Silica-Rich Sol-Gel Ink for Two-Photon Direct Laser Writing of Microscale Structures and Optical Elements

Innovative materials enable two-photon polymerization for precise additive fabrication of intricate optical components. Existing polymeric inks suffer from poor optical performance due to their high organic content. Silica-rich sol-gel ink (75 wt%, under ambient conditions) is presented for high-precision three-dimensional (3D) printing of microscale structures and optical devices. A photoinitiator with high-efficiency nonlinear absorption is introduced to initiate two-photon polymerization. Utilizing a commercial direct laser writing system, 3D-printing is demonstrated including the optimization of printing parameters and ink characterization. The optical performance of the printed microscale elements using the new sol-gel ink surpasses commercially available polymeric inks on key metrics: Printed elements exhibit extremely low surface roughness, 3nm; visible and near-IR light transmission is greater than 90%; Printed elements present enhanced mechanical and chemical resistance to common organic solvents; Structures exhibit low isotropic shrinkage, <10%; Elements withstand continuous-wave laser intensities exceeding 7 × 10⁵ W cm⁻². Direct writing onto an optical fiber tip with no need for surface functionalization is presented, with the demonstration of a tall waveguide taper (≈1:5 aspect ratio) with low losses and modal crosstalk, and a freestanding photonic lantern mode multiplexer. The new ink can be utilized in a variety of applications and across many materials, requiring compact, durable, and complex optical elements.