Scientists design fish-inspired eye that can see in dark

Scientists are looking to the light-gathering abilities of the African elephant nose fish's retina to design new types of night vision devices such as an artificial eye that can work well even in a very dark environment.

Currently, most such devices focused on improving their image sensors' performance under low light conditions by using higher photoactive materials or adding external or on-chip intensifiers.

Hongrui Jiang, professor at the University of Wisconsin, described this week in the U.S. journal Proceedings of the National Academy of Sciences a new solution on the optics level, that is, to collect more light to the image sensor.

"This approach of ours has a very distinct advantage in that it is independent and does not exclude other approaches," Jiang said in an email to Xinhua.

"Rather, it can be combined with other approaches to further enhance the photosensitivity. In other words, we can improve any night-vision cameras and endoscopes, including the current ones."

The researchers took their inspiration from the elephant nose fish's retina, which has a series of deep cup-shaped structures with reflective sidewalls.

That design helps gather light and intensify particular wavelengths, enabling the African tropical freshwater fish to spot predators in the muddy rivers where it swims.

In the new study, the researchers used a technology called laser ablation to make arrays of tiny "cups," which have tapering parabolic sidewalls serving as focusing mirrors.

Jiang and his team then made the device onto a spherical, flexible substrate to model the curved human retina and found the artificial eye can make the image about four times brighter.

"That improvement is on top of any imager technology," he said.

"Without our device, the imager could not form a visually distinguishable image of an object in a very dark environment. With our device, a bright and sharp image is present, even though the object is in the same dark environment."

The new device overcame several engineering challenges, including making parabolic shaped sidewalls, making these sidewalls into reflective mirrors and designing imaging algorithm to recover lost due to the use of the light-collecting "cups."

One advantage was that it functioned in a wide light spectrum while the fish eye reflects only red light.

Jiang said the application is for low-light imaging systems such as night-vision cameras and endoscopes but it can be extended to a wide spectrum, including for search-and-rescue robots and space exploration.

Next, they planned to further improve the photosensitivity enhancement factor by making the sidewalls of the "cups" even smoother to reduce the scattering of the light.

"We expect the photosensitivity can be further improved by at least one order of magnitude," Jiang said. "We also need to lower the fabrication cost by implementing large-scale, batch fabrication. I think these issues can be addressed in about five years." Enditem