Dual-Cure Photopolymer Resin Design for Vat-Based DLP Printing of Gradient Refractive Index Optics

Abstract

Gradient-index (GRIN) optical elements allow compact designs and better control of optical aberrations. While conventional fabrication methods can produce these components reliably, they limit the shapes and refractive index profiles that can be achieved. Additive manufacturing offers an alternative approach, en- abling complex three-dimensional geometries and spatially tailored optical properties. Digital light process- ing (DLP), in particular, provides high spatial resolution and grayscale exposure control, but UV exposure alone produces only small changes in refractive index. This thesis explores a dual-cure resin strategy to print GRIN optics. Hardware modifications to a commercial DLP printer allowed controlled grayscale exposure, enabling the fabrication of linear and radial GRIN demonstrators. These results show that combining a dual-cure resin system with controlled exposure can introduce spatial refractive index variation in a single printed compo- nent. A custom dual-cure resin was created by blending UV-curable photopolymers with a thermally activated epoxy. During DLP printing, UV light defines the geometry and initial polymer network, while subsequent heating activates the epoxy. Measurements on printed prism samples show that uniform UV curing changes the refractive index only slightly, with values around n = 1.52–1.53 for Formlabs Clear V4 and n = 1.53 for Elegoo ABS-like Transparent. Adding epoxy and applying thermal post-curing increases the refractive index, with shifts of ∆n ≈ 0.01–0.04 for Formlabs-based blends and ∆n ≈ 0.01–0.03 for Elegoo-based blends, depending on epoxy content. In summary, this work demonstrates a practical material-based approach for tuning refractive index in DLP- printed optics. Incorporating a thermally activated epoxy allows larger refractive index changes than UV curing alone, providing a foundation for future research on 3D-printed GRIN lenses.