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Researchers at Northwestern Engineering have come up with a new method to make a low-cost, high-quality lens quickly using a 3D printer. The technique has promising potential to create optical imaging lenses, customized contact lenses for correcting distorted vision, or to even turn iPhones into microscopes for disease diagnosis. Developed by the researchers after two years of research, the customized optical component, which is 5 millimeters in height and 5 millimeters in diameter, can be 3D printed in about four hours.

The research was published on in Advanced Materials. It includes images taken with the lens connected to an Apple iPhone 6s, including high-quality detailed images of a sunset moth’s wing and a spot on a weevil’s elyta. Like all 3D printing, creating these lenses involves placing layer upon layer of material. The researchers likened building the lens to running a film projector. Instead of projecting one frame, one image after another, they layer one frame on top of another. It is like playing a movie in a vertical fashion.

But when researchers first printed the lens, its curved layers, made of a photo-curable resin, created a visible stepping. They realized that the layers on top of each other created surface roughness. The layer thickness is typically 5 microns, while the wavelength of visible light is around 0.5 micron. This creates an optically rough surface. That was the bottleneck. The roughness made the lens incapable of clear optics.

This lead to the group’s simple guiding research question: Can they make the surface smooth without slowing down the printing speed? To solve that challenge, the group developed a two-step process of layering and polishing. First, they used grayscale images to create more transitions between steps. Then, they coated the surface with the same photo-curable resin. That then forms the meniscus that further smoothes the surface. The result: a transparent lens with a smooth surface.

This lens, however, is not the first high-quality lens created by 3D printing. German-based company Nanoscribe has developed a high-precision femto-second 3D printer with 150 nanometer precision, but it builds the lens in a point-by-point fashion instead of layering. It is a time-consuming process and that is their limitation.

The new process could lead to a plethora of new devices with a wide variety of applications in optics and biomedical imaging. Next, the group will experiment in making larger lenses as well as investigating how to integrate the 3D-printed lens with medical devices, such as an endoscope or optical microscope. The lenses could also be used by doctors in underdeveloped areas for diagnostic imaging or by field scientists as portable microscopes. They could also be fashioned into a customized contact lens for people with distorted corneas caused by keratoconus.

The work was supported by the National Science Foundation under grant EEC-1520734 and DBI-1353952, along with a donation from the Farley Foundation.