What's it about?
Freeform optical surfaces, which have little to no symmetry, are gaining popularity with lens designers and optical system integrators. These freeform optics can enhance optical performance by reducing the number of elements, enabling lighter and more efficient systems, and by reducing aberrations. Most traditional manufacturing techniques cannot yield polished freeform optical surfaces. Likewise, traditional metrology equipment has difficulty accurately measuring the deviation of freeform surfaces from their nominal shape, the surface form error.
The inclusion of mechanical fiducials on freeform optics can ease some of this difficulty. Well placed fiducials can provide alignment features for contact metrology equipment such as coordinate measuring machines (CMMs). Mechanical fiducials allow for precise locating of all surfaces of an optic in reference to one another and provide a reference from which the freeform surface can be measured against. This allows a CMM to output the deviation of a surface from its nominal shape, as well as the wedge and center thickness of the optic. Alignment fiducials also enable more precise locating of the surface during the manufacturing process, shortening the time required for production and lowering the cost of fabricating freeform optics. This paper will explore the advantages of including locating fiducials on freeform optics and how they can aid in the manufacture and measurement of optical surfaces.