Diffractive Optical Element Test Field for Interferometer
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Solution Overview
Problem
Existing test interferometers struggle to accurately measure geometric properties of diffraction structures on diffractive optical elements, particularly in distinguishing surface defects from manufacturing defects in computer-generated holograms (CGHs).
Innovation Solution
A diffractive optical element for a test interferometer is designed with diffractive shape measuring structures and test fields arranged on its surface. The test fields are surrounded by diffractive shape measuring structures, allowing for high-accuracy measurement of profile properties such as flank angle, profile depth, and microtrench depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diffraction measuring station is used to measure CGH defects, then manufacturing defects can be detected, but geometric properties of diffraction structures (profile line) cannot be measured with high accuracy
Solution Approach 1:
The patent creates a test field with test structures that are copies of the actual diffraction structures on the CGH. These test structures replicate the same geometric properties (profile line, flank angle, depth) but are positioned in a accessible location for measurement. By measuring the test structures instead of the actual diffraction structures, the patent enables high-accuracy measurement of geometric properties without compromising the measurement capability of the diffraction measuring station.
Solution Approach 2:
The test field acts as an intermediary element between the CGH and the measurement system. It provides accessible test structures that mediate the measurement process, allowing the diffraction measuring station to accurately determine geometric properties of the CGH diffraction structures through the test structures without direct measurement of the difficult-to-access CGH surface.
2Measurement precision
If test fields are integrated into the CGH surface, then geometric properties can be measured with high accuracy, but the CGH structure becomes more complex
Solution Approach 1:
The patent applies local quality by creating a dedicated test field region with specific test structures that have different functional requirements than the main CGH diffraction structures. This test field is positioned at a specific location on the CGH surface, allowing localized measurement functionality without requiring the entire CGH structure to be complex. The test structures are confined to a specific area, maintaining simplicity in the majority of the CGH while providing enhanced measurement capability where needed.
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 configuration enables precise measurement of geometric properties of the diffractive shape measuring structures, improving the accuracy of surface defect detection and distinguishing them from manufacturing defects.
Implementation Method 1
a diffractive optical element in the form of a computer-generated hologram (CGH) is used for adapting the test wave to a target shape of the mirror surface to be tested
Implementation Method 2
a test interferometer for measuring a shape of an optical surface
Data Source
AI summary
A diffractive optical element (10) for a test interferometer (100) measures a shape of an optical surface (102). Diffractive shape measuring structures (16) are arranged on a used surface (14) of the element and generate a test wave (122) irradiating the surface when the element is arranged in the interferometer. At least one test field (18) several profile properties of test structures contained in the test field. The profile properties characterize a profile line of the test structures extending transversely with respect to the used surface and include a flank angle of the profile line, a profile depth and a depth of a microtrench in a bottom region of a trench-shaped profile of the test structures. The test field is arranged at one location of the used surface instead of the diffractive shape measuring structures such that the test field is surrounded by several diffractive shape measuring structures.