Graphene Surface Plasmon Polaritons Research Articles

Graphene plasmon for optoelectronics

Surface plasmon polaritons (SPPs) can achieve light transmission beyond the diffraction limit due to their special dispersion relationship. As a novel two-dimensional material, graphene has attracted extensive attention in recent years because of its unique band structure, excellent electronic and optical properties, and ability to support SPPs transmission on its surface. Graphene surface plasmon polaritons (GSPPs) are characterized by high carrier mobility, strong localization, low consumption and high tunability. It has functional and future applications in the transmission of optical knowledge, photodetectors, surface plasmon waveguides, metamaterials and nanolasers.

Graphene Surface Plasmon Polariton Modulator Based on Biased Nanowires

Graphene Surface Plasmon Polariton Modulator Based on Biased Nanowires

Dual-channel optical switch, refractive index sensor and slow light device based on a graphene metasurface.

In this paper, we propose a graphene-based metasurface that exhibits multifunctions including tunable filter and slow-light which result from surface plasmon polaritons (SPPs) of graphene and plasmon induced transparency (PIT), respectively. The proposed metasurface is composed by two pairs of graphene nano-rings and a graphene nanoribbon. Each group of graphene rings is separately placed on both sides of the graphene nanoribbon. Adjusting the working state of the nanoribbon can realize the functional conversion of the proposed multifunctional metasurface. After that, in the state of two narrow filters, we put forward the application concept of dual-channel optical switch. Using phase modulation of PIT and flexible Fermi level of graphene, we can achieve tunable slow light. In addition, the result shows that the graphene-based metasurface as a refractive index sensor can achieve a sensitivity of 13670 nm/RIU in terahertz range. These results enable the proposed device to be widely applied in tunable optical switches, slow light, and sensors.

Ultra-extraordinary optical transmission induced by cascade coupling of surface plasmon polaritons in composite graphene-dielectric stack.

Surface plasmon polaritons have been extensively studied owing to the promising characteristics of near fields. In this paper, the cascade coupling of graphene surface plasmon polaritons (GSPPs) originating from cascading excitation and multiple coupling within a composite graphene-dielectric stack is presented. GSPPs confined to graphene layers are distributed in the entire stack as waveguide modes. Owing to the near-field enhancement effect and large lifetime of the GSPPs, the terahertz wave-graphene interaction is significantly enhanced, which induces an ultra-extraordinary optical transmission (UEOT) together with the reported negative dynamic conductivity of graphene. Furthermore, owing to cascade coupling, the UEOT exhibits considerable transmission enhancement, up to three orders of magnitude, and frequency and angle selections. Based on the key characteristics of cascade coupling, the mode density and coupling intensity of GSPPs, the dependences of the number of graphene layers in the stack, the thickness of dielectric buffers, and the effective Fermi levels of the graphene on the UEOT are also analyzed. The proposed mechanism can pave the way for using layered plasmonic materials in electric devices, such as amplifiers, sensors, detectors, and modulators.

High performance dielectric loaded graphene plasmonic waveguide for refractive index sensing

In this study, a new dielectric loaded plasmonic waveguide is proposed by inserting a vertical graphene layer into the dielectric ridge in order to realize propagation of SPP waves symmetrically on both sides of the graphene. This waveguide is numerically analyzed for sensing applications at the wavelength of 1550 nm. The effective refractive indices of its guided modes are calculated by the full-wave modal analysis based upon finite element method. The guiding and sensing properties of the biosensor based on the desired mode of the presented waveguide is investigated for several values of structural parameters and compared with dielectric loaded graphene surface plasmon polariton waveguide (DL-GSPPW). The results show that not only the suggested waveguide is more suitable for sensing applications as compared with other dielectric loaded plasmonic waveguides, but also it can be an appropriate candidate for ultra-compact optical interconnects in the integrated photonics owing to the strong confinement of the optical field inside the ridge. By considering optimized dimensions of the ridge for an improved sensing performance, the biosensor based on suggested waveguide has high sensitivity up to 9.2 W/RIU with a minimum limit of detection (resolution) equal to 0.43 μRIU.

