Multiple Plasmon-induced Transparency Research Articles

Tunable optical devices with multiple plasmon-induced transparency based on graphene-black phosphorus hybrid metasurface

In this research, we propose a simple and novel graphene-black phosphorus composite structure. Through the coupling mechanism of bright–bright mode, four layers of graphene and one layer of black phosphorus produce a quadruple plasmon-induced transparency (PIT) effect. The response of the proposed structure to the angle of polarized light is investigated, and it is found that the sensitivities of graphene and black phosphorus to the polarization angle of light are different. In addition, the dynamic regulation of PIT by the Fermi level of graphene and the carrier concentration of black phosphorus are discussed. The modulation depths of the fivefold optical switching are 96%, 99%, 87%, 93%, and 80%, respectively. The quadruple PIT can also be converted into triple PIT, in which single, dual, or triple optical switching are realized, respectively. Finally, with the change in the refractive index of the environment medium, the sensitivity response of the proposed structure is as high as 4.790 THz⋅RIU−1. We believe that this research will contribute to the development of optical switches, modulators, and sensors.

Dynamically tunable multiple plasmon-induced transparency effect based on monolayer graphene structure system with rectangular defect cavities

In this article, a dynamically tunable multiple plasmon-induced transparency (PIT) effect in monolayer graphene structure system with rectangular defect cavities is investigated both theoretically and numerically. Because the graphene of our structure exists in a continuous form, the Fermi level of the graphene can be dynamically tuned by simply applying a bias voltage. The expressions of the theoretical transmittance are correctly deduced, and the fitting theoretical results are very consistent with the numerical simulation data. When the Fermi level of the graphene is increased from 0.8 eV to 1.2 eV, the group index of the dual-PIT system is controlled between 383 and 766. Alternatively, the group index of the triple-PIT system is maintained between 445 and 812. Moreover, the maximum group index can reach 812 at 1.2 eV, which shows that it can be designed as an excellent slow light device. Therefore, the proposed structures and results may provide strong guidance towards multichannel optical filters, dynamically tunable and excellent slow light and light storage devices.

Tunable multiple plasmon-induced transparencies in multiple T-shaped cavities waveguide based on Dirac semimetals

We study the multiple plasmon-induced transparencies (PIT) in the waveguide structure based on bulk Dirac semimetal (BDS) containing multiple side-coupled T-shaped cavities. Using the finite element method, we mainly investigate the transmission spectra, the transmission phase shifts, the delay times, and the magnetic field distributions of the two T-shaped cavities waveguide structure. It is shown that their transmission characteristics strongly depend on the geometric parameters of the waveguide structure. In addition, we discuss the effect of the Fermi level of BDS and the refractive index of the medium on the transmission spectrum of the two T-shaped cavities structure. To get more PIT peaks, we try to simulate the transmission spectrum of three T-shaped cavities waveguide structure. All the results about the multiple PIT phenomena may have some possible applications in designing lenses, high-capacity storage devices, and new filters.

Multiple plasmon-induced transparency based on black phosphorus and graphene for high-sensitivity refractive index sensing.

A hybrid bilayer black phosphorus (BP) and graphene structure with high sensitivity is proposed for obtaining plasmon-induced transparency (PIT). By means of surface plasmon resonance in the rectangular-ring BP structure and ribbon graphene structure, a PIT effect with high refractive index sensitivity is achieved, and the surface plasmon hybridization between graphene and anisotropic BP is analyzed theoretically. Meanwhile, the PIT effect is quantitatively described using the coupled oscillator model and the strong coherent coupling phenomena are analyzed by adjusting the coupling distance between BP and graphene, the Fermi level of graphene, and the crystal orientation of BP, respectively. The simulation results show that the refractive index sensitivity S = 7.343 THz/RIU has been achieved. More importantly, this is the first report of tunable PIT effects that can produce up to quintuple PIT windows by using the BP and graphene hybrid structure. The high refractive index sensitivity of the quintuple PIT system for each peak is 3.467 THz/RIU, 3.467 THz/RIU, 3.600 THz/RIU, 4.267 THz/RIU, 4.733 THz/RIU and 6.133 THz/RIU, respectively, which can be used for multiple refractive index sensing function.

