Plasmon-induced Transparency Phenomenon Research Articles

Symmetry-Engineered Dual Plasmon-Induced Transparency via Triple Bright Modes in Graphene Metasurfaces

Dynamical manipulation of plasmon-induced transparency (PIT) in graphene metasurfaces is promising for optoelectronic devices such as optical switching and modulating; however, previous design approaches are limited within one or two bright/dark modes, and the realization of dual PIT windows through triple bright modes in graphene metasurfaces is seldom mentioned. Here, we demonstrate that dual PIT can be realized through a symmetry-engineered graphene metasurface, which consists of the graphene central cross (GCC) and graphene rectangular ring (GRR) arrays. The GCC supports a bright mode from electric dipole (ED), the GRR supports two nondegenerate bright modes from ED and electric quadrupole (EQ) due to the C2v symmetry breaking, and the resonant coupling of these three bright modes induces the dual PIT windows. A triple coupled-oscillator model (TCM) is proposed to evaluate the transmission performances of the dual PIT phenomenon, and the results are in good agreement with the finite-difference time-domain (FDTD) method. In addition, the dual PIT windows are robust to the variation of the structural parameters of the graphene metasurface except for the y-directioned length of the GRR. By changing the carrier mobility of graphene, the amplitudes of the two PIT windows can be effectively tuned. The alteration of the Fermi level of graphene enables the dynamic modulation of the dual PIT with good performances for both modulation degree (MD) and insertion loss (IL).

Terahertz refractive index sensor based on dual plasmon-induced transparency in a graphene metasurface

A novel graphene metasurface is proposed in this article, which is simulated by the finite difference time domain (FDTD) and found to exhibit a significant dual Plasmon-induced transparency (PIT) phenomenon in the terahertz frequency band. For further research, new transmission spectra are simulated using the coupled mode theory (CMT), and after comparison, it is found that the images were basically consistent and had a high degree of agreement. In addition, through observation and analysis of the PIT window, it is found that the PIT phenomenon can be effectively tuned by adjusting the Fermi level. Finally, the metasurface is proposed in this article, which has excellent sensing properties. After calculation and comparison of different refractive indices of surrounding media, it is found that the maximum sensitivity can reach 1.567 THz RIU−1 at a frequency of f = 4.8716 THz, with a figure of merit (FOM) of 23.855. Compared with other sensors of the same type, the sensor in this paper has great advantages. In summary, the graphene metasurface proposed in this article provides more theoretical support for manufacturing dynamically adjustable graphene sensors.

Hybrid inverse design scheme for nanophotonic devices based on encoder-aided unsupervised and supervised learning.

Machine learning methods have been regarded as practical tools for the inverse design of nanophotonic devices. However, for the devices with complex expected targets, such as the spectrum with multiple peaks and valleys, there are still many sufferings remaining for these data-driven approaches, such as overfitting. To resolve it, we firstly propose a hybrid inverse design scheme combining supervised and unsupervised learning. Compared with the previous inverse design schemes based on artificial neural networks (ANNs), clustering algorithms and an encoder model are introduced for data preprocessing. A typical metamaterial composed of multiple metal strips that can produce tunable dual plasmon-induced transparency phenomena is designed to verify the performance of our proposed hybrid scheme. Compared with the ANNs directly trained by the entire dataset, the loss functions (mean squared error) of the ANNs in our hybrid scheme can be effectively reduced by more than 51% for both training and test datasets under the same training conditions. Our hybrid scheme paves an efficient improvement for the inverse design tasks with complex targets.

Dual band symmetry-protected terahertz bound states in the continuum inside the spoof localized surface plasmon induced-transparency windows

A new phenomenon of dual band symmetry-protected bound state in the continuum (BIC) is revealed inside the plasmon-induced transparency (PIT) windows. A metasurface of circular periodically grooved cavity integrated with a complimentary symmetric double-gap split-ring resonator (DSRR) is employed. Intrinsic spoof localized surface plasmon (SLSP) interferes destructively with dipole oscillation of DSRR. A PIT phenomenon is generated between the two bright side-modes (ν 1 = 0.49 THz, ν 2 = 0.79 THz) when the metasurface is in C 2v symmetry. The displacement of upper-gap (while keeping the lower gap fixed) of DSRR results in three dark modes inside the frequency range of induced transparency windows, two of which are quasi-BIC. At a relatively low degree of asymmetry, one anapole dark mode ν 3 = 0.55 THz dominate quasi-BIC I and another magnetic dipole coupled quadrupole dark mode ν 4 = 0.75 THz dominates quasi-BIC II. At a relatively larger degree of asymmetry, one more dark mode ν 5 = 0.75 THz occurs in the frequency spectra as is a tilted SLSP intrinsic mode. Since the dark mode ν 5 is not sensitive to the asymmetric displacement of DRSS. A coupled five oscillators’ model reveal that coupling strength with free space and the damping ratios are attributed to the asymmetry of the structure. The leaky channels of both BICs have a much lower damping ratio than the bright side-mode of PIT. The coupling coefficients indicate that quasi-BIC I is affiliated to the lower frequency bright side-mode ν 1, and quasi-BIC II is affiliated to the higher frequency bright side-mode ν 2. The measured Q factors fit well with the relation function of geometric asymmetry, among which the maximum Q factor measured of the quasi-BIC-II exceeds 20. The realization of above results paves a new way to achieve dual band terahertz quasi-BIC by tuning SLSP-induced transparency window. This provides a feasible solution for the design of multi-band terahertz thin-film sensors.

