The need for fiducials on freeform optical surfaces

The evolution from spherical, to aspheric, to freeform optics is quickly progressing towards more complex freeform surfaces. Freeform surfaces typically have little to no symmetry making the alignment of the surfaces difficult. The alignment of such freeform surfaces relative to the other features on the optic has been little considered. A typical alignment specification like wedge (edge thickness difference) is not well defined for freeform optics, nor is the wedge measurement. We show that by using fiducials during the manufacturing of freeform surfaces, the alignment and locating of the freeform surface can be specified and measured.