Gradient-Index (GRIN) lenses by Slurry-based Three-Dimensional Printing (S-3DP)

Abstract

GRIN lenses with vertical index variation and radial index variation have been successfully fabricated using S-3DPTM. Two silica-based material systems, A1203-SiO₂ and BaO-SiO₂, have been studied and used for the fabrication of GRIN lenses. Aluminum nitrate was dissolved in water to provide the dopant salt solution for S-3DPTM. The pre-sintering treatment at 1000 ⁰Cfor 24 hours in. vacuum (-5x10-6 torr) was used to remove the hydroxyl groups that cause bubbles during sintering. The sintering condition for the A1203-SiO₂ material system was found to be 1650 ⁰C for 30 minutes in vacuum. Two alumina-doped silica GRIN lenses with vertical index variation, Design 1.63 [percent] max and Design 2.5 [percent] max, were fabricated with effective focal lengths of 10.00 cm and 6.10 cm, respectively. An alumina-doped silica GRIN lens with radial parabolic index variation also was fabricated with effective focal lengths of 63.75 cm in the x direction and 52.50 cm in the y direction. The BaO-SiO₂ material system, which has a 2.4 stronger index changing ability than the A1203-SiO₂ material system, also was developed. Barium acetate was used as the dopant source. The pre-sintering treatment was found to be 900 ⁰C for 18 hours in air to convert barium acetate to barium oxide. The sintering condition was found to be 1725 ⁰C for 10 minutes in vacuum. A barium oxide-doped GRIN lens with radial parabolic index variation was fabricated. Its effective focal length was measured to be 14.63 cm in the x direction and 11.14 cm in the y direction. The barium oxide concentration profiles were measured. The theoretical focal lengths were calculated and compared with the effective focal lengths.