Additive Manufacturing of High-Refractive-Index, Nanoarchitected Titanium Dioxide for 3D Dielectric Photonic Crystals.

Additive manufacturing at small scales enables advances in micro- and nanoelectromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nanoscale, especially for optical applications, are limited. State-of-the-art AM processes for high-refractive-index materials typically suffer from high porosity and poor repeatability and require complex experimental procedures. We developed an AM process to fabricate complex 3D architectures out of fully dense titanium dioxide (TiO2) with a refractive index of 2.3 and nanosized critical dimensions. Transmission electron microscopy (TEM) analysis proves this material to be rutile phase of nanocrystalline TiO2, with an average grain size of 110 nm and <1% porosity. Proof-of-concept woodpile architectures with 300-600 nm beam dimensions exhibit a full photonic band gap centered at 1.8-2.9 µm, as revealed by Fourier-transform infrared spectroscopy (FTIR) and supported by plane wave expansion simulations. The developed AM process enables advances in 3D MEMS, micro-optics, and prototyping of 3D dielectric PhCs.