Characteristics of Plasmonic Bragg Reflectors with Graphene-Based Silicon Grating

Tunable dual-channel slow light in a graphene grating plasmonic waveguide

We propose a plasmonic waveguide comprising a single-layer graphene, a silica dielectric layer, and a silicon grating substrate to realize dual-channel slow surface plasmon polaritons. The dual-channel results from the introduction of two kinds of periodic structures with defects in the waveguide. According to the Bragg equation, we match the appropriate structure parameters to ensure the slow light dual-channel working around λ₁=9369.1nm (32 THz) and λ₂=7138.2nm (42 THz). The influence of the structure parameters on the slow light effect is discussed, and the largest value of the normalized delay bandwidth product (NDBP) is up to 7.38. Then, by shifting the gate voltage, obvious linear blueshift of the dual-channel is achieved. In this process, the slow light performance of the dual-channel exhibits good stability, and the average values of the NDBP are 4.5 and 4.4. Due to the flexible tunability, the waveguide may pave the way for the design of slow light devices.

Tunable plasmonic resonator using conductivity modulated Bragg reflectors

We design a tunable plasmonic resonator that may have applications in sensing and plasmon generation-our design uses graphene-based Bragg reflectors of periodically modulated conductivity. Specifically, we explore and utilize the ability to use an array of Gaussian conductivity gratings as fully reflecting mirrors for surface plasmon polaritons (SPPs) propagating along a two-dimensional graphene sheet sandwiched between two dielectric materials. Graphene supports SPPs in the near-infrared to terahertz (THz) regime of the electromagnetic spectrum compared to those observed in metal-dielectric systems. Our resonator is fundamentally different from other similar published resonator designs because the distributed reflectors provide light confinement in both the horizontal and the vertical directions. As a result, the resonator is compact in the vertical-direction as we no longer use traditional mirrors or dielectric assisted gratings. Besides, conventional resonator designs only support a single, fixed resonant frequency, set by the mirror reflectivity and the cavity material's properties. The versatility of graphene is that its Fermi energy can be electrically varied, thus allowing us to change the peak reflectivity of the graphene Bragg-grating without physically changing its physical dimensions. Therefore, by varying the Bragg wavelength, we can shift the resonance frequency of the cavity. One use of our resonator is in plasmonic lasers. We illustrate this use by analyzing the resonator parameters such as the linewidth and the quality factor of the plasmonic resonator.

Peak modulation in multicavity-coupled graphene-based waveguide system

Plasmonically induced transparency (PIT) in a multicavity-coupled graphene-based waveguide system is investigated theoretically and numerically. By using the finite element method (FEM), the multiple mode effect can be achieved, and blue shift is exhibited by tunable altering the chemical potential of the monolayer graphene. We find that the increasing number of the graphene rectangle cavity (GRC) achieves the multiple PIT peaks. In addition, we find that the PIT peaks reduce to just one when the distance between the third cavity and the second one is 100 nm. Easily to be experimentally fabricated, this graphene-based waveguide system has many potential applications for the advancement of 3D ultra-compact, high-performance, and dynamical modulation plasmonic devices.

Tunable Multiple Plasmon-Induced Transparencies Based on Asymmetrical Grapheme Nanoribbon Structures

We present plasmonic devices, consisting of periodic arrays of graphene nanoribbons (GNRs) and a graphene sheet waveguide, to achieve controllable plasmon-induced transparency (PIT) by numerical simulation. We analyze the bright and dark elements of the GNRs and graphene-sheet waveguide structure. Results show that applying the gate voltage can electrically tune the PIT spectrum. Adjusting the coupling distance and widths of GNRs directly results in a shift of transmission dips. In addition, increased angle of incidence causes the transmission to split into multiple PIT peaks. We also demonstrate that PIT devices based on graphene plasmonics may have promising applications as plasmonic sensors in nanophotonics.