Optical Refractive Index Sensors Based on Plasmon-Induced Transparency phenomenon in a Plasmonic Waveguide Coupled to Stub and Nano-disk Resonators

Optical Refractive Index Sensors Based on Plasmon-Induced Transparency phenomenon in a Plasmonic Waveguide Coupled to Stub and Nano-disk Resonators

Plasmon-Induced Transparency for Tunable Atom Trapping in a Chiral Metamaterial Structure.

Plasmon-induced transparency (PIT), usually observed in plasmonic metamaterial structure, remains an attractive topic for research due to its unique optical properties. However, there is almost no research on using the interaction of plasmonic metamaterial and high refractive index dielectric to realize PIT. Here, we report a novel nanophotonics system that makes it possible to realize PIT based on guided-mode resonance and numerically demonstrate its transmission and reflection characteristics by finite element method simulations. The system is composed of a high refractive-index dielectric material and a two-dimensional metallic photonic crystal with 4-fold asymmetric holes. The interaction mechanism of the proposed structure is analyzed by the coupled-mode theory, and the effects of the parameters on PIT are investigated in detail. In addition, we first consider this PIT phenomenon of such fields on atom trapping (87Rb), and the results show that a stable 3D atom trapping with a tunable range of position of about ~17 nm is achieved. Our work provides a novel, efficient way to realize PIT, and it further broadens the application of plasmonic metamaterial systems.

Tunable dual plasmon-induced transparency and slow-light analysis based on monolayer patterned graphene metamaterial

We propose a novel terahertz metamaterial structure based on patterned monolayer graphene. This structure produces an evident dual plasmon-induced transparency (PIT) phenomenon due to destructive interference between bright and dark modes. Since the Fermi level of graphene can be adjusted by an external bias voltage, the PIT phenomenon can be tuned by adjusting the voltage. Then the coupled-mode theory (CMT) is introduced to explore the internal mechanism of the PIT. After that, we investigate the variation of absorption rate at different graphene carrier mobilities, and it shows that the absorption rate of this structure can reach 50%, which is a guideline for the realization of graphene terahertz absorption devices. In addition, through the study of the slow-light performance for this structure, it is found that its group index is as high as 928, which provides a specific theoretical basis for the study of graphene slow-light devices.

Dynamically tunable plasmon-induced transparency effect based on graphene metasurfaces

Plasmon-induced transparency (PIT) is theoretically explored for a graphene metamaterial using finite-difference time-domain numerical simulations and coupled-mode-theory theoretical analysis. In this work, the proposed structure consists of one rectangular cavity and three strips to generate the PIT phenomenon. The PIT window can be regulated dynamically by adjusting the Fermi level of the graphene. Importantly, the modulation depth of the amplitude can reach 90.4%. The refractive index sensitivity of the PIT window is also investigated, and the simulation results show that a sensitivity of 1.335 THz RIU−1 is achieved. Additionally, when the polarization angle of the incident light is changed gradually from 0° to 90°, the performance of the structure is greatly affected. Finally, the proposed structure is particularly enlightening for the design of dynamically tuned terahertz devices.

Dynamical manipulation of a dual-polarization plasmon-induced transparency employing an anisotropic graphene-black phosphorus heterostructure.

Dynamical tunable plasmon-induced transparency (PIT) possesses the unique characteristics of controlling light propagation states, which promises numerous potential applications in efficient optical signal processing chips and nonlinear optical devices. However, previously reported configurations are sensitive to polarization and can merely operate under specific single polarization. In this work we propose an anisotropic PIT metamaterial device based on a graphene-black phosphorus (G-BP) heterostructure to realize a dual-polarization tunable PIT effect. The destructive interference coupling between the bright mode and dark modes under the orthogonal polarization state pronounced anisotropic PIT phenomenon. The coupling strength of the PIT system can be modulated by dynamically manipulating the Fermi energy of the graphene via the external electric field voltage. Moreover, the three-level plasmonic system and the coupled oscillator model are employed to explain the underlying mechanism of the PIT effect, and the analytical results show good consistency with the numerical calculations. Compared to the single-polarization PIT devices, the proposed device offers additional degrees of freedom in realizing universal tunable functionalities, which could significantly promote the development of next-generation integrated optical processing chips, optical modulation and slow light devices.

