OCT improves S-GRIN lens manufacturing process

Ashley N. Rice, ashley.rice@photonics.com

Spherical gradient in refractive index (S-GRIN) lenses are lightweight and easily deformable, but manufacturing them with high quality and consistency is challenging. Now, researchers at the University of Rochester are embedding OCT into the manufacturing process to get a better view of the lens’ complete structure.

“I had done the calculation and thought we could do it,” said Jannick Rolland, the Brian J. Thompson Professor of optical engineering at the university’s Institute of Optics. “And sure enough, after several months of work we had 3-D movies of the whole structure of the lenses and also clear pictures of each of the layers. It was amazing.”

Kyle Fuerschbach, left, a graduate student at the University of Rochester’s Institute of Optics, and Jannick Rolland, the Brian J. Thompson Professor and director of the R.E. Hopkins Center, work on a freeform lens experiment in Goergen Hall.

The researchers obtained the images by shining IR light onto the lenses – which were developed by Eric Baer at Case Western Reserve University in Cleveland and consist of thousands of layers of compressed plastic bent into a lens-type shape – using a technique similar to ultrasound. They observed how each of the lens’ layers bent the scattered light, and by counting how much time the light took to come back, they were able to determine how deep into the material it scattered from.

“In the same way that in ultrasound we measure the time of flight to the tissue and back to localize the presence of the structure, we can do this with light that has a much smaller wavelength, which means a much higher resolution,” Rolland said.

Being able to see the complete lens structure enabled the researchers to pinpoint some areas of the manufacturing process that could be improved. For example, they saw that some of the layers were thicker than PolymerPlus, the developer of the manufacturing process, had hoped for.

The S-GRIN lenses could be used in lightweight single-lens cameras, ball lenses for solar collectors and night-vision goggles.

The results appeared in Scientific Reports (doi: 10.1038/srep01709).