Additive Manufacturing of Polymeric Gradient Index Optics via Grayscale Digital Light Processing Vat Photopolymerization Technology

Fabrication has historically posed significant challenges in the implementation of gradient index (GRIN) optics. Here, we present an expedient additive manufacturing method for producing polymeric GRIN optical elements using grayscale digital light processing (g-DLP) vat photopolymerization (VPP) technology. The index gradient was achieved by controlling the spatial distribution of chemical conversion. A conversion prediction model previously developed to address the issue of uncontrolled light penetration inherent in VPPs utilizing the concept of accumulated light dose, was employed to generate numerical matrices of printing parameters tailored to attain a target index/conversion profile. During the printing process, multiple grayscale images were projected for predicted time durations to build each layer. Millimeter-to centimeter-sized lenses were produced within hours and did not require postprocessing. Experimental results showed that the printed radial GRIN lenses exhibited optical performance consistent with measured index profiles. More importantly, we demonstrated the versatility of this approach by fabricating arbitrary GRIN elements, which paves the path toward the realization of true freeform GRIN optics.