Annular lithography for fabricating micro- and mesoscale optical structures on curved surfaces

This paper presents an advanced exposure system that, we believe, for the first time, enables annular lithography to create micro- and mesostructures on curved surfaces. The principle of ring creation is based on an axicon zoom system whereas the exposure tool exhibits several features that enhance its performance over previous models. Its optical design features a high numerical aperture, resulting in narrow ring widths and high resolution. Additionally, the ring diameter, which can be varied between 400 μm and 8 mm, remains constant along the optical axis due to telecentric imaging. Further functional components include an observation unit for alignment and monitoring, as well as an integrated autofocus system. In addition to determining the exposure ring width (∼ 10 μm), diffractive lenses on planar substrates as well as on a spherical lens with a radius of curvature of 68.8 mm were structured. The periods of the diffractive structure varied between 60 μm and 460 μm.