A Tunable Slow Light Device with Multiple Channels Based on Plasmon-Induced Transparency

Slow light devices with buffering capability play a critical role in all-optical signal processing. In this paper, multiple slow light phenomena are implemented based on plasmon-induced transparency (PIT) in our device. The device mainly consists of dual tooth cavities coupled with stub resonators, respectively. Temporal coupled-mode theory model illustrates that the triple PIT phenomena can be achieved based on different formation mechanisms. The simulation results calculated by the finite-difference time-domain method reveal that significant slow light response occurs at two wavelength regions. In addition, the parameters of structure have an important influence on PIT response and slow light characteristics. Moreover, the separate manipulation of wavelength, transmission and group index at transparency peak can be achieved in different slow light channels by adjusting the structural parameters. This plasmonic device is of great significance for the design of optical networks on chips.

Applications of chip-scale semiconductor metamaterials based on plasmon-induced transparency in modulation and sensing

We propose and simulate the tunable plasmon-induced transparency (PIT) phenomenon of semiconductor-based H-shaped chip-scale metamaterials. Numerical analysis shows that the PIT phenomenon is caused by the destructive interference between two bright modes, and the equivalent Lorentz model also proves its physical mechanism appropriately. In addition, in practical applications, changing the polarization angle can adjust the group delay, and the maximum group delay is 41.92 ps; changing the temperature can adjust the transmission peak frequency of the PIT effect, which can be applied to temperature sensing and thermo-optic switches. The amplitude modulation depth can reach 97.8%. The application of this chip-scale semiconductor metamaterial in modulators and sensors opens up new ways.

Active control of plasmon-induced transparency with large tunability and high Q-factor in graphene-black phosphorus hybrid system

Plasmon-induced transparency phenomena in the mid-infrared caused by the coupling behavior between dipole (bright element) and higher-order modes (dark element) in graphene as well as black phosphorus (BP) nanoribbons are investigated. The transparent windows can be adjusted flexibly by varying the carrier concentration of graphene and BP. It is also shown that the carrier mobility and refractive index of the substrate are the key factors affecting destructive interference. Obvious group delays are obtained near the transparent windows so that the slow light effect can be achieved. Our results allow a better understanding of efficient exploration of surface plasmons with integrated properties of building blocks from a family of two-dimensional materials, with the aim of expanding both photonic bands and functionalities.

Dynamically adjustable plasmon-induced transparency and switching application based on bilayer graphene metamaterials

A bilayer metamaterial composed of double graphene strips and square-ring graphene is proposed to realize plasmon induced transparency (PIT). The couple mode theory (CMT) is employed to explain the phenomenon of PIT, whose results are in good agreement with the simulation of the finite-difference time-domain. The dynamically adjustable PIT is investigated, where an on-to-off modulation composed of synchronous and asynchronous switching is realized by modulating the Fermi levels of graphene, the modulation degrees of amplitude are 67.5%, 86.1%, and 65.3%, respectively. The changes of transmission spectra are also studied by adjusting the coupling distance between double graphene strips and square-ring graphene, and the result shows that PIT is gradually disappeared with the increase of coupling distance and the decrease of coupling strength. Then, the corresponding relationships between dips of PIT and modes of CMT are described clearly, which are affected by the relative location between resonant points of the bright and dark modes.

Tunable slow light effect based on dual plasmon induced transparency in terahertz planar patterned graphene structure

We have studied a simple novel graphene ribbon structure. A very excellent and prominent dual graphene plasmon induced transparency phenomenon could be achieved by the destructive interference resulted from the excited plasmonic modes in terahertz band. Using the simple relationship between graphene and applied voltage, a good tunable effect of this structure can be achieved. The transmission of this proposed structure is theoretically investigated by using the equivalent resonator coupled mode method. The theoretical data from our proposed method are in good agreement with the numerical simulation results. Moreover, utilizing the high dispersion property, we have also researched the slow light effect for this proposed system. The results of theoretical research have indicated that the group refractive index of our proposed structure can maintain an excellent numerical value. This investigation can play a significant role in the tunable graphene-based slow light devices.

Investigation of plasmon-induced transparency and reflection in patterned graphene metamaterial

Plasmon-induced transparency (PIT) and plasmon-induced reflectance (PIR) are explored in a patterned graphene metamaterial using finite-difference time-domain numerical simulations and coupled-mode-theory calculations, and both PIT and PIR phenomena can be tailored dynamically by adjusting the Fermi level of graphene. Surprisingly, the group index of the proposed structure can be increased abruptly to 630, indicating ultraslow light can be achieved. Furthermore, the reflectance of the PIR can reach 70%. Therefore, the proposed structure provides a solid foundation for the realization of excellent slow-light devices, reflectors, and modulators.

