Graphene Metasurface Research Articles

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.

Inverse design of twisted bilayer graphene metasurface for terahertz absorption broadening based on artificial neural network

With the development of terahertz (THz) technology, achieving ultra-wideband absorption of THz waves has become a significant challenge that researchers are striving to address. Different from the complex stacking of multiple graphene layers in the traditional design, inspired by the twisted magic angle of graphene structures, a twisted bilayer graphene metasurface absorber (TBGMA) is innovatively investigated for THz wave absorption broadening inverse design based on artificial neural network (ANN). Compared with the traditional manual parameter tuning, the ANN-based inverse design method can quickly accomplish the selection of the structural parameters and twist angles of the TBGMA, realizing the ultra-wideband absorption of THz waves (6.046 THz). The relationship between twisted SGLs and broadened effective absorption bandwidths is thoroughly analyzed through a combination of the electric field distribution and effective medium theory (EMT). Additionally, the tunability and absorption spectra of TBGMA under different incidence conditions have been discussed. The study of the twisted angle of SGLs can provide a unique idea for expanding the absorption bandwidth, and the inverse design of structural and angle parameters in conjunction with ANN is expected to be extended to the design of other precision structures in nanophotonics.

Tunable broadband terahertz graphene metasurface for complex-amplitude vortex beam generator and hologram

The independent controls of phase and amplitude, known as complex-amplitude modulation, play a crucial role for modulating the electromagnetic wavefronts. In this paper, a tunable broadband terahertz (THz) graphene metasurface with complex-amplitude modulation is proposed. A novel hybrid modulation mechanism that combines the absorption, polarization conversion, and Pancharatnam–Berry (PB) phase is employed to achieve a wide complex-amplitude modulation range over a broad frequency band. In addition, the metasurface can be dynamically tuned from the electrically tunable nature of the graphene in the THz range. To reveal the tunability characteristics of the metasurface as the graphene chemical potential varies, we study the Kubo formula of the graphene conductivity model and combine it with the equivalent circuit model. Two THz graphene meta-devices are designed for complex-amplitude vortex beam generator and hologram. By varying the graphene chemical potentials of 0 and 1 eV as the ON and OFF states, a THz quad-vortex-beam generator with switchable modes is designed and verified. We also demonstrate a THz hologram with complex-amplitude modulation by adjusting the chemical potential, exhibiting low imaging noise and high image quality. The proposed method is promised to be applied to the design of more complex-amplitude THz graphene meta-devices.

Metasurface computing components that support dual channel parallel processing and provide full type logic gate options

The logic gate components based on electromagnetic waves are crucial for building a digital computing platform with batch computing and low-cost energy consumption requirements. However, most of the reported logic gates have only one computational channel and have a single function. In order to improve the channel capacity and versatility of logic gates, we design a simple and compact graphene metasurface for dual channel parallel computing, with each channel's function being switchable across all types of logic functions. In the design, we combine the advantages of reconfigurable metasurfaces and polarization sensitive metasurfaces. Based on the polarization sensitive characteristics, we integrate two polarization logic gates into a single device. These two polarization logic gates can work simultaneously, and the crosstalk between them is 0. Based on the reconfigurable feature, the functions of both logic gates can be freely selected from NOT, AND, NAND, OR, NOR, XOR and XNOR. So, this component can achieve simultaneous operation of any two logical functions, and there are 49 combinations available. Our design philosophy provides inspiration for achieving ultra fast and high-density integrated signal processing.

Particles Transport and Sorting Based on Light Field Regulation in Tunable Graphene Metasurface

Particles Transport and Sorting Based on Light Field Regulation in Tunable Graphene Metasurface

Dual-tunable and high-efficiency multifunctional terahertz device based on black phosphorus and graphene metasurface

This paper proposes a dual-tunable and high-efficiency terahertz (THz) device based on black phosphorus (BP) and graphene metasurface with four functions, including broadband absorption, narrowband absorption, linear dichroism (LD) and electromagnetically induced transparency (EIT). Dynamic tunability is achieved by adjusting the carrier density of BP, the chemical potential of graphene and the conductivity of vanadium dioxide (VO2). When VO2 is in the metallic state, the device can work as a broadband absorber in the range of 1.18–3.49 THz with absorption rate above 90% and the relative bandwidth of 98.9%. The device also has a narrowband absorption function with an absorption rate of 99.9% at 4.19 THz. Additionally, the device can achieve LD function at frequencies of 4.6 THz and 3.81 THz, with peak LD values of 0.95 and −0.90, respectively. When VO2 is in the insulating state, the device shows an EIT function with a highly transparent window at 4.68 THz. It is worth noting that all functions are switchable and the operating frequencies are adjustable. The dual-tunable multifunctional device may have great potential in miniaturized THz systems.

