3D printed gradient index glass optics

Abstract

We demonstrate an additive manufacturing approach to produce gradient refractive index glass optics. Using direct ink writing with an active inline micromixer, we three-dimensionally print multimaterial green bodies with compositional gradients, consisting primarily of silica nanoparticles and varying concentrations of titania as the index-modifying dopant. The green bodies are then consolidated into glass and polished, resulting in optics with tailored spatial profiles of the refractive index. We show that this approach can be used to achieve a variety of conventional and unconventional optical functions in a flat glass component with no surface curvature.

Fig. 1. Process of additive manufacturing of gradient index (GRIN) silica-titania glass via DIW.

(A) Two silica-based inks with different titania dopant concentrations are mixed under active shear in a microfluidic nozzle. The composition is dictated by the respective flow rates of the two inks. (B) The 3D printed green body is thermally treated to remove all organic components and densify to glass, and then polished flat. The pink color in the first image is the result of an organic dye added to one ink for visualization. (C) The addition of titania to the silica glass increases the refractive index (41, 42); as a result, the 3D printed glass contains spatial variation in refractive index prescribed by the compositional gradient. wt %, weight %; ppm, parts per million. (D) GRIN glass optics with a variety of shapes, sizes, and optical functions can be designed and produced. Grid pitch in all images is 1 mm. Photo credit: Nikola Dudukovic, Lawrence Livermore National Laboratory.

Fig. 2. CFD and experimental results for mixing efficiency in the active mixing geometry.

(A) Comparison of composition at outlet cross section from simulations and experiments shows good qualitative agreement. (B) Calculated COV values indicate that the best mixing is achieved at active mixer rotational speeds >100 rpm. The deviation in the calculated COV at high mixing speeds stems from imaging inconsistencies and pixelation of the experimental data.

Fig. 3. 3D printed GRIN glass optics based on conventional lens types.

The 3D printed optics contain a spatial gradient in titania concentration across the silica glass matrix, which results in the prescribed refractive index profile and focusing features. All lenses were polished to a flat figure. (A) Spherical lens. (B) Cylindrical lens. (C) Aspheric negative lens. Scale bars, 5 mm. Photo credit: Nikola Dudukovic, Lawrence Livermore National Laboratory.

Fig. 4. Unconventional 3D printed GRIN glass optics featuring nonmonotonic and sharp change profiles.

(A) Sinusoidal profile. (B) Sharp, nonmonotonic linear profile. Scale bars, 5 mm. Photo credit: Nikola Dudukovic, Lawrence Livermore National Laboratory.