Ultrathin lenses – 1% of a hairbreadth

Metasurface optical elements

A groundbreaking paper on metasurface optical elements, by Dr. Tal Ellenbogen of the Physical Electronics Dept. at the School of Electrical Engineering and Ori Avayu, an MSc student at the School, was published in the leading scientific journal Nature Communications.

Photography with ultrathin lenses

Convex lenses are the basis of all optical devices, such as cameras, microscopes, telescopes etc. Usually, in order to attain a high-quality image, a large number of lenses is required. One of the reasons is that when we wish to get a non-monochromatic image, for instance in daylight photography, the various wavelengths that make up the white light come to a focus in slightly different places, and the picture looks distorted. This phenomenon, known as chromatic aberration, complicates the design of optical devices (thus raising their price), while also setting a limit on their minimum thickness – in smartphones for example. This problem has engendered a growing demand for thinner alternatives for these lenses, which would also retain high quality focusing and reduce production costs.

Three-in-one lens

In a paper published in the prestigious scientific journal Nature Communications, Ori Avayu and Dr. Tal Ellenbogen of TAU's Nano-Electro-Optics Lab, in collaboration with Dr. Euclides Almeida and Prof. Yehiam Prior of the Weizmann Institute, showed how three ultrathin layers of metasurfaces can be used to create a lens without chromatic aberrations.  The researchers used nanotechnology to write setups of nano-antennas made of different metals, each reacting to visible light in a different way, and acting as a lens for a different color. Combining these three layers of metasurfaces in a structure as thin as 1% of a hairbreadth, the researchers were able to build a device that focuses the resulting white light at a single point.  Also presenting a range of other optical elements based on the new technology, the study attracted considerable interest from industrial developers of cameras and miniaturized optical elements.

For the full paper: Composite functional metasurfaces for multispectral achromatic optics