Dual-Band All-Optical Logic Gates by Coherent Absorption in an Amorphous Silicon Graphene Metasurface.

The dual-band polarization-independent all-optical logic gate by coherent absorption effect in an amorphous silicon (a-Si) graphene metasurface is investigated theoretically and numerically. Taking the substrate effect into consideration, the coherent perfect absorption condition of the a-Si graphene metasurface is derived on the basis of the Cartesian multipole method. The coherent nearly perfect absorption of the a-Si graphene metasurface is realized by the interference of multipole moments and the interband transition of monolayer graphene, achieving peak values of 91% and 92% at 894.5 nm and 991.5 nm, respectively. The polarization independence of the coherent absorption is revealed due to the center symmetry of the structure of the a-Si graphene metasurface. The dual-band polarization-independent all-optical XOR and OR logic gates are implemented at 894.5 nm and 991.5 nm by the a-Si graphene metasurface based on the coherent nearly perfect absorption, which has the opportunity to be utilized in all-optical computing, all-optical data processing, and future all-optical networks.

Polarization-insensitive, frequency- and amplitude-tunable transparent microwave absorber based on graphene metasurface

Transparent and flexible metamaterial absorbers can provide solutions for electromagnetic compatibility and electromagnetic radiation pollution. They also play key roles in platforms with optical windows that require low detectability and immunity to electromagnetic interference. Due to the lack of active adaptability to complex electromagnetic environments, early metamaterial absorbers need to be redesigned and manufactured once the application scenarios change. The new two-dimensional material graphene provides a practical technical approach for the realization of transparent tunable absorbers. In this work, we propose a polarization-insensitive dual-tunable microwave absorber based on graphene metasurface. By controlling two separate bias voltages applied to patterned graphene or continuous graphene, independent dynamic regulation of electromagnetic wave absorption frequency and amplitude is achieved. It also possesses the features of optical transparency and flexibility. The measurement results show that the absorption frequency can be shifted from 9.8 to 11.3 GHz, the peak absorption rate at each absorption frequency remains above 99.6%, and the reflection amplitude modulation can be achieved simultaneously at each absorption frequency. The proposed absorber integrates multiple modulation functions for electromagnetic waves, and the overall structure is optically transparent and flexible. Therefore, it can contribute to many practical wave absorbing applications.

Quasi-bound state in the continuum based strong light confinement in graphene metasurfaces

The bound state in the continuum (BIC) is exploited to metasurfaces for the purpose of arising strong confinement of light and high quality (Q) factor resonances. In this paper, a BIC symmetry-protected metasurface consisting of rectangular graphene patches is synthesized and realistically modeled with intrinsic losses in a far-infrared regime. The quasi-BIC with three asymmetry approaches is applied to attain strong tailored confinement of the incident light, and the resulting resonances with tailored line widths and selective confinement of light are exhibited. Asymmetry parameters of length, rotation, and material feature of chemical potential regulate dual specifications of resonance linewidth and intensity. Efficiency analysis of the results illustrates that rotation asymmetry is the foremost among the three suggested methods, and it establishes the highest Q-factor of 945 with an achievable asymmetry parameter of 5.5%. The high Q and tunable resonances realized in the graphene quasi-BIC metasurfaces promise various practical applications in the infrared spectra, such as narrow band filters, sensors, optical switches, and light-matter interaction platforms.

Dual-band perfect absorption graphene metasurface with high modulation in near-infrared

Graphene has garnered significant attention in tunable metasurfaces due to its unique optical properties. The absorption of the graphene metassurface can be dynamically adjusted by manipulating the chemical potential. However, the working wavelengths of most graphene metasurfaces are limited in terahertz and mid-infrared, or have a low reflection range. In this paper, we design a hybrid graphene metasurface with a slot structure. The working wavelengths are optimized to 1550 nm and 1910 nm. Additionally, the slot structure greatly enhances the field intensity near the monolayer graphene to improve its interaction with light. As a result, perfect absorption is achieved at both working wavelengths, along with a maximum reflection range of 0.9 and a modulation depth of 99%.

