Additive manufacturing glass optics

When it comes to advanced glass optics, additive manufacturing provides a new level of freedom to create and customise the structure or composition of optical elements. It is this promise of developing new configurations and optical components to extend the possibilities for designers that has helped to drive the development of the direct ink writing (DIW) process for 3D printing glass.

I started developing the process for DIW-printed glass along with my team at Lawrence Livermore National Laboratory three and a half years ago. The technique enables blending of multiple compositions together to create new gradients and patterns in glass lenses, and our ultimate goal is to apply it to improve the size, weight and power of optical systems.

Direct ink writing – an explanation

Like other additive manufacturing systems, DIW is extrusion-based. The flow properties of the silica paste ‘inks’ have been specially formulated and tuned to be extrudable when they come out of the nozzle and to then hold their shape. This enables the material to be deposited filament by filament, forming a determined structure. We call these initial geometries ‘green bodies’. They contain silica, solvents and organic species, and due to their porosity, are low density.

Using a series of heat treatments, we remove the organic materials from the green bodies and then densify to remove the porosity. Fully dense silica is left behind - forming optically homogeneous glass that rivals conventionally prepared optical grade fused silica. The printed glass is then polished using standard polishing techniques to ensure the surface finish meets exacting optical standards.

Customisation, control and consistency

The true advantage of glass by DIW lies in its potential for customisation - the optical, thermal and mechanical properties of the glass can now be tuned within the same structure. By blending the custom inks and directly depositing the material in the desired composition at the desired position, DIW enables both structural and composition change, making it ideal for creating gradient refractive index lenses, multi-composition components, or structurally complex lightweight mirrors that can manipulate light differently.

This capability to customise the structure or composition of an optical element gives designers access to configurations that were previously unrealisable. For example, new gradient refractive index lenses or correctors that can be polished flat could save time and money over more expensive traditional methods.

Control is an important aspect of creating quality, industrial grade optics. The refractive index of a glass is dependent on many factors, including chemical homogeneity and thermal history.   Inconsistencies can result in optical distortion, which can compromise the glass’s integrity and performance. The DIW approach to glass formation helps to achieve homogeneity through thoughtful design of ink feedstocks, improved mixing at the filament level and uniformity of thermal profiles.  In contrast to melt-based glass 3d-printing approaches, in the DIW method, the entire component is exposed to the same thermal treatment at the same time.

Future developments

The team at Lawrence Livermore National Laboratory continues to make advances in the additive manufacture of glass and optics by DIW. We are working on strategies to reduce the time to development of new materials and structures and have taken steps towards producing new printed glass compositions aimed at increasing the range of the refractive index change achievable.  A future challenge on the horizon is to scale up the size of the components we can create from 1 cm – 2 cm to include up to 10 cm components.  To do this, we must develop procedures to reliably remove the organic material from larger green bodies.

In addition to driving improvements in single optical components, we’d like to combine the functionality of different optics into a single component, using DIW to manufacture a more capable product in a more compact package. By reducing the weight of optical systems while increasing their functionality, military and aerospace markets open up for potential future applications. The DIW glass technique may also find use outside of optics applications, in markets such as microfluidics and custom packaging.

Rebecca Dylla-Spears - Group Leader in Advanced Optical Materials & Processing S&T at Lawrence Livermore National Laboratory

 To learn more about additive manufacturing in glass, optics and direct ink writing, come along to to hear Rebecca present at this year’s Additive International summit. It takes place at the Nottingham Belfry on 10^th- 11^th July, with a pre-conference day focused on Future Additive Manufacturing on the 9th. Register at: https://www.additiveinternational.com/register/