Alignment Reference Module for Hologram Spindle Axis Positioning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The high cost and unavailability of large computer-generated holograms (CGHs) for testing large convex aspheric surfaces pose challenges in accurately aligning nulling CGHs with respect to the spindle axis, leading to errors in measurement due to the non-rotational symmetry of the substrate and holographic patterns.
Innovation Solution
An alignment reference module (ARM) with a flat and spherical reflective surface is used in conjunction with an interferometer to detect the alignment of the hologram with respect to the spindle axis by comparing reflected light from these surfaces with a reference surface, allowing for precise alignment of the hologram to ensure accurate optical surface measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sub-aperture testing is used with a small NCGH for large convex aspheric surfaces, then the cost and availability of the hologram is improved, but the alignment precision of the hologram with respect to the spindle axis deteriorates due to non-rotational symmetry of the substrate and holographic patterns
Solution Approach 1:
An alignment reference module (ARM) with rotationally symmetric reflective surfaces (flat and spherical) is introduced as an intermediary between the non-symmetric NCGH and the spindle axis. The ARM provides rotationally symmetric reference features that enable precise alignment detection, mediating the mismatch between the asymmetric hologram and the rotational testing geometry.
Solution Approach 2:
The ARM introduces homogeneous (rotationally symmetric) reflective surfaces with known geometry adjacent to the non-symmetric NCGH. This creates uniform reference features in all angular directions, enabling consistent alignment measurement regardless of the asymmetric pattern of the hologram itself.
2Device complexity
If the NCGH substrate is not rotationally symmetric and the holographic pattern is not well-centered, then the device complexity is reduced, but the difficulty of detecting and measuring alignment with the spindle axis increases
Solution Approach 1:
The ARM serves as a detection intermediary that converts the difficult task of measuring alignment of the asymmetric NCGH into the easier task of measuring alignment of the symmetric ARM features. The interferometer measures the symmetric reflective surfaces of the ARM, which provide clear alignment references.
Solution Approach 2:
The ARM creates optical copies (reflected wavefronts) of known symmetric geometric features (flat and spherical surfaces) that serve as alignment references. These copied reference features are measured by the interferometer to detect misalignment, avoiding direct measurement of the complex asymmetric hologram structure.
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 ARM enables accurate alignment of the hologram to within 1 arcsec tilt and less than 3 um decenter, minimizing misalignment errors and improving the precision of optical surface measurements.
Implementation Method 1
The ARM comprises a flat portion having a reflective surface for reflecting light back toward the hologram member and a spherical portion having a reflective surface adjacent the flat portion for transmitting light back toward the hologram member
Implementation Method 2
the interferometer is configured to compare (i) the reflected light from the flat portion of the ARM with light reflected from the reference surface, and (ii) the reflected light from the spherical portion of the ARM with, light reflected from the reference surface
Implementation Method 3
Nulling computer generated holograms (NCGHs) have been used to measure optical surfaces or the wavefronts from the optical surfaces. The NCGHs usually include patterns of lines which act as diffraction gratings.
Data Source
AI summary
An alignment reference module (ARM) for detecting an alignment of a hologram with respect to a spindle axis of a spindle that supports an optic device under test (DUT). The hologram is employed for testing an optical surface of the DUT. The ARM includes a flat portion having a reflective surface for reflecting light back toward the hologram member to detect tilting of the hologram relative to the spindle axis. The ARM also includes a spherical portion having a reflective surface adjacent the flat portion for transmitting light back toward the hologram member to detect a radial position of the hologram relative to the spindle axis.