Surface Plasmon Polariton Resonance Research Articles

Tunable ultra-broadband terahertz metamaterial absorbers based on complementary split ring-shaped graphene

In the design of graphene-based tunable broadband terahertz (THz) metamaterial absorbers (MAs), simplifying the gating structure to control the Fermi energy of graphene is a critical requirement for practical applications. To solve this problem, we numerically demonstrate two kinds of tunable ultra-broadband THz MAs based on complementary split ring-shaped graphene. The first absorber exhibits an ultra-broadband absorption performance with an absorptance of above 90% in the frequency range of 2.06–4.24 THz, with a relative absorption bandwidth of 69.2%. By changing the Fermi energy of graphene from 0 to 0.8 eV through bias voltage, the absorptance can be tuned from 32.8% to 99.9%. The ultra-broadband absorption mechanism is based on the surface plasmon polariton resonances caused by the surface charges of complementary split ring-shaped graphene. In addition, to further expand the absorption bandwidth, we cover another dielectric layer on the first absorber to make the second absorber have an increased relative absorption bandwidth of 108.27%.

Ultra-broadband and wide-angle plasmonic absorber based on all-dielectric gallium arsenide pyramid nanostructure for full solar radiation spectrum range

Broadband and plasmonic absorbers (PAs) are key components for numerous applications in the fields of energy harvesting, thermal photonics, optoelectronic devices, and enhanced spectroscopy. In this work, we propose a simple and cost-effective metamaterial plasmonic absorber (MPA) design based on an all-dielectric GaAs pyramid nanostructure for the full solar radiation spectrum range. Simulation results demonstrate that the absorbance of the proposed MPA exceeds 85% in the full solar spectrum range, and it exceeds 90% from 0.25 μm to 3.1 μm with a relative bandwidth of approximately 170.74%, with an absorption peak up to 99% at resonance wavelength. The high absorption is attributed to the excitation of wave-guide mode, surface plasmon polariton (SPP) resonance modes combined with coupling effect and intrinsic lossy of dielectric GaAs and metallic tungsten (W). Furthermore, the proposed MPA is polarization-independent and wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. Additionally, the MPA can tolerate certain structural parameter errors during practical fabrication applications. Furthermore, the photophysical properties of this MPA for solar cell applications are investigated, revealing the achievement of high short-circuit current density. Our proposed design is highly promising for applications in solar energy harvesting, thermoelectric, and thermal emitter applications.

Ultra-broadband tunable terahertz metasurface absorber with multi-mode regulation based on artificial neural network

The multi-window tunable absorption of terahertz (THz) waves faces challenges such as a small tunable bandwidth, discontinuous tuning windows, and a complex design process. This study addresses these issues by employing inverse design based on artificial neural networks (ANN) to achieve an ultra- broadband tunable THz metasurface absorber (UTTMA). Leveraging the electrically tunable property of graphene and the phase transition property of vanadium dioxide (VO2), the UTTMA achieves multi-domain dynamic operation across a large frequency band. The design allows for arbitrary switching between multiple windows by transforming between graphene surface-localized plasmon resonance (LSPR), fundamental order surface plasmon polaritons (SPP) resonance, and graphene surface plasmon resonance (SPR), and second order SPP resonance. The tunable windows cover the range between 1.90 and 10.00 THz, encompassing four-fifths of the entire THz band, surpassing previously reported absorbers. The accuracy of the ANN inverse design is verified, and a systematic analysis of the optical performance of the UTTMA is conducted. These findings offer a viable and effective method for expanding the tunable bandwidth and simplifying the design process for THz metasurfaces.

Enhanced terahertz frequency mixing in all-dielectric metamaterial with multiple surface plasmon polaritons resonances

Nonlinear metamaterials hold a promising platform for generating terahertz (THz) waves. In this paper, we present an all-dielectric metamaterial with multiple surface plasmon polariton (SPP) resonances for enhanced THz frequency mixing. The metamaterial is composed of graphene ribbons, a dielectric layer, and a one-dimensional photonic crystal, displaying the multiple absorptions with simultaneous excitation of three SPP resonances. Taking advantage of SPP resonances with high Q factor and strong localized field at the input frequency, the third-order nonlinear processes are remarkably enhanced, including third-harmonic generation and four-wave mixing, producing a variety of frequencies in the THz range. The proposed efficient nonlinear metamaterials offer promising applications for THz frequency synthesis.

