CGH Calibration Using Imaging Lens for Wavefront Measurement
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Solution Overview
Problem
Current systems using computer-generated holograms (CGHs) for calibrating optical surfaces, such as interferometers and nulling devices, face discrepancies in imaging results due to poor focus and spatial frequency calibration, leading to inaccuracies in wavefront error measurements.
Innovation Solution
Incorporating an imaging lens in the optical path between the wavefront measuring system and the CGH, positioned near the center of curvature, to form a pupil image and ensure proper conjugation, thereby improving the calibration fidelity by reducing wavefront errors and grating ring density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a CGH is placed near the center of curvature without an imaging lens, then the radial size of the CGH is minimized, but the pupil image is not properly conjugated and wavefront errors increase
Solution Approach 1:
An imaging lens is introduced as an intermediary component between the wavefront measuring system and the CGH. This lens creates a properly conjugated pupil image at the CGH location, enabling accurate wavefront error measurements while maintaining the benefit of a compact CGH radial size when positioned near the center of curvature.
Solution Approach 2:
The system changes the optical parameters by introducing an imaging lens that modifies the conjugation relationship between the pupil and the CGH. This parameter change enables proper imaging while maintaining the compact CGH configuration near the center of curvature.
2Area of stationary object
If the CGH is located close to the center of curvature, then the radial size of the CGH is minimized, but middle and high spatial frequencies are not properly calibrated
Solution Approach 1:
The imaging lens serves as a mediator that enables proper spatial frequency calibration by creating a conjugated pupil image at the CGH. This allows the CGH to be positioned near the center of curvature with minimized radial size while still achieving accurate middle and high spatial frequency calibration.
3Device complexity
If no imaging lens is used, then the device complexity is reduced, but the pupil image diameter on the CGH increases and calibration fidelity deteriorates
Solution Approach 1:
The imaging lens modifies key optical parameters including pupil image diameter, conjugation relationship, and spatial frequency calibration. These parameter changes improve calibration fidelity and reduce the pupil image diameter on the CGH, while the added complexity is justified by the significant improvement in measurement accuracy.
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 enhances the calibration of middle and high spatial frequencies, reduces wavefront errors, and minimizes the diameter of the pupil image on the CGH, achieving better data fidelity and manufacturing feasibility.
Implementation Method 1
an imaging lens disposed in the axial path between the WMS and the CGH
Implementation Method 2
computer generated hologram (CGH) disposed in an axial path of light traveling to or from the WMS
Data Source
AI summary
A device for calibrating a wavefront measuring system (WMS) includes a computer generated hologram (CGH) disposed in an axial path of light traveling to or from the WMS, and an imaging lens disposed in the axial path between the WMS and the CGH. An entrance port of the WMS is configured to form a pupil image of a device under test, where a center of curvature (CoC) of the device under test is located along the axial path between the pupil image and the device under test. The CGH is located along the axial path at the CoC, when the imaging lens is inserted between the CoC and the WMS.