Graphene-based THz Research Articles

Single/Multi-band graphene-based disk THz absorbers with single graphene layer: conceptual design

Single/Multi-band graphene-based disk THz absorbers with single graphene layer: conceptual design

Retraction Note: A graphene-based triple-band THz metamaterial absorber for cancer early detection

Retraction Note: A graphene-based triple-band THz metamaterial absorber for cancer early detection

Switchable THz wave absorber based on disks and its complement graphene surfaces

A new geometrical vision for a graphene-based THz wave absorber is investigated in this work. A high-performance THz absorber is proposed to exploit complementary conventional periodic arrays of graphene disks. The equivalent circuit model is modified to take account of the complement pattern. The absorber works in two different operational modes based on chemical potential values. One mode shows absorption around 1 THz while the other one expresses perfect absorption at 6 THz and 9 THz. Such a considerable shifting ability via gate stimulations makes the proposed absorber an ideal block for reconfigurable metasurface. The comparison between the circuit model and full-wave simulation verifies an excellent match while ample sensitivity analysis are reported to show the reliability of the proposed switchable THz absorber.

Switchable circular polarization in flower-shaped reconfigurable graphene-based THz microstrip patch antenna

Switchable circular polarization in flower-shaped reconfigurable graphene-based THz microstrip patch antenna

Logic operation and all-optical switch characteristics of graphene surface plasmons.

Terahertz logic gates play a crucial role in optical signal processing and THz digitization. In this paper, we propose a design strategy for graphene-based metamaterial THz all-optical logic gate devices based on the induced transparency effect of surface isolated. Theoretically, we realize Boolean operations by coupling of a hexagonal graphene resonant cavity with dual embedded rotatable ellipses. Based on the coupled mode theory, the elliptical rotation angle of the resonator is an important factor affecting the PIT phenomenon. We control the logic input by adjusting the rotation angles of the two embedded ellipses. The analysis results show that: under the incidence of y-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 30° represents the input signal '1'. Through numerical simulation, the structure realizes two logical operations of NAND and AND. Under the incidence of x-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 90° represents the input signal '1'. Through numerical simulation, the structure realizes three logical operations of NAND, XNOR and OR. Finally, we analyze the performance of the logic gates by extinction ratio. The extinction ratio of the logic gate is up to 10.38 dB when performing OR Boolean operations. Numerically simulated all-optical logic gates can be key components of optical processing and telecommunication equipment.

RETRACTED ARTICLE: A graphene-based triple-band THz metamaterial absorber for cancer early detection

RETRACTED ARTICLE: A graphene-based triple-band THz metamaterial absorber for cancer early detection

Method of Autonomous Blocks with Floquet Channels for Solving Linear and Nonlinear Problems of Diffraction for Graphene-based THz Devices

Method of Autonomous Blocks with Floquet Channels for Solving Linear and Nonlinear Problems of Diffraction for Graphene-based THz Devices

Equivalent circuit model for a graphene-based high efficiency tunable broadband terahertz polarizer.

An equivalent circuit model for a graphene-based high-efficiency tunable broadband THz polarizer is presented. The conditions for linear-to-circular polarization conversion in the transmission mode are utilized to derive a set of closed-form design formulas. Given a set of target specifications, the key structural parameters of the polarizer are directly calculated using this model. The proposed model is rigorously validated by comparing the circuit model and full-wave electromagnetic simulation results, from which it is found that the model is accurate and effective, accelerating the analysis and design processes. This offers a further step in developing a high-performance and controllable polarization converter with potential applications in imaging, sensing, and communications.

Designing of a circularly polarized reconfigurable graphene-based THz patch antenna with cross-shaped slot

Designing of a circularly polarized reconfigurable graphene-based THz patch antenna with cross-shaped slot

Multi-channel THz perfect absorber using graphene-based Fibonacci photonic crystals

A graphene-based multi-channel THz perfect absorber is proposed in this paper. The absorber consists of a graphene layer, a Fibonacci quasi-periodic layer, a spacer, and a substrate. We demonstrate that the structure we proposed can lead to multi-channel perfect THz absorption because of the graphene surface plasmon polaritons and multiple photonic stop bands in this structure. The multi-channel working frequencies and absorption peaks can be flexibly tuned by controlling the incidence angle, size of component materials, and Fermi energy. Moreover, by adjusting the Fibonacci quasi-period orders of the structure, the number of working channels can be flexibly expanded without reoptimizing the structure size. Moreover, by adjusting the Fibonacci quasi-period orders of the structure, the number of working channels can be flexibly expanded without reoptimizing the structure size. Using existing technology, our design scheme is easy to realize, which will be helpful to promote the development and application of novel tunable optoelectronic devices.

Enhancing the efficiency of graphene-based THz modulator by optimizing the Brewster angle.

