3D Printed Glass Enhances Optical Design Flexibility

Lawrence Livermore National Laboratory researchers have used 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 new technique could achieve a variety of conven­tional and uncon­ventional optical functions in a flat glass component, offering new optical design versatility in environ­mentally stable glass materials. The team was able to tailor the gradient in the material compo­sitions by actively 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.

Artistic rendering of an aspirational future automated production process for custom GRIN optics, showing multi-material 3D printing of a tailored composition optic preform, conversion to glass via heat treatment, polishing and inspection of the final optics with refractive index gradients. (Source: J. Long & B Chavez)

The project started in 2016 when the team began looking at ways that additive manu­facturing could be used to advance optics and optical systems. Because additive manu­facturing offers the ability to control both structure and composition, it provided a new path to manu­facturing of gradient refractive index glass lenses. 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. GRIN optics already exist in nature because of the evolution of eye lenses. Examples can be found in most species, where the change in refractive index across the eye lens is governed by the varying concen­tration of structural proteins.

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. In addition, it has been shown that the use of optics with combined surface curvature and gradients in refrac­tive index has the potential to reduce the size and weight of optical systems. By tailoring the index, a curved optic can be replaced with a flat surface, which could reduce finishing costs. 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. For example, it’s critical that optics used by soldiers in the field are light and portable. “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. (Source: LLNL)

Reference: R. Dylla-Spears et al.: 3D printed gradient index glass optics, Sci. Adv. 6, eabc7429 (2020); DOI: 10.1126/sciadv.abc7429

Link: Materials for Laser Systems, Lawrence Livermore National Laboratory LLNL, Livermore, USA

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