Analytical modeling of terahertz graphene metasurfaces

Control over the optical response of graphene metasurfaces enables many promising applications in terahertz devices, including beam filters, polarizers, and absorbers. In this paper, we provide an analytical theory that enables us to use equivalent circuit models to simulate these responses. Closed-form expressions are provided for their associated scattering spectra, including an infinity of parallel R-L-C circuits for each metasurface of arbitrary morphology. These models’ accuracy is verified by comparing their results with those that are derived from full-wave simulations. Moreover, applications of these models are presented to anticipate both tunable optical response in interacting graphene disks and refractive index sensing via the response of graphene squares to ambient media. These models open up a new way of controlling the structure’s performance and refining it to meet our application-specific requirements.

Tunable quintuple plasmon-induced transparency and the effect of symmetry breaking based on monolayer graphene split rings metasurface

A monolayer graphene metasurface composed of two large graphene split rings (TLGSRs) and two small graphene split rings (TSGSRs) is designed and proposed to achieve a tunable quintuple plasmon-induced transparency (QPIT) by coupled mode theory (CMT) and finite-difference time-domain (FDTD) simulations. We successfully realized and designed quintuple-frequency asynchronous, sextuple-frequency asynchronous, and sextuple-frequency synchronous photoelectric switches by dynamically adjusting the Fermi energy levels of graphene. The switches exhibit remarkable performance characteristics, including amplitude modulation degree (AMD) ranging from 71.0 % to 90.0 % and extinction ratio from 5.37 dB to 9.8 dB. The sensitivity of the proposed metasurface was studied and could reach 474 GHz/RIU. The proposed metasurface exhibits polarization-sensitive features due to its non-central symmetry in the metasurface. Finally, the metasurface symmetry-breaking effect on QPIT is further investigated, and results indicate that triple-PIT, quadruple-PIT, quintuple-PIT, and sextuple-PIT can be mutually transformed and regulated through structural symmetry breaking. In summary, the findings provide valuable guidance for the design of optoelectronic switches, sensors, and modulators.

Tunable and switchable multifunctional terahertz meta-mirror based on graphene and vanadium dioxide.

We design a multifunctional THz polarization modulation meta-mirror integrated with polarization conversion and dichroism functions switched by temperature and voltage. The meta-mirror is composed of two-layered graphene metasurfaces and a layer of vanadium dioxide (VO2) on a gold film substrate. Linear-to-linear polarization conversion and linear dichroism (LD) can be switched by temperature control in the VO2 film and Fermi level adjustments in the graphene metasurfaces, where the polarization conversion ratio (PCR) is higher than 0.9 in the range of 2.89 THz to 4.02 THz, LD value reached a maximum of 0.6 at 3.84 THz, and linear-to-circular polarization conversion and circular dichroism (CD) can also be tuned with ellipticity higher than 0.9 in the range of 2.32 THz to 2.69 THz and CD value as high as 0.71 at 2.45 THz. The proposed meta-mirror is the first THz metamaterial device integrating four switchable functions, including linear-to-linear polarization conversion, linear-to-circular polarization conversion, linear dichroism and circular dichroism. The meta-mirror is a promising design for compact system integration in THz imaging, sensing and biological detection applications.

Toroidal Dipole-Integrated Graphene Metasurfaces for Ultrasensitive Detection of Amino Acids

Toroidal Dipole-Integrated Graphene Metasurfaces for Ultrasensitive Detection of Amino Acids

Terahertz Liquid Biosensor Based on A Graphene Metasurface for Ultrasensitive Detection with A Quasi-Bound State in the Continuum.

