CGH Null Optical Testing System with Imaging Element
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Solution Overview
Problem
Conventional computer-generated holograms (CGHs) used in optical testing systems suffer from reduced capacity to measure middle and high spatial frequencies due to image distortion and are not optimally placed, leading to suboptimal calibration of optical surfaces.
Innovation Solution
Incorporating an imaging element, such as an imaging lens, into the optical testing system with the CGH, positioned at specific distances relative to the wavefront measuring system, to improve imaging properties and eliminate the need for conventional nulling devices, allowing for better measurement of low, middle, and high spatial frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional CGH is used without an imaging element, then the device complexity is reduced, but the measurement precision of middle and high spatial frequencies deteriorates due to image distortion
Solution Approach 1:
An imaging element (lens or mirror) is introduced as an intermediary component between the CGH and the wavefront measuring system. This imaging element forms an intermediate image that corrects the image distortion affecting middle and high spatial frequency measurements, thereby improving measurement precision without significantly increasing overall system complexity
Solution Approach 2:
The optical testing system is segmented into distinct functional components: the CGH for wavefront modulation, the imaging element for image formation and distortion correction, and the wavefront measuring system for detection. This segmentation allows each component to be optimized independently, maintaining simplicity while improving measurement precision
2Device complexity
If the CGH is placed close to the center of curvature to minimize radial size, then the device complexity is reduced, but the imaging quality deteriorates due to suboptimal positioning
Solution Approach 1:
The imaging element serves as a mediator that decouples the CGH positioning from the imaging quality requirement. The CGH can remain close to the center of curvature for simplicity, while the imaging element forms a corrected intermediate image at the appropriate location, achieving both simple configuration and high imaging quality
Solution Approach 2:
The solution moves the problem from the spatial dimension of CGH positioning to the optical dimension of image formation. By using the imaging element to create an intermediate image, the system achieves optimal imaging quality without requiring the CGH to be positioned at complex locations
3Measurement precision
If conventional nulling devices are used, then the measurement of low spatial frequencies is achieved, but the device complexity increases and middle/high spatial frequency measurement is lost
Solution Approach 1:
The imaging element and CGH are merged into a single integrated unit called the ICGH null. This combined structure simultaneously provides low spatial frequency measurement capability (through the imaging element) and middle/high spatial frequency measurement capability (through the CGH), eliminating the need for separate conventional nulling devices and reducing overall system complexity
Solution Approach 2:
The ICGH null is designed as a universal component that performs multiple functions: it acts as both an imaging element for low spatial frequency measurement and a CGH for middle/high spatial frequency measurement. This multi-functionality replaces multiple specialized components, reducing device complexity while maintaining comprehensive measurement capability
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 enhances the imaging of optical surfaces, reduces wavefront asphericity, and minimizes spatial frequency errors, providing more accurate calibration and reduced grating density requirements, making the system more accessible and effective.
Implementation Method 1
The CGH is configured to provide a null wavefront for the image of the object under test at the CGH
Implementation Method 2
the IE forms an image of the object under test at the CGH
Data Source
AI summary
An optical testing system includes a computer generated hologram (CGH) and an imaging element (IE). Both are disposed in a path of light traveling between a wavefront measuring system (WMS) and an object under test. The CGH is located a first distance from the WMS and the IE is located a second distance from the WMS. The IE is further away from the WMS, than the CGH is from the WMS, along the path of light. The center of curvature (CoC) of the object under test is also disposed in the path of light, in which the CoC is located a third distance from the WMS. The third distance is larger than the second distance, along the path of light. The IE forms an image of the object under test at the CGH; and the CGH is configured to provide a null wavefront for the image of the object under test at the CGH. The null wavefront is received by the WMS. Moreover, the IE of the optical testing system may include an imaging lens having a planar surface facing away from the CGH and a convex surface facing toward the CGH. The IE may also include an imaging mirror.