A new type of lens developed in the United States is capable of focusing light without distorting it. While conventional lenses do impart some modifications to the photon beams they focus, the new, ultrathin devices do not.
Developed by experts at the Harvard University School of Engineering and Applied Sciences
(SEAS), the flat lens is only 60-nanometer (billionths of a meter) thick, and functions at the same wavelengths as various telecommunications technologies.
One of its most amazing features is that its focusing capabilities approach the diffraction limit, which is imposed by the laws of physics themselves. Instilling this level of performance into what is basically a two-dimensional material is a tremendous achievement.
According to a paper the SEAS team published in the latest online issue of the scientific journal Nano Letters, the lens is scalable from near-infrared to terahertz wavelengths, and is very easy to produce. It could contribute significantly to improving fiber-optic communications, experts add.
The lens itself is made out of an ultrathin silicon wafer, which was covered with a nanometer-thin sheet of gold. Using a special technique, researchers then removed some of the gold they applied on the wafer, leaving behind small, V-shaped patterns.
What these patterns do is hold on to photons for very brief intervals, as the particles stream through. As soon as the light is released, its direction changes slightly. The V-shaped patterns are basically nanoscale antennas tuned to focus photons in specific ways.
“Our flat lens opens up a new type of technology. We’re presenting a new way of making lenses,” explains the SEAS Robert L. Wallace professor of applied physics, and Vinton Hayes senior research fellow. Federica Capasso. He was also the principal investigator of the study.
“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,” he adds.
The device is capable of eliminating fish-eye-type defects, which regularly occur in wide-angle lenses. Coma aberrations and astigmatism are also removed, leaving behind an extremely accurate signal that requires no corrections.
“In the future we can potentially replace all the bulk components in the majority of optical systems with just flat surface. It certainly captures the imagination,” concludes Università Politecnica delle Marche gradutate student and lead study author, Francesco Aieta.