Ultra-broadband infrared metamaterial absorber based on MDMDM structure for optical sensing

Infrared observation is a crucial tool in the study of astronomical celestial bodies. Metamaterials have a vast prospect for applications in the field of optics due to their unique electromagnetic tunable characteristics. In order to obtain an ultra-broadband high absorption material in the infrared region, we proposed a metal-dielectric-metal-dielectric-metal (MDMDM) metamaterial absorber using a titanium (Ti) nano-cross layer based on surface plasmon polariton (SPP) resonance and magnetic resonance cavity principles. The geometrical parameters of each layer have been examined carefully. The influence of incident angle from 0° to 60° is investigated for transverse electric and transverse magnetic plane-waves. Near-perfect absorption performance is achieved from near-infrared to mid-infrared region. The average absorption reaches as high as 97.41% from 2.05 to 6.08 μm. The absorber exhibits polarization-sensitive characteristics. The absorption peaks are 99.50% and 99.80% at 2.55 and 5.24 μm, respectively. The proposed material has potential applications in astronomical imaging, volcano and fire detection, remote sensing, biological monitoring, and other optical devices.

Multi-band perfect absorber based on an elliptical cavity coupled with an elliptical metal nanorod.

We proposed a triple-band narrowband device based on a metal-insulator-metal (MIM) structure in visible and near-infrared regions. The finite difference time domain (FDTD) simulated results illustrated that the absorber possessed three perfect absorption peaks under TM polarization, and the absorption efficiencies were about 99.76%, 99.99%, and 99.92% at 785 nm, 975 nm, and 1132 nm, respectively. Simulation results matched well with the results of coupled-mode theory (CMT). Analyses of the distributions of the electric field indicated the "perfect" absorption was due to localized surface plasmon polaritons resonance (LSPPR) and Fabry-Perot resonance. We developed a multi-band absorber with more ellipsoid pillars. The four band-absorbing device presented perfect absorption at 767 nm, 1046 nm, 1122 nm, and 1303 nm, and the absorption rates were 99.45%, 99.41%, 99.99%, and 99.94%, respectively. By changing the refractive index of the surrounding medium, the resonant wavelengths could be tuned linearly. The maximum sensitivity and Figure of Merit were 230 nm RIU-1 and 10.84 RIU-1, respectively. The elliptical structural design provides more tuning degrees of freedom. The absorber possessed several satisfactory performances: excellent absorption behavior, multiple bands, tunability, incident insensitivity, and simple structure. Therefore, the designed absorbing device has enormous potential in optoelectronic detection, optical switching, and imaging.

A sensing method based on InSb grating coupled terahertz surface plasmon polariton resonance

A grating-coupled terahertz (THz) surface plasmon polariton (SPP) resonant biochemical sensing structure is designed with simulation, which can be easily prepared by etching a submillimeter grating on the surface of indium antimonide (InSb) substrate. The simulation results based on the phase matching equation show that when the TM-polarized broadband terahertz collimated beam is incident on the InSb grating at a 30° angle, the low-frequency SPP and high-frequency SPP with opposite propagation directions can be simultaneously excited by the –1st and +1st order diffraction beams of the grating, respectively. Since the low-frequency SPP is easy to accurately measure with a commercial THz time-domain spectroscopy devices, the dependence of the resonance characteristics and sensing characteristics of low-frequency SPP on the grating structure parameters is systematically simulated in this paper. The simulation results show that the refractive-index sensitivity of the InSb grating-coupled THz-SPP resonant sensor chip decreases with the increase of the grating period, and is 1.05 THz/RIU at a grating period of 120 μm and an incident angle of 30°. Under these conditions, the sensor chip cannot make a detectable response to the monolayer adsorption of biomolecules, because the evanescent field penetration depth of the low-frequency SPP is much greater than the biomolecular size, resulting in insufficient field-biomolecular interaction at the surface. In order to detect biomolecules, a sensitivity enhancement method based on porous thin films is proposed and analyzed with simulation. The porous films enable not only to enrich biomolecules, but also to extend the interaction between THz-SPP and biomolecules from the molecular size to the entire film thickness, thereby improving the sensitivity of the sensor to biomolecular adsorption. Taking tyrosine adsorption as an example, the simulation results show that when the InSb grating is covered with a porous polymethyl methacrylate (PMMA) film with a thickness of 120 μm and a porosity of 0.4, the sensor sensitivity to tyrosine adsorption is 0.39 THz/unit volume fraction.

