Two-photon grayscale lithography for free-form micro-optical arrays

Compared to standard rotationally symmetric macroscopic optical components, free-form micro-optical arrays (FMOAs), sometimes termed microstructured optical surfaces, offer greater design freedom and a smaller footprint. Hence, they are used in optical devices to deliver new functionalities, enhanced device performance, and/or a greater degree of miniaturization. But their more complex surface shape is a challenge for traditional manufacturing technologies, and this has triggered a substantial effort by research institutes and industry to develop alternative fabrication solutions. Two-photon polymerization (2PP) is a promising additive manufacturing technology to manufacture 3D optical (micro)structures. The manufacturing times involved are, however, often impractically long, especially for the excellent surface quality required for optical applications. Recently, Nanoscribe GmbH has reduced manufacturing times substantially with the introduction of so-called two-photon grayscale lithography (2GL). However, its acceleration potential and consequent impact on surface quality have, to the best of our knowledge, yet to be reported. A direct comparison between 2PP and 2GL indicates that, for the investigated FMOA, 2GL is around five times faster than 2PP and also delivers better surface quality. This study therefore confirms the potential of 2GL to manufacture complexly shaped FMOAs.