25 Nov 2020
Multi-material 3D printing creates tailored gradient RI optics that promise better military eyewear and VR goggles.Lawrence Livermore National Laboratory (LLNL), Livermore, CA, have employed multi-material 3D printing to create tailored gradient refractive index glass optics that could make for better military specialized eyewear and virtual reality goggles.
The LLNL scientists say the new technique could achieve a variety of conventional and unconventional optical functions in a flat glass component (with no surface curvature), offering new optical design versatility in environmentally stable glass materials.
The team was able to tailor the gradient in the material compositions by controlling the ratio of two different glass-forming pastes or “inks” blended together inline using the direct ink writing (DIW) method of 3D printing. After the composition-varying optical preform is built using DIW, it is then densified to glass and can be finished using conventional optical polishing.
“The change in material composition leads to a change in refractive index once we convert it to glass,” said LLNL scientist Rebecca Dylla-Spears, lead author of a paper published in Science Advances.
Gradient refractive index (GRIN) optics provide an alternative to conventionally finished optics. GRIN optics contain a spatial gradient in material composition, which provides a gradient in the material refractive index, altering how light travels through the medium. A GRIN lens can have a flat surface figure yet still perform the same optical function as an equivalent conventional lens.
The ability to fully spatially control material composition and optical functionality provides new options for GRIN optic design. For example, multiple functionalities could be designed into a single optic, such as focusing combined with correction of common optical aberrations.
By tailoring the index, a curved optic can be replaced with a flat surface, which could reduce finishing costs, says the LLNL team. Surface curvature also could be added to manipulate light using both bulk and surface effects. The new technique also can save weight in optical systems, which could be significant in military applications, for example.
“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,” said Dylla-Spears.