This study proposes an ultrathin chiral metamaterial slab stacked with twisted complementary split-ring resonators (CSRRs) for highly efficient broadband polarization transformation. The polarization of linearly polarized electromagnetic waves can be rotated in a specific direction by passing it through such a slab having a thickness of about one-tenth the operational wavelength. Microwave experiments verified the theoretically predicted conversion efficiency of up to 96% covering a bandwidth of 24% of the central wavelength. CSRRs with circular symmetry provide increased interlayer coupling strength, which produces a high-efficiency broadband response and strong isolation of the original polarization.

We propose an ultra-thin planar metasurface with phase discontinuities for highly efficient beam steering. The effect benefits from the broadband transparency and flexible phase modulation of stacked metal/dielectric multi-layers that is perforated with coaxial annular apertures. Proof-of-principle experiments verify that an efficiency of 65% and a deflection angle of ${18}^{\text{o}}$ at 10GHz are achieved for the transmitted beam, which are also in good agreement with the finite-difference-method-in-time-domain (FDTD) simulations. The scheme shall be general for the design of beam-steering transmitters in all frequencies.

2D optics is gradually emerging as a frontier in modern optics. Plasmons in graphene provide a prominent platform for 2D optics in which the light is squeezed into atomic scale. This report highlights some recent progresses in graphene plasmons toward the 2D optics. The launch, observation, and advanced manipulation of propagating graphene plasmons for 2D optical circuits are described. Representative achievements associated with graphene metasurfaces, challenges, recent progresses like photoexcited graphene metasurfaces, and the transformation optics linking 2D to bulk optics with singularity are investigated.

We experimentally observe toroidal dipolar response in a planar metamaterial comprised of asymmetric split-ring resonators (ASRRs) at microwave frequency. It is shown that a toroidal molecule can be constructed through rational arrangement of planar ASRRs as meta-atoms via manipulating structural symmetry and thus coupling of the meta-atoms. We find that the toroidal resonance provides a subwavelength-scale electromagnetic localization style, and that confining the electromagnetic field inside a dielectric medium with toroidal geometry is beneficial for low-loss metamaterials. The planar scheme of manipulating the coupling among the ASRRs may stimulate research in optical regions involving toroidal multipoles. The toroidal geometry together with the Fano resonance of ASRR-induced high-$Q$ response will have enormous potential applications in enhancing light-matter interactions, e.g., for low-threshold lasing, low-power nonlinear processing, and sensitive biosensing.