The gate-controllable electronical property of graphene provides a possibility of active tuning property for THz modulator. However, the common modulation technology which only depends on voltage cannot solve the problem of power consumption limitation in communication applications. Here, we demonstrated a Brewster angle-controlled graphene-based THz modulator, which could achieve a relatively high modulation depth with low voltage. First, we explored the complex relationships among the Brewster angles, reflection coefficients and the conductivities of graphene. Then, we further investigated the optimal incident angle selection based on the unusual reflection effect which occurs at Brewster angle. Finally, an improved scheme by dynamically adjusting the incident angle was proposed in this paper. It would make it possible that the modulator could achieve a modulation depth of more than 90% with a Fermi level as low as 0.2eV at any specific frequency in the range of 0.4THz-2.2THz. This research will help to realize a THz modulator with high-performance and ultra-low-power in quantities of applications, such as sensing and communication.

A graphene-based THz metasurface sensor with air-spaced structure

Owing to the unique electromagnetic response ability, electromagnetic metasurface have potential applications in medical, imaging, sensing, and other fields. In this paper, a graphene-based THz metasurface sensor with an air spacer layer is designed by combining the advantages of the air spacer structure and the dynamic tunability of graphene materials. The proposed metasurface sensor consists of six layers, which are silicon dioxide (SiO2) substrate, metal reflector, air layer, graphene metasurface etched with microstructure, ion-gel layer and silicon dioxide dielectric layer from bottom to top. A comprehensive study of the absorption properties and sensing performance are carried out which is simulated and analyzed with the help of CST Microwave Studio software. The calculation results show that the two obvious resonance absorption peaks located at 0.95 THz and 1.53 THz with absorption of 94.9% and 79%, respectively, and there is a good linear relationship between the absorption peak and dielectric parameters of analyte. The frequency shift sensitivity of the two resonance peaks M1 and M2 can reach 450 GHz/RIU and 717 GHz/RIU, respectively. By changing the thickness of the air layer, when the two resonance peaks M1 and M2 reach the maximum absorption at h2=140 μm and h2=280 μm, respectively, the frequency shift sensitivity is still as high as close to 450 GHz/RIU. The influence of structure parameters and incident angle on the absorption spectrum shows that the proposed structure has good stability and reliability. The proposed graphene-based absorption sensor has good biocompatibility, broadening the application range of terahertz functional devices.

Numerical investigation and comparative analysis of tunable graphene-gold metasurface-based polarizer structures for infrared frequency

We present the comparative analysis of tunable graphene-based metasurface polarizer structure THz frequency range. These polarizer structures have been numerically investigated over the 10 THz to 25 THz frequency range. Reflectance co-efficient, phase variation, and phase difference parameters have been investigated to identify the behavior of polarization effect over the range of 10 THz to 25 THz of the frequency. The proposed polarizer has also been investigated for the different shapes of the top gold resonator structure. The proposed structure is tunable for the range of 0.1 eV–0.9 eV of the graphene Fermi energy. The proposed structure also works on the wide range of the input incident wave of the X and Y polarization. This structure has a small, compact, tunable design and can be used as a fundamental building block in the large THz circuits and structures.

Graphene-Based Absorption-Transmission Multi-Functional Tunable THz Metamaterials.

The paper reports an absorption–transmission multifunctional tunable metamaterial based on graphene. Its pattern graphene layer can achieve broadband absorption, while the frequency selective layer can achieve the transmission of specific band. Furthermore, the absorption and transmission can be controlled by applying voltage to regulate the chemical potential of graphene. The analysis results show that the absorption of the metamaterial is adjustable from 22% to 99% in the 0.72 THz~1.26 THz band and the transmittance is adjustable from 80% to 95% in 2.35 THz. The metamaterial uses UV glue as the dielectric layer and PET (polyethylene terephthalate) as the flexible substrate, which has good flexibility. Moreover, the metamaterial is insensitive to incident angle and polarization angle, which is beneficial to achieve excellent conformal properties.

A graphene based dual-band metamaterial absorber for TE polarized THz wave

A graphene based tunable metamaterial perfect absorber is designed, which is a classic and simple sandwich structure composed of a non-rotationally symmetric graphene pattern layer, a TOPAS dielectric layer and a thick enough gold ground plane. The dynamically adjustable absorption property of the proposed absorber is polarization sensitive, which is novel compared with the widely studied polarization insensitive metamaterial absorber. For TE polarized incident electromagnetic waves (EMW), the dual-band absorption can be generated at frequencies of 4.268 THz and 6.032 THz with peak absorption coefficients up to 99.99% and 99.79%, respectively. But for TM light, there is only one near unity absorption band located at about 4.148 THz. So it will have potential application value for the polarization state resolution of THz waves. The research mainly concentrates on the dual-band tunable absorption under TE polarized incident light. The factors affecting the absorption properties of the proposed absorber are studied by discussing the dependence of the geometric parameters as well as chemical potential and relaxation time of the graphene on the absorption. The simulation results are verified by using multiple reflection interference theory (MRIT) and impedance matching theory (IMT), and the results show that the theoretical results match well with the simulation results. The absorber can achieve good absorption performance in a wide range of incident angles for TE light. Furthermore, by selecting two different graphene chemical potential, good performance of THz switching can be realized. In addition, the application in the field of refractive sensing is also investigated in detail, and higher sensitivity and better figure of merit (FOM) can be obtained. Thus, the designed graphene-based dual-band THz metamaterial absorber has great potential in polarization resolution, EMW absorbing, THz switching, refractive index sensing and so on.

