Tunable Surface Plasmon Polaritons Research Articles

Terahertz and Infrared Plasmon Polaritons in PtTe2 Type-II Dirac Topological Semimetal.

Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric. SPPs provide a promising path in nanophotonic devicesforlight manipulation at the micro and nanoscale with applications in optoelectronics, biomedicine, and energy harvesting. Recently, SPPs are extended to unconventional materials like graphene, transparent oxides, superconductors, and topological systems characterized by linearly dispersive electronic bands. In this respect, 3D Dirac and Weyl semimetals offer a promising frontier for infrared (IR) and terahertz (THz) radiation tuning by topologically-protected SPPs.In this work, the THz-IR optical response of platinum ditelluride (PtTe2) type-II Dirac topological semimetal films grown on Si substrates is investigated. SPPs generated on microscale ribbon arrays of PtTe2are detected in the far-field limit,finding an excellent agreement among measurements, theoretical models, and electromagnetic simulation data.The far-field measurements are further supported by near-field IR data which indicate a strong electric field enhancement due to the SPP excitation near the ribbon edges. The present findings indicate that the PtTe2ribbon array appears an idealactive layout for geometrically tunable SPPs thus inspiring a new fashion of optically tunable materials in the technologically demanding THz and IR spectrum.

Near-Field Photodetection in Direction Tunable Surface Plasmon Polaritons Waveguides Embedded with Graphene.

2D materials have manifested themselves as key components toward compact integrated circuits. Because of their capability to circumvent the diffraction limit, light manipulation using surface plasmon polaritons (SPPs) is highly-valued. In this study, plasmonic photodetection using graphene as a 2D material is investigated. Non-scattering near-field detection of SPPs is implemented via monolayer graphene stacked under an SPP waveguide with a symmetric antenna. Energy conversion between radiation power and electrical signals is utilized for the photovoltaic and photoconductive processes of the gold-graphene interface and biased electrodes, measuring a maximum photoresponsivity of 29.2mAW-1 . The generated photocurrent is altered under the polarization state of the input light, producing a 400% contrast between the maximum and minimum signals. This result is universally applicable to all on-chip optoelectronic circuits.

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.

Active tuning hBN phonon polaritons and spontaneous emission rates based on VO<sub>2</sub> and graphene

<sec>Active tunability of phonon dispersion and spontaneous emission (SE) are still open problems due to their exciting potential applications. In view of the fact that polaritons are very sensitive to the dielectric environment, in this study, with the help of the differences in optical property between the phase change material vanadium dioxide (VO<sub>2</sub>) during the phase transition from the insulating state to metallic state and the tunable surface plasmon polaritons (SPPs) in graphene, a heterostructure composed of hyperbolic material hexagonal boron nitride (hBN) and graphene and VO<sub>2</sub> is proposed to investigate the active tunability of hBN phonon polaritons (PhPs). In order to illustrate the underlying physical mechanism of the above heterostructures, the dispersion distributions of the above heterostructures are calculated and represented by the imaginary part of the p-polarized Fresnel reflection coefficient of the heterostructure, meanwhile the dispersion relation of the hBN/VO<sub>2</sub> heterostructure in hyperbolic region is verified by the quasi-static approximation method.</sec><sec>Results indicate that the active tunability of hBN PhPs inside type-I and type-II hyperbolic bands can be achieved by controlling VO<sub>2</sub> phase transition in hBN/VO<sub>2</sub> heterostructure. The PhP dispersion change of the hBN/VO<sub>2</sub> heterostructure is mainly caused by the change of the VO<sub>2</sub> dielectric function when VO<sub>2</sub> substrate changes from the insulating state into metallic state, which affects the total Fresnel reflection coefficient of the heterostructure, finally resulting in the PhP dispersion change of hBN/VO<sub>2</sub> heterostructure. When graphene is introduced into the hBN/VO<sub>2</sub> heterostructure, coupled hyperbolic plasmon-phonon polaritons (HPPPs) are obtained within type-I and type-II hyperbolic band of hBN, while the surface plasmon-phonon polaritons (SPPPs) are generated outside its hyperbolic bands. Moreover, comparative analysis of SE rates is presented for a quantum emitter positioned with the hBN/VO<sub>2</sub> and graphene/hBN/VO<sub>2</sub> heterostructure, revealing that the SE rates of these heterostructures can be modulated by the passive means including changing the hBN thickness and distance between the dipole emitter and the proposed heterostructure, and also by the active means including tuning VO<sub>2</sub> phase states and graphene chemical potential without changing structural configurations. This study provides a theoretical guidance in realizing active tunability of both phonon dispersion and SE rate of the natural or artificial anisotropic optical materials by using functional materials including phase change materials and graphene.</sec>

