurements. In one embodiment, a path-matching stage is incorporated into a dynamic interferometer where orthogonally polarized test and reference beams are fed to a dynamic imaging system. In another embodiment, orthogonal linearly polarized test and reference beams are injected into a remote dynamic interferometer by means of one single-mode polarization-maintaining optical fiber.