Plasmon-induced Transparency Effect Research Articles

Optimized graphene metamaterial for dual plasmon-induced transparency in terahertz band with multifunctional applications

Abstract This paper proposes a patterned graphene periodic metamaterial structure, optimized using an improved genetic algorithm to adjust the position and size of each graphene strip, thereby achieving dual plasmon-induced transparency (PIT) effects in the terahertz band, resulting in extraordinary multifunctionality. The finite difference time domain method is employed to obtain the transmission spectrum, and coupled mode theory is used for theoretical analysis and verification of the dual-PIT effect. The structure exhibits multifunctionality: when used as a photoelectric switch, it achieves a modulation depth of up to 99.04% with an insertion loss as low as 0.16 dB by tuning the Fermi level. Additionally, the structure demonstrates excellent sensing performance, with a maximum sensitivity and figure of merit reaching 0.84 THz/RIU and 88.55, respectively. Furthermore, the slow light performance of the structure is investigated, showing a group delay of up to 0.5 picoseconds.

Tunable plasmon-induced transparency in anisotropic graphene-black phosphorus photonic device for high-performance sensors and switchers

A novel photonic device composed of graphene and black phosphorus (G-BP) has been proposed, which achieves high-performance plasmon-induced transparency (PIT) effect within the THz range and maintains substantial tunability and anisotropy. The anisotropy of the PIT effect arises from the near-field coupling between two bright modes characterized by distinct effective electron masses of BP, resulting transparency window at 33.35 THz for TE polarization and at 26.92 THz for TM polarization. Through the modulation of Fermi energy in graphene, doping levels of BP and geometric parameters separately, a tunable transparency window is achieved. Notably, the convergence or divergence of the anisotropic transparency windows can be well manipulated with different BP doping levels. Furthermore, the proposed G-BP photonic device exhibits a high sensitivity to changes in the surrounding refractive index and substrates, with a maximum sensitivity of 12.04 THz/RI, rendering it suitable for sensor applications. Overall, the proposed photonic device exhibits notable PIT effects characterized by high anisotropic performance, substantial tunability, great sensitivity, and stability, making it a promising candidate for applications in sensors, polarizers, and switchers.

Tunable triple plasmon-induced transparency in E-type graphene metamaterials

Enhancing light-matter interaction is crucial for boosting the performance of nanophotonic devices, which can be achieved via plasmon-induced transparency (PIT). This study introduces what we believe to be a novel E-type metamaterial structure crafted from a single graphene layer. The structure, comprising a longitudinal graphene ribbon and three horizontal graphene strips, leverages destructive interference at terahertz frequencies to manifest triple plasmon-induced transparency (triple-PIT). Through a comparison of simulations using the finite difference time domain (FDTD) method and theoretical coupled-mode calculations, we elucidate the physical mechanism behind triple-PIT. Our analysis shows that the PIT effect arises from the interplay between two single-PITs phenomena, further explored through field distribution studies. Additionally, we investigate the impact of varying Fermi levels and carrier mobility on the transmission spectrum, achieving amplitude modulation in photoelectric switches of 85.5%, 99.2%, and 93.8% at a carrier mobility of 2 m2/(V·s). Moreover, we explore the relationship between Fermi levels and carrier mobility concerning the slow light effect, discovering a potential group index of up to 1021 for the structure. These insights underscore the significant potential of this graphene-based metamaterial structure in enhancing optical switches, modulators, and slow light devices.

All-optical multichannel switch and slow light based on dynamically tunable plasmon-induced transparency

The triple plasmon-induced transparency (PIT) effect based on a metal–insulator–metal waveguide structure comprising two groups of big and small disk resonators (BSDRs) is investigated theoretically and numerically. As a tool employed to explain the PIT, N-order coupled mode theory (CMT), is established, and the calculated results of the triple-PIT effect exhibit excellent consistency with finite-difference time-domain simulations. The influence of the separation between the small disk resonators on the triple-PIT response is discussed in detail through the dynamical equation. Further research shows that the central wavelengths of the triple-PIT transmission window can be adjusted with extremely low pump intensity and ultrafast optical response when monolayer graphene covers the surface of the BSDRs. Meaningfully, light traveling at resonant wavelengths can be effectively slowed down, with the highest group index reaching 368. Based on the PIT effect, a low-power and ultrafast switch is realized with a modulation amplitude of more than 93% at the corresponding wavelengths of the eight depressions. Thus, not only do the insights put forward new ideas, to the best of our knowledge, for highly tunable optoelectronic devices, but the results from the N-order CMT also offer new theory progress and references in the plasmonic waveguide structures.