Time-domain finite element method and analysis for modeling of surface plasmon polaritons

In this paper, we formulate a time-dependent model for simulating surface plasmon polaritons (SPPs) in graphene. The stability for the governing equations of the model is established. Then we propose a time-domain finite element method for solving the system of the governing equations. The discrete stability similar to the continuous level is proved. Numerical results are presented to demonstrate the effectiveness of our model for simulating SPPs along graphene slabs. To the best of our knowledge, this is the first time-domain finite element analysis and simulation obtained for SPPs in graphene.

Ultrathin, polarization-insensitive multi-band absorbers based on graphene metasurface with THz sensing application

This article presents multi-band plasmonic absorbers based on a graphene array at terahertz frequencies. The absorbers are made of a very simple structure including a graphene disk array printed on the top surface of a dielectric spacer backed by a metallic ground plane. Multi-band performance is achieved with more than 90% absorption in the 1–8 THz frequency range by exciting surface plasmon polaritons of graphene. It is shown that the resonance frequencies of the proposed absorber can be tuned by varying the chemical potential between 0.8–1 eV for a triple-band absorber and 0.7–0.9 eV for a quad-band one, while keeping more than 80% absorption. The results obtained by means of full-wave simulation are verified with the results obtained by the analytical circuit model. The proposed absorbers are polarization-insensitive and provide stable absorption performance for both of the TE and TM polarizations. As an application, we designed a refractive index sensor based on the triple-band absorber. The results verify that the absorption bands are sensitive to the variations of the refractive index of the coating layer.

Surface plasmon dispersion and modes on the graphene metasurface with periodical ribbon arrays

Graphene plasmonics on the structured metasurface demonstrate many exotic properties which can combine novel nanomaterials and well-established plasmonics, providing unique opportunities to develop a series of novel photonic, plasmonic and optoelectronic devices across a wideband spectrum. Dispersion theory and its propagating characteristics of surface plasmon polaritons (SSPs) mode along the graphene metasurface can provide a powerful guidance to design related devices and systems. In this paper, the fundamental dispersion theory and the numerical studies of graphene SSPs (GSPs) on a graphene metasurface i.e. periodical ribbon arrays which are bounded by a superstrate and substrate dielectric are presented. The dispersion expression of GSPs is deduced and revealed by a modal expansion method combined with periodical boundary conditions on the structure. According to this fully analytical dispersion expression of SSPs mode on the graphene metasurface, the dispersion characteristics, propagation loss and field profiles of SSPs mode with different graphene material parameters (e.g. graphene ribbon width and chemical potential) and bounded dielectric mediums are studied and analyzed in detail in terahertz (THz) band. Moreover, the dynamical tunable dispersion characteristics of SSPs mode on the graphene metasurface via electrostatic gating of a ground metal plate can be readily obtained by applying a graphene biased voltage model to this analytical dispersion theory. The presented studies on the dispersion theory of the graphene metasurface provide an analytical method to understand the propagation characteristics of SSPs mode on the structure. Besides, the calculation results on the structure can also be used to design some novel graphene-based optoelectronic and plasmonic devices with planar gradient-index distributions such as couplers, tunable focused lens and enhanced radiation sources in THz band.

Dynamically Tunable Integrated Device for Attenuation, Amplification, and Transmission of SSPP Using Graphene

In this article, a dynamically tunable integrated device based on graphene and spoof surface plasmon polariton (SSPP) transmission line is proposed for the first time, which can realize attenuation, amplification, and transmission at the microwave frequency simultaneously. It consists of an SSPP waveguide with mirror symmetric structure, a low-noise amplifier chip, and two graphene sandwich structures (GSSs). Both the amplification gain and the attenuation of this integrated device can be dynamically tuned with the bias voltage that utilizes on GSSs concurrently. The calculated, simulated, and measured results manifest a satisfactory dynamic regulation effect on the attenuation, transmission, and amplification, which can be varied from 15 to −10 dB as the bias voltage rises from 0 to 4 V. This dynamically tunable integrated design paves the way to engineer compact and highly integrated adjustable devices or circuits.

