3D Janus plasmonic helical nanoapertures for polarization-encrypted data storage

Abstract

Helical structures have attracted considerable attention due to their inherent optical chirality. Here, we report a unique type of 3D Janus plasmonic helical nanoaperture with direction-controlled polarization sensitivity, which is simply fabricated via the one-step grayscale focused ion beam milling method. Circular dichroism in transmission of as large as 0.72 is experimentally realized in the forward direction due to the spin-dependent mode coupling process inside the helical nanoaperture. However, in the backward direction, the nanoaperture acquires giant linear dichroism in transmission of up to 0.87. By encoding the Janus metasurface with the two nanoaperture enantiomers having specified rotation angles, direction-controlled polarization-encrypted data storage is demonstrated for the first time, where a binary quick-response code image is displayed in the forward direction under the circularly polarized incidence of a specified handedness, while a distinct grayscale image is revealed in the backward direction under linearly polarized illumination with a specified azimuthal angle. We envision that the proposed Janus helical nanoapertures will provide an appealing platform for a variety of applications, which will range from multifunctional polarization control, enantiomer sensing, data encryption and decryption to optical information processing.

Data storage: Helical holes for polarized encryption

Tiny helical apertures etched in gold could act as unit cells for data storage technologies based on the manipulation of polarized light. Helical nanostructures are suited to storing binary data because they exist in two forms, left- and right-handed helixes. Xiaodong Yang, Jie Gao and Yang Chen at Missouri University of Science and Technology used ion beam milling to carve arrays of helter-skelter-shaped helical ‘nanoapertures’ in 180-nanometer-thick gold films. Their samples allow selective transmission of certain types of polarized light, while blocking others. Moreover, this polarization sensitivity depends on the direction of the incoming light, meaning that when light is directed in one direction the array produces binary images such as QR codes, while in the other direction it can reproduce grayscale photographs. This opens exciting possibilities for data encryption and optical information processing.