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.
Highlights
Chirality, as first defined by Lord Kelvin, describes any geometrical figure or group of points whose mirror image cannot be brought to coincide with itself[1]
We propose and experimentally demonstrate a 3D Janus plasmonic helical nanoaperture as a new type of helical nanostructure
Depending on whether the depth of the gradient groove is increased counterclockwise or clockwise, the chiral helical nanoapertures exist in two enantiomeric forms, namely, Form A and Form B, which are mirror-symmetric with each other
Summary
As first defined by Lord Kelvin, describes any geometrical figure or group of points whose mirror image cannot be brought to coincide with itself[1]. It is a ubiquitous property for biological objects, which range from small biomolecules, such as amino acids and nucleotides, to biological macromolecules, such as proteins and nucleic acids, and even to our hands and feet[2]. Chiroptical effects are extremely weak in natural materials. To overcome this problem, chiral plasmonic structures have been used to significantly boost the CD signals of chiral molecules. In addition to enantiomer sensing, chiral structures have been widely applied in miniature polarizers[9,10,11], nonlinear optics[12,13,14], and spin-controlled optical devices[15,16,17,18]
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