An ultrathin metasurface can alter light polarization with 50 percent efficiency, hinting at future microscale devices for controlling light. A team from the University of Michigan and its Lurie Nanofabrication Facility created the device, which is 250 × 250 µm and is 400 nm thick. “The performance of our metasurface is more than sufficient for many applications that require optical elements with very small form factors, such as a lab-on-a-chip, pocket cameras and biomedical optics,” said Carl Pfeiffer, a doctoral researcher in U-M’s Department of Electrical Engineering and Computer Science. Right-handed circularly polarized (RHCP) light enters the metasurface, but exits as left-handed circularly polarized (LHCP) light. RHCP is reflected off the back side of the surface. Images courtesy of University of Michigan. The metasurface is composed of three 28-nm patterned gold sheets fabricated using electron-beam lithography and separated at subwavelength intervals by dielectric substrates. The researchers found that when right-handed circularly polarized (RHCP) light enters the front of the metasurface, it emerges on the opposite side as left-handed circularly polarized (LHCP) light. When the operating optical wavelength is 1.5 µm, the transmittance from RHCP to LHCP is 50 percent and the extinction ratio is 20:1, which the researchers said represents an order of magnitude improvement over previous optical structures exhibiting asymmetric transmission. Only 2.5 percent LHCP light entering the front face of the metasurface is transmitted; the rest is reflected. Such metasurfaces in the future could be used to control light’s phase and amplitude, the researchers said. “One day, we believe that we will be able to replace the optical components that are currently used in analytic chemistry, biology and crystallography to identify the spatial structures of molecules with our ultrathin metasurfaces,” Pfeiffer said. “These metasurfaces could also be used in applications such as infrared identifiers, which utilize the unique polarization signature emitted by an infrared ID tag in a similar way that newer credit card readers use near-field communication to read a credit card without swiping it.” The work was funded by National Science Foundation’s Materials Research Science and Engineering Center for Photonic and Multiscale Nanomaterials and the U.S. Air Force Research Laboratory. The research was published in Physical Review Letters (doi: 10.1103/PhysRevLett.113.023902). For more information, visit www.umich.edu. Scanning electron microscope images of the three different gold layers used to create the metasurface.