A group at Lawrence Livermore National Laboratory reports that they've successfully fabricated optical grade glass with a new printing technique. Optical grade glass is tricky. It's hard to convey just how clear and distortion-free optical grade glass is compared to other glasses you've seen in your life. Eyeglasses, which are virtually always polycarbonate or a softer plastic, are nowhere near as transparent as optical glass is. The LLNL group isn't using a printer to produce a familiar eyeglass lens; the breakthrough here is the ability to print special mixes of optical glass with a different refractive index in each layer, which may allow more exotic shapes and performance.
Because the refractive index of glass is sensitive to its thermal history, it can be difficult to ensure that glass printed from the molten phase will result in the desired optical performance, researchers said. Depositing the LLNL-developed material in paste form and then heating the entire print to form the glass allows for a uniform refractive index, eliminating optical distortion that would degrade the optic's function.Their goal is to improve the ability to manufacture difficult things, such as gradient index (GRIN) lenses. The promise of the technique is to manufacture optical glass in novel shapes, reducing component count in some systems, and probably allowing new types of optical systems as well.
“Components printed from molten glass often show texture from the 3D printing process, and even if you were to polish the surface, you would still see evidence of the printing process within the bulk material,” says LLNL chemical engineer Rebecca Dylla-Spears, the project’s principal investigator. “Using paste lets us obtain the uniform index needed for optics. Now we can take these components and do something interesting.”
For the study, researchers printed small, simple-shaped optics as proof of concept, but Dylla-Spears said the technique eventually could be applied to any device that uses glass optics and could result in optics made with geometric structures and with compositional changes that were previously unattainable by conventional manufacturing methods. For example, gradient refractive index lenses could be polished flat, replacing more expensive polishing techniques used for traditional curved lenses.
“Additive manufacturing gives us a new degree of freedom to combine optical materials in ways we could not do before,” Dylla-Spears said. “It opens up a new design space that hasn’t existed in the past, allowing for design of both the optic shape and the optical properties within the material.”
(Pictured: LLNL chemical engineer and project lead Rebecca Dylla-Spears and LLNL materials engineer Du Nguyen.)
As the article said, the lenses that they show in the picture are "small, simple-shaped" optics, and I'm not clear on how it's processed. It sounds as if their paste will have to heated to the melting point of the glass, which means it will have to be held in a mold so that it doesn't flow away while it's liquid. The treatment in the molten state is one of the things the distinguishes optical glass from regular slabs of glass. Holding it at some temperature between molten and solid, annealing the glass until it's stress free and shows no swirl-like irregularities when looked through onto a flatly lit surface (or sky). All those steps are still needed and still there. I'm guessing the main interest here is the novel structures with different refractive indices in different stack-ups, or perhaps in rings or other shapes.