Phase-Difference-Dependent Surface Plasmon Polariton Waveguide Coupling in a Symmetrical Dual-Channel Metal-Insulator-Metal Structure

This work reports a phase difference modulated coupling of two surface plasmon polariton (SPP) sources in a symmetrical two-channel metal-insulator-metal (MIM) waveguide device. In the device, two sources with different initial phases interact indirectly through the function of a rectangular cavity. With the phase difference varying, we have achieved tunable SPP coupling followed by continuously adjustable filtering property and Fano resonance. Further results show that the tunable SPP coupling in the resonance cavity can be well described by the electromagnetic wave interference theory. Moreover, we have also demonstrated the excellent performance of this phase-difference-dependent MIM waveguide in refractive-index sensing and have achieved considerable sensitivity as high as 818.8 nm/RIU. This research has great significance for tunable filtering and signal compensation in MIM waveguide-based photonic chips and also provides a device with high potential in refractive-index sensing.

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.

High-Resolution Two-Dimensional Atomic Localization Via Tunable Surface Plasmon Polaritons

The two-dimensional (2D) atomic localization is theoretically investigated via tunable surface plasmon polaritons (SPPs), generated on the metal (Ag) surface coupled to a quantum coherent three-level $$\lambda$$ -type medium ( $$^{87}$$ Rb) embedded as a dielectric host. Such a useful scheme for highly precise atomic localization is reported by using the absorption spectrum of SPPs. Owing to space-dependent light–matter interaction, the sharp localized peaks are observed in a single wavelength domain of 2D space with maximum probability. By properly varying the system parameters, the precision and numbers of the localized peaks are controlled. Consequently, highly efficient and high-resolution atomic localization can be achieved in a region smaller than $$\lambda /20\times \lambda /20$$ . The spatial resolution of atomic localization is greatly improved as compared to the previously studied cases. These results may have potential useful applications in the fields of quantum nanoplasmonics, nanolithography, and nanophotonics.

RETRACTED: Ultrahigh resolution two-dimensional atomic localization via tunable surface plasmon polaritons

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). This article has been retracted at the request of Authors We are retracting this Article because the result is wrong for the following two crucial reasons. This article considered a nanohybrid system consisted of a core of atomic medium with dielectric constant e1 and an outer Ag metallic nanoparticle (MNP) shell with dielectric constant e2. Such nano-structures make the light fields inside the nanohybrid system highly inhomogeneous. It is impossible for the controlling fields to form the strong standing waves in such spherical shell nanostructures. Thus the Equation (1) of the modelling for the driving laser field with Rabi frequency Wc(x,y) inside the NMP shell is not valid. Furthermore, the modes inside such spherical structures are usually the well-known whispering gallery modes. The surface plasmonic dispersion relation given in (12), which is usually used for a plane interface, is not applicable in the spherical nanohybrid system. Since these two equations (1) and (12) are fundamentally wrong, we think that all results based on them are incorrect. Therefore all authors wish to retract this Article. We deeply regret for the inconvenience caused to Optics and Laser Technology and apologize to the scientific community.

Dual-Gated Graphene Devices for Near-Field Nano-imaging

Graphene-based heterostructures display a variety of phenomena that are strongly tunable by electrostatic local gates. Monolayer graphene (MLG) exhibits tunable surface plasmon polaritons, as revealed by scanning nano-infrared experiments. In bilayer graphene (BLG), an electronic gap is induced by a perpendicular displacement field. Gapped BLG is predicted to display unusual effects such as plasmon amplification and domain wall plasmons with significantly larger lifetime than MLG. Furthermore, a variety of correlated electronic phases highly sensitive to displacement fields have been observed in twisted graphene structures. However, applying perpendicular displacement fields in nano-infrared experiments has only recently become possible [Li, H.; Nano Lett. 2020, 20, 3106-3112]. In this work, we fully characterize two approaches to realizing nano-optics compatible top gates: bilayer MoS2 and MLG. We perform nano-infrared imaging on both types of structures and evaluate their strengths and weaknesses. Our work paves the way for comprehensive near-field experiments of correlated phenomena and plasmonic effects in graphene-based heterostructures.