Multi-channel switch and sensing applications based on multilayered annular graphene metamaterials at terahertz frequency

In this study, a novel silica-graphene–silica periodic graphene structure consisting of six graphene semi-rings is proposed. The structure is based on a three-layer graphene metamaterial with a semicircular ring that achieves a tunable double plasmon-induced transparency (PIT) effect. In the proposed structure, the double-PIT window can be switched simultaneously at multiple frequencies through the dynamic tunability of graphene. Besides, the sensitivities of the refractive index for the PIT windows are investigated with the maximum values of 1.42 THz RIU−1 and 1.09 THz RIU−1, respectively, indicating the structure’s performance as a terahertz sensor. Overall, it shows the potential of PIT effect in graphene metamaterials in controlling electromagnetic field responses. It has made positive contributions to the development of terahertz technology and related fields.

Multifunctional terahertz device based on plasmon-induced transparency

Enhancing light-matter interaction is crucial in optics for boosting nanophotonic device performance, which can be achieved via plasmon-induced transparency (PIT). In this study, a polarization-insensitive PIT effect at terahertz frequencies is achieved using a novel metasurface composed of a cross-shaped graphene structure surrounded by four graphene strips. The high symmetry of this metasurface ensures its insensitivity to changes in the polarization angle of incident light. The PIT effect, stemming from the coupling of graphene bright modes, was explored through finite difference time domain (FDTD) simulations and coupled mode theory (CMT) analysis. By tuning the Fermi level in graphene, we effectively modulated the PIT transparent window, achieving high-performance optical switching with a modulation depth (88.9% < MD < 98.0%) and insertion losses (0.17 dB < IL < 0.51 dB) at a carrier mobility of 2 m2/(V·s). Furthermore, the impact of graphene carrier mobility on the slow-light effect was examined, revealing that increasing the carrier mobility from 0.5 m2/(V·s) to 3 m2/(V·s) boosts the group index from 126 to 781. These findings highlight the potential for developing versatile terahertz devices, such as optical switches and slow-light apparatus.

High sensitivity terahertz biomedical sensing with graphene metamaterial

Identification of biomedical molecules by terahertz (THz) sensing is a quite promising noninvasive technique. Here, we present a THz graphene metamaterial with plasmon-induced transparency (PIT) for high sensitivity biosensing. The strong PIT effect is generated by the destructive interference between the plasmon modes excited by two graphene strips. For testing different biomedical analytes, a distinct frequency shift at PIT resonance can be observed due to the effect of surrounding refractive index variation. The metamaterial scheme for noninvasive biomedical sensing can achieve the sensitivity as high as 2.6 THz/RIU. Particular, it can not only detect the phase of red blood cell infected by malaria but also the concentration of ethanol aqueous solution. The underlying mechanism is discussed for understanding the THz sensing operation.

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.

Triple-band transparency effect by multiple couplings based on toroidal dipole resonance

We explored multiple couplings properties in composite metastructure. One part is the asymmetric double rings, supporting the narrow toroidal dipole resonance, and the other component is an upright rod that excites the broad electric dipole resonance. When these two resonant modes coincide in the spectrum, dual-band plasmon induced transparency (PIT) behavior can be obtained, which is attributed to in-phase and out-of-phase couplings between the toroidal dipole and electric dipole modes. Meanwhile, the dual-band features will become a single PIT band by varying the rotation offset angle between the upper- and lower-rings. Moreover, by introducing lateral displacement of the rod with respect to the toroidal component, a triple-band PIT effect can be achieved. In particular, under a large lateral displacement, a broadband transparency window appears across a wavelength range greater than 120 nm, where the transmission exceeds 0.9. It is derived from the hybrid coupling between toroidal dipole, electric dipole and induced high-order resonance modes. The toroidal-based PIT metamaterials not only promote the understanding of toroidal dipole moment but also provide a positive reference for toroidal-based meta-devices.

