Line-wave waveguide engineering using Hermitian and non-Hermitian metasurfaces.

Line waves (LWs) refer to confined edge modes that propagate along the interface of dual electromagnetic metasurfaces while maintaining mirror reflection symmetries. Previous research has both theoretically and experimentally investigated these waves, revealing their presence in the microwave and terahertz frequency ranges. In addition, a comprehensive exploration has been conducted on the implementation of non-Hermitian LWs by establishing the parity-time symmetry. This study introduces a cutting-edge dual-band line-wave waveguide, enabling the realization of LWs within the terahertz and infrared spectrums. Our work is centered around analyzing the functionalities of existing applications of LWs within a specific field. In addition, a novel non-Hermitian platform is proposed. We address feasible practical implementations of non-Hermitian LWs by placing a graphene-based metasurface on an epsilon-near-zero material. This study delves into the advantages of the proposed framework compared to previously examined structures, involving both analytical and numerical examinations of how these waves propagate and the underlying physical mechanisms.

Babinet-complementary structures for implementation of pseudospin-polarized waveguides.

In this work, a theorem is proved stating that in various types of waveguides with mirror reflection symmetries, the electromagnetic duality correspondence between eigenmodes of complementary structures induces counterpropagating spin-polarized states. The mirror reflection symmetries may be preserved around one or more arbitrary planes. Pseudospin-polarized waveguides supporting one-way states manifest robustness. This is similar to topologically non-trivial direction-dependent states guided by photonic topological insulators. Nevertheless, a remarkable aspect of our structures is that they can be implemented in extremely broad bandwidth by simply using complementary structures. Based on our theory, the concept of the pseudospin polarized waveguide can be realized using dual impedance surfaces ranging from microwave to optical regime. Consequently, there is no need to employ bulk electromagnetic materials to suppress backscattering in waveguiding structures. This also includes pseudospin-polarized waveguides with perfect electric conductor-perfect magnetic conductor boundaries where the boundary conditions limit the bandwidth of waveguides. We design and develop various unidirectional systems and the spin-filtered feature in the microwave regime is further investigated.

Variational-based approach to investigate Fano resonant plasmonic metasurfaces.

Considering the widespread applications of resonant phenomena in metasurfaces to bend, slow, concentrate, guide and manipulate lights, it is important to gain deep analytical insight into different types of resonances. Fano resonance and its special case electromagnetically induced transparency (EIT) which are realized in coupled resonators, have been the subject of many studies due to their high-quality factor and strong field confinement. In this paper, an efficient approach based on Floquet modal expansion is presented to accurately predict the electromagnetic response of two-dimensional/one-dimensional Fano resonant plasmonic metasurfaces. Unlike the previously reported methods, this method is valid over a wide frequency range for different types of coupled resonators and can be applied to practical structures where the array is placed on one or more dielectric layers. Given that the formulation is written in a comprehensive and flexible way, both metal-based and graphene-based plasmonic metasurfaces under normal/oblique incident waves are investigated, and it is demonstrated that this method can be posed as an accurate tool for the design of diverse practical tunable/untunable metasurfaces.