The concept of a quasi-bound state in a continuum (QBIC) has garnered significant attention in various fields such as sensing, communication, and optical switching. Within metasurfaces, QBICs offer a reliable platform that enables sensing capabilities through potent interactions between local electric fields and matter. Herein, a novel terahertz (THz) biosensor based on the integration of QBIC with graphene is reported, which enables multidimensional detection. The proposed biosensor is distinctive because of its ability to discern concentrations of ethanol and N-methylpyrrolidone in a wide range from 100% to 0%, by monitoring the changes in the resonance intensity and maximum wavelet coefficient. This approach demonstrates an excellent linear fit, which ensures robust quantitative analysis. The remarkable sensitivity of our biosensor enables it to detect minute changes in low-concentration solutions, with the lowest detection concentration value (LDCV) of 0.21pgmL-1 . 2D wavelet coefficient intensity cards are effectively constructed through continuous wavelet transforms, which presents a more accurate approach for determining the concentration of the solution. Ultimately, the novel sensing platform offers a host of advantages, including heightened sensitivity and reusability. This pioneering approach establishes a new avenue for liquid-based terahertz biosensing.

Intervalley Scattering Induced Terahertz Field Enhancement in Graphene Metasurface

Intervalley Scattering Induced Terahertz Field Enhancement in Graphene Metasurface

Performance Enhancement of THz Antenna with Reduced Size of Graphene Metasurface Unit Cell Structure Array

Performance Enhancement of THz Antenna with Reduced Size of Graphene Metasurface Unit Cell Structure Array

Nonreciprocal reflection based on asymmetric graphene metasurfaces.

We propose a scheme to achieve controllable nonreciprocal behavior in asymmetric graphene metasurfaces composed of a continuous graphene sheet and a poly crystalline silicon slab with periodic grooves of varying depths on each side. The proposed structure exhibits completely asymmetric reflection in opposite directions in the near-infrared range, which is attributed to the pronounced structural asymmetry and its accompanying nonlinear effects. The obtained nonreciprocal reflection ratio, reaching an impressive value of 21.27 dB, combined with a minimal insertion loss of just -0.76 dB, highlights the remarkable level of nonreciprocal efficiency achieved by this design compared to others in its category. More importantly, the proposed design can achieve dynamic tunability by controlling the incident field intensity and the graphene Fermi level. Our design highlights a potential means for creating miniaturized and integratable nonreciprocal optical components in reflection mode, which can promote the development of the integrated isolators, optical logic circuits, and bias-free nonreciprocal photonics.

Graphene-Enabled Tunable Phase Gradient Metasurface for Broadband Dispersion Manipulation of Terahertz Wave.

With the increasing demand for the miniaturization and flexibility of optical devices, graphene-based metasurfaces have emerged as a promising ideal design platform for realizing planar and tunable electromagnetic or optical devices. In this paper, we propose a tunable metasurface with low-dispersion phase gradient characteristics that is composed of an array of double-layer graphene ribbons sandwiched with a thin insulating layer and a polymer substrate layer with a gold ground plane. As two typical proof-of-concept examples, metasurfaces act as a planar prism and a planar lens, respectively, and the corresponding performances of tunable broadband dispersion are demonstrated through full-wave simulation experiments. By changing the Fermi level of each graphene ribbon individually to introduce abrupt phase shifts along the metasurface, the broadband continuous dispersion effect of abnormal reflection and beam focusing is achieved within a terahertz (THz) frequency region from 3.0 THz to 4.0 THz, and the dispersion results can be freely regulated by reconfiguring the sequence of Fermi levels via the bias voltage. The presented graphene metasurface provides an avenue for the dispersion manipulation of a broadband terahertz wave and may have great prospects in the fields of optics, imaging, and wireless communication.

Active control of terahertz surface plasmonic wave excitation using electromagnetically induced transparency based graphene metasurfaces.

Surface plasmonic waves (SPWs) that propagate at meta-dielectric interface are a good source of information carrier waves for on-chip photonic devices, where SPW excitation is one key procedure. Recently, controlling SPW excitation using metasurface methods has drawn considerable attention owing to their design flexibility, wherein achieving dynamic control is of great importance. However, most studies in the terahertz regime so far are working in a passive way or only dynamically controllable at the propagation process. In this work, an active design for controlling terahertz SPWs at the excitation process is proposed using graphene metasurfaces based on the manipulation of the electromagnetically induced transparency (EIT) effect. Large modulation depth with controllable SPW excitations is demonstrated. Our method is flexible and promising in achieving more controlling degree of freedom, which can find broadband applications in future integrated devices and systems.