Aspheric Optical Alignment Using Holographic Reference Frames
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Solution Overview
Problem
Existing methods for measuring aspheric optical wavefronts face challenges in achieving precise alignment across all six degrees of freedom, particularly for complex aspheric surfaces required in high-performance optical systems.
Innovation Solution
The proposed apparatus includes a wavefront sensor and repositionable systems with alignment and measurement holograms, allowing for alignment of optical workpieces with respect to all six degrees of freedom. This system uses a metrology frame with fiduciary references and a positioner to simultaneously adjust the alignment reference component and the optical workpiece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phase-shifting interferometry is used for measuring aspheric surfaces, then measurement capability is achieved, but alignment precision across all six degrees of freedom deteriorates
Solution Approach 1:
The patent introduces computer-generated holograms (CGHs) as intermediary elements that encode alignment information and serve as reference objects for automated alignment. These holograms act as mediators between the measurement system and the aspheric workpiece, enabling precise alignment without complex manual adjustment procedures. The CGHs contain embedded alignment features that guide the positioning system across all six degrees of freedom.
Solution Approach 2:
The patent replaces manual mechanical alignment procedures with an automated optical-mechanical system. Instead of relying on operators to physically adjust components, the system uses wavefront sensing, CGH-based reference patterns, and computer-controlled positioning to automatically achieve precise alignment. This substitution eliminates human error and enables consistent sub-wavelength alignment precision.
2Productivity
If manual alignment procedures are used for optical workpieces, then device simplicity is maintained, but productivity deteriorates
Solution Approach 1:
The patent implements a self-aligning measurement system where the optical components automatically position themselves using feedback from wavefront sensors and reference CGHs. The system performs self-calibration and self-alignment without requiring external intervention, enabling rapid successive measurements. This self-service capability eliminates time-consuming manual alignment for each workpiece while maintaining system simplicity through automated routines.
Solution Approach 2:
The patent employs pre-aligned reference CGHs and pre-calibrated optical paths that are prepared in advance. These preliminary actions establish a known reference frame before actual measurements begin, allowing workpieces to be quickly positioned relative to the pre-established alignment. This preliminary setup enables high throughput by eliminating the need for time-consuming alignment procedures during each measurement cycle.
3Measurement precision
If conventional measurement methods are used for complex aspheric surfaces, then measurement capability is achieved, but measurement precision deteriorates
Solution Approach 1:
The patent applies local quality by using customized CGHs designed for specific aspheric surface characteristics. Each CGH is tailored to match the local geometry and optical properties of the particular aspheric workpiece, enabling precise measurement of complex surfaces with varying curvatures and aspheric coefficients. This localized customization allows the system to adapt to different aspheric designs while maintaining sub-wavelength measurement precision.
Solution Approach 2:
The patent utilizes parameter changes by varying the diffraction orders, wavelengths, and CGH design parameters to optimize measurements for different aspheric surface types. The system can switch between different measurement configurations and adjust optical parameters to accommodate a wide range of aspheric geometries, from mild to extreme aspherics, thereby enhancing both precision and adaptability.
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 solution enables quick and precise alignment of optical workpieces with aspherical surfaces, facilitating high-throughput measurement of complex optical elements by accurately controlling all six degrees of freedom.
Implementation Method 1
optical interferometry
Implementation Method 2
phase-shifting interferometry
Implementation Method 3
alignment hologram, measurement hologram
Implementation Method 4
interferometric fringes
Data Source
AI summary
An analytic tool for supporting alignment of an optical component in preparation for an interferometric test and performance of such a test. Apparatus and methods involve employment of the datum features on the optical component and/or metrology frame supporting such component. The metrology frame may include a secondary set of holograms (provided for use with a conventional system already employing a primary hologram that forms the testing optical wavefront). The conventional primary hologram is preferably substituted with a set of primary holograms (contained in the same, unitary or spatially-complementary housing sets) that perform different but complementary functions and that facilitate the alignment of the metrology frame with or without the tested optical component.