3D-Printed Polymer Waveguides for Spatially Redistributing Light

Conventional silica-based optical fibers provide one-dimensional (1D) point-to-point light transmission, enabling illumination only at the distal end and offering limited control over the spatial distribution of light intensity. In contrast, three-dimensional (3D) waveguide architectures have the potential to convert a single-point input into multipoint, spatially distributed illumination, enabling volumetric light–matter interactions. However, fabrication of optically transparent silica waveguides with complex 3D geometries remains challenging due to material constraints and manufacturing complexity. In this work, a wide range of polymer waveguide architectures are designed and fabricated using commercially available stereolithographic (SLA) 3D printing. Optical characterization demonstrates high transparency and effective light confinement in the printed polymer materials. We identify postprint surface finishing as a primary factor governing light transmission efficiency, achieving a 3.6-fold increase in transmittance compared to unfinished prints. In addition, geometric parameters were systematically investigated to determine their impact on light preservation. Smaller diameters, shorter lengths, reduced branching angles, and smoothly curved junctions are found to minimize optical losses in Y-shaped waveguide architectures. Building on these design principles, we further demonstrate that multibranch and multilayer architectures enable uniform light distribution in both linear and planar configurations. These 3D-printed multibranch waveguides provide a general strategy for efficient light delivery in light-absorbing environments. As a representative application, embedding multibranch waveguides within dense microalgal cultures redistributed light throughout the strongly absorbing aquatic environment, mitigating light attenuation and enhancing biomass productivity. These results together establish a geometry-engineered optical redistribution platform that enables 3D spatial light delivery beyond conventional point-to-point waveguiding.