Cascaded plasmon-induced transparency in spoof surface plasmon polariton waveguide

Manipulating spoof surface plasmon polaritons (SPPs) effectively has promising applications in developing ultracompact plasmonic circuits. Research on versatile components in planar spoof SPP waveguides has attracted widespread attention over the decades. In particular, cascaded chip-scale devices play an important role in enhancive buffering, highly-sensitive sensing and nonlinear interaction. Herein, we propose a novel strategy to manipulate the switching and slow wave features of spoof SPPs on the basis of plasmon-induced transparency (PIT) spectral responses. A combined module consisting of split square-ring resonators and electric-LC resonators is loaded with a spoof SPP waveguide along the propagating trajectory, where the destructive interference between the two resonators contributes to the PIT behavior and the group delay of the spoof SPPs. A modulation contrast of up to 16.2 dB is achieved for the spoof SPP transmission at the PIT peak frequency. The measurements are consistent with both full-wave simulations and theoretical calculations. Cascaded capabilities performed by installing multiple PIT modules at an interval of an equivalent wavelength are accomplished in the planar spoof SPP waveguide. The proposed strategy opens up fascinating prospects on highly integrated plasmonic circuits and networks.

Polarization-controlled and symmetry-dependent multiple plasmon-induced transparency in graphene-based metasurfaces.

In this paper, we theoretically and numerically demonstrate a polarization-controlled and symmetry-dependent multiple plasmon-induced transparency (PIT) in a graphene-based metasurface. The unit cell of metasurface is composed of two reversely placed U-shaped graphene nanostructures and a rectangular graphene ring stacking on a dielectric substrate. By adjusting the polarization of incident light, the number of transparency windows can be actively modulated between 1 and 2 when the nanostructure keeps a geometrical symmetry with respect to the x-axis. Especially, when the rectangular graphene ring has a displacement along the y-direction, the number of transparency windows can be arbitrarily switched between 2 and 3. The operation mechanism behind the phenomena can be attributed to the near-field coupling and electromagnetic interaction between the bright modes excited in the unit of graphene resonators. Moreover, the electromagnetic simulations obtained by finite-difference time-domain (FDTD) method agree well with the theoretical results based on the coupled modes theory (CMT). In addition, as applications of the designed nanostructure, we also study the modulation degrees of amplitude, insertion loss and group index of transmission spectra for different Fermi energies, which demonstrates an excellent synchronous switch functionality and slow light effect at multiple frequencies. Our designed metasurface may have potential applications in mid-infrared optoelectronic devices, such as optical switches, modulators, and slow-light devices, etc.

Tunable Multi-band Switch with Uncoupled Graphene-based Metamaterial Patches

We present the tunable multiple plasmon-induced transparency (PIT) in the terahertz region by using a metamaterial made of two graphene bands and a graphene square ring. As the different modes of multiple PIT effects are independent of each other, the physical mechanism behind multiple PIT effects can be revealed by CMT theory. The PIT window changes significantly with the Fermi energy levels and structural parameters of graphene. The both three resonant frequencies increase linearly with the parameters and the Fermi energy changing, which can exhibit high sensitivities and figure of merit (FOM). Meanwhile, the amplitude modulation system can reach 99.63%, which can achieve excellent photoelectric switching. In addition, the group index can be as high as 2739. Therefore, the graphene-based metamaterial could be widely used in switches, modulators, excellent slow-light functional devices and filters in the terahertz region.

