Advanced Metrology
SSI® metrology systems deliver unprecedented capabilities that enable our experts to develop a cost-effective solution that addresses your needs and specifications.

Why does SSI metrology matter?
Stitching makes the difference. A picture of the entire surface (or full-aperture metrology) is clearly needed for precision optics. However, full aperture metrology is often available only at great cost, or with significant lead-time. SSI technology makes it possible to perform absolute metrology on nearly every optic, without expensive investments, keeping manufacturing costs lower. Because the SSI helps reduce the dependence on test plates and radius benches, it helps manufacturers reduce over-all cycle times and costs.

The key to the SSI’s revolutionary capabilities is subaperture stitching. The stitching process essentially reconstructs a full-aperture map of a surface from a collection of smaller (sub-aperture) maps, each covering only a portion of the whole surface. While this would be fairly straightforward for flat (plano) optics, it becomes much more complicated for non-flat surfaces, especially for aspheric shapes.

Advanced software and hardware developments enable, with very high accuracy, an automated, subaperture metrology solution that was previously unrealizable. QED’s stitching algorithms use a novel optimization method to minimize the discrepancies between overlapping regions of subapertures caused by several sources of systematic and random measurement error. Through its integrated calibration capability, the system can deliver better accuracy than a standard full-aperture test.

Extending Stitching to Aspheres
The ASI takes asphere metrology to the next level of performance.To achieve this, QED Technologies® developed Variable Optical Null™ technology. The ASI is powered by QED’s powerful Subaperture Stitching Interferometry (SSI®); the surface of an optic is measured by first examining smaller subsections, or subapertures, of the surfaces and then stitching together the results into a cohesive, full-aperture picture. Because the ASI only considers a smaller portion of the lens at a time, the fringes from mild aspheric departures can be resolved. However, with more severe aspheric departures, the fringe density of each subaperture is too great. The Variable Optical Null solves this problem; it is an advanced opto-mechanical subsystem that generates a wavefront that closely matches the surface of each aspheric subaperture being measured. This technique produces an interferogram with reduced fringe density compared with one produced by using a normal spherical wavefront.

SSI metrology systems help manufacturers gain greater control of their optics shops, providing you with greater confidence in the optics you’re buying.

For more information, including technical data, on SSI, please visit the QED Technologies website.