Optical Surface Eccentricity Measurement Using Interferometric Filtering
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Solution Overview
Problem
Existing methods for measuring eccentricity of optical surfaces in optical systems face challenges with accuracy due to background noise from reflections on non-target surfaces and aberrations, especially when dealing with multiple optical surfaces or large eccentricities, leading to blurred images and reduced measurement precision.
Innovation Solution
A measurement apparatus utilizing a first light source to illuminate a chart with asymmetric patterns, an objective lens, a low-coherence interferometer, and a spatial filter to separate measurement light from unnecessary reflections, allowing for high-accuracy eccentricity measurement by adjusting the relative position of the objective lens and target optical system to form clear chart images and reducing background noise through interference fringe processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional measurement method is used to measure eccentricity of optical surfaces, then the measurement can be performed on multiple optical surfaces, but background noise from reflections on non-target surfaces causes reduced measurement precision
Solution Approach 1:
The patent converts the harmful background reflections into beneficial interference fringes by using low-coherence interferometry. The measurement light interferes with reference light to produce fringes that encode eccentricity information, while the spatial filter selectively removes unwanted reflected light from non-target surfaces. This transforms the problematic background noise into a useful measurement signal through interference patterning.
Solution Approach 2:
The patent introduces a spatial filter as an intermediary component between the optical system and the detector. This filter acts as a mediator that selectively transmits measurement light while blocking reflected light from non-target surfaces. The spatial filter uses the specific spatial characteristics of the measurement light to distinguish it from background reflections, thereby improving measurement precision by removing harmful interference.
2Measurement precision
If the measurement is performed on optical systems with large eccentricities, then more optical surfaces can be measured, but aberrations cause blurred images and reduced measurement accuracy
Solution Approach 1:
The patent changes the measurement parameter from direct image analysis to interference fringe analysis. By measuring the phase information encoded in interference fringes rather than relying on sharp image formation, the system can accurately measure eccentricity even when large aberrations cause image blurring. The interferometric approach extracts quantitative phase information that remains measurable despite degradation in spatial coherence and image quality.
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
The apparatus achieves precise eccentricity measurement by minimizing background noise and ensuring clear interference fringes, thereby improving the accuracy of optical surface positioning in complex optical systems.
Implementation Method 1
a low-coherence light source (second light source) that emits low-coherence light, a beam splitter that divides the low-coherence light into test light and reference light, a reference stage that changes a position of a reference mirror, and an imaging element that receives interference fringes formed by interference of the test light and the reference light
Implementation Method 2
an objective lens that adjusts a position where an image of a chart is formed
Implementation Method 3
a reduction unit configured to reduce an intensity of light reflected on an optical surface other than the target surface
Data Source
AI summary
An apparatus includes a first light source for illuminating a chart including an index surface on which an index is provided, an objective lens for guiding index light emitted from the chart to an optical system, a first element for receiving the index light reflected on an optical surface in the optical system, an interferometer configured to include a second light source and a second element, and acquire a wavefront of measurement light, the measurement light being test light reflected on the target surface, and a reduction unit for reducing an intensity of a signal of light reflected on an optical surface other than the target surface, of the test light reflected on the plurality of optical surfaces and received by the second element.