Stiching is at the heart of all QED's SSI technology.
The key to the QED's revolutionary metrology 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 an advanced 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.
QED then combines interferometry, patented stitching algorithms and software to automate the entire package. Integration of the measurement design, motion control, phase data acquisition and data analysis allows complex stitched measurements to be made with a simple push of a button.
Beyond Spheres... asphere metrology with the ASI(q)
With the introduction of QED's Aspheric Metrology sytems, optics manufacturers can measure a wide range of aspheres with up to 1000 waves of departure, without relying on dedicated, expensive null-optics. The ASI(Q) has been designed to accurately test mild to steep aspheres with one fast, easy-to-use, accurate system.
To achieve this, QED Technologies developed Variable Optical Null technology. The ASI(Q) 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 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.
Until now, it was not possible to measure the full aperture of high departure aspheres with a commercially available system. Contact us if you would like to learn more about the ASI metrology system.