Researchers have always thought that flat, ultrathin lenses for cameras and other devices were impossible because of the way the full colour spectrum of light must bend through them. To capture an image in a camera, the light must pass through the lenses and bend to converge to a point on the camera sensor, a principle known as refraction. Because different colours bend differently, cameras typically use a stack of multiple curved lenses to focus each colour of light in the spectrum to a single point. Consequently, photographers have had to put up with more cumbersome and heavier curved lenses.
However, University of Utah electrical and computer engineering professor Rajesh Menon and his team have developed a new method of creating optics that are flat and paper thin, yet can still perform the function of bending light to a single point.
Menon and his team discovered a way to design a flat lens that can be 10 times thinner than the width of a human hair or millions of times thinner than a camera lens today. They do it through a principle known as diffraction in which light interacts with microstructures in the lens and bends.
“If you look at a rainbow, it’s from diffraction,” he says. “What’s new is we showed that we could actually engineer the bending of light through diffraction in such a way that the different colours all come to focus at the same point. That is what people believed could not be done.”
Menon’s research team use specially created algorithms to calculate the geometry of a lens so different colours can pass through it and focus to a single point. The resulting lens, called a super-achromatic lens, can be made of any transparent material such as glass or plastic.
“Instead of the lens having a curvature, it can be very flat so you get completely new design opportunities for imaging systems like the ones in your mobile phone,” Menon says. The new kind of lens that can be used in cameras and other devices where the lens does not have to jet out of the body. “Our results correct a widespread misconception that flat, diffractive lenses cannot be corrected for all colours simultaneously.”
Menon and his doctoral students, Peng Wang and Nabil Mohamma, coauthored a research paper that was published in Scientific Reports.
Now that the team has proved the concept can work, Menon said he believes the first applications of their research could become a reality within five years.