Cambridge, MA--A 2D metamaterial pattern consisting of an array of subwavelength-spaced optical nanoantennas on a flat silicon surface serves as an aberration-free focusing lens of high-enough quality that it could potentially be used as a microscope objective. The array of V-shaped nanoantennas can also be fabricated on axicon surfaces.
The team, consisting of Federico Capasso and his group as the Harvard School of Engineering and Applied Sciences (SEAS) and other researchers at the Università Politecnica delle Marche (Ancona, Italy), Texas A&M University (College Station, Texas), and Università degli Studi di Trento (Trento, Italy), as published the results online in the journal Nano Letters.
Similar to Fresnel zone plate
The V shapes can be altered to increase or increase the local phase discontinuity; arranging the different shapes in rings of varying with allows the researchers to create Fresnel-zone-plate-like devices. The nanoantennas are of gold and are only 60 nm thick. Operating at telecom wavelengths, the new lens is scalable from near-IR to terahertz wavelengths, and is simple to manufacture.
“Our flat lens opens up a new type of technology,” says Capasso, the principal investigator. “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 flat lens eliminates optical aberrations such as astigmatism and coma, as well as the fish-eye effect that results from conventional wide-angle lenses. The array of nanoantennas can be tuned for specific wavelengths of light by simply changing the size, angle, and spacing of the antennas.