Screening and optimization of metal-insulator-metal selective emitter in thermophotovoltaic system

In thermophotovoltaic (TPV) systems, it is crucial that the selective emitters can tailor emission spectrum to match the bandgap of photovoltaic (PV) cells and largely enhance the system efficiency. In this work, a metamaterial emitter based on the metal-insulator-metal (MIM) structure is proposed to obtain the high energy conversion efficiencies. The geometric parameters of MIM emitter have been investigated to obtain an excellent radiation spectrum of emitter composed of W and HfO2. The excellent emission performance of MIM emitter is attributed to the excitation of surface plasmon polariton (SPP) and cavity resonance, and the structure of MIM emitter is insensitive for different polarization modes. The 21 material combinations of MIM emitters have been screened to obtain the optimal emitter matching GaSb and InGaAsSb cells. This work identifies the crucial role of structure and materials into the emitter of a TPV system. In the evaluation of MIM emitter and TPV System, when the operating temperature of emitter increases from 1400[Formula: see text]K to 2000[Formula: see text]K, the system efficiency of optimal W/HfO2/W MIM emitter increases from 20.26% to 30.41%, while the output electric power increases from 3.59[Formula: see text]kW/m2 to 42.48[Formula: see text]kW/m2. The phenomenon indicates that the MIM emitter with the optimal material combinations and geometric parameters can significantly improve the matching degree with GaSb and InGaAsSb cells. Our results will be helpful to expand the optimization scope of metamaterial emitters in TPV systems.

Tunable extraordinary optical transmission spectrum properties of long-wavelength infrared metamaterials.

Metamaterial filters represent an essential method for researching the miniaturization of infrared spectral detectors. To realize an 8-2µm long-wave infrared tunable transmission spectral structure, an extraordinary optical transmission metamaterial model was designed based on the grating diffraction effect and surface plasmon polariton resonance theory. The model consisted of an Al grating array in the upper layer and a Ge substrate in the lower layer. We numerically simulated the effects of different structural parameters on the transmission spectra, such as grating height (h), grating width (w), grating distance (d), grating constant (p), and grating length (S 1), by utilizing the finite-difference time-domain method. Finally, we obtained the maximum transmittance of 81.52% in the 8-12µm band range, with the corresponding structural parameters set to h=50n m, w=300n m, d=300n m, and S 1=48µm, respectively. After Lorentz fitting, a full width at half maximum of 0.94±0.01µm was achieved. In addition, the Ge substrate influence was taken into account for analyzing the model's extraordinary optical transmission performance. In particular, we first realized the continuous tuning performance at the transmission center wavelength (8-12µm) of long-wave infrared within the substrate tuning thickness (D) range of 1.9-2.9µm. The structure designed in this paper features tunability, broad spectral bandwidth, and miniaturization, which will provide a reference for the development of miniaturized long-wave infrared spectral filter devices.

Surface plasmon-polariton resonances and optical rectification in finite gratings

Surface plasmon-polariton resonances and optical rectification in finite gratings

Highly tunable and ultrasensitive hybrid plasmonic platform for multi-spectral sensing: Non-invasive diabetes surveillance and global warming directives

The development of tunable and extremely sensitive devices, as well as the emergence of metamaterials, has tremendously aided the evolution of plasmonic sensing technologies. However, the natural property of metamaterials severely restricts the scalability and application potential of mono-functional sensor systems. To address this shortcoming, we have investigated an ultranarrow five-band plasmonic sensor with structural tunability and high sensing behaviors in compatibility with multi-purpose application scenarios, using the finite-difference time-domain approach rigorously. Meanwhile, we theoretically formulated a hybridization model for the mutual induction of Fabry–Pérot resonances and localized surface plasmon polariton resonance, providing a theoretical basis for the utilization and conception of the highly-sensitive tunable plasmonic sensor. Most notably, we discovered and interpreted far-field phase extinction inducing separation of polarization resonance peaks in physical mechanisms. The tunability of its mutual inductance effect at the intersection distances from two-intersecting silver nanogroove was adequately exploited to further validate and effectively attain five ultra-narrow absorptivities of 96.70%, 93.93%, 99.73%, 100.00%, and 89.72% by top-level optimization. In addition, the redundant proximity between nearby peaks is compensated, extending the operating band and enhancing the practicability in multi-purpose scenarios. As a reliable source for future optical sensing, it performs well in the visible to near-infrared region, enabling detection response to non-invasive diabetes mellitus, global climate warming, and unrestricted temperature and pressure measurement. Meanwhile, minimum FWHM = 4.806 nm and maximum FOM = 115.13 RIU−1 are obtained at 293.15 K, with an associated highest sensitivity of 557.93 nm/RIU. Moreover, the fabrication technologies development of electron beam lithography and focused ion beam etching technologies enables large-scale mass production at low cost and long-term stability.

