New 3D printed microlenses with adjustable refractive index – ready to improve image, computing and communications

Illinois researchers developed a spherical lens that allows light coming into the lens from any direction to be focused at a very small spot on the lens surface exactly in the direction of the entrance. This is the first time such a lens is made for visible light. Credit: Graphic by Michael Vincent

Researchers have developed new 3D printed microlenses with adjustable refractive indices – a property that gives them highly specialized light-focusing capabilities. This advancement is ready to improve image, computing and communications by significantly increasing the data routing capability of computer potatoes and other optical systems, the researchers said.

The study was led by Illinois Urbana-Champaign Universa researchers Paul Braun and Lynford Goddard and is the first to demonstrate the ability to adjust the direction in which light bends and travels through a lens with sub-micrometer accuracy.

The results of the study were published in the journal Light: Science and Application.

“Having the ability to fabricate optics with different optics shapes and parameters provides a solution to the common problems faced by optics,” said Brown, who is a professor of materials science and engineering. “For example, in image applications, focusing on a specific object often results in blurry edges. Or, in data transfer applications, higher speeds are required without damaging the space on a computer chip. Our new lens fabrication technique addresses these problems in an integrated device. “

As a demonstration, the team produced three lenses: a flat lens; the world’s first lens with visible light Luneburg – a previously spherical lens impossible to fabricate with unique focusing properties; and 3D wave guides that can enable massive data routing capabilities.

SCRIBE Search Team

Illinois scholars, from left, Raman Kumar, Corey Richards, Alex Littlefield, Lynford Goddard, Haibo Gao, Paul Braun, Dajie Xie, Christian Ocier and Andrea Perry. Credit: Photo by Brian Stauffer

“A standard lens has a single refractive index and therefore only one path that light can pass through the lens,” said Goddard, who is a professor of electrical and computer engineering. “Having control over the internal refractive index and the shape of the lens during fabrication, we have two independent ways of bending light within a single lens.”

In the lab, the team uses a process called laser direct writing to create the lenses. A laser solidifies liquid polymers and forms small geometric optical structures up to 100 times smaller than human hairs. Direct laser writing has been used in the past to create other microlenses that had only one refractive index, the researchers said.

“We addressed the refractive index limitations by pressing inside a nanoporous scaffolding backing material,” Brown said. “The scaffolding encloses the micro-optics printed in place, allowing the fabrication of a 3D system with suspended components.”

The researchers theorize that this refractive index control is the result of the polymer setting process. “The amount of polymer trapped inside the pores is controlled by the laser intensity and exposure conditions,” Brown said. “While the optical properties of the polymer itself do not change, the overall refractive index of the material is controlled as a function of laser exposure.”

Team members said they expect their method to significantly impact the production of complex optical components and imaging systems and will be useful in advancing personal computing.

“An excellent example of implementing this development will be its impact on data transfer within a personal computer,” Goddard said. “Current computers use electrical connections to transmit data. However, data can be sent at a significantly higher rate using an optical waveguide because different colors of light can be used to send data in parallel. A major challenge is that ordinary wave guides can only be made in a single plane and so a limited number of points on the chip can be connected. By creating three-dimensional wave guides, we can dramatically improve data rate, transfer speed, and energy efficiency. “

Reference: “Direct laser writing of volumetric gradient index lenses and wave guides” by Christian R. Ocier, Corey A. Richards, Daniel A. Bacon-Brown, Qing Ding, Raman Kumar, Tanner J. Garcia, Jorik van de Groep, Jung- Hwan Song, Austin J. Cyphersmith, Andrew Rhode, Andrea N. Perry, Alexander J. Littlefield, Jinlong Zhu, Dajie Xie, Haibo Gao, Jonah F. Messinger, Mark L. Brongersma, Kimani C. Toussaint Jr., Lynford L. Goddard and Paul V. Braun, December 3, 2020, Light: Science & Applications.
DOI: 10.1038 / s41377-020-00431-3

U.S. graduate students I. Christian Ocier and Corey Richards are the lead authors of the study.

Brown is the director of the Materials Research Laboratory and an associate of the Beckman Institute for Advanced Science and Technology. Goddard is director of the Institute for Inclusion, Diversity, Equality and Access at Grainger College of Engineering and is an associate of the Holonyak Micro and Nanotechnology Laboratory in Illinois.

The U.S. Department of Energy, the U.S. Department of Energy, and the National Science Foundation supported this research.

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