Creation of 3D terahertz photonic crystals by the direct writing technique with a TiO2 sol-gel ink

Three-dimensional TiO2 woodpile terahertz photonic crystals with feature size less than 100m were created by the direct writing technique with a TiO2 sol-gel ink. With proper heat treatment, the rheological properties of the TiO2 sol-gel ink were modulated to meet the requirement to construct 3D-TPCs with feature size less than 100m by the direct writing technique. Well-crystallized rutile TiO2 3D-TPCs were obtained by the calcination process to provide the required high refractive indices, while the lattice periods of these TiO2 3D-TPCs could be changed to tune their terahertz properties. With the increase of the lattice period, a shift of their THz photonic band gap peaks toward the lower frequency was observed in both the simulated and experimental investigations.