Room-Temperature Gate Voltage Modulation of Plasmonic Nanolasers.

Stable electrical modulation of plasmonic nanolasers is achieved on a hybrid graphene-insulator-metal (GIM) platform at room temperature. To support surface plasmon polariton (SPP) resonance, a zinc oxide (ZnO) nanowire is placed on the GIM platform to create a plasmonic cavity with a compact mode volume of 2.6 × 10-2 λ3, and the graphene layer is used as a transparent electrode for electrical modulation. When a gate voltage is applied, the surface electron density of Al varied, which results in the shifting of its plasma frequency and thus affects its SPP dispersion. In particular, this variation strongly changes the internal loss of the SPP mode; thus, the lasing thresholds of the ZnO nanowire plasmonic nanolasers on the GIM platform can be modulated by the gate voltage. This study demonstrates the gate voltage modulation of ZnO nanowire plasmonic nanolasers on a GIM platform at room temperature. These nanolasers can exhibit ultrahigh modulation speed on the order of terahertz. Accordingly, plasmonic nanolasers with gate voltage modulation have high potential for plasmonic circuit applications with high operation speed and versatility.

Ga2O3 metal–insulator-semiconductor solar-blind photodiodes with plasmon-enhanced responsivity and suppressed internal photoemission

Metal-semiconductor-metal (MSM) architectures are popular for achieving high-responsivity Ga2O3 solar-blind photodetectors (SBPDs), however, the hot-electron-induced internal photoemission (IPE) effect restricts their detecting performance. Herein, we demonstrate the rational design of an Al/Al2O3/Ga2O3 metal–insulator-semiconductor (MIS) SBPD that has merits of enhanced responsivity, suppressed sub-gap response and ultralow dark current based on the simulation results obtained using Lumerical software. For the cylindrical patterned detectors with Al/Al2O3/Ga2O3 MIS structures, the optimized dimensions of Al electrodes with a conformed ultra-thin (2 nm) Al2O3 layer support the surface plasmon polariton resonances at 250 nm, thus improving the photoresponsivity to 74 mA W−1. Furthermore, the sandwiched Al2O3 layer lifts the barrier for hot electrons in electrodes, which significantly suppresses the IPE-induced sub-gap photoresponse by more than 105 in magnitude with respect to the Al/Ga2O3 MSM counterpart. Optical and electrical field distributions are overlapped in cylindrically patterned MIS detectors, simultaneously improving the excitation and collection efficiencies of excess carriers and resulting in the 103-boosted rejection ratio.

High-Quality Surface Plasmon Polaritons in Large-Area Sodium Nanostructures.

Sodium (Na) is predicted to be an ideal plasmonic material with ultralow optical loss across visible to near-infrared (NIR). However, there has been limited research on Na plasmonics. Here we develop a scalable fabrication method for Na nanostructures by combining phase-shift photolithography and a thermo-assisted spin-coating process. Using this method, we fabricated Na nanopit arrays with varying periodicities (300-600 nm) and with tunable surface plasmon polariton (SPP) modes spanning visible to NIR. We achieved SPP resonances as narrow as 9.3 nm. In addition, Na nanostructures showed line width narrowing from visible toward NIR, showing their prospect operating in the NIR. To address the challenges associated with the high reactivity of Na, we designed a simple encapsulation strategy and stabilized the Na nanostructures in ambient conditions for more than two months. As a low-cost and low-loss plasmonic material, Na offers a competitive option for nanophotonic devices and plasmon-enhanced applications.

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.

