Metasurfaces composed of in‐plane subwavelength nanostructures have unprecedented capability in manipulating the amplitude, phase, and polarization states of light. Here, a unique type of direction‐controlled bifunctional metasurface polarizer is proposed and experimentally demonstrated based on plasmonic stepped slit‐groove dimers. In the forward direction, a chiral linear polarizer is enabled which only allows the transmission of a certain incident handedness and converts it into the specified linear polarization. In the backward direction, the metasurface functions as an anisotropic circular polarizer to selectively convert a certain linear polarization component into the desired circularly polarized transmission. The observed direction‐controlled polarization selection and conversion are explained by the spin‐dependent mode coupling process inside the bilayer structure. Anisotropic chiral imaging based on the proposed metasurface polarizer is further demonstrated. The results provide new degrees of freedom to realize future multifunctional photonic integrated devices for structured light conversion, vector beam generation, optical imaging and sensing, and optical communication.
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.
more » « less- NSF-PAR ID:
- 10150136
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Light: Science & Applications
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2047-7538
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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