Manipulating line waves in flat graphene for agile terahertz applications

Abstract

Reducing open waveguides enabled by surface waves, such as surface plasmon polaritons, to a one-dimensional line is attractive due to the potentially enhanced control over light confinement and transport. This was recently shown to be possible by simply interfacing two co-planar surfaces with complementary surface impedances, which support transverse-magnetic and transverse-electric modes, respectively. Attractively, the resultant “line wave” at the interface line features singular field enhancement and robust direction-dependent polarizations. Current implementations, however, are limited to microwave frequencies and have fixed functionality due to the lack of dynamic control. In this article, we examine the potential of using gate-tunable graphene sheets for supporting line waves in the terahertz regime and propose an adequate graphene-metasurface configuration for operation at room temperature and low voltage conditions. In addition, we show the occurrence of quasi-line wave under certain conditions of non-complementary boundaries and qualify the degradation in line wave confinement due to dissipation losses. Furthermore, we show the possibility to alter the orientation of the line wave’s spin angular momentum on demand unlike conventional surface waves. Our results on active manipulation of electromagnetic line waves in graphene could be useful for various applications including reconfigurable integrated circuits, modulation, sensing and signal processes.

Exceptional Points in the Flatland: A Non-Hermitian Line-Wave Scenario

“…The results in Fig. 5 suggest some possible tunability mechanisms, which may become particularly interesting in platforms based on gate-tunable and/or photoexcited graphene sheets [28,29]. With a view toward possible implementations, it is worth recalling that the PT -symmetry condition in (1) imposes a rather stringent constraint on the gain/loss balance, which is quite challenging to attain in practice.…”

“…This enables a truly one-dimensional (1-D) energy flow, with a wealth of attractive features in terms of singular field enhancement, near-field structure, chiral coupling and topologicallike robustness, which can be tailored and reconfigured by resorting to graphene [29] and/or gain-based [28] implementations. These characteristics are of great interest for "flat" optics and photonics scenarios, with potential applications ranging from subdiffractive sensing and near-field imaging to optical and quantum computing.…”

Electromagnetic‐Dual Metasurfaces for Topological States along a 1D Interface

“…Importantly, unlike the majority of existing PTIs, including those with finite thickness, the topological phases here arise due to engineering surface waves rather than bulk waves. Consequently, the ensued topological edge modes, which occur at the boundary of such system, are confined along a 1D line rather than a 2D surface interface, despite the lack of enclosing structures. In addition, we present a proof‐of‐concept in the microwave regime and experimentally show backscattering‐immune propagation of the gapless edge modes around sharp corners by direct imaging of the near field.…”

Adiabatic Mode-Matching Techniques for Coupling Between Conventional Microwave Transmission Lines and One-Dimensional Impedance-Interface Waveguides

“…In the past several years, researchers have found a different one-dimensional (1D) impedance-interface mode, called a line wave (LW) mode, at the interface of two planes with different surface impedances from microwave to optical bands [22][23][24]. Further researches focusing on similar waveguides were reported recently [25,26]. LW modes show robustness with wave-vector-locked states as well as field confinement ability.…”

“…Our research paves the way to implement LW modes into systems with hybrid guiding structures. Although the proposed designs operate at microwave bands, some recent work on LW modes based on plasmonic and flat graphene structures has been reported at higher frequency bands [22,26]. Therefore, the proposed methodology can also open a door to develop mode matching techniques in integrated circuits at terahertz and optical bands.…”