High‐Speed 3D-Printing of Optical Lenses

A new method uses 3D-printing to make high-quality customized lenses quickly and at low-cost. (Source: NWU)

A new method to make a low-cost, high-quality lens quickly using a 3D-printer 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 North­western Engineering 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.

“Up until now, we relied heavily on the time-con­suming and costly process of polishing lenses,” said Cheng Sun, associate professor of mechanical engi­neering and whose lab deve­loped the 3D-printing process. “With 3D-printing, now you have the freedom to design and custo­mize a lens quickly.” Like all 3D-printing, creating tiny lenses involves placing layer upon layer of material. Sun likened building the lens to running a film pro­jector. “Instead of projec­ting one frame, one image after another, we layer one frame on top of another,” Sun said. “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. “We 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,” he said. “That was the bottle­neck. The roughness made the lens inca­pable of clear optics.” This lead to the group’s simple guiding research question: Can we make the surface smooth without slowing down the printing speed? To solve that challenge, Sun’s group deve­loped a two-step process of layering and polishing.

“First, we used grayscale images to create more transitions between steps,” Sun said. “Then, we coated the surface with the same photo-curable resin. That then forms the meniscus that further smooths the surface.” The result: a trans­parent lens with a smooth surface. “I must have tried more than 100 times to get this just right,” said Xiang­fan Chen, a PhD candidate in mechanical engi­neering. 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, Sun said. “It is a time-consuming process. That is their limitation,” he added. “We wanted to make something com­parable but faster and with better quality.”

“If you want to make a lens, do you want to make it in two hours or two weeks?” Chen said. “We are very excited about this lens.” This process could lead to a plethora of new devices with a wide variety of appli­cations in optics and bio­medical imaging, Sun said. 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. “These lenses could help detect some genetic disease or cancer,” said Biqin Dong, a post-doctoral fellow focused on bio­medical and mecha­nical engi­neering, who also worked on the research.

Dong also envisions that these lenses could be used by doctors in under­developed areas for diagnostic imaging or by field scientists as portable micro­scopes. The lens could also be fashioned into a customized contact lens for people with distorted corneas caused by kera­toconus. “The contact lens would feature the custo­mized surface, matching it to the shape of the patient’s cornea,” Sun said. (Source: NWU)

Reference: X. Chen et al.: High‐Speed 3D Printing of Millimeter‐Size Customized Aspheric Imaging Lenses with Sub 7 nm Surface Roughness, Appl. Mat., online 24 March 2018; DOI: 10.1002/adma.201705683

Link: Cheng Sun Research Group, Northwestern University, Evanston, USA

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