Multiple and tunable plasmon induced transparency with L-shape graphene strips structure at terahertz frequency

Firstly, in this paper, the proposed structure is composed of a transverse graphene rectangular cavity and a vertical graphene rectangular cavity, so as to produce the plasmon-induced transparency (PIT) phenomenon. The PIT of graphene metamaterials is theoretically explored by using the finite-difference time-domain (FDTD) simulation and the coupled-mode-theoretical (CMT) analysis. Then, by adjusting the Fermi level of graphene, the PIT window is dynamically adjusted, so that the structure can be used as an optical switch. Furthermore, the refractive index sensitivity of the PIT window is investigated and the simulation results show that a sensitivity of 2.725 THz/RIU is achieved. In addition, multiple PIT windows are also generated by adding additional matched L-type graphene strips. Finally, the proposed structure may enlighten the developments of dynamically tuned terahertz devices.

Multiple and Tunable Plasmon Induced Transparency with L-Shape Graphene Strips Structure at Terahertz Frequency

Multiple and Tunable Plasmon Induced Transparency with L-Shape Graphene Strips Structure at Terahertz Frequency

Numerical Analysis of Multiple Plasmon-Induced Transparency Effects of Side-Coupled Waveguide with Double Loop-Stub

Numerical Analysis of Multiple Plasmon-Induced Transparency Effects of Side-Coupled Waveguide with Double Loop-Stub

Theoretical analysis of tunable double plasmon induced transparency in three-ellipse-shaped resonator coupled waveguide

The tunable double plasmon-induced transparency (PIT) effects are investigated in a waveguide coupled by the three ellipse-shaped resonators. By the finite element method, we study the influences of coupling modes of the three ellipse-shaped resonators, waveguide structure parameters and the refractive indices of dielectric in three ellipse-shaped resonators on double PIT effects. The waveguide structure consists of three ellipse-shaped resonators, and is similar to a four-level structure of the atomic system. The bottom ellipse-shaped resonator can be named a bright mode, the middle and top ellipse-shaped resonators each can be seen as a dark mode. In order to obtain an ideal double PIT transparency window, we also numerically analyze the optical transmission characteristics of structures of several three-ellipse-shaped resonator coupled waveguides. Furthermore, we mainly discuss the transmission spectra in the better three-ellipse-shaped resonator coupled waveguide structure as a function of the radii of the long axis in ellipse-shaped resonators, the coupling distance between the bottom ellipse-shaped resonator and the bus waveguide, the coupling distance between ellipse-shaped resonators, and the symmetry broken degree. In addition, we also consider the effect of the refractive indices of dielectric in three ellipse-shaped resonators on double PIT spectra. It is found that the transmission spectra in the three-ellipse-shaped resonator coupled waveguide have obvious red shift when the refractive indices of dielectric in the three ellipse-shaped resonators increase. All the simulation results may provide the theoretical basis for the potential application of multiple PIT in plasma switches and sensors.

Multiple plasmon-induced transparency with extra-high FOM based on a MIM waveguide composed of stubs

A plasmon structure based on a metal-insulator-metal (MIM) waveguide composed of three stubs (TSs) is proposed, and its transmission characteristics are studied numerically by the finite element method (FEM). The simulation results show that multiple plasmon-induced transparencies (PITs) with high transmission can be produced in the structure and can be tuned effectively. By adjusting the structure parameters, more high-order PITs with narrower window are generated. Furthermore, the proposed MIM waveguide is sensitive to the environment and the maximum values of refractive index sensitivity and figure of merit (FOM) are 1340 nm R−1IU−1 and 251/RIU, respectively. Multiple, adjustable and narrow PITs with high FOM can be induced in the proposed structure, which can be used in the fields of multi-channel filters, optical switches, storages, sensors, and so on.

