Search

In this paper, we review and discuss how the recently discovered two-dimensional (2D) Dirac materials, particularly graphene, may be utilized as new efficient platforms for excitations of propagating and localized surface plasmon polaritons (SPPs) in the terahertz (THz) and mid-infrared (MIR) regions. The surface plasmon modes supported by the metallic 2D materials exhibit tunable plasmon resonances that are essential, yet missing, ingredients needed for THz and MIR photonic and optoelectronic devices. We describe how the atomically thin graphene monolayer and metamaterial structures based on it may tailor and control the spectral, spatial, and temporal properties of electromagnetic radiation. In the same frequency range, the newly unveiled nonlocal, nonlinear, and nonequilibrium electrodynamics in graphene show a variety of nonlinear and amplifying electromagnetic responses, whose potential applications are yet unexplored. With these 2D material platforms, virtually all plasmonic, optoelectronic, and nonlinear functions found in near-infrared (NIR) and visible devices can be analogously transferred to the long-wavelength regime, even with enhanced tunability and new functionalities. The spectral range from THz to MIR is particularly compelling because of the many spectral fingerprints of key chemical, gas, and biological agents, as well as a myriad of remote sensing, imaging, communication, and security applications.

Although Polarization Modulation offers a high spectral efficiency, it has been not exploited much in modern communication systems because of the involvement of high switching speeds and complexity of associated hardware. We propose a dynamically controllable graphene metasurface capable to switch the polarization state of incident THz waves in real-time. The metasurface is designed by patterning two-dimensional graphene sheets with Fano-resonant chiral unit cells. Since the reflectance spectrum is characterized with co and cross polarized fields that bear asymmetric Fano line-shapes, several combinations of linear and elliptical polarization states are observed in a narrowband spectrum. At a fixed frequency, the electrostatic tunability property of graphene allows to switch between different polarization states by varying the chemical potential between 500 and 700 meV. The polarization state modulation with the proposed chiral graphene based metasurface is applied to implement a quaternary modulated digital communication system. Full-wave simulation results show the strong possibility of polarization modulation in THz communication systems. Graphene metasurfaces on account of the high electron mobility and discrete Fermi levels offer high switching speeds and seamless integration with digital systems. [ABSTRACT FROM AUTHOR]

In this paper, we review and discuss how the recently discovered two-dimensional (2D) Dirac materials, particularly graphene, may be utilized as new efficient platforms for excitations of propagating and localized surface plasmon polaritons (SPPs) in the terahertz (THz) and mid-infrared (MIR) regions. The surface plasmon modes supported by the metallic 2D materials exhibit tunable plasmon resonances that are essential, yet missing, ingredients needed for THz and MIR photonic and optoelectronic devices. We describe how the atomically thin graphene monolayer and metamaterial structures based on it may tailor and control the spectral, spatial, and temporal properties of electromagnetic radiation. In the same frequency range, the newly unveiled nonlocal, nonlinear, and nonequilibrium electrodynamics in graphene show a variety of nonlinear and amplifying electromagnetic responses, whose potential applications are yet unexplored. With these 2D material platforms, virtually all plasmonic, optoelectronic, and nonlinear functions found in near-infrared (NIR) and visible devices can be analogously transferred to the long-wavelength regime, even with enhanced tunability and new functionalities. The spectral range from THz to MIR is particularly compelling because of the many spectral fingerprints of key chemical, gas, and biological agents, as well as a myriad of remote sensing, imaging, communication, and security applications. [ABSTRACT FROM AUTHOR]

Weinvestigate here active metasurfaces obeying parity-time (PT) symmetry and their sensing applications, taking advantage of singularities unique to non-Hermitian systems, such as the spontaneous PT-symmetry-breaking point (exceptional point or EP) and the coherent perfect absorber-laser (CPAL) point. We show theoretically that a PT-symmetric metasurface sensor may provide enhanced sensitivities compared to traditional passive sensors based on metamaterial/metasurface resonators, because the singular point of one-way zero reflection arising from the EP or the CPAL-related sharp resonance may result in dramatically modulated scattering responses or resonance offsets. We demonstrate the proposed concept with realistic metasurface sensors based on photopumped graphene metasurfaces that simultaneously offer terahertz optical gain and (bio) chemical sensing functions. The proposed PT-symmetric metasurfaces may impact not only loss compensation and extraordinary manipulation of electromagnetic waves, but also practical sensing and detection applications. [ABSTRACT FROM AUTHOR]

We propose a concept that allows for efficient excitation of surface plasmon spolaritons (SPPs) on a thin graphene sheet located on a substrate by an incident electromagnetic field. Elastic vibrations of the sheet, which are generated by a flexural wave, act as a grating that enables the electromagnetic field to couple to propagating graphene SPPs. This scheme permits fast on-off switching of the SPPs and dynamic tuning of their excitation frequency by adjusting the vibration frequency (grating period). Potential applications include single molecule detection and enhanced control of SPP trajectories via surface wave patterning of graphene metasurfaces. Analytical calculations and numerical experiments demonstrate the practical applicability of the proposed concept. [ABSTRACT FROM AUTHOR]

We propose a spectrometer-free refractive index sensor based on a graphene plasmonic structure. The spectrometer-free feature of the device is realized thanks to the dynamic tunability of graphene's chemical potential, through electrostatic biasing. The proposed sensor exhibits a 1566 nm/RIU sensitivity, a 250.6 RIU−1 figure of merit in the optical mode of operation and a 713.2 meV/RIU sensitivity, a 246.8 RIU−1 figure of merit in the electrical mode of operation. This performance outlines the optimized operation of this spectrometer-free sensor that simplifies its design and can bring terahertz sensing one step closer to its practical realization, with promising applications in biosensing and/or gas sensing. [ABSTRACT FROM AUTHOR]