Researchers developed an artificial eye that can autocorrect astigmatism – or blurry vision – and focus on near and far objects much like a healthy human eye.
The nanoengineered eye, which combines a “metalens” with artificial muscle technology, bests its human counterpart in some instances, for instance by overcoming image shift and “healing” cases of astigmatism. In human beings, astigmatism occurs when the eyeball loses its round shape and bends light in a way that makes images blurry.
Normally, a person with astigmatism will require contact lenses, glasses or surgery to return the eye to normal functioning.
“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 lead author Alan She, a graduate student the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
“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,” added She.
The complex eye will have use for a wide range of applications, “including cell phone cameras, eyeglasses and virtual and augmented reality hardware,” said senior author Federico Capasso. “It also shows the possibility of future optical microscopes, which operate fully electronically and can correct many aberrations simultaneously.”
Mega-sizing the Metalens
Prior research into metalenses had created devices that were extremely small, no larger than a bread crumb. To get from the tiny structure of prior lenses, the Harvard researchers went mega on the metalens.
“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 10,000. Whenever we tried to scale-up the lens, the file size of the design alone would balloon up to gigabytes or even terabytes.”
By writing new software, the researchers were able to overcome this challenge – and maintain a manageable metalens even as they built it to a centimeter or more in diameter.
For the next step, researchers took another cue from the human eye. They attached the metalens to an artificially developed muscle, essentially mimicking how the lens of the human eye is centered among finely tuned muscles that can manipulate the eye lens to change its shape and focus.
The researchers used an artificial muscle known as an elastomer that would allow light to travel through it to the lens. The researchers could control the elastomer, and how it moved or focused the artificial eye, by applying an electrical current.
They found that the lens could fix astigmatism, focus and conduct image shift all at the same time.
“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,” She added.
The study appeared in the journal Science Advances.