Tunable and Multiple Plasmon-Induced Transparency in a Metasurface Comprised of Silver S-Shaped Resonator and Rectangular Strip

The plasmon-induced transparency (PIT) in planar metasurface comprising of resonators having one S-shaped structure and a rectangular strip (both made of silver) was investigated. It was found that the S-shaped component of metasurface induces a single bright mode, whereas the rectangular strip manifests two bright modes with strong coupling of incidence electromagnetic waves. When both the metasurface components were placed in the proximity, the PIT-like phenomenon was observed. The effects of rotational angle of the metasurface as well as the angle of incidence on the transmission spectra (of the metasurface) were also investigated. Both the transverse electric (TE) and transverse magnetic (TM) waves were used to explore the PIT effect. It was noticed that the PIT window could be easily tuned by altering the horizontal distance between the resonator components (i.e., the S-shaped structure and rectangular strip). It is expected that the proposed metasurface structure would be prudent in switching, ultrafast sensing and optical applications.

Coherently controllable terahertz plasmon-induced transparency using a coupled Fano-Lorentzian metasurface.

Metamaterials have been engineered to achieve electromagnetically induced transparency (EIT)-like behavior, analogous to those in quantum optical systems. These meta-devices are opening new paradigms in terahertz communication, ultra-sensitive sensing and EIT-like anti-reflection. The controlled coupling between a sub-radiant and a super-radiant particle in the unit cells of these metamaterial can enable multiple narrow plasmon induced transparency (PIT) windows over a broad band, with considerable group delay of electromagnetic field (slow light effect). Phase coherence between these PIT windows is highly desired for next-generation multichannel communication network. Herein, we numerically and experimentally validate a controllable frequency hopping mechanism between "slow light" windows in the terahertz (THz) regime. The effective media are composed of plasmonic "molecules" in which an asymmetric split-ring resonator (ASRR) or Fano resonator is displaced on the side of a cut-wire (Lorentz oscillator). Two metasurfaces where ASRR is on opposite side of the cut-wire are investigated. In these two cases, the proximity of the cut-wire to the gap on the ASRR having asymmetry is different. On one side, when the gap is nearer to the cut wire, displacing the ASRR along the cut-wire, produces only one narrow transparency window at 0.8 THz, corresponding to 20 ps group delay. When the ASRR is positioned on the opposite side, such that the gap is further, two transparency windows are observed when the ASRR is displaced along the cut-wire. That is, the transparency window hops from 0.8 THz to 1.2 THz. This corresponds to an increase from 20 to 30 ps in slow light effect. Numerical simulations suggest these single or multiple PIT windows occur if the couplings between the plasmonic modes in the different arrangements are either in-phase or out-of-phase, respectively.

Tunable multiple plasmon-induced transparency in a simple terahertz Dirac semimetal based metamaterial

We proposed a bulk Dirac semimetal (BDS) based metamaterial that consists of two identical vertical BDS rods and two horizontal BDS rods with different lengths. Numerical simulation results show that the proposed structure can realize the tunable multiple plasmon-induced transparency (multi-PIT) effect. The multi-PIT effect is mainly attributed to the introduction of the bonding mode simply by manipulating the lengths of horizontal rods. By changing the Fermi energy of the BDS, the tunable multi-PIT spectrum and tunable multi-band group delay can be achieved. The multi-PIT peaks are also sensitive to the background refractive index and can lead high FOM values of 16, 50.9 and 10.6, respectively. The proposed structure is desirable for designing tunable THz sensors, modulators and slow light devices.

Multispectral Plasmon Induced Transparency in a Defective Metasurface Plasmonic Nanostructure

The investigation of plasmon induced transparency (PIT) resonances is performed in a system based on defective and complete silver nanostrips. The response of metasurface systems to electromagnetic fields under normal incidence is endowed by unique features, including some exquisite spatial phenomena. These phenomena are embodied in confined light-matter hybrid modes where the defective silver nanostrip excites superradiant dipole and quadrupole modes, resulting in a PIT window. Moreover, multispectral PIT resonances are observed, which involves quadrupole mode as superradiant to excite the proximity nanostrip. It can reveal much about the defective metasurface structure, such as exact tuning of the gap distance between these two nanostrips, variation in defect parameters and modulating in electric polarization angles of excitation. Still, our research realizes multiple PIT resonances in one nanostructure, which may have interesting applications of plasmonic switching devices in highly integrated circuits.

