Alumina-doped silica gradient-index (GRIN) lenses by slurry-based three-dimensional printing (S-3DP™)

The traditional slurry-based three-dimensional printing (S-3DP™) process has been used to fabricate complex structure materials by printing organic binders in selective positions of each printing layer. This process has been modified to fabricate functional graded materials, such as gradient index (GRIN) lenses, by depositing different concentrations of dopant into selective positions. Aluminum nitrate, which decomposes into alumina during heat treatment, is dissolved in deionized water and inkjet printed into the silica powder bed as the source of dopant. Continuous dopant jets and drop-on-demand (DoD) printing heads are used to control the dopant concentration profile in one dimension and two dimension, respectively. GRIN lenses with different concentration profiles are fabricated. The alumina-doped silica powder beds are then dehydrated at 1000 °C for 24 h and sintered to optical transparency at 1650 °C for 30 min in a vacuum furnace (5 × 10−6 Torr). The dopant distributions after sintering are measured and compared with the design profiles. The resulting optical effects are examined by measuring the effective focal lengths of the GRIN lenses.