Excitation of graphene surface plasmons polaritons by guided-mode resonances with high efficiency.

An Otto-like configuration for the excitation of graphene surface plasmon polaritons (GSPPs) is proposed. The configuration is composed of a metallic grating-dielectric-waveguide structure and a monolayer graphene with a subwavelength vacuum gap between them. The evanescent field located at the bottom surface of the dielectric waveguide corresponding to grating-coupled guided-mode resonances (GMRs) is utilized to efficiently excite the highly confined GSPPs. The finite difference time domain method is used to investigate the behaviors of the GMR-GSPP hybrid modes. The dispersion relations of GMRs and GSPPs are calculated and the numerical results further identify the excitation of GMR-GSPP hybrid modes. By changing the gap between the graphene layer and the bottom of the dielectric waveguide and the Fermi energy of graphene, the resonant frequencies of GMR-GSPP hybrid modes can be continuously tuned. When the optimized excitation condition is satisfied, the maximum energy enhancement factor in the gap can reach about 500 at the resonant frequencies. The proposed structure can be used to realize highly sensitive, compatible with planar fabrication technology, and electrically (mechanically) tunable sensors.

Electrical Phase Control Based on Graphene Surface Plasmon Polaritons in Mid-infrared.

Phase modulation of light is the core of many optoelectronic applications, such as electro-optic switch, sensors and modulators. Graphene Surface plasmon polaritons (SPPs) exhibit unique properties in phase modulation including dynamic tunability, a small driving voltage and small device size. In this paper, the novel phase modulation capability of graphene SPPs in mid-infrared are confirmed through theory and simulation. The results show that graphene SPPs can realize continuous tuning of the phase shift at multiple wavelengths in mid-infrared, covering the phase range from 0° to 360°. Based on these results, a sandwich waveguide structure of dielectric–graphene–dielectric with a device length of 800 nm is proposed, which shows up to 381° phase modulation range at an operating wavelength of 6.55 µm, given a 1 V driving voltage. In addition, the structure size is much shorter than the wavelength in mid-infrared and can realize sub-wavelength operation. This work paves the way to develop graphene-based tunable devices for mid-infrared wave-front control.

Quantization of graphene plasmons

In this article we perform the quantization of graphene plasmons using both a macroscopic approach based on the classical average electromagnetic energy and a quantum hydrodynamic model, in which graphene charge carriers are modeled as a charged fluid. Both models allow to take into account the dispersion of graphenes optical response, with the hydrodynamic model also allowing for the inclusion of non-local effects. Using both methods, the electromagnetic field mode-functions, and the respective frequencies, are determined for two different graphene structures. we show how to quantize graphene plasmons, considering that graphene is a dispersive medium, and taking into account both local and nonlocal descriptions. It is found that the dispersion of graphene's optical response leads to a non-trivial normalization condition for the mode-functions. The obtained mode-functions are then used to calculate the decay of an emitter, represented by a dipole, via the excitation of graphene surface plasmon-polaritons. The obtained results are compared with the total spontaneous decay rate of the emitter and a near perfect match is found in the relevant spectral range. It is found that non-local effects in graphene's conductivity, become relevant for the emission rate for small Fermi energies and small distances between the dipole and the graphene sheet.