Tunable multiple plasmon-induced transparency in three-dimensional Dirac semimetal metamaterials

Tunable plasmonic Dirac semimetal metamaterials featuring multiple transparency windows in the terahertz (THz) frequency region are numerically investigated in this study. The proposed multiple plasmon-induced transparency (PIT) system is composed of two types of H-shaped structures, each of which can be regarded as an independent PIT system. Unlike in the conventional metallic PIT systems, the multiple PIT effect in three-dimensional Dirac semimetals can be tuned by varying the Fermi energy instead of the geometrical parameters. The proposed multiple PIT structure could pave the way for potential applications in various areas such as multiple-frequency slow-light devices, optical sensing, and active plasmonic switching.

Characteristics of multiple Fano resonances in waveguide-coupled surface plasmon resonance sensors based on waveguide theory

We observe and analyze multiple Fano resonances and the plasmon-induced transparency (PIT) arising from waveguidecoupled surface plasmon resonance in a metal-dielectric Kretschmann configuration. It is shown that the simulation results for designed structures agree well with those of the dispersion relation of waveguide theory. We demonstrate that the coupling between the surface plasmon polariton mode and multi-order planar waveguide modes leads to multiple Fano resonances and PIT. The obtained results show that the number of Fano resonances and the linewidth of resonances depend on two structural parameters, the Parylene C and SiO2 layers, respectively. For the sensing action of Fano resonance, the figure of merit for the sensitivity by intensity is estimated to be 44 times higher than that of conventional surface plasmon resonance sensors. Our research reveals the potential advantage of sensors with high sensitivity based on coupling between the SPP mode and multi-order PWG modes.

Tunable high-channel-count bandstop graphene plasmonic filters based on plasmon induced transparency

A high-channel-count bandstop graphene plasmonic filter based on ultracompact plasmonic structure is proposed in this paper. It consists of graphene waveguide side-coupled with a series of graphene filtering units. The study shows that the waveguide-resonator system performs a multiple plasmon induced transparency (PIT) phenomenon. By carefully adjusting the Fermi level of the filtering units, any two adjacent transmitted dips which belong to different PIT units can produce coherent coupling superposition enhancement. This property prevents the attenuation of the high-frequency transmission dips of multiple PIT and leads to an excellent bandstop filter with multiple channels. Specifically, the bandwidth and modulation depth of the filters can be flexibly adjusted by tuning the Fermi energy of the graphene waveguide. This ultracompact plasmonic structure contributes to the achievement of frequency division multiplexing systems for optical computing and communications in highly integrated optical circuits.

Dynamically controllable plasmon induced transparency based on hybrid metal-graphene metamaterials

Novel hybrid metal-graphene metamaterials featuring dynamically controllable single, double and multiple plasmon induced transparency (PIT) windows are numerically explored in the terahertz (THz) regime. The designed plasmonic metamaterials composed of a strip and a ring with graphene integration generate a novel PIT window. Once the ring is divided into pairs of asymmetrical arcs, double PIT windows both with the spectral contrast ratio 100% are obtained, where one originates from the destructive interference between bright-dark modes, and the other is based on the interaction of bright-bright modes. Just because the double PIT windows are induced by two different mechanisms, the continuously controllable conductivity and damping of graphene are employed to appropriately interpret the high tunability in double transparency peaks at the resonant frequency, respectively. Moreover, multiple PIT windows can be achieved by introducing an additional bright mode to form the other bright-bright modes coupling. At the PIT transparent windows, the dispersions undergo tremendous modifications and the group delays reach up to 43 ps, 22 ps, and 25 ps, correspondingly. Our results suggest the existence of strong interaction between the monolayer graphene layer and metal-based resonant plasmonic metamaterials, which may hold widely applications in filters, modulators, switching, sensors and optical buffers.