A team of applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) has managed to create an ultrathin, flat lens that is only a mere 60 nanometers thick. Despite being so thin, and being close to the ultimate physical limit set by the laws of diffraction, the lens is able to focus light without imparting the distortions of conventional lenses.
The team’s achievement was announced in the journal Nano Letters, where they stated the new device is completely scalable, from near-infrared to terahertz wavelengths, and simple to manufacture.
“Our flat lens opens up a new type of technology,” says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in a statement. “We’re presenting a new way of making lenses. Instead of creating phase delays as light propagates through the thickness of the material, you can create an instantaneous phase shift right at the surface of the lens. It’s extremely exciting.”
The ultrathin lens was created by plating a very thin wafer of silicon with a nanometer-thin layer of gold. They then stripped away parts of the gold layer to leave behind an array of V-shaped structures, all of which were evenly spaced in rows across the surface. When the team shone a laser onto the flat lens, these structures then acted as nanoantennas, which captured the incoming light and held onto it briefly before releasing it again. When this was precisely tuned across the surface of the entire lens, it was able to change the direction of the light in the same way that a thick glass lens would – but with an important distinction.
As it is so flat and thin, the new lens eliminates optical aberrations such as the “fish-eye” effect that results from conventional wide-angle lenses. Astigmatism and coma aberrations also do not occur with the flat lens, so the resulting image or signal is completely accurate.
“In the future we can potentially replace all the bulk components in the majority of optical systems with just flat surfaces,” said lead author Francesco Aieta, a visiting graduate student from the Università Politecnica delle Marche in Italy. “It certainly captures the imagination.”