Magnetoplasmonic manipulation of nanoscale thermal radiation using twisted graphene gratings

In this paper, magnetoplasmonic manipulation of near-field radiative heat transfer (NFRHT) is realized using two twisted graphene gratings. As a result of the quantum Hall regime of magneto-optical graphene and the grating effect, three types of graphene surface plasmon polaritons (SPPs) modes are observed in the system: near-zero modes, high-frequency hyperbolic modes, and elliptic modes. The elliptic SPPs modes, which are caused by the combined effect of magnetic field and grating, are observed in the graphene grating system for the first time. In addition, the near-zero modes can be greatly enhanced by the combined effect grating and magnetic field, rendering graphene devices promising for thermal communication at ultra-low frequency. In particular, the near-zero modes result in a unique enhancement region of heat transfer, no matter for any twisted angle between gratings. The combined effect of grating and magnetic field is investigated simultaneously. By changing the strength of magnetic field, the positions and intensities of the modes can be modulated, and hence the NFRHT can be tuned accordingly, no matter for parallel or twisted graphene gratings. The magnetic field endows the grating action (graphene filling factors and twisted angles) with a higher modulation ability to modulate the NFRHT compared with zero-field. Moreover, the modulation ability of twist can be tuned by the magnetic field at different twisted angles. In sum, the combined effect of magnetic field and grating provides a tunable way to realize the energy modulation or multi-frequency thermal communications related to graphene devices.

High-efficiency couplers for graphene surface plasmon polaritons in the mid-infrared region

We numerically demonstrate a novel, to the best of our knowledge, variety of high-efficiency couplers for mid-infrared graphene surface plasmon polaritons (SPPs). The proposed couplers are composed of a dual-parabolic-tapered transition to compress and couple the SPPs of a GaAs slab waveguide into the graphene layer. The dispersion relation, field distributions, transmittance, and coupling efficiency of the couplers are systematically analyzed. It is found that broadband coupling transmission with a transmittance around 0.3 is achieved for the coupler without a silver substrate. To further reduce radiation and enhance the transmittance, a silver substrate is introduced in the proposed coupler design, which achieves a transmittance over 0.5 ranging from 1960 to 2320 c m − 1 with a peak transmittance of 0.75. Furthermore, both couplers with and without a silver substrate achieve a similar coupling efficiency of more than 48% in the whole wavelength range of 1900 − 2400 c m − 1 and a coupling efficiency peak of over 80% around 2120 c m − 1 . This Letter may provide an efficient excitation method for graphene SPPs, which is of great importance for the development of various graphene plasmonic devices.

Long-range Graphene Surface Plasmon Polariton induced Tunable Optical Bistability in Terahertz Range

An idea towards the low threshold optical bistability and tunability of bistable thresholds at THz frequency under realistic situation is analyzed through a proposed multilayered configuration. The proposed configuration comprises a coupling prism of silicon, and monolayer graphene sheets spatially separated through 35 nm thick polymer which is sandwiched between an air gap of thickness 4.6 μm and a kerr polymer (GaAs) at 300 K temperature and at an incident light frequency of 2 THz. Utilizing the large nonlinear effect of the configuration obtained by the nonlinearity of the kerr polymer and the high local field effect due to long-range graphene surface plasmon resonance, the switching-down and switching-up threshold values for optical bistability have been markedly reduced upto 1.21×105 V/m and 1.24×105 V/m respectively thereby rendering a minimum threshold intensity of 7.2 kW/cm2 than the articles reported till date. Tunability of the switching-down and switching-up threshold values have also been realized from 1.21×105 V/m to 5.18×105 V/m and 1.24×105 V/m to 1.424×106 V/m respectively through electrical or chemical modification of the charge carrier density and hence fermi energy of the graphene from 0.23 eV to 0.41 eV and from 1.21×105 V/m to 1.56×105 V/m and 1.24×105 V/m to 2.12×105 V/m respectively for the variation in incident angle from 70° to 88°. The effect of damping rate of graphene on optical bistability behavior has also been observed. Therefore the proposed optical bistable configuration finds potential applications in the field of all-optical switching, optical transistor, optical logic, nano-illumination and optical memory with low input threshold at THz frequency and can also be used to realize tunable optical bistable device for future THz optical communication technology.

Plasmonic Jackiw-Rebbi Modes in Graphene Waveguide Arrays

We investigate the topological bound modes of surface plasmon polaritons (SPPs) in a graphene pair waveguide array. The arrays are with uniform inter-layer and intra-layer spacings but the chemical potential of two graphene in each pair are different. The topological bound modes emerge when two arrays with opposite sequences of chemical potential are interfaced, which are analogous to Jackiw-Rebbi modes with opposite mass. We show the topological bound modes can be dynamically controlled by tuning the chemical potential, and the propagation loss of topological bound modes can be remarkably reduced by decreasing the chemical potential. Thanks to the strong confinement of graphene SPPs, the modal wavelength of topological bound modes can be squeezed as small as 1/70 of incident wavelength. The study provides a promising approach to realizing robust light transport beyond diffraction limit.

Low power third harmonic generation and all-optical switching by graphene surface plasmons

In this study, we aimed at optimizing the nonlinear properties of the guiding structure of graphene surface plasmon polaritons. The structure is a graphene–metal hybrid waveguide with applicable mode confinement. Focusing electromagnetic power in the graphene sheet improves the harmonic conversion efficiency (0.2% (−27 dB)) and high self-phase modulation. The third harmonic generation phase-matching condition was satisfied in three-dimensional simulations for longer harmonic generation length. Low loss performance is vital for devices that operate in the terahertz regime (0.3–30 THz), because of the low efficiency offered by the available terahertz pulse generation methods. In this study, low loss propagation was achieved by engineering the chemical potential of graphene. Finally, a frequency-selective all-optical switch was designed by placing a subwavelength resonator in the waveguide. Self-phase modulation enabled optical control of the frequency-selective switch.

Surface plasmon-polaritons in graphene, embedded into medium with gain and losses

The paper deals with the theoretical consideration of surface plasmon-polaritons in the graphene monolayer, embedded into dielectric with spatially separated gain and losses. It is demonstrated, that presence of gain and losses in the system leads to the formation of additional mode of graphene surface plasmon-polaritons, which does not have its counterpart in the conservative system. When the gain and losses are mutually balanced, the position of exceptional point—transition point between unbroken and broken -symmetry—can be effectively tuned by graphene’s doping. In the case of unbalanced gain and losses the spectrum of surface plasmon-polaritons contains spectral singularity, whose frequency is also adjustable through the electrostatic gating of graphene.

Optical Transport Properties of Graphene Surface Plasmon Polaritons in Mid-Infrared Band

The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation results indicate that graphene SPPs show unique properties in the mid-infrared region including ultra-compact mode confinement and dynamic tunability, which allow these SPPs to overcome the defects of metal SPPs and traditional silicon-based optoelectronic devices. Thus, they can be used to manufacture subwavelength devices. The work in this paper lays a theoretical foundation for the application of graphene SPPs in the mid-infrared region.

Electrically defined topological interface states of graphene surface plasmons based on a gate-tunable quantum Bragg grating

Abstract A periodic metagate is designed on top of a boron nitride-graphene heterostructure to modulate the local carrier density distribution on the monolayer graphene. This causes the bandgaps of graphene surface plasmon polaritons to emerge because of either the interaction between the plasmon modes, which are mediated by the varying local carrier densities, or their interaction with the metal gates. Using the example of a double-gate graphene device, we discuss the tunable band properties of graphene plasmons due to the competition between these two mechanisms. Because of this, a bandgap inversion, which results in a Zak phase switching, can be realized through electrostatic gating. Here we also show that an anisotropic plasmonic topological edge state exists at the interface between two graphene gratings of different Zak phases. While the orientation of the dipole moments can differentiate the band topologies of each graphene grating, the angle of radiation remains a tunable property. This may serve as a stepping stone toward active control of the band structures of surface plasmons for potential applications in optical communication, wave steering, or sensing.