Tunable surface plasmon-polariton resonance in organic light-emitting devices based on corrugated alloy electrodes

Tunable surface plasmon-polariton resonance in organic light-emitting devices based on corrugated alloy electrodes

Theoretical study of SPP properties based on black phosphorus–graphene van der Waals heterostructure

We theoretically investigate the surface plasmon polariton (SPP) properties based on black phosphorus–graphene van der Waals heterostructures that can be tuned by both the incident light angle of black phosphorus and Fermi level of graphene. We elucidate the angle-dependent SPP properties for the hybrid structure from the visible regime to mid-infrared regime. The results show that the largest SPP propagation distance is obtained in the zigzag direction of black phosphorus except when the wavelength is tuned from 380 nm to 480 nm in the visible regime and 1 µm–1.2 µm in the near infrared regime. We also reveal the quasi-linear and quasi-square linear relationship between the SPP propagation distance and Fermi level of graphene for different regimes. Our work would be of great value to construct and optimize the angle-dependent and tunable SPP devices based on the hybridization of different 2D materials.

Dynamically Tunable Plasmon-induced Transparency in a T-shaped Cavity Waveguide Based on Bulk Dirac Semimetals

We propose a dynamically tunable surface plasmon polaritons (SPPs) waveguide system based on bulk Dirac semimetals (BDS) containing only a side-coupled T-shaped cavity. Plasmon-induced transparency (PIT) is achieved in the terahertz band by introducing a position offset. We have analytically investigated the spectral characteristics of PIT in this system, indicating that the larger the position offset, the higher the peak of the PIT window. The spectrum responses of PIT system can be flexibly regulated via transforming the geometric parameters of the structure. At the same time, it is particularly sensitive to the refractive index of the surrounding medium, which is promising for sensing devices. In addition, the resonance frequency and peak transmission can be actively adjusted by controlling the Fermi energy of the BDS without reconstructing the geometric structure. Moreover, the optical delay time near the PIT peak reaches 11.001 ps, which has good slow-light characteristics and is a candidate in the field of slow-light equipment. The structure we designed may have potential application value in the design of SPPs light-guide devices.

Applications of Tamm plasmon-liquid crystal devices

ABSTRACT The Tamm-plasmon-polariton (TPP) occurs at the interface between a metallic film and the photonic-crystal (PC) substrate. Unlike conventional surface-plasmon-polariton (SPP), TPP can be directly excited by both the transverse electric (TE) and transverse magnetic (TM) electromagnetic waves without using additional coupling optics. The fact that the optical functionality of most plasmonics devices is determined after fabrication limits their applications. Tunable SPP devices by applying liquid crystals (LCs) have been widely demonstrated due to their large birefringence and easy controllability via external stimuli. However, actively tuning TPP is difficult because the localised electric field is between the metallic film and PC substrate, the change of refractive index above the metallic film has only small influences on TPP. This article is intended to briefly review recent progress towards using LCs for actively tuning TPP devices. Not only TPP devices can gain benefits from LCs, we will also discuss the applications of TPP for measuring the anisotropy of the alignment films of LC devices. The sensitivity of the proposed scheme will be discussed.

A highly sensitive and tunable plasmonic sensor based on a graphene tubular resonator

A novel configuration of dynamically tunable surface plasmon polaritons (SPPs) is proposed based on two waveguides and one nanotube graphene in the terahertz range and is numerically investigated as a highly sensitive sensor. In the proposed structure, the two graphene waveguides coupled to the nanotube have two plasmonic modes which have two high sensitivities in different frequencies. The results show that in this structure, the sensitivity values are measured as the order of 7714 nm/RIU inside the tube and 18500 nm/RIU in the total environment. The sensitivity value in the total environment is at least 148.3% larger than those of previously reported waveguides which is an excellent result. This graphene waveguide sensor can have an important practical application in biosensors and lab-on-chip systems.

A Review of Unidirectional Surface Plasmon Polariton Metacouplers

Efficient and unidirectional excitation of surface plasmon polaritons (SPPs) and their low-frequency counterparts (i.e., spoof SPPs) is highly desired in the research area of photonics and plasmonics, while being at the same time rather challenging. Recent progress in gradient metasurfaces, ultrathin, and planar materials composed of sub-wavelength unit cells, has opened up new possibilities for efficiently coupling of free-space propagating waves to surface waves. In this paper, we will discuss the recent achievements in gradient metasurface-based unidirectional SPP couplers (i.e., metacouplers). Starting with explaining the basic concept of generalized Snell's law, we then introduce some typical examples of unidirectional SPP metacouplers, followed by an overview of polarization-controlled tunable SPP metacouplers. We also describe metacouplers that also feature other functionalities, beyond the unidirectional SPP excitation. The review is concluded with a short summary and perspective for future developments.

