Harvard engineers have gotten considerably closer to crafting a truly functional artificial eye with the potential to help those needing fake eyes to regain sight.
A team from the John A. Paulson School of Engineering and Applied Sciences (SEAS) developed a new metalens that can control focus, astigmatism and image shift. The technology takes inspiration from the way the human eye naturally adjusts in real time.
"This research combines breakthroughs in artificial muscle technology with metalens technology to create a tunable metalens that can change its focus in real time, just like the human eye," said Alan She, a graduate student at SEAS and first author of the paper. "We go one step further to build the capability of dynamically correcting for aberrations such as astigmatism and image shift, which the human eye cannot naturally do."
While this technology might not be in fake eyes just yet, researchers noted that the lens could be applied to other technology with ease.
"This demonstrates the feasibility of embedded optical zoom and autofocus for a wide range of applications including cell phone cameras, eyeglasses and virtual and augmented reality hardware," said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. "It also shows the possibility of future optical microscopes, which operate fully electronically and can correct many aberrations simultaneously."
Early versions of the metalens were roughly the size of a single piece of glitter. The team needed to focus light through densely woven nanostructures.
"Because the nanostructures are so small, the density of information in each lens is incredibly high," said She. "If you go from a 100 micron-sized lens to a centimeter sized lens, you will have increased the information required to describe the lens by ten thousand. Whenever we tried to scale-up the lens, the file size of the design alone would balloon up to gigabytes or even terabytes."
They then created an algorithm to further shrink the size of the metalens in order to integrate the technology with other circuits. After that, the researchers needed to scale the lens back up in order to stick it to an artificial muscle and test its ability to focus light. They used a thin elastomer that allowed light to travel through it without much scattering.
"Elastomers are so different in almost every way from semiconductors that the challenge has been how to marry their attributes to create a novel multi-functional device and, especially how to devise a manufacturing route," said professor David Clarke. "As someone who worked on one of the first scanning electron microscopes (SEMs) in the mid 1960's, it is exhilarating to be a part of creating an optical microscope with the capabilities of an SEM, such as real-time aberration control."
The elastomer stretches and repositions the nanopillars of the lens to shift. The lens can simultaneously focus and perform image shift.
"All optical systems with multiple components -- from cameras to microscopes and telescopes -- have slight misalignments or mechanical stresses on their components, depending on the way they were built and their current environment, that will always cause small amounts of astigmatism and other aberrations, which could be corrected by an adaptive optical element," said She. "Because the adaptive metalens is flat, you can correct those aberrations and integrate different optical capabilities onto a single plane of control."
The researchers are looking to make the technology more efficient by reducing the energy needed to control it while still ensuring its functionality.