Perturbative solution for terahertz two-wire metallic waveguides with different radii

Tuning transmission properties of 3D printed metal rod arrays by breaking the structural symmetry

In this work, one metallic photonic crystal waveguide composed of periodic metal rod arrays (MRAs) is experimentally and numerically demonstrated in terahertz frequencies. Such waveguides fabricated by 3D printers exhibit two resonant modes: the fundamental mode and the high-order mode, separating by a broad bandgap. Compared to the fundamental mode, the high-order mode shows higher field confinement and more sensitive to the geometry changes. By breaking the structure parameter, i.e., increasing or decreasing the metal rod interspace, the spectral positions, bandwidths, as well as the transmittances of high-order modes can be optimized. With broken symmetry in MRAs, the third resonant mode having high transmittance has emerged in the transmission spectrum. Results showing that fine-tuning in the alignment of metal rods leads to a great change in the transmission of high-order modes. These findings suggest that the transportation efficiency of THz waves through an MRA is tunable by breaking the structural symmetry.

Graphene-Coated Nanowire Waveguides and Their Applications

In recent years, graphene-coated nanowires (GCNWs) have attracted considerable research interest due to the unprecedented optical properties of graphene in terahertz (THz) and mid-infrared bands. Graphene plasmons in GCNWs have become an attractive platform for nanoscale applications in subwavelength waveguides, polarizers, modulators, nonlinear devices, etc. Here, we provide a comprehensive overview of the surface conductivity of graphene, GCNW-based plasmon waveguides, and applications of GCNWs in optical devices, nonlinear optics, and other intriguing fields. In terms of nonlinear optical properties, the focus is on saturable absorption. We also discuss some limitations of the GCNWs. It is believed that the research of GCNWs in the field of nanophotonics will continue to deepen, thus laying a solid foundation for its practical application.

Graphene-coated nanowire dimers for deep subwavelength waveguiding in mid-infrared range

In this paper, we show that the graphene-coated nanowire dimers could enable outstanding waveguiding performance in the mid-infrared range. The propagating properties of the fundamental graphene plasmon mode and their dependence on the nanowire radius, gap distance, nanowire permittivity and chemical potential of graphene are revealed in detail and compared with the graphene-coated circular nanowire. By improving the geometric parameters and the surface conductivity of graphene, the propagation length could reach about 9 μm, which is larger than that of the graphene-coated circular nanowire plasmon mode. Meanwhile, the effective mode area is only 10^-4A₀, which is one order of magnitude smaller than that of the graphene-coated circular nanowire plasmon mode. Theoretically, the propagation length could be further enhanced by increasing the chemical potential. Besides, the proposed graphene-coated nanowire dimers show quite good fabrication tolerance. The manipulation of mid-infrared waves at the deep subwavelength scale using graphene plasmons may offer potential applications in tunable integrated nanophotonic devices and infrared sensing.