Fabrication and Measurement of Micro Three‐Dimensional Photonic Crystals of SiO 2 Ceramic for Terahertz Wave Applications

Three‐dimensional (3D) photonic crystals with a diamond structure made of a dense SiO 2 ceramic were successfully fabricated using a CAD/CAM micro‐stereolithography and sintering process. The designed lattice constant of the diamond unit cell was 500 μm and the forming tolerance from 50 vol% SiO 2 paste (before sintering) was around 15 μm. After the SiO 2 ‐resin photonic crystals were formed via micro‐stereolithography, they were converted to pure SiO 2 ceramic photonic crystals of 99% theoretical density by sintering at 1400°C. The electromagnetic wave propagation in these dense SiO 2 photonic crystals was measured by terahertz‐time‐domain spectroscopy. The results showed that the band gap appeared between 470 and 580 GHz in the Γ– X 〈100〉 direction, between 490 and 630 GHz in the Γ– K 〈110〉 direction, and between 400 and 510 GHz in the Γ– L 〈111〉 direction, resulting in the formation of a common band gap in all directions between 490 and 510 GHz. These results agreed well with the band gaps calculated by the plane wave expansion method.