A 2-bit graphene encoder based on the plasmon-induced transparency effect and its sensing characteristics

A 2-bit encoder based on the plasmon-induced transparency (PIT) effect was proposed and investigated in the range from 2 to 7 THz. The Lorentz oscillation coupling model was utilized to confirm the simulation. By tuning the Fermi levels of cross1 and cross2, the 2-bit encoder was achieved. And the minimum MD was 94.73 %, the minimum ER was 12.77 dB, and the maximum IL was 0.32 dB. As a sensor, the structure had a sensitivity of up to 2.33 THz/RIU. In addition, due to the insensitivities to incidence angle and polarization angle, the encoder could be utilized to complex environments. Therefore, these results reveals that our work is significant in terahertz encoders, optical switches, sensors, slow light devices, and modulators.

Polarization-sensitive asynchronous switch and notable slow-light based on tunable triple plasmon-induced transparency effect

We have achieved a tunable triple plasmon-induced transparency (PIT) effect on a metasurface aligned with continuous graphene strips. We also introduce coupled mode theory (CMT) as an explanation of the triple-PIT, obtaining theoretical calculation data consistent with time-domain finite-difference method (FDTD) simulations. A five-frequency asynchronous switch is developed by exploiting the sensitivity of the PIT to polarized light, and the modulation depths at the five resonance frequencies can reach 85.5 %, 83.03 %, 84.7 %, 87.5 %, and 79.8 %, respectively. Notably, altering the length of certain bright modes within the structure, either increasing or decreasing the length, will lead to the degradation of the triple-PIT to a double-PIT. Furthermore, it is demonstrated that the structure exhibits outstanding slow-light performance, possessing a group refractive index above 1000. Our findings thus offer a theoretical foundation for further investigation into high-performance slow light devices as well as multi-frequency modulators operating at terahertz frequencies.

Double plasmon-induced transparency 3 bit graphene encoder

In this paper, a 3 bit encoder was proposed which was based on double plasmon-induced transparency (PIT) effect. This structure consists of the bright-bright mode and realizes a double PIT window in the 0.1–3 THz range. Electric field distributions reveal that the double PIT effect is originated from the strong destructive interference between three bright modes, the Lorentz oscillation coupling model is utilized to confirm the finite-integration time-domain (FITD) simulation regardless of the x-polarization direction or y-polarization direction. When the incident light is x-polarized, encoding frequencies were at 0.976 THz, 1.525 THz and 2.069 THz, respectively; while in y-polarization, encoding frequencies were at 1.579 THz, 1.935 THz and 2.589 THz, respectively. Results depict that the Modulation Depth (MD) could reach 98 % regardless of the x-polarization direction or the y-polarization direction. As an electro-optical switch, the maximum MD could reach ≥98 %, the minimum IL could reach 0.35 dB, the maximum ER could reach ≥14 dB. Besides the encoder, the proposed structure is of great importance for the design of optical switches, terahertz modulators and slow light devices.

A carbon nanotube metamaterial sensor showing slow light properties based on double plasmon-induced transparency.

In this study, we proposed a bifunctional sensor of high sensitivity and slow light based on carbon nanotubes (CNTs). An array of left semicircular ring (LSR), right semicircular ring (RSR), and circular ring (CR) resonators are utilized to form the proposed metamaterial. The proposed structure can achieve double plasmon-induced transparency (PIT) effects under the excitation of a TM-polarization wave. The double PIT originated from the destructive interference between two bright modes and a dark mode. A coupled harmonic oscillator model is used to describe the destructive interference between the two bright modes and a dark mode, and the simulation results agree well with the calculated results. Moreover, we investigate the influence of the coupling distance, period, and flare angle on the PIT spectra. The relationship between the resonant frequencies, full width at half maximum (FWHM), amplitudes, quality factors (Q), and the coupling distance is also studied. Finally, a high sensitivity of 1.02 THz RIU-1 is obtained, and the transmission performance can be maintained at a good level when the incident angle is less than 40°. Thus, the sensor can cope with situations where electromagnetic waves are not perpendicular to the structure's surface. The maximum figure of merit (FOM) can reach about 8.26 RIU-1; to verify the slow light property of the device, the slow light performance of the proposed structure is investigated, and a maximum time delay (TD) of 22.26 ps is obtained. The proposed CNT-based metamaterial can be used in electromagnetically induced transparency applications, such as sensors, optical memory devices, and flexible terahertz functional devices.

