Defocus digital light processing stereolithography for rapid manufacture of microlens arrays

Abstract

This study applied defocusing to digital light processing (DLP) stereolithography for the fabrication of microlens arrays (MLAs) within 1 s. We studied the effects of exposure energy, defocus distance, and a diameter adjustment algorithm to ensure printed MLAs with designed dimensions. Experiment results demonstrate that our simple fabrication method is applicable to the manufacture of various MLA designs, while achieving nanoscale surface roughness and good image quality. We determined that the height of the MLAs is proportional to the exposure energy. The highest height-to-diameter ratio achieved in this study was 0.63 (diameter = 200 µm; height = 126 µm). Our use of defocusing significantly reduced the average surface roughness (Ra) of the printed MLAs to 129 nm with a corresponding improvement in image resolution 45.3 lp/mm. Our use of a diameter adjustment algorithm in designing the digital mask helped preserve the dimensionality of the printed MLAs. The proposed manufacturing process was used to create a variety of MLAs with numerical apertures as high as 0.980, multiple focal lengths on a single substrate (from 21 µm to 199 µm), and fill factors as high as 77.98 %.