Helical plasmonic nanostructures have attracted considerable attention in materials science and chemistry due to their inherent optical chirality. In a new report, Yang Chen and a research team in the department of Mechanical and Aerospace Engineering in the U.S. developed unique 3-D Janus (nanoparticles with two or more surface properties) plasmonic helical nanoapertures (helical holes), with direction-controlled polarization sensitivity. They engineered the helical structures using one-step grayscale focused ion beam milling (FIB). Chen et al. then encoded the Janus metasurface with two nanoaperture enantiomers (left and right handed mirror image molecules of each other) with specific rotational angles to demonstrate direction-controlled polarization data encryption for the first time.
The samples engineered in the work allowed the selective transmission of certain types of polarized light, while blocking others. This sensitivity to polarization depended on the direction of the incoming light; for instance, light in a specific direction prompted the arrays to produce binary images, whereas light in the opposite direction could reproduce grayscale photographs. Chen et al. envision using the proposed Janus helical nanoapertures for a variety of applications ranging from polarization control within built in photonic devices, advanced enantiomer sensing, data encryption and decryption as well as optical information processing. The new results are now published in Light: Science & Applications.
Chirality was first defined by Lord Kelvin to describe any geometrical figure whose mirror image could not coincide with itself. The property is ubiquitous in biological objects that range from small biomolecules such as amino acids and nucleotides to larger macromolecules such as proteins and nucleic acids, and even our hands and feet. While the left-handed and right-handed versions of a molecule known as enantiomers can have similar chemical and physical properties, they can perform entirely different biological functions in diverse fields of applications.