Researchers at Lawrence Livermore National Laboratory (LLNL) used multimaterial 3D printing to develop tailored gradient refractive index glass optics, delivering a result that could enable the manufacture of improved military specialized eyewear and virtual reality goggles. The technique has the potential to realize a variety of conventional and unconventional optical properties in a flat glass component, expanding the versatility in performance of environmentally stable glass materials. The team tailored the gradient in material compositions by controlling the ratio of two different glass-forming pastes or “inks” blended together inline using the direct ink writing method of 3D printing. After completing the composition-varying optical preform, the scientists densified it to glass. The material, they said, can be finished using conventional optical polishing methods. Artistic rendering of an aspirational future automated production process for custom GRIN optics, showing multimaterial 3D printing of a tailored composition optic preform, conversion to glass via heat treatment, and polishing and inspection of the final optics with refractive index gradients. Courtesy of Jacob Long and Brian Chavez. “The change in material composition leads to a change in refractive index once we convert it to glass,” said Rebecca Dylla-Spears, lead author of the paper presenting the research. Additive manufacturing offers certain advantages in its ability to control both structure and composition. Gradient refractive index (GRIN) optics offer an alternative to conventionally finished optics as they contain a spatial gradient in material composition, which provides a gradient in the material refractive index, altering how light travels through the medium. Being able to spatially control material composition and optical function allows a single optic to possess multiple functions — for example, focusing and the correction of optical aberrations. Additionally, optics with curved surfaces and gradient refractive indices have the potential to reduce size and weight in optical systems. “This is the first time we have combined two different glass materials by 3D printing and demonstrated their function as an optic. Although demonstrated for GRIN, the approach could be used to tailor other material or optical properties as well,” Dylla-Spears said. The research was published in Science Advances (www.doi.org/10.1126/sciadv.abc7429).