Terahertz sensor based on plasmon-induced transparency in a carbon nanotube metamaterial

In this paper, the plasmon-induced transparency (PIT) effect based on a carbon nanotube (CNT) resonator structure is achieved. An array of two split ring resonators (SRRs) and a cut wire (CW) resonator are utilized to form the proposed metamaterial. A PIT transparency window is achieved under a TM polarization terahertz light. Results show that the PIT effect is originated from the near-field coupled of the bright mode and dark mode. A coupled harmonic oscillator model is used to describe the near-field coupling between the bright mode and subradiant mode, and the results agree well with the FDTD simulation. The effect of geometrical sizes, like structure period, the radius and the splitting degree of the split ring resonator, the length of the cut wire resonator, and the coupling distance on the PIT window is analyzed in detail. Besides, the sensing and slow light performance of the proposed CNT metamaterial are studied, a maximum sensitivity of 0.74 THz RIU, and a time delay of 0.54 ps are obtained. Therefore, the proposed CNT-based device can be applied to the PIT effect, near-infrared modulators, slow light devices, sensors, and other fields.

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.

Multifunctional terahertz device with active switching between bimodal perfect absorption and plasmon-induced transparency

In this paper, we propose a terahertz (THz) micronano device that can actively switch between bimodal absorption and plasmon-induced transparency (PIT). The device mainly consists of a continuous top layer of graphene, an intermediate layer of silica and a bottom layer of vanadium dioxide, and has a simple structure, easy tuning and wide angle absorption. Through impedance matching and electromagnetic field distribution, we explain the generation of perfect absorption with double peaks. The simulation and multiple reflection interference theory (MRIT) show that the device achieves perfect absorption at 3.02 THz and 3.68 THz, and is highly sensitive to environmental refractive index, with a sensitivity of 1.1 THz/RIU. In addition, when the PIT effect is realized through the phase change characteristic of VO2, the device not only has the function of three-frequency asynchronous optical switch, but also has a strong slow light effect, and the maximum group delay (τg) is 35.4 ps. Thus, our design allows simultaneous switching, modulation, sensing, and slow light functions in the optical path and will greatly facilitate the development of THz multifunctional devices.

An efficient biosensor based on plasmon-induced transparency effect in plasmonic-graphene-black phosphorous absorber for diabetes diagnosis

In this work, an efficient absorber (biosensor) based on the combinations of graphene – plasmonic - black phosphorous configurations is proposed and investigated. The presented absorber is considered to operate based on the plasmon-induced transparency (PIT) effect. The presented absorber is based on various layers of graphene, phosphorene and gold in the ring and plate shapes. In the bio-sensing application, the analyte would be inserted in the upper layer while being in contact with the incident light wave. By considering the PIT effect, the absorber would be further improved (improving the absorption's peak value). In order to fulfill the improvement, effects of structural parameters (R1, R2, R3, R4, h1, h2, h3) and chemical potential(Ef) would be investigated. After the improvement process, the structure would be utilized as a biosensor for detection the Glucose concentrations in blood samples. By detecting Glucose concentrations in blood samples, physicians can diagnose diabetes in early stages. Finally, the sensitivity factor, figure of merit (FOM), full width at half maximum (FWHM) and Q-Factor of 2686.5 nm/RIU, 134.325 RIU−1, 20 nm and (58.5–76.5) would be achieved, respectively. As a result, the proposed absorber (biosensor) can be a remarkable and great candidate for bio-sensing applications in optical integrated circuits.