Programmable Manipulations of Terahertz Beams by Graphene-Based Metasurface With Both Amplitude and Phase Modulations

Terahertz metasurface with digital, programmable control recently gained considerable attention for its potential applications in high-speed imaging, nondestructive sensing, and wireless communication. With elaborate design, the metasurface can perform amplitude, phase, and polarization modulations of electromagnetic waves. Most digital programmable metasurfaces focus on only one of the three dimensions. Here, we propose a graphene-based THz metasurface with both phase and amplitude modulations, which consists of an artificially constructed metal-insulator-metal structure and two-dimensional graphene material. Each meta-atom of the metasurface is divided into two sub-atoms, and the two sub-atoms can reflect terahertz waves with a phase difference of 180°. Meanwhile, the amplitude of the sub-atom can be effectively modulated or even switched off by applying different gate voltages to the graphene. By independently controlling the amplitude response of the two sub-atoms, the whole meta-atom can dynamically control both amplitude and phase responses of the cross-polarization waves. By carefully designing the coding patterns, the digital metasurface can control both beam direction and intensity, which may lead to various advanced applications in beam shaping, radar detection systems, and high-quality holography.

Analysis of graphene-based tunable THz four-band absorption sensors.

A novel, to the best of our knowledge, four-band tunable absorber sensor, based on a graphene layer, is presented. The proposed sensor configuration is composed of a single monolayer of graphene placed on top of a SiO2 dielectric substrate, whereas a gold grounding plane is placed beneath the SiO2. In addition, the resonant frequencies of the sensor can be directly controlled by adjusting the Fermi level of graphene, while the absorption rate reaches a value greater than 99% at all resonant peaks. The acquired calculation results of the refractive index sensitivity of our proposed sensor show that the four resonant peaks possess superior sensing characteristics. Additionally, by covering the measured objects with different refractive indices, the acquired results indicate that the sensing performance of the sensor exhibits good linearity. From our analysis, it is concluded that the absorbing sensor exhibits a broad range of potential applications in the biomedical field.

A reconfigurable narrow and wide band multi bias graphene based THz absorber

A three layers graphene-based THz absorber composed of multi-bias graphene ribbons is presented. The structure is described using equivalent circuit model and design methodology is developed via impedance matching concept. Also, relatively heavy optimization is utilized to obtain two sets of chemical potential values. Two operational behaviors are expressed corresponding to each bias set. Leveraging both equivalent circuit representation and impedance matching concept, the proposed structure is able to show both narrow multi band and wide band absorption over 0.1 THz to 5 THz frequency range. The first mode of operation can perfectly absorb THz incident waves in 0.5 THz, 1.4 THz, 2.35 THz, 3.23 THz and 4.11 THz while the second mode of operation absorbs THz incident waves between 0.5 THz to 2.5 THz as wide band response. Additionally, to investigate device dependency against geometrical parameters, electron relaxation time, chemical potentials and incident angle, ample simulations are reported for both modes of operations. Achieving both multi band and wide band absorption via a unique structure, makes the proposed device an ideal candidate to be used in optical systems and sensors for medical imaging, indoor communications and security.

Graphene-based magneto-optical THz modulator with 100% depth of modulation for communication purposes

In this article, we introduce a Faraday modulator based on graphene, gyroelectric (InSb), SiO2, and Si materials at 0.35 THz, considered as a band of the atmospheric window promising for the future wireless communications. The maximum value of Faraday rotation, transmission and depth of modulation are obtained at 0.35 THz for low static magnetic field B as 45 deg, 80%, and 100%, respectively. The THz signal transmission can be modified from 0 to 80% by varying applied static magnetic fields. This design opens up a new way for ultrathin magneto-optical nanophotonic devices to realize polarization modulators with high transmittance in the THz band.

Refractive Index-Based Terahertz Sensor Using Graphene for Material Characterization.

In this paper, a graphene-based THz metamaterial has been designed and characterized for use in sensing various refractive index profiles. The proposed single-band THz sensor was constructed using a graphene-metal hybridized periodic metamaterial wherein the unit cell had a footprint of 1.395λeff × 1.395λeff and resonated at 4.4754 THz. The realized peak absorption was 98.88% at 4.4754 THz. The sensitivity of the proposed metamaterial sensor was estimated using the absorption characteristics of the unit cell. The performance of the sensor was analyzed under two different categories, viz. the random dielectric loading and chemical analytes, based on the refractive index. The proposed THz sensor offered a peak sensitivity of 22.75 GHz/Refractive Index Unit (RIU) for the various sample loadings. In addition, the effect of the sample thickness on the sensor performance was analyzed and the results were presented. From the results, it can be inferred that the proposed metamaterial THz sensor that was based on a refractive index is suitable for THz sensing applications.