These Super-Light Polymer Lenses May Eventually Replace Human Corneas

A new artificial lens that mimics the one found in human eyes is set to dramatically lower the weight of night-vision goggles, laser rangefinders and cameras aboard micro unmanned aerial vehicles that soldiers and marines must carry in the field.

Optics and materials engineers have been working for a decade on a process that places thousands of transparent polymer layers on top of each other to make what's called a gradient-index (GRIN) lens.

It's the same method that humans and some other animals have evolved to build the lens in their eyes. In the natural version, thousands of layers of clear protein layers are deposited one on top of the other to allow light through and focus images onto the retina.

"We were curious about what makes our own eyes work," says Dr Michael Ponting, the president of PolymerPlus, a spinoff from Case Western Reserve University founded to bring the new GRIN lenses to market. "We've always been interested in how smart evolved natural systems are at getting things done. So we looked to nature to find the most efficient scientist."

Fine-Tuning Refractive Power

For the artificial version PolymerPlus is building, each polymer layer can be fine-tuned by changing its chemical composition to minutely alter how much it bends light, a phenomenon called refraction. The process then stacks 4000 polymer layers into paper-thin films that are in turn placed on top of each other. This method allows scientists to precisely configure the refractivity of the lens. Their work was published in November in the journal Optics Express.

The amalgamated layers of these GRIN lenses are allowing the researchers to dial in the desired optical characteristics they are looking for, like focusing or defocusing light and shielding out unwanted wavelengths. "Another neat thing you can do is create flat optics that makes light bend inside of them so they work like convex or concave lenses," Ponting says.

Military Applications

The US Defense Advanced Research Projects Agency and the Office of Naval Research have contributed funding and brainpower to make the new lens technology.

DARPA managers have laid out their hopes for GRIN on the technology's product page. "What if a laser range finder or night-vision goggle could be reduced to half its size and weight? Imaging systems could benefit by using fewer optical elements to achieve better control of light with equal or better performance than conventional optics. For example, this translates to high-resolution cameras for micro unmanned aerial vehicles.

"Recent advances in the design and fabrication of GRIN optics promises to make this possible, and the implications will be far-reaching."

The sandwiched layers of polymers are about half the weight of glass equivalents, and their focusing abilities mean that one polymer lens can do the work of three that are made of glass. The result, Ponting says, is night-vision goggles that are a seventh of the weight compared to those currently available.

Part of the new technique's efficiency is the way that it refracts light. Most lenses must be shaped to change the direction that light travels when it passes through because the refraction happens at the surface of the material. The composition of the polymer layers in the new GRIN lens can actually refract light internally thanks to their varying chemical composition, which is precisely engineered.

"It's everything the state of the art in optics was plus the ability to change how light travels internally in the material instead of just at the surface," Ponting says. "We take advantage of the wasted internal space to bend where the light goes. It's a design degree of freedom."

Other Uses On the Horizon

The civilians and military working on the technology are already looking at what it can be used for besides military and other surveillance applications.

"In the past century, every component of an optical system has become lighter and smaller, except the optics," says Stefanie Tompkins, DARPA's GRIN program manager. "The impact of smaller, lighter optics on anything used to focus light, from contact lenses and corneal implants to lasers and solar arrays would be enormous."

Ponting says that the lenses will one day be used to replace faulty or damaged ones in human eyes. They may also make it into orbit-their better optical characteristics mean that they could find a use in communications and earth-observing satellites.

"The lenses made from this process allow finer detail, better colour resolution, higher contrast and much lower weight," Ponting says. "This can fill a gap in society that no one has hit yet."

Txchnologist is a digital magazine presented by GE that explores the wider world of science, technology and innovation. Subscribe to Txchnologist's daily email.

Michael Keller is the Managing Editor of Txchnologist. His science, technology and international reporting work has appeared online and in newspapers, magazines and books, including the graphic novelCharles Darwin's On the Origin of Species. Reach him at [email protected]

Top image: Flickr user Michele Catania.

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