Multi-frequency polarization and electro-optical modulator based on triple plasmon- induced transparency in monolayer graphene metamaterials

In this paper, a dynamically tunable triple plasmon-induced transparency (PIT) is numerically investigated in a simple monolayer graphene- patterned structure. The structure is composed of five graphene strips and a silicon substrate. Electric field distributions show that the triple PIT effect is originated from the strong destructive interference between three bright modes and one dark mode, coupled mode theory (CMT) is utilized to confirm the finite-difference-time-domain (FDTD) simulation. Results show the maximum figure of merit (FOM) and sensitivity can reach 15.88 and 0.91 THz/RIU. A on-to-off electro-optical modulator is realized by tuning the Fermi levels of the graphene, the modulation degrees of amplitude are 79.3 %, 87.1 %, 70.5 %, 79.2 %, and 84.3 %, corresponding to 2.35 terahertz (THz), 3.12THz, 3.58 THz, 3.91THz, and 4.31 THz, respectively. In addition, the effect of polarized angle on the transmission spectra was studied in detail. A multi-frequency polarization modulator can also be realized with modulation degrees of amplitude (MDA) of 77.6 %, 85.9 %, and 93.7 % at 2.09 THz, 2.82 THz, and 3.59 THz, respectively, and the corresponding polarization extinction ratio (PER) are 6.5 dB, 8.5 dB, and 12.1 dB, respectively. Therefore, the results of the paper are significant to the design of multi-frequency, terahertz sensors, slow light, and modulators.

Dynamically Adjusting Borophene-Based Plasmon-Induced Transparency in a Polymer-Separated Hybrid System for Broadband-Tunable Sensing.

Borophene, an emerging two-dimensional (2D) material platform, is capable of supporting highly confined plasmonic modes in the visible and near-infrared wavebands. This provides a novel building block for light manipulation at the deep subwavelength scale, thus making it well-suited for designing ultracompact optical devices. Here, we theoretically explore a borophene-based plasmonic hybrid system comprising a continuous borophene monolayer (CBM) and sodium nanostrip gratings (SNGs), separated by a polymer spacer layer. In such a structure, a dynamically tunable plasmon-induced transparency (PIT) effect can be achieved by strongly coupling dark and bright plasmonic modes, while actively controlling borophene. Here, the bright mode is generated through the localized plasmon resonance of SNGs when directly excited by TM-polarized incident light. Meanwhile, the dark mode corresponds to a propagating borophene surface plasmon (BSP) mode in the CBM waveguide, which cannot be directly excited, but requires phase matching with the assistance of SNGs. The thickness of the polymer layer has a significant impact on the coupling strength of the two modes. Owing to the BSP mode, highly sensitive to variations in the ambient refractive index (RI), this borophene-based hybrid system exhibits a good RI-sensing performance (643.8 nm/RIU) associated with a wide range of dynamically adjustable wavebands (1420-2150 nm) by tuning the electron density of borophene. This work offers a novel concept for designing active plasmonic sensors dependent on electrically gating borophene, which has promising applications in next-generation point-of-care (PoC) biomedical diagnostic techniques.

Tunable terahertz double plasmon induced-transparency based on monolayer patterned graphene structure

In this paper, tunable double plasmon-induced transparency (PIT) is achieved in a monolayer-patterned graphene structure. The proposed structure is composed of a middle graphene-strip and two π-shape graphene microstructures. Results show that the double PIT effect is originated from the destructive interference between two bright modes and one dark mode, a equivalent coupled mode theory (CMT) model is utilized to confirm the finite-difference-time-domain (FDTD) simulation. The influences of the chemical potential, scattering rate, and geometrical size on the double PIT transmission spectrum are investigated. The modulation properties of the proposed structure have been studied in detail and it shows excellent modulation depth (MD) and relatively low insertion loss (IL). Moreover, the proposed structure shows a maximum refractive index sensitivity about2.38THz/RIU, and the maximum figure of merit (FOM) can reach 43.4. The effect of the refractive index of the substrate on the sensing performance is also investigated. Thus, the proposed structure can be applied in the areas of multi-function optical switches, terahertz slow light devices, modulators, and sensors.