Digital Holographic Surface Shape Measurement Without Reference Plane
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Solution Overview
Problem
Conventional surface shape measuring devices, such as Fizeau interferometers, face challenges in achieving high accuracy and large area measurement without requiring a physical reference plane or mechanical adjustments, and are limited by the dimension of the measurable object and the contrast of interference fringes.
Innovation Solution
A surface shape measuring device and method using digital holography that acquires data of an object light and an inline spherical wave reference light as off-axis holograms, reconstructs the surface shape by dividing the reconstructed object light hologram by a spherical wave light hologram, and performs shape measurement without a physical reference plane or mechanical adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a physical reference plane is used in conventional interferometric measuring devices, then measurement accuracy can be maintained, but the device complexity increases and mechanical adjustments are required
Solution Approach 1:
The patent extracts and eliminates the physical reference plane from the measurement system. Instead of using a conventional reference plane that requires mechanical adjustments, the invention uses digital reference data stored in memory to represent the reference surface, thereby simplifying the device structure while maintaining measurement accuracy through computational comparison
Solution Approach 2:
The patent replaces the mechanical reference plane adjustment system with a digital data-based reference system. The reference surface information is stored as digital data, and adjustments are performed through data processing rather than mechanical movements, eliminating the need for complex mechanical adjustment mechanisms
2Measurement precision
If a physical reference plane is used in conventional interferometric measuring devices, then measurement can be performed, but the measurable object dimension is limited
Solution Approach 1:
The patent transitions from a physical spatial reference plane to a digital data dimension for storing reference surface information. This dimensional change allows the reference surface to be represented without physical constraints, enabling measurement of larger objects that would exceed the physical dimensions of conventional reference planes
3Measurement precision
If conventional interferometric methods are used, then surface shape measurement can be performed, but interference fringe contrast is limited
Solution Approach 1:
The patent introduces digital data processing as an intermediary between light interference and measurement results. By capturing interference patterns and processing them digitally rather than relying solely on optical fringe contrast, the system can extract surface shape information even when optical contrast is limited, effectively decoupling measurement capability from fringe contrast requirements
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 highly accurate surface shape measurement over large areas without the limitations of conventional methods, improving measurement accuracy and extending the measurable object diameter beyond conventional limits.
Implementation Method 1
interference fringes of lights reflected, respectively from the reference plane and the object to be measured, are recorded
Data Source
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AI summary
The present invention provides a surface shape measuring device and a surface shape measuring method which do not require a physical reference plane and can improve measurement accuracy without using a mechanical adjustment mechanism. The illumination light condensing point PQ and the reference light condensing point PL are arranged as mirror images of each other with respect to the virtual plane VP, and each data of the object light O, being a reflected light of the spherical wave illumination light Q, and the inline spherical wave reference light L is recorded on each hologram. On the virtual plane VP, the reconstructed object light hologram hV for measurement is generated, and the spherical wave optical hologram sV representing a spherical wave light emitted from the reference light condensing point PL is analytically generated. The height distribution of the surface to be measured of the object 4 is obtained from the phase distribution obtained by dividing the reconstructed object light hologram hV by the spherical wave light hologram sV. High-accuracy surface shape measurement without requiring a reference plane such as a glass substrate is realized by comparing the phase data of the reflected light acquired from the surface to be measured and the phase distribution on the plane cut surface of the spherical wave obtained analytically.