Morpheus™ CGH Data Processing Software

Overview

Morpheus™ is a comprehensive software package for reducing CGH measurement data, enabling fast and accurate processing of interferometric data taken using a computer-generated hologram (CGH). Designed for manufacturing and engineering teams, Morpheus streamlines metrology workflows and facilitates deterministic polishing of complex optics.

Why Does CGH Data Require Extra Processing?

Interferometry offers a host of benefits for optical metrology. It is a full aperture snapshot measurement. It’s very fast; measurements usually take less than a second. It’s high resolution – both laterally and in height information. But the interferometer is limited in one key way: the surface shapes it can address are limited to plano and spherical. While these are common optical surface types, many optical components produced today are more complex.

CGHs unlock the beneficial aspects of interferometry for a wide range of complex surface shapes—cylinders, aspheres, off-axis parabolas and other conic sections, toroids, and even freeforms. CGHs are used every day in industry to produce high-precision optics like these, but the story isn’t over after pressing the “measure” button!

Interferometric measurements made using a CGH come with a few tradeoffs for unlocking this great metrology benefit:

• Substrate Error – The CGH itself is an optical element within the interferometric cavity. Although it is a precision optic, its slight imperfections in the surfaces and material inhomogeneity impart errors in the measurement wavefront. The magnitude of this “substrate error” is typically on the order of 10-15 nm RMS, but can be reduced to well under 5 nm when compensated for.
• Mapping Distortion – A CGH creates a null test, meaning that it generates rays normal to the test optic surface at all locations. If the curvature varies over the test optic (as is always the case for complex surface shapes) then the mapping of points on the surface will differ from the mapping at the CGH plane. In some cases, this mapping difference can be extreme. Correcting this issue is critical, particularly when using measurement data for deterministic polishing or finishing, processes that require absolute knowledge of the location of surface height information.
• Alignment Error – A CGH is designed to provide a perfect null test, which occurs when a test optic is perfectly aligned to it. In reality, perfect alignment is impossible, and small misalignments always occur. The result of CGH to test optic misalignment is small aberrations imparted into the surface measurement data. These “misalignment errors” are coupled into the measurement data and are impossible to distinguish from surface error. However, they should be eliminated before making polishing or finishing correction runs as they are only due to the test alignment and not in the surface itself.

How Does Morpheus Help?

Morpheus data reduction software from AOM facilitates the compensation and correction of these primary measurement error sources when using a CGH. Purpose-built for this kind of analysis, Morpheus requires only 2 inputs:

Measurement Data

Measurement data is taken with registration fiducials marked in the data. Every AOM CGH is fabricated with a series of fiducials used to register the location of the CGH and measurement data on the interferometer detector. The user places fiducials on the image of the CGH in the interferometer software and then makes the measurement—that’s all it takes from the measurement side, and Morpheus does the rest!

The .cgh File

The .cgh file includes all the detailed information about each unique CGH. This includes the transmitted wavefront error map as measured at the factory, the mapping relation between the test surface and CGH, and the test geometry with alignment perturbation analysis by design. And, of course, all maps and analyses are mapped to the registration fiducials, which makes downstream processing look easy.

With the fiducialized measurement data and .cgh file input, Morpheus does the rest automatically!

Morpheus Data Analysis Features

Substrate Correction

The CGH substrate transmitted wavefront error is qualified at the AOM factory using best practices, and the error map is fiducialized and stored within the .cgh file. The substrate correction module in Morpheus unpacks the substrate error map and automatically aligns the fiducials in the measurement map to the fiducials in the substrate error map. Note that the measurement data may appear rotated relative to the orientation in which it was acquired, data is oriented to the CGH coordinate frame with +Y up and +X to the right. A fiducial registration result is shown here to provide feedback for the positioning of fiducials in the measurement data: < 2 pixels indicates good fiducial placement, > 5 pixels indicates there may be an issue that warrants another look at the fiducial placement in the measurement data. Finally, Morpheus provides a fiducial editor screen to adjust the position of the fiducials manually.

Mapping Correction

As discussed above, the CGH relays a regularly spaced grid of points on the optical surface to the interferometer in an irregular way, depending on the variation of curvature of the test optic. This is a function of the test optic and test geometry, but it can be easily corrected using Morpheus. At the time of CGH design, all the parameters of the test geometry and test optic curvature are known, and the mapping relation from CGH to test optic is defined and stored in the .cgh file. After the substrate error is calibrated, the mapping correction is done in Morpheus to take as-measured data and convert it to test optic space, such that polishing and finishing equipment can directly have insight into the position of surface features for correction.

Alignment Correction

Finally, with substrate error and mapping distortion corrected, the critical step of characterizing and removing errors due to misalignment of the test optic to the CGH can be done. As with the mapping relationship, at the time of CGH design, all misalignment degrees of freedom between the test optic and CGH are analyzed and stored in the .cgh file. Morpheus analyzes measurement data (corrected for mapping) for the specific misalignment signature (or modes) of the CGH to the test optic. It is important to note that these aberrations are often not single Zernike terms, so fitting Zernikes may not provide an accurate picture of misalignment errors in a CGH test. With the specific misalignment modes fit to the measurement data, Morpheus provides the user with a host of useful data and tools. Start by reviewing the magnitude of each alignment degree of freedom and make decisions if the optical alignment can be improved with the hardware available for adjustment. Once the misalignment is fit, simply remove the specific mode from the data to be left with errors in the surface figure for correction.

Finally, output the data from Morpheus in the same common interferometer file formats as input, and take the data directly to the polishing or correction processing step.

Morpheus at a Glance

• Streamlined Data Reduction – Automates CGH measurement data processing for efficient results
• Substrate Correction – Ensures precise and reliable measurement data by minimizing error contribution
• Misalignment Correction – Removes CGH-to-UUT misalignment errors to improve accuracy
• Mapping Correction – Scales measurement data to part space for precise polishing feedback
• Uncertainty Analysis – Provides a comprehensive understanding of test uncertainties before making a measurement
• Report Generation – Creates detailed test reports for production traceability and documentation

How to Get Started with Morpheus

• Obtain a CGH with a Digital Twin (.cgh file) – Each CGH includes an optional .cgh file containing the CGH as-built information and analysis. Ask your AOM representative for a quote for a .cgh file with your next CGH metrology project.
• When your CGH ships – the .cgh file, and a Morpheus installer download link will be provided as deliverables.
• Install and run Morpheus – bring your own data, or practice using included .cgh files and sample measurement data to get familiar with features and functions.

Compatibility

Morpheus is compatible with most interferometry systems and accepts standard data file formats. It runs in parallel with interferometry software, allowing seamless integration into existing workflows.

Learn More & Watch the Demo

For a video demo measuring an off-axis parabola, visit our blog post:
🔗 Read the post & watch the demo