Broadband optical transmission through two-dimensional hole arrays

We suggest that a metal film perforated with two-dimensional (2D) hole arrays can support broadband optical transmission. This phenomenon is based on the impedance matching between the perforated metal film and incoming light waves at oblique incidence. Theoretical formulas for the effective impedance of the hole arrays and Brewster angle of broadband transmission have been derived in the infrared regime, taking account of the field penetration effect on the hole walls. With the numerical simulations, the predicted optical effect has also been demonstrated. Compared with the narrow transmission band due to surface-plasmon polariton resonance, our results present a non-resonant, broadband, and robust transmission channel for the 2D hole arrays.

Terahertz frequency selective surfaces using heterostructures based on two-dimensional diffraction grating of single-walled carbon nanotubes

ABSTRACT For single-walled carbon nanotubes (SWCNTs) with a length of 1–50 µm, the surface plasmon-polariton (SPP) resonance is within the terahertz frequency range; therefore, SWCNT lattices can be used to design frequency-selective surface (FSS). A numerical model of electromagnetic wave diffraction on a two-dimensional periodic SWCNT lattice can be described by an integro-differential equation of the second-order with respect to the surface current along SWCNT. The equation can be solved by the Bubnov–Galerkin method. Frequency dependence of reflecting and transmitting electromagnetic waves for FSSs near the SPP resonance is studied numerically. It is shown that the resonances are within the lower-frequency part of the terahertz range. We also estimate the relaxation frequency of an individual SWCNT and demonstrate the applicability of the Kubo formula for graphene conductivity to array of strips similar in size to SWCNTs under consideration.

Simulated Performance of a Broadband Solar Absorber Composed of Sectioned Au Disk Structures and ZnS/Au Thin Layers

Solar energy is considered an essential source of energy because of cleanliness and ubiquity. However, how to effectively absorb solar energy within the range of solar radiation is an urgent problem to be solved. The design of high-performance broadband perfect absorbers is an important way to collect solar energy efficiently. In this paper, we propose a novel broadband solar energy absorber based on zinc sulfide (ZnS). It is a three-layer (Au-ZnS-Au) structure with new types of sectioned disks employed in the top layer. The sectioned disks can enhance the absorption efficiency. Surface plasmon polariton (SPP) and electric dipole resonance increase the absorption of light, so the proposed absorber can achieve broadband perfect absorption. Simulation by a finite element analysis (COMSOL) method shows that absorption with a bandwidth of 354 THz from 430 THz–784 THz has been achieved, and the average absorption is 95%. This indicates that the perfect absorption range of the proposed absorber is 78.7% of the visible range. The perfect absorber has four perfect absorption peaks, which can reach a maximum absorption rate of 99.9%. In addition, our absorber is polarization insensitive due to the design of the rotational symmetry structure of the sectioned disks. The absorber is composed of refractory metals so that it can work under actual solar radiation and high-temperature conditions. The proposed solar energy absorber is important for many applications such as solar cells, thermal photovoltaic technology, and sensing.

Versatile terahertz graphene metasurface based on plasmon-induced transparency

A monolayer terahertz graphene metasurface is designed to achieve tunable plasmon-induced transparency (PIT) effect in two perpendicular polarization directions based on surface plasmon polariton resonance. The penta-frequency and dual-frequency switch can be easily implemented by adjusting the Fermi levels of graphene, and the switch has excellent performances including modulation degree of amplitude (81.4 % < MDA < 97.1 %) and insertion loss (0.01 dB < IL < 0.04 dB). Moreover, the metasurface has high sensitivity, which can be up to 30500 nm/RIU. Also, the designed PIT metasurface has a good slow light effect, and group indexes are respectively 1100 and 2396 corresponding to x-polarized and y-polarized light. This work demonstrates that graphene metasurface has potential applications in switch, sensor and slow-light devices.

Enhanced graphene surface plasmonics through incorporation into metallic nanostructures.

A methodology for enhancing the surface plasmon polariton (SPP) resonance associated with graphene, through nanoscale metal-dielectric-metal (MDM) gaps, is proposed. The modulation of the resonances, in the range of 0.7 µm to 1 µm was done through tuning the carrier density in graphene and has been shown to be of potential utility for surface analyte sensing. It was shown, from finite element simulations in the frequency domain, that the related hybrid SPP modes could be clearly delineated in far field spectroscopy.