Graphene-mediated near field thermostat based on three-body photon tunneling

We theoretically demonstrate a near field thermostat based on the mechanism of three-body photon heat tunneling and tunability of graphene. The system consists of three separated parallel plates at different temperatures, with the hot and cold body (located at either side of the system) coated with a monolayer of graphene. As a unique two-dimensional material, graphene owns the tunable plasmonic dispersion relation which can be rapidly modulated by changing its chemical potential in an electronical manner. By changing the chemical potentials of graphene, the near field radiative heat flux (NFRHF) transporting in the system can be tuned accordingly. As a consequence, the equilibrium temperature of the intermediate body can be adjusted from the temperature of the hot body to that of the cold one. The results show that the equilibrium temperature can be adjusted from 326 K to 388 K in SiO2-SiO2-SiO2 configuration, which occupies about sixty percent of the temperature range with respect to the cold and hot body. This phenomenon implies that near field contactless temperature adjustment can be carried out by the proposed configuration. The underlying mechanism is attributed to the varied NFRHF with tunable surface plasmon polaritons of graphene. Moreover, three-body photon heat tunneling can benefit the regulation function of the system in the near field regime and an enhanced region for adjusting temperature is observed. An interesting phenomenon is observed that the mismatch between different materials raises the regulation ability to 82 K in SiO2-SiC-SiO2 configuration. The results obtained in this study could find significant applications in the field of near field thermal management and controlling temperature in the separation of micrometer and millimeter scale, especially paves a new way toward improving the performance of near field thermal transistor based on insulator-metal transition material.

Tunable surface plasmon-polaritons based on quantum coherence.

Tunable surface plasmons on the interface of a multilevel atomic medium with a cross coupling of the electric and magnetic components of a plasmonic field are investigated. The strong chirality resulting from the quantum coherence leads to some exciting properties of the surface plasmons. Compared to the traditional chiral-metal interface, surface plasmonic mode can still be found at the interface between such atomic media and a dielectric even when both the permittivity and the permeability of the medium are positive. This is in contrast to the conventional plasmonic systems where the signs of the permittivities or permeabilities on the two sides of the interface are opposite. We call this phenomenon an electromagnetically induced plasmon. Additionally, as the chirality and effective refractive index of the atomic medium are dependent on the intensity and phase of the controlling field, we can conveniently manipulate the properties of the surface plasmons.

Tunable-Focusing of Surface Plasmon Polaritons With a Slightly Irregular Line of Nanofootprints

Tunable surface plasmon polariton launchers are highly demanded in various applications of nanophotonics for achieving controllable plasmonic signals coupling and multiplexing. Here, a tunable-focusing device with simplified structure is suggested. It consists of an array of nanofootprints. This device allows us polarization-controlled tunable plasmonic directing and focusing on the two-dimensional metallic surface. The simulation and experimental results indicate that the focal position of the excited plasmon field can be flexibly tuned between two distinct positions just by manipulating the incident polarization state. Hence, this nanofootprints structure can serve effectively as controllable plasmonic routers and demultiplexers. It also has promising application prospects in many other fields of optics.

非碰撞磁化等离子体与介质表面色散特性研究

基于麦克斯韦方程组和边界条件，推导磁化非碰撞等离子体和介质表面的色散关系，讨论了外加磁场对色散特性的影响，得到了基于磁场可调的表面等离子体激元。 The dispersion relations on the surface of a non-collision magnetized plasma and dielectric material are derived based on Maxwell’s Equations and boundary conditions. The dispersion characteristics affected by the applied magnetic field are discussed, and it is found that the tunable surface plasmon polaritons can appear in the surface.

Directive Surface Plasmons on Tunable Two-Dimensional Hyperbolic Metasurfaces and Black Phosphorus: Green’s Function and Complex Plane Analysis

We study the electromagnetic response of two- and quasi-two-dimensional hyperbolic materials, on which a simple dipole source can excite a well-confined and tunable surface plasmon polariton (SPP). The analysis is based on the Green's function for an anisotropic two-dimensional surface, which nominally requires the evaluation of a two-dimensional Sommerfeld integral. We show that for the SPP contribution this integral can be evaluated efficiently in a mixed continuous-discrete form as a continuous spectrum contribution (branch cut integral) of a residue term, in distinction to the isotropic case, where the SPP is simply given as a discrete residue term. The regime of strong SPP excitation is discussed, and complex-plane singularities are identified, leading to physical insight into the excited SPP. We also present a stationary phase solution valid for large radial distances. Examples are presented using graphene strips to form a hyperbolic metasurface, and thin-film black phosphorus. The Green's function and complex-plane analysis developed allows for the exploration of hyperbolic plasmons in general 2D materials.