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Abstract Metasurfaces, as a two-dimensional (2D) version of metamaterials, have drawn considerable attention for their revolutionary capability in manipulating the amplitude, phase, and polarization of light. As one of the most important types of metasurfaces, geometric metasurfaces provide a versatile platform for controlling optical phase distributions due to the geometric nature of the generated phase profile. However, it remains a great challenge to design geometric metasurfaces for realizing spin-switchable functionalities because the generated phase profile with the converted spin is reversed once the handedness of the incident beam is switched. Here, we propose and experimentally demonstrate chiral geometric metasurfaces based on intrinsically chiral plasmonic stepped nanoapertures with a simultaneously high circular dichroism in transmission (CDT) and large cross-polarization ratio (CPR) in transmitted light to exhibit spin-controlled wavefront shaping capabilities. The chiral geometric metasurfaces are constructed by merging two independently designed subarrays of the two enantiomers for the stepped nanoaperture. Under a certain incident handedness, the transmission from one subarray is allowed, while the transmission from the other subarray is strongly prohibited. The merged metasurface then only exhibits the transmitted signal with the phase profile of one subarray, which can be switched by changing the incident handedness. Based on the chiral geometric metasurface, both chiral metasurface holograms and the spin-dependent generation of hybrid-order Poincaré sphere beams are experimentally realized. Our approach promises further applications in spin-controlled metasurface devices for complex beam conversion, image processing, optical trapping, and optical communications.
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Chiral Nonlocal Metasurfaces for Frequency-Selective Wavefront Shaping
We propose, design, and experimentally demonstrate a nonlocal metasurface with frequency-selective, wavefront shaping capabilities and at the same time polarization-selective chiral response. This operation requires the implementation of bilayer metasurfaces with engineered nonlocal response, wherein each layer controls locally a specific linear polarization, while the coupled system supports arbitrary polarization states. We demonstrate that this platform enables unprecedented control over wavefront manipulation, including frequency-selective, spin-selective reflection with arbitrary geometric phase. We observe a highly chiral response with record-high reflectance efficiency over a narrow frequency window, both for a uniform metasurface and for one with tailored phase gradient for anomalous reflection. Both devices provide an efficiency well above the theoretical limit of 25% for conventional single-layer devices. Our work opens exciting opportunities for augmented reality and enhanced secure wireless communications.
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- Award ID(s):
- 2106752
- PAR ID:
- 10341788
- Date Published:
- Journal Name:
- IEEE Antennas and Propagation Symposium
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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