Two-Dimensional Chiral Metasurfaces Obtained by Geometrically Simple Meta-atom Rotations

Abstract

Two-dimensional chiral metasurfaces seem to contradict Lord Kelvin’s geometric definition of chirality since they can be made to coincide by performing rotational operations. Nevertheless, most planar chiral metasurface designs often use complex meta-atom shapes to create flat versions of three-dimensional helices, although the visual appearance does not improve their chiroptical response but complicates their optimization and fabrication due to the resulting large parameter space. Here we present one of the geometrically simplest two-dimensional chiral metasurface platforms consisting of achiral dielectric rods arranged in a square lattice. Chirality is created by rotating the individual meta-atoms, making their arrangement chiral and leading to chiroptical responses that are stronger or comparable to more complex designs. We show that resonances depending on the arrangement are robust against geometric variations and behave similarly in experiments and simulations. Finally, we explain the origin of chirality and behavior of our platform by simple considerations of the geometric asymmetry and gap size.

Thin-Film-Assisted Photothermal Deformation of Gold Nanoparticles: A Facile and In-Situ Strategy for Single-Plate-Based Devices

“…Therefore, such a thin-film-assisted photothermal deformation can trim NPs of different shapes into nanoplates. Moreover, this unconventional approach that overcomes the energy barrier of surface tension has local addressability and selectivity on single-particle level, which is highly useful for optimized performance of single-particle-based devices such as interferometric tweezers, SERS, − nanopore sensing, chiroptic metasurfaces, and gating electrode for transistors …”

Inverse designed WS2 planar chiral metasurface with geometric phase

“…The notable distinction in the electric field distribution, resulting in the large variation in absorption, may account for the large extinction ratio of the chiral resonator in this work. The optical chiral density [48,58] distribution is displayed in figure 4(c) to visualize the polarization conversion process induced by the chiral resonator. The optical chiral density is calculated from the equation,− ϵ0ω 2 Im(E * • B), and normalized by its maximum absolute value.…”

A Multiband and Multifunctional Metasurface for Linear and Circular Polarization Conversion in Reflection Modes

“…Recent years have seen the emergence of different metasurface-based polarization converter types that can convert various electromagnetic wave polarization states, such as cross-polarization conversion [15,16], linear polarization conversion (LP) to circular polarization (CP) conversion [17][18][19][20][21][22], and right-to left-handed CP conversion [23,24]. The main issue with a metasurface in the electromagnetic field remains the same, i.e., maximum polarization converters still only operate a single function, and multiband polarization converters have relatively narrow bandwidths [25,26]. Recently, some all-metal phaseshifting structures have been proposed; these structures are either single-frequency or polarization-dependent structures.…”