Improving the performance of nanostructure multifunctional graphene plasmonic logic gates utilizing coupled-mode theory

Nanostructure ring resonators are suitable devices for photonic integrated circuits. A nano-scale multifunctional logic device based on plasmon-induced transparency (PIT) is presented here. This device consists of a pair of hexagonal ring resonators coupled with two parallel metal–insulator–metal (MIM) waveguides. According to the coupled-mode theory, the appropriate detuning between the resonances wavelengths of two resonators acts as the key factor to achieve the PIT phenomenon. For this purpose, the PIT phenomenon for several metals utilized in MIM waveguides is studied. Also, graphene has been employed as the replacement for the metal under the hexagonal ring resonator and its parallel waveguides. However, the interaction of light with graphene as a 2D material is weak, by varying the dimensions of waveguides, rings, and their distances, and also, incident light wavelength and graphene chemical potential, we have achieved the desired couplings in the structure. Finite-difference-time-domain (FDTD) simulations confirm that “1” and “0” logic states which represent the high and low levels of the optical power can be achieved at the through and drop ports by changing the refractive index. It has been demonstrated that the proposed structure implements the function of logical operations including XOR and XNOR, simultaneously.

Demonstration of group delay above 40 ps at terahertz plasmon-induced transparency windows.

Herein, we demonstrate one of the highest terahertz group delay of 42.4 ps achieved experimentally at 0.23 THz, on a flexible planar metamaterial. The unit cell of metasurface is made up of a textured closed cavity and another experimentally concentric metallic arc. By tuning the central angle of the metallic arc, its intrinsic dipolar mode is in destructive interference with the spoof localized surface plasmon (SLSP) on textured closed cavity, which results in a plasmon-induced transparency phenomenon. The measured transmittances of as-fabricated samples using terahertz-time domain spectroscopy validate numerical results using extended coupled Lorentz oscillator model. It is found that the coupling coefficient and damping ratio of SLSP relies on the radius of the ring structure of textured closed cavity. As a consequence, the slow light maximum values become manoeuverable in strength at certain frequencies of induced transparency windows. To the best of our knowledge, our experimental result is currently the highest value demonstrated so far within metasurface at terahertz band.

Slow light effect based on tunable plasmon-induced transparency of monolayer black phosphorus

Black phosphorus (BP) is a novel plasmonic materials at the infrared and terahertz regions. We have theoretically investigated the anisotropic of in-plane monolayer BP in terms of conductivity. We have designed a periodic structure for a special shape and achieved an obvious plasmon-induced transparency phenomenon. The results of finite difference time domain simulation and coupled mode theory are in consistent good agreement. It is found that the bandwidth of plasmon-induced transparency phenomenon window can be effectively adjusted by changing the shape of the BP structure. Since the structure of the monolayer BP is completely continuous, it is easy to change the carrier density to adjust its resonance intensity and resonance frequency, which basically ensures the tunability of the plasmon-induced transparency phenomenon. This structure has an excellent slow light effect, and the maximum group index of this structure is 112. This research may open new doors for the application of monolayer BP in transmission modulation, especially for the modulation of slow light device.

Dual dynamically tunable plasmon-induced transparency in H-type-graphene-based slow-light metamaterial.

An H-type-graphene-based slow-light metamaterial is proposed to produce a dual plasmon-induced transparency phenomenon, which can be effectively modulated by Fermi level, carrier mobility of graphene, and the medium environment. The data calculated by coupled mode theory and results of numerical simulation show prominent agreement. In addition, both the simplicity and continuity of the units of graphene-based metamaterial are extraordinary advantages. Furthermore, the slow-light characteristics of the proposed structure show that the group refractive index is as high as 237, which is more competitive than some other slow-light devices.

Dynamically tunable dual plasmon-induced transparency and absorption based on a single-layer patterned graphene metamaterial.

Dual plasmon-induced transparency (PIT) and plasmon-induced absorption (PIA) are simultaneously achieved in an integrated metamaterial composed of single layer of graphene. Electric field distribution and coupled mode theory (CMT) are used to demonstrate the physical mechanism of dual PIT and PIA, and the theoretical result of CMT is highly consistent with the finite-difference time-domain (FDTD) method simulation result. Further research shows that both the dual PIT and PIA phenomenon can be effectively modulated by the Fermi level, the carrier mobility of the graphene and the refractive index of the surrounding environment. It is meaningful that the absorption of the dual PIA spectrum can be abruptly increased to 93.5% when the carrier mobility of graphene is 0.8m2/Vs. In addition, the group index can be as high as 328. Thus, our work can pave new way for developing excellent slow-light and light absorption functional devices.