Graphene Surface Plasmon Polaritons Research Articles

An electrical/thermal dual-controlled quad-functional terahertz metasurface absorber.

Although the design of graphene-based tunable broadband terahertz (THz) absorbers has attracted much attention, improving the functionality of the absorbers to adapt to different scenarios is still worth studying. This paper presents an innovative design of a quad-functional metasurface absorber (QMA) in the THz region, which can switch the absorption frequency/band by means of dual voltage/thermal manipulation. By electrically manipulating the chemical potential of graphene, the QMA can switch freely between the narrowband absorption mode ("NAM") and the broadband absorption mode ("BAM"), while thermally manipulating the phase transition of VO2 allows switching between the low-frequency absorption mode ("LAM") and the high-frequency absorption mode ("HAM"). Detailed mechanistic analysis shows that the "NAM" and "BAM" are due to the switching of the fundamental and second order graphene surface plasmon polariton (SPP) resonances, respectively, and the switching between "LAM" and "HAM" is due to the phase transformation of VO2. Furthermore, the QMA is polarization insensitive in all absorption modes and maintains excellent absorption performance at large angular incidence of TE- and TM-polarized waves. All the results indicate that the proposed QMA has great potential for stealth, sensing, switching, and filtering applications.

An Innovative method for adjustable broadband THz to Mid-IR optical modulator using Graphene Gratings surface plasmon Fabry–Perot resonances with low insertion loss, high speed and modulation depth

Through numerical modeling, we present an ultrasensitive tunable Terahertz (THz) to Mid-IR modulator composed of single-layer graphene-based gratings combined with a Fabry–Perot (FP) cavity. The perpendicular-polarized incident light on gratings causes the grating edges to act as an electrical dipole, resulting in an FP interferometer of induced plasmonic waves on the graphene surface. The electric field in the cavity is substantially limited by the activation of standing-waves (SWs) graphene surface plasmon polaritons. The multi-mode SWs formation inside the gratings provides an excellent platform for THz to Mid-IR light modulation with promising features. We have demonstrated a modulation depth of 100% in desired frequencies with near zero insertion loss via full-wave electromagnetic simulations at the normal incident in the THz to Mid-IR range. The light reflection and absorption of the proposed structure have a multi-band profile due to the FP behavior. Therefore, it can be easily tuned by electrically directing the chemical potential of graphene. Due to multi-resonance-based reflected light, each resonance represents different behavior with different modulation parameters. In other words, not only any desired frequency can be chosen, but also at the constant frequency of interest; by choosing the appropriate mode, the desired linewidth, FWHM, and modulation depth can be easily obtained. Finally, we investigated the device bandwidth. The THz modulator requires a large device area for an average number of gratings, and the device area at the 3 dB frequency reaches as high as 1.5 THz, which depicts the high modulation speed in the proposed modulator. The proposed graphene plasmonic grating scheme is a promising candidate for developing the on-chip integrated THz to Mid-IR optical telecommunications. Moreover, the perfect absorption of graphene opens an opportunity to design photodetectors with high responsivity and quantum efficiency, which gives the proposed structure a multi-function capability.

HBN-based enhancement and regulation of radiative heat transfer between two monolayer graphene sheets

Near-field radiative heat transfer (NFRHT) in many-body systems has opened pathways for enabling novel thermal-radiation applications. In this Letter, we investigate hBN-based enhancement and regulation of NFRHT between two monolayer graphene sheets. On the one hand, we predict that adding an intermediate hBN plate can greatly compensate the exponential damping of evanescent waves due to its hyperbolic modes, thus leading to 1.5 times enhancement of the NFRHT without introducing additional thermal source compared to the graphene-graphene system. On the other hand, we find that adjusting the shift frequency of hBN can greatly change the coupling of its hyperbolic modes and graphene surface plasmon polaritons, thus enabling the remarkable thermal regulation with a ratio of 3.5. We hope that our work may facilitate nanoscale thermal management in many-body systems and benefit the comprehension of hBN-based photon tunneling.

Tunable Plasmonic Devices by Integrating Graphene with Ferroelectric Nanocavity

AbstractGraphene plasmons can become the fundamental of novel conceptual photonic devices, resulting from their unique characteristics containing excitation at room temperature and tunable spectral selectivity in different frequencies. The pursuit of efficiently exciting and manipulating graphene plasmons is necessary and significant for high‐performance devices. Here, the graphene plasmon wave propagating in ferroelectric nanocavity array is investigated. It has been experimentally shown that the periodic ferroelectric polarizations can be used for doping graphene into desired spatial carrier density patterns. Based on a theoretical model that considers periodic ununiform conductivity across graphene sheet, the simulation results show surface plasmon polaritons (SPP) in graphene can be excited by an incident light in a similar way to the excitation of photonic crystal resonant modes. The graphene SPP resonance can be tuned from ≈720 to ≈1 000 cm−1 by rescaling the ferroelectric nanocavity array, and from ≈540 to ≈780 cm−1 by dynamically changing the applied gate voltage. This strategy of graphene carrier engineering to excite SPP offers a promising way for large‐scale, nondestructive fabrication of novel graphene photonic devices.

Robust and Broadband Graphene Surface Plasmon Waveguide Coupler via Quantum Control

In this article, a novel graphene subwavelength waveguide coupler is designed based on the quantum control theory. Compared with metal surface plasmon polaritons (SPPs), graphene surface plasmon polaritons (GSPPs) have a smaller SPP wavelength and tunable properties. The dielectric load graphene plasmon waveguide (DLGPW) is used for designing to avoid the influence of the edge shape of the graphene nanoribbons on the waveguide mode. The coupling coefficient between the waveguides is calculated by using the coupled-mode theory (CMT). Due to the subwavelength properties of the graphene surface plasmons (GSP) and the robustness of the quantum control technique, our device is more compact and robust against perturbations of geometrical parameters under the premise of high transmission efficiency. The device we designed also has broadband characteristics, ranging from 30 THz to 40 THz, with high transmission efficiency when considering the transmission loss. We believe that our device will significantly contribute to integrated optics and photo-communication.

Tunable Planar Focusing Based on Hyperbolic Phonon Polaritons in α-MoO3.

Manipulation of the propagation and energy-transport characteristics of subwavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, and thermal management. In this context, metamaterials are useful composite materials, although traditional metal-based structures are constrained by their weak mid-IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid-IR region is reported by exploiting highly oriented in-plane hyperbolic phonon polaritons in α-MoO3 . Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 μm is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon-plasmon hybridization. The high confinement characteristics of phonon polaritons in α-MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in α-MoO3 are combined with tunable surface-plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon-polariton-based planar nanophotonic applications.

Topological edge modes and localization transition in quasiperiodic graphene multilayer arrays

By using rational and irrational on-site modulation in graphene waveguide arrays, we construct both commensurate and incommensurate Aubry-André-Harper (AAH) models and achieve the topological edge states and localization transition for graphene surface plasmon polaritons (SPPs). We show that when the commensurate AAH graphene array is truncated, topological edge states emerge, which are immune to the random perturbation of modulation depth in each individual graphene sheet. While for an incommensurate AAH array, localization transition for SPPs modes have also been achieved when the modulation depth reaches a critical value. Our work points out that graphene waveguide array provides a promising platform for robust light transport and compact localization within a fully deep subwavelength scale.

High-quality multi-band absorber in a hybrid all-dielectric system using the surface plasmon polaritons

High confinement of surface plasmon polaritons in graphene have important applications in many aspects. In this paper, we have demonstrated that high-quality multi-band absorption can be achieved by using a hybrid system where periodic monolayer graphene nanoribbons is coated on an all-dielectric nanostructure. The effect of the monolayer graphene nanoribbons on plasmonic resonances absorption is investigated theoretically and numerically. It is found that the high tunability and large near field enhancement of the system is observed by changing the grating period and Fermi level. After delicate optimization, the system can achieve high-Q resonances in the vicinity of the bound states in the continuum, and the Q factors of the two resonance modes are respectively significantly enhanced (＞450, 600). In addition, the multi-band light absorption enhancement with high quality can be observed by altering the carrier mobility of graphene. Wherein the optimized absorption efficiency up to 97% is reached. More interestingly, the proposed structure puts up palpable advantage in absorption stability when the incident angle is varied from 0° to 60°. Thus, this work may facilitate the design of high-performance optoelectronic devices based on all-dielectric configuration, such as tunable optical sensors and perfect absorbers.

Enhanced Near-Field Radiative Heat Transfer between Graphene/hBN Systems.

Near-field radiative heat transfer (NFRHT) can exceed the blackbody radiation limit owing to the coupled evanescent waves, implying a significant potential for energy conversion and thermal management. Coupled surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs) with small ohmic losses enable a long propagation wavelength that is essential in NFRHT. However, so far, there still lacks knowledge about the experimental investigation of the coupling of SPPs and HPPs in terms of NFRHT. In this study, the NFRHT between graphene/hexagonal boron nitride (hBN) systems that can be readily transferred onto various substrates, with a gap space of ≈400nm is measured. NFRHT enhancements in the order of three and six times higher than the blackbody limit for graphene/hBN heterostructures and graphene/hBN/graphene multilayers, respectively are demonstrated. In addition, the largest ever radiative heat flux using graphene/hBN/graphene multilayers under similar gap space of 400nm is obtained. Consequently, analyzing the photon tunneling modes reveal that these phenomena are consequences of coupled SPPs of graphene and HPPs of hBN.

Polaritons in low-dimensional materials and their coupling characteristics

Polaritons, i.e. new collective modes formed by the strong coupling between light and electrons, phonons, excitons, or magnons in matter, have recently received extensive attention. Polaritons in low-dimensional materials exhibit strong spatial confinement, high quality factor, and gate-tunability. Typical examples include gate-tunable graphene surface plasmon polaritons, high-quality hyperbolic phonon polaritons in hexagonal boron nitride, topological phonon polaritons in <i>α</i>-MoO<sub>3,</sub> and one-dimensional Luttinger-liquid plasmon polaritons in carbon nanotubes. These unique properties make polaritons an excellent candidate for future nano-photonics devices. Further, these polaritons can significantly interact with each other, resulting in a variety of polariton-polariton coupling phenomena, greatly expanding their applications. In this review paper, we first introduce scanning near-field optical microscopy, i.e. the technique used to probe polaritons in low-dimensional materials, then give a brief introduction to the basic properties of polaritons. Next, we discuss in detail the coupling behavior between various polaritons. Finally, potential applications of polaritons coupling are proposed.

Efficient mid-infrared wavelength converter based on plasmon-enhanced nonlinear response in graphene nanoribbons

Graphene plasmons with enhanced localized electric field have been used for boosting the light–matter interaction in linear optical nano-devices. Meanwhile, graphene is an excellent nonlinear material for several third-order nonlinear processes. We present a theoretical investigation of the mechanism of plasmon-enhanced third-order nonlinearity susceptibility of graphene nanoribbons. It is demonstrated that the third-order nonlinearity susceptibility of graphene nanoribbons with excited graphene surface plasmon polaritons can be an order of magnitude larger than the intrinsic susceptibility of a continuous graphene sheet. Combining these properties with the relaxed phase matching condition due to the ultrathin graphene, we propose a novel plasmon-enhanced mid-infrared (MIR) wavelength converter with arrays of graphene nanoribbons. The wavelength of signal light is in the MIR range, which can excite the tunable surface plasmons polaritons in arrays of graphene nanoribbons. The efficiency of the converter from MIR to near-infrared wavelength can be remarkably improved by 60 times compared with a graphene sheet without graphene plasmons. This work provides a novel idea for the efficient application of graphene in nonlinear optical nano-devices. The proposed MIR wavelength converter is compact, tunable and has promising potential in graphene-based MIR detectors with high detection efficiency.

Mid-infrared sensor based on resonance excitation of graphene plasmon polariton-coupled Bloch surface modes at the interface of anisotropically truncated one-dimensional ternary photonic crystal

In this article, we have theoretically demonstrated the sensor performance in mid-IR frequency domain by resonance excitation of Bloch surface modes through energy coupling with graphene surface plasmon polaritons in truncated one-dimensional (1D) ternary photonic crystal (TPC) under Kretschmann configuration coupling technique. The involvement of optical anisotropy via graphene monolayer enhances light-matter interaction thus enabling excellent control over the resonance wavelength (RW) of the excited Bloch surface modes (EBSMs). For incident transverse magnetic-polarized electromagnetic waves, the band structure, reflection spectra and field profile are computed using 2 × 2 transfer matrix method. The control over the RW has been established by examining the effect of variation of different model parameters like thickness of truncation layer, refractive index of external medium, temperature, chemical potential and the periodicity of TPC. The variations in periodicity result in the expansion of the range of confinement of EBSMs in photonic band gaps from 19 THz to 65 THz . We proved that the variation in temperature between 300 ∘ K and 500 ∘ K confines the EBSMs with high coupling efficiency (CE). Also, at room temperature the best achievable quality factor (QF) is 1421 and a high Q.F. of 8170 is attained at 260 ∘ K .

Extended frequency range of transverse-electric surface plasmon polaritons in graphene

The dispersion relation of surface plasmon polaritons in graphene that includes optical losses is often obtained for complex wave vectors while the frequencies are assumed to be real. This approach, however, is not suitable for describing the temporal dynamics of optical excitations and the spectral properties of graphene. Here we propose an alternative approach that calculates the dispersion relation in the complex frequency and real wave vector space. This approach provides a clearer insight into the optical properties of a graphene layer and allows us to find the surface plasmon modes of a graphene sheet in the full frequency range, thus removing the earlier reported limitation $(1.667<\ensuremath{\hbar}\ensuremath{\omega}/\ensuremath{\mu}<2)$ for the transverse-electric mode. We further develop a simple analytic approximation which accurately describes the dispersion of the surface plasmon polariton modes in graphene. Using this approximation, we show that transverse-electric surface plasmon polaritons propagate along the graphene sheet without losses even at finite temperature.

Dual dynamically tunable plasmon-induced transparency and absorption in I-type-graphene-based slow-light metamaterial with rectangular defect

A simple quasi-continuous I-type-graphene-based metamaterial with rectangular defect is proposed to realize a dual dynamically tunable plasmon-induced transparency (PIT) and plasmon-induced absorption (PIA) effect. The desired Fermi levels of the monolayer graphene can be dynamically tuned by applying the bias voltage, which can produce the spectral shift of the dual PIT and PIA. What’s interesting is that the dual PIT (PIA) can be evolved into the single PIT (PIA) by tuning the distance between two vertical graphene ribbons in the metamaterial. In addition, the distribution intensity and directions of electric field vectors are used to illustrate the distributions of electric field magnitude in the monolayer graphene metamaterial under the action of the polarized incident light. Both theoretical analysis and numerical simulation methods are introduced to study the mechanism of the PIT and PIA effect at terahertz frequency range, and they display very good consistency. Moreover, the surface plasmon polaritons (SPPs) of the monolayer graphene have a better dispersion property and a broad frequency range of the group delay, the maximum group delay of about 0.25 ps is obtained in the proposed metamaterial structure. The proposed metamaterial may have extensive applications in absorbers, tunable switches and slow light devices, et al.

Mechano-Optical Resonant Emission by Edge Angle Modulation of Wrinkled Graphene on Plasmonic Metal Gratings

Graphene coated on top of photonic-plasmonic metasurfaces can produce resonant radiative emission in the mid-infrared region. Narrowband emission peaks are observed through folding graphene into “origami” ridges over metal grating grooves, creating a complementary cavity mode above the trench. This geometrically tuned phenomenon of graphene surface plasmon excitation along the folded sheet enhances the emission when added to magnetic polariton (MP) resonance induced within the plasmonic grating groove. Our analytical models describe how this graphene surface plasmon polariton (SPPG) is a function of folded graphene geometric parameters, and most importantly, the graphene edge angle that distends from the grating surface. The frequency-dependent phase shift of SPPG is fitted to grating parameters, and a modified inductor-capacitor circuit model was developed for predicting MP resonance mode with graphene influence. It was found that the edge angle of wrinkled graphene blue-shifts the groove MP resonance and SPPG resonant emission peak in both wrinkled graphene alone and with the grating substrate. The understanding of geometrically modulated graphene adhered on plasmonic gratings impacts the design and capability of narrowband cavity emitters and contributes toward the development of mechanical-optical environmental sensors.

Tunable dual-band mid-infrared absorber based on the coupling of a graphene surface plasmon polariton and Tamm phonon-polariton.

We propose and demonstrate a tunable dual-band mid-infrared absorber structure based on the coupling effect of a surface plasmon polariton (SPP) and Tamm phonon-polariton (TPhP). The structure is composed of the distributed Bragg reflector (DBR), air layer, SiC and graphene ribbons. In the air layer, the graphene ribbons are embedded to realize the localized SPP (LSPP), which makes the structure support both the graphene LSPP (GLSPP) and TPhP. The absorption properties of the structure are investigated theoretically and numerically. It is found that strong coupling of the GLSPP and TPhP can be realized by choosing reasonable parameters, which causes a dual-frequency perfect absorption and makes the maximum Rabi splitting of the coupled mode reach 5.76 meV. Furthermore, the mode coupling and absorption intensity can be tuned by adjusting the thickness of the air layer and the Fermi level of the graphene ribbons. This work might provide new possibilities for the development of mid-infrared band sensors, filters and emitters based on the coupling of multiple modes.

Behavior of SPPs in chiral-graphene-chiral structure.

In this Letter, considering the chiral-graphene-chiral structure, we investigate the more universal dispersion relation covering the achiral cases, the effect of the chirality of a medium, and the chemical potential of graphene on the behavior of graphene surface plasmon polaritons (GSPPs) and transverse spin density, which is key to understanding the lateral optical force. This research is dedicated to looking for a regulating mechanism based on chirality and graphene to apply in devices of information processing and biosensor for identifying molecular chirality. We found the averaging effect of chirality in both sides of graphene in tuning the behavior of GSPPs. We believe this work can make contributions to enrich SPP theory and benefit the development of novel detection techniques for chiral molecules based on graphene.

Study on THz SPPs excitation and field distributions of graphene microribbons

Surface plasmon polaritons have wide applications in sensing, biasing, absorption, and beam splitting, etc. because they can break diffraction limits and have strong field localization. So far, most of the research on terahertz surface plasmon polaritons is in the far-field spectrum, and exploring near-field properties is further needed. In this paper, based on the graphene strip structure, the excitation and field distribution characteristics of terahertz surface plasmon polaritons were studied. Specifically, the graphene microribbons that could excite surface plasmon polaritons by terahertz waves were designed, and the field distribution was calculated. Then, we experimentally fabricated the designed structure and measured its surface plasmon polaritons by terahertz near-field microscope. Finally, the effects of resonance detuning on surface plasmon polaritons field distribution were investigated. Our results provide a research basis for the application of graphene surface plasmon polaritons components in terahertz detection, biomedicine, safety detection, and high data rate communication.

Substrate-enhanced photothermal nano-imaging of surface polaritons in monolayer graphene

Surface polaritons comprise a wealth of light–matter interactions with deep sub-wavelength scale confinement of electromagnetic modes. However, their nanoscale localized dissipation and thermalization processes are not readily accessible experimentally. Here, we introduce photothermal force microscopy to image surface plasmon polaritons (SPPs) in monolayer graphene through their non-radiative SiO2 substrate dissipation. We demonstrate the real-space SPP imaging via photo-induced atomic force detection, and from comparison with scattering-type scanning near-field optical microscopy imaging attribute the force response to substrate dissipation-enhanced thermal expansion. This work illustrates that nano-optical tip–sample induced dissipative forces facilitate a direct mechanical detection of surface polariton interactions with monolayer sensitivity.

Dispersion characteristics of surface plasmon polaritons (SPPs) in graphene–chiral–graphene waveguide

The theoretical analysis of hybrid surface plasmon polaritons in a planar waveguide filled with chiral material surrounded by graphene layers is presented in this manuscript. The Kobo formula is used to calculate the graphene’s conductivity and Maxwell’s equation in differential form is used to solve the analytical problem. It is demonstrated that graphene’s parameters relaxation time as well as chemical potential and chirality strength can be used to modulate the resonance surface plasmon frequencies for the proposed structure. The characteristic curve, normalized propagation constant, attenuation phase constant or propagation loss, propagation length, and normalized field distribution for graphene–chiral–graphene interfaces are examined numerically. The presented work based on plasmonics theory provides new possibilities for the design of more compact nanophotonic devices